3.13 Case Study Conclusion: Diet Dilemma
After reading this chapter, you should be able to see numerous connections between chemistry, human life, and health. In Joseph’s situation, chemistry is involved in the reasons why his father has diabetes, why his personal risk of getting diabetes is high, and why the dietary changes he is considering could be effective.
Type 2 diabetes affects populations worldwide and is caused primarily by a lack of response in the body to the hormone insulin, which causes problems in the regulation of blood sugar, or glucose. Insulin is a peptide hormone, and as you have learned, peptides are chains of amino acids. Therefore, insulin is in the class of biochemical compounds called proteins. Joseph is at increased risk of diabetes partly because there is a genetic component to the disease. DNA, which is a type of chemical compound called a nucleic acid, is passed down from parents to their offspring, and carries the instructions for the production of proteins in units called genes. If there is a problem in a gene (or genes) that contributes to the development of a disease, such as type 2 diabetes, this can get passed down to the offspring and may raise that child’s risk of getting the disease.
But genetics is only part of the reason why Joseph is at an increased risk of diabetes. Obesity itself is a risk factor, and one that can be shared in families due to shared lifestyle factors (such as poor diet and lack of exercise), as well as genetics. Consumption of too many refined carbohydrates (like white bread and soda) may also contribute to obesity and the development of diabetes. As you probably now know, these simple carbohydrates are more easily and quickly broken down in the digestive system into glucose than larger complex carbohydrate molecules, such as those found in vegetables and whole grains. This can lead to dramatic spikes in blood sugar levels, which is particularly problematic for people with diabetes because they have trouble maintaining their blood sugar at a safe level. You can understand why Joseph’s father limits his consumption of refined carbohydrates, and in fact, some scientific studies have shown that avoiding refined carbohydrates may actually help reduce the risk of getting diabetes in the first place.
Joseph’s friend recommended eating a low fat, high carbohydrate diet to lose weight, but you can see that the type of carbohydrate — simple or complex — is an important consideration. Eating a large amount of white bread and rice may not help Joseph reduce his risk of diabetes, but a healthy diet that helps him lose weight may lower his risk of diabetes, since obesity itself is a factor. Which specific diet will work best to help him lose weight probably depends on a variety of factors, including his biology, lifestyle, and food preferences. Joseph should consult with his doctor about his diet and exercise plan, so that his specific situation can be taken into account and monitored by a medical professional.
Drinking enough water is usually good advice for everyone, especially if it replaces sugary drinks like soda. You now know that water is important for many of the chemical reactions that take place in the body. But you can have too much of a good thing — as in the case of marathon runners who can make themselves sick from drinking too much water! As you can see, proper balance, or homeostasis, is very important to the health of living organisms.
Finally, you probably now realize that “chemicals” do not have to be scary, toxic substances. All matter consists of chemicals, including water, your body, and healthy fresh fruits and vegetables, like the ones pictured in Figure 3.12.2. When people advocate “clean eating” and avoiding “chemicals” in food, they are usually referring to avoiding synthetic — or man-made — chemical additives, such as preservatives. This can be a healthy way to eat because it involves eating a variety of whole, fresh, unprocessed foods. But there is no reason to be scared of chemicals in general — they are simply molecules and how they react depends on what they are, what other molecules are present, and the environmental conditions surrounding them.
Chapter 3 Summary
By now, you should have a good understanding of the basics of the chemistry of life. Specifically, you have learned:
- All consists of chemical substances. A chemical substance has a definite and consistent composition and may be either an or a .
- An is a pure substance that cannot be broken down into other types of substances.
- An is the smallest particle of an element that still has the properties of that element. Atoms, in turn, are composed of subatomic particles, including negative , positive , and neutral . The number of protons in an atom determines the element it represents.
- Atoms have equal numbers of electrons and protons, so they have no charge. Ions are atoms that have lost or gained electrons, so they have either a positive or negative charge. Atoms with the same number of protons but different numbers of neutrons are called isotopes.
- There are almost 120 known elements. The majority of elements are metals. A smaller number are nonmetals, including carbon, hydrogen, and oxygen.
- A is a substance that consists of two or more elements in a unique composition. The smallest particle of a compound is called a molecule. Chemical bonds hold together the atoms of molecules. Compounds can form only in chemical reactions, and they can break down only in other chemical reactions.
- Biochemical compounds are carbon-based compounds found in living things. They make up and other structures of organisms and carry out life processes. Most biochemical compounds are large molecules called that consist of many repeating units of smaller molecules called .
- There are millions of different biochemical compounds, but all of them fall into four major classes: , , , and .
- Carbohydrates are the most common class of biochemical compounds. They provide cells with energy, store energy, and make up organic structures, such as the cell walls of plants. The basic building block of carbohydrates is the monosaccharide.
- Sugars are short-chain carbohydrates that supply us with energy. Simple sugars, such as glucose, consist of just one monosaccharide. Some sugars, such as sucrose (or table sugar) consist of two monosaccharides and are called disaccharides.
- Complex carbohydrates, or polysaccharides, consist of hundreds or even thousands of monosaccharides. They include starch, glycogen, cellulose, and chitin.
- is made by plants to store energy and is readily broken down into its component sugars during digestion.
- Glycogen is made by animals and fungi to store energy and plays a critical part in the homeostasis of blood glucose levels in humans.
- is the most common biochemical compound in living things. It forms the cell walls of plants and certain algae. Humans cannot digest cellulose, but it makes up most of the crucial dietary fibre in the human diet.
- makes up organic structures, such as the cell walls of fungi and the exoskeletons of insects and other arthropods.
- Lipids include fats and oils. They store energy, form cell membranes, and carry messages.
- Lipid molecules consist mainly of repeating units called . Fatty acids may be or , depending on the proportion of hydrogen atoms they contain. Animals store fat as saturated fatty acids, while plants store fat as unsaturated fatty acids.
- Types of lipids include triglycerides, phospholipids, and steroids.
- contain glycerol (an alcohol) in addition to fatty acids. Humans and other animals store fat as triglycerides in fat cells.
- contain phosphate and glycerol in addition to fatty acids. They are the main component of cell membranes in all living things.
- are lipids with a four-ring structure. Some steroids, such as cholesterol, are important components of cell membranes. Many other steroids are hormones.
- In living things, proteins include , antibodies, and numerous other important compounds. They help cells keep their shape, make up muscles, speed up chemical reactions, and carry messages and materials (among other functions).
- are made up of small monomer molecules called .
- Long chains of amino acids form polypeptides. The sequence of amino acids in polypeptides makes up the primary structure of proteins. Secondary structure refers to configurations such as helices and sheets within polypeptide chains. Tertiary structure is a protein’s overall three-dimensional shape, which controls the molecule’s basic function. A quaternary structure forms if multiple protein molecules join together and function as a complex.
- The chief characteristic that allows proteins’ diverse functions is their ability to bind specifically and tightly with other molecules.
- include and . They encode instructions for making proteins, helping make proteins, and passing the encoded instructions from parents to offspring.
- Nucleic acids are built of monomers called , which bind together in long chains to form polynucleotides. DNA consists of two polynucleotides, and RNA consists of one polynucleotide.
- Each nucleotide consists of a sugar molecule, phosphate group, and nitrogen base. Sugars and phosphate groups of adjacent nucleotides bind together to form the “backbone” of the polynucleotide. Bonds between complementary bases hold together the two polynucleotide chains of DNA and cause it to take on its characteristic double helix shape.
- DNA makes up genes, and the sequence of nitrogen bases in DNA makes up the genetic code for the synthesis of proteins. RNA helps synthesize proteins in cells. The genetic code in DNA is also passed from parents to offspring during reproduction, explaining how inherited characteristics are passed from one generation to the next.
- A is a process that changes some chemical substances into others. A substance that starts a chemical reaction is called a , and a substance that forms in a chemical reaction is called a . During the chemical reaction, bonds break in reactants and new bonds form in products.
- Chemical reactions can be represented by . According to the , mass is always conserved in a chemical reaction, so a chemical equation must be balanced, with the same number of atoms of each type of element in the products as in the reactants.
- Many chemical reactions occur all around us each day, such as iron rusting and organic matter rotting, but not all changes are chemical processes. Some changes, such as ice melting or paper being torn into smaller pieces, are physical processes that do not involve chemical reactions and the formation of new substances.
- All chemical reactions involve energy, and they require to begin. release energy. absorb energy.
- are chemical reactions that take place inside living things. The sum of all the biochemical reactions in an organism is called . Metabolism includes catabolic reactions (exothermic reactions) and anabolic reactions (endothermic reactions).
- Most biochemical reactions require a biological called an to speed up the reaction by reducing the amount of activation energy needed for the reaction to begin. Most enzymes are proteins that affect just one specific substance, called the enzyme’s substrate.
- Virtually all living things on Earth require liquid water. Only a tiny per cent of Earth’s water is fresh liquid water. Water exists as a liquid over a wide range of temperatures, and it dissolves many substances. These properties depend on water’s polarity, which causes water molecules to “stick” together through weak bonds called hydrogen bonds.
- The human body is about 70 per cent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including photosynthesis and cellular respiration.
- A solution is a mixture of two or more substances that has the same composition throughout. Many solutions consist of water and one or more dissolved substances.
- is a measure of the hydronium ion concentration in a solution. Pure water has a very low concentration and a pH of 7, which is the point of neutrality on the . Acids have a higher hydronium ion concentration than pure water and a pH lower than 7. Bases have a lower hydronium ion concentration than pure water and a pH higher than 7.
- Many acids and bases in living things are secreted to provide the proper pH for enzymes to work properly.
Now you understand the chemistry of the molecules that make up living things. In the next chapter, you will learn how these molecules make up the basic unit of structure and function in living organisms — cells — and you will be able to understand some of the crucial chemical reactions that occur within cells.
Chapter 3 Review
- The chemical formula for the complex carbohydrate glycogen is C24H42O21.
- What are the elements in glycogen?
- How many atoms are in one molecule of glycogen?
- Is glycogen an ion? Why or why not?
- Is glycogen a monosaccharide or a polysaccharide? Besides memorizing this fact, how would you know this based on the information in the question?
- What is the function of glycogen in the human body?
- What is the difference between an ion and a polar molecule? Give an example of each in your explanation.
- Define monomer and polymer.
- What is the difference between a protein and a polypeptide?
- People with diabetes have trouble controlling the level of glucose in their bloodstream. Knowing this, why do you think it is often recommended that people with diabetes limit their consumption of carbohydrates?
- Identify each of the following reactions as endothermic or exothermic.
- cellular respiration
- photosynthesis
- catabolic reactions
- anabolic reactions
- Pepsin is an enzyme in the stomach that helps us digest protein. Answer the following questions about pepsin:
- What is the substrate for pepsin?
- How does pepsin work to speed up protein digestion?
- Given what you know about the structure of proteins, what do you think are some of the products of the reaction that pepsin catalyzes?
- The stomach is normally acidic. What do you think would happen to the activity of pepsin and protein digestion if the pH is raised significantly?
Attributions
Figure 3.13.1
Prevalence_of_Diabetes_by_Percent_of_Country_Population_(2014)_Gradient_Map by Walter Scott Wilkens [Wwilken2], University of Illinois – Urbana Champaign Department of Geography and GIScience, on Wikimedia Commons, is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 3.13.2
Healthy plate by Melinda Young Stuart on Flickr is used under a CC BY-NC-ND 2.0 (https://creativecommons.org/licenses/by-nc-nd/2.0/) license.
Anything that takes up space and has mass.
Elements are chemically the simplest substances and hence cannot be broken down using chemical reactions. An element is a substance whose atoms all have the same number of protons.
A substance consisting of atoms or ions of two or more different elements in definite proportions joined by chemical bonds into a molecule.
The smallest particle of an element that still has the properties of that element.
A sub-atomic particle with a charge of -1.
A sub-atomic particle with a charge of +1.
Created by CK-12 Foundation/Adapted by Christine Miller
Vampires
From Bram Stoker’s famous novel about Count Dracula, to films such as Van Helsing and the Twilight Saga, fantasies featuring vampires (like the one in Figure 14.5.1) have been popular for decades. Vampires, in fact, are found in centuries-old myths from many cultures. In such myths, vampires are generally described as creatures that drink blood — preferably of the human variety — for sustenance. Dracula, for example, is based on Eastern European folklore about a human who attains immortality (and eternal damnation) by drinking the blood of others.
What Is Blood?
The average adult body contains between 4.7 and 5.7 litres of blood. More than half of that amount is fluid. Most of the rest of that amount consists of blood cells. The relative amounts of the various components in blood are illustrated in Figure 14.5.2. The components are also described in detail below.
is a fluid connective tissue that circulates throughout the body through blood vessels of the cardiovascular system. What makes blood so special that it features in widespread myths? Although blood accounts for less than 10% of human body weight, it is quite literally the elixir of life. As blood travels through the vessels of the , it delivers vital substances (such as nutrients and oxygen) to all of the , and carries away their metabolic wastes. It is no exaggeration to say that without blood, cells could not survive. Indeed, without the oxygen carried in blood, cells of the start to die within a matter of minutes.
Functions of Blood
Blood performs many important functions in the body. Major functions of blood include:
- Supplying tissues with oxygen, which is needed by all cells for .
- Supplying cells with nutrients, including , , and fatty acids.
- Removing metabolic wastes from cells, including carbon dioxide, urea, and lactic acid.
- Helping to defend the body from and other foreign substances.
- Forming clots to seal broken blood vessels and stop bleeding.
- Transporting and other messenger molecules.
- Regulating the of the body, which must be kept within a narrow range (7.35 to 7.45).
- Helping regulate body temperature (through and ).
Blood Plasma
is the liquid component of human blood. It makes up about 55% of blood by volume. It is about 92% water, and contains many dissolved substances. Most of these substances are , but plasma also contains trace amounts of glucose, mineral ions, hormones, carbon dioxide, and other substances. In addition, plasma contains blood cells. When the cells are removed from plasma, as in Figure 14.5.2 above, the remaining liquid is clear but yellow in colour.
Blood Cells
The cells in blood include , , and . These different types of blood cells are shown in the photomicrograph (Figure 14.5.3) and described in the sections that follow.
Erythrocytes
The most numerous cells in blood are red blood cells, also called s. One microlitre of blood contains between 4.2 and 6.1 million red blood cells, and red blood cells make up about 25% of all the cells in the human body. The cytoplasm of a mature erythrocyte is almost completely filled with hemoglobin, the iron-containing protein that binds with oxygen and gives the cell its red colour. In order to provide maximum space for hemoglobin, mature erythrocytes lack a cell and most s. They are little more than sacks of hemoglobin.
Erythrocytes also carry proteins called antigens that determine blood type. is a genetic characteristic. The best known human blood type systems are the ABO and Rhesus systems.
- In the ABO system, there are two common antigens, called antigen A and antigen B. There are four ABO blood types, A (only A antigen), B (only B antigen), AB (both A and B antigens), and O (neither A nor B antigen). The ABO antigens are illustrated in Figure 14.5.4.
- In the Rhesus system, there is just one common antigen. A person may either have the antigen (Rh+) or lack the antigen (Rh-).
Blood type is important for medical reasons. A person who needs a blood transfusion must receive blood of a compatible type. Blood that is compatible lacks antigens that the patient's own blood also lacks. For example, for a person with type A blood (no B antigen), compatible types include any type of blood that lacks the B antigen. This would include type A blood or type O blood, but not type AB or type B blood. If incompatible blood is transfused, it may cause a potentially life-threatening reaction in the patient’s blood.
Leukocytes
s (also called white blood cells) are cells in blood that defend the body against invading microorganisms and other threats. There are far fewer leukocytes than red blood cells in blood. There are normally only about 1,000 to 11,000 white blood cells per microlitre of blood. Unlike erythrocytes, leukocytes have a nucleus. White blood cells are part of the body’s immune systemno post. They destroy and remove old or abnormal cells and cellular debris, as well as attack pathogens and foreign substances. There are five main types of white blood cells, which are described in Table 14.5.1: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. The five types differ in their specific immune functions.
Type of Leukocyte | Per cent of All Leukocytes | Main Function(s) |
---|---|---|
Neutrophil | 62% | Phagocytize (engulf and destroy) bacteria and fungi in blood. |
Eosinophil | 2% | Attack and kill large parasites; carry out allergic responses. |
Basophil | less than 1% | Release histamines in inflammatory responses. |
Lymphocyte | 30% | Attack and destroy virus-infected and tumor cells; create lasting immunity to specific pathogens. |
Monocyte | 5% | Phagocytize pathogens and debris in tissues. |
Thrombocytes
s, also called platelets, are actually cell fragments. Like erythrocytes, they lack a nucleus and are more numerous than white blood cells. There are about 150 thousand to 400 thousand thrombocytes per microlitre of blood.
The main function of thrombocytes is blood clotting, or . This is the process by which blood changes from a liquid to a gel, forming a plug in a damaged blood vessel. If blood clotting is successful, it results in , which is the cessation of blood loss from the damaged vessel. A blood clot consists of both platelets and proteins, especially the protein fibrin. You can see a scanning electron microscope photomicrograph of a blood clot in Figure 14.5.5.
Coagulation begins almost instantly after an injury occurs to the endothelium of a blood vessel. Thrombocytes become activated and change their shape from spherical to star-shaped, as shown in Figure 14.5.6. This helps them aggregate with one another (stick together) at the site of injury to start forming a plug in the vessel wall. Activated thrombocytes also release substances into the blood that activate additional thrombocytes and start a sequence of reactions leading to fibrin formation. Strands of fibrin crisscross the platelet plug and strengthen it, much as rebar strengthens concrete.
Formation and Degradation of Blood Cells
Blood is considered a , because blood cells form inside bones. All three types of blood cells are made in red marrow within the medullary cavity of bones in a process called . Formation of blood cells occurs by the proliferation of stem cells in the marrow. These stem cells are self-renewing — when they divide, some of the daughter cells remain stem cells, so the pool of stem cells is not used up. Other daughter cells follow various pathways to differentiate into the variety of blood cell types. Once the cells have differentiated, they cannot divide to form copies of themselves.
Eventually, blood cells die and must be replaced through the formation of new blood cells from proliferating stem cells. After blood cells die, the dead cells are phagocytized (engulfed and destroyed) by white blood cells, and removed from the circulation. This process most often takes place in the and .
Blood Disorders
Many human disorders primarily affect the blood. They include cancers, genetic disorders, poisoning by toxins, infections, and nutritional deficiencies.
- is a group of cancers of the blood-forming tissues in the bone marrow. It is the most common type of cancer in children, although most cases occur in adults. Leukemia is generally characterized by large numbers of abnormal leukocytes. Symptoms may include excessive bleeding and bruising, fatigue, fever, and an increased risk of infections. Leukemia is thought to be caused by a combination of genetic and environmental factors.
- refers to any of several genetic disorders that cause dysfunction in the blood clotting process. People with hemophilia are prone to potentially uncontrollable bleeding, even with otherwise inconsequential injuries. They also commonly suffer bleeding into the spaces between joints, which can cause crippling.
- occurs when inhaled carbon monoxide (in fumes from a faulty home furnace or car exhaust, for example) binds irreversibly to the in erythrocytes. As a result, oxygen cannot bind to the red blood cells for transport throughout the body, and this can quickly lead to suffocation. Carbon monoxide is extremely dangerous, because it is colourless and odorless, so it cannot be detected in the air by human senses.
- is a virus that infects certain types of leukocytes and interferes with the body’s ability to defend itself from pathogens and other causes of illness. HIV infection may eventually lead to (acquired immunodeficiency syndrome). AIDS is characterized by rare infections and cancers that people with a healthy immune systemno post almost never acquire.
- is a disorder in which the blood has an inadequate volume of erythrocytes, reducing the amount of oxygen that the blood can carry, and potentially causing weakness and fatigue. These and other signs and symptoms of anemia are shown in Figure 14.5.8. Anemia has many possible causes, including excessive bleeding, inherited disorders (such as sickle cell hemoglobin), or nutritional deficiencies (iron, folate, or B12). Severe anemia may require transfusions of donated blood.
Feature: Myth vs. Reality
Donating blood saves lives. In fact, with each blood donation, as many as three lives may be saved. According to Government Canada, up to 52% of Canadians have reported that they or a family member have needed blood or blood products at some point in their lifetime. Many donors agree that the feeling that comes from knowing you have saved lives is well worth the short amount of time it takes to make a blood donation. Nonetheless, only a minority of potential donors actually donate blood. There are many myths about blood donation that may help explain the small percentage of donors. Knowing the facts may reaffirm your decision to donate if you are already a donor — and if you aren’t a donor already, getting the facts may help you decide to become one.
Myth | Reality |
---|---|
"Your blood might become contaminated with an infection during the donation." | There is no risk of contamination because only single-use, disposable catheters, tubing, and other equipment are used to collect blood for a donation. |
"You are too old (or too young) to donate blood." | There is no upper age limit on donating blood, as long as you are healthy. The minimum age is 16 years. |
"You can’t donate blood if you have high blood pressure." | As long as your blood pressure is below 180/100 at the time of donation, you can give blood. Even if you take blood pressure medication to keep your blood pressure below this level, you can donate. |
"You can’t give blood if you have high cholesterol." | Having high cholesterol does not affect your ability to donate blood. Taking cholesterol-lowering medication also does not disqualify you. |
"You can’t donate blood if you have had a flu shot." | Having a flu shot has no effect on your ability to donate blood. You can even donate on the same day that you receive a flu shot. |
"You can’t donate blood if you take medication." | As long as you are healthy, in most cases, taking medication does not preclude you from donating blood. |
"Your blood isn’t needed if it’s a common blood type." | All types of blood are in constant demand. |
14.5 Summary
- is a that circulates throughout the body in the . Blood supplies tissues with oxygen and nutrients and removes their metabolic wastes. Blood helps defend the body from and other threats, transports and other substances, and helps keep the body’s and temperature in homeostasis.
- is the liquid component of blood, and it makes up more than half of blood by volume. It consists of water and many dissolved substances. It also contains blood cells, including erythrocytes, leukocytes and thrombocytes.
- , (also known as red blood cells) are the most numerous cells in blood. They consist mostly of , which carries oxygen. Erythrocytes also carry that determine .
- Leukocytes (also referred to as white blood cells) are less numerous than erythrocytes and are part of the body’s immune systemno post. There are several different types of leukocytes that differ in their specific immune functions. They protect the body from abnormal cells, microorganisms, and other harmful substances.
- Thrombocytes (also called platelets) are cell fragments that play important roles in blood clotting, or coagulation. They stick together at breaks in blood vessels to form a clot and stimulate the production of fibrin, which strengthens the clot.
- All blood cells form by proliferation of stem cells in red bone marrow in a process called . When blood cells die, they are phagocytized by leukocytes and removed from the circulation.
- Disorders of the blood include , which is cancer of the bone-forming cells; , which is any of several genetic blood-clotting disorders; , which prevents erythrocytes from binding with oxygen and causes suffocation; infection, which destroys certain types of leukocytes and can cause ; and , in which there are not enough erythrocytes to carry adequate oxygen to body tissues.
14.5 Review Questions
- What is blood? Why is blood considered a connective tissue?
- Identify four physiological roles of blood in the body.
- Describe plasma and its components.
14.5 Explore More
https://youtu.be/e-5wqwp64MM
Joe Landolina: This gel can make you stop bleeding instantly, TED, 2014.
https://youtu.be/hgp8LtwFSBA
Can Synthetic Blood Help The World's Blood Shortage? Science Plus, 2016.
https://youtu.be/1Qfmkd6C8u8
How bones make blood - Melody Smith, TED-Ed, 2020.
Attributions
Figure 14.5.1
vampire_PNG32 from pngimg.com is used under a CC BY-NC 4.0 (https://creativecommons.org/licenses/by-nc/4.0/) license.
Figure 14.5.2
Blood-centrifugation-scheme by KnuteKnudsen at English Wikipedia on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 14.5.3
SEM_blood_cells by Bruce Wetzel and Harry Schaefer (Photographers)/ NCI AV-8202-3656 on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:Public_domain).
Figure 14.5.4
ABO_blood_type.svg by InvictaHOG on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:Public_domain).
Figure 14.5.5
Blood_clot_in_scanning_electron_microscopy by Janice Carr from CDC/ Public Health Image LIbrary (PHIL) ID #7308 on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:Public_domain).
Figure 14.5.6
Blausen_0740_Platelets by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 14.5.7
Platelet_Party_900x by Awkward Yeti (used with permission of the author) © All Rights Reserved
Figure 14.5.8
Symptoms_of_anemia.svg by Mikael Häggström on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:public_domain).
References
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
Blood, organ and tissue donation. (2020, April 28). Government of Canada. https://www.canada.ca/en/public-health/services/healthy-living/blood-organ-tissue-donation.html#a3
Canadian Blood Services. (n.d.). There is an immediate need for blood as demand is rising. https://www.blood.ca
Science Plus. (2016, March 2). Can synthetic blood help the world's blood shortage? https://www.youtube.com/watch?v=hgp8LtwFSBA&feature=youtu.be
TED. (2014, November 20). Joe Landolina: This gel can make you stop bleeding instantly. YouTube. https://www.youtube.com/watch?v=e-5wqwp64MM&feature=youtu.be
TED-Ed. (2020, January 27). How bones make blood - Melody Smith. YouTube. https://www.youtube.com/watch?v=1Qfmkd6C8u8&feature=youtu.be
The smallest unit of life, consisting of at least a membrane, cytoplasm, and genetic material.
A large molecule, or macromolecule, composed of many repeated subunits.
A molecule that can undergo polymerization, creating macromolecules. Large numbers of monomers combine to form polymers in a process called polymerization.
A biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1. Complex carbohydrates are polymers made from monomers of simple carbohydrates, also termed monosaccharides.
A substance that is insoluble in water. Examples include fats, oils and cholesterol. Lipids are made from monomers such as glycerol and fatty acids.
A class of biological molecule consisting of linked monomers of amino acids and which are the most versatile macromolecules in living systems and serve crucial functions in essentially all biological processes.
A complex organic substance present in living cells, especially DNA or RNA, whose molecules consist of many nucleotides linked in a long chain.
A stored form of glucose used by plants.
Created by: CK-12/Adapted by Christine Miller
Case Study: Cancer in the Family
People tend to carry similar traits to their biological parents, as illustrated by the family tree. Beyond just appearance, you can also inherit traits from your parents that you can’t see.
Rebecca becomes very aware of this fact when she visits her new doctor for a physical exam. Her doctor asks several questions about her family medical history, including whether Rebecca has or had relatives with cancer. Rebecca tells her that her grandmother, aunt, and uncle — who have all passed away — had cancer. They all had breast cancer, including her uncle, and her aunt also had ovarian cancer. Her doctor asks how old they were when they were diagnosed with cancer. Rebecca is not sure exactly, but she knows that her grandmother was fairly young at the time, probably in her forties.
Rebecca’s doctor explains that while the vast majority of cancers are not due to inherited factors, a cluster of cancers within a family may indicate that there are mutations in certain genes that increase the risk of getting certain types of cancer, particularly breast and ovarian cancer. Some signs that cancers may be due to these genetic factors are present in Rebecca’s family, such as cancer with an early age of onset (e.g., breast cancer before age 50), breast cancer in men, and breast cancer and ovarian cancer within the same person or family.
Based on her family medical history, Rebecca’s doctor recommends that she see a genetic counselor, because these professionals can help determine whether the high incidence of cancers in her family could be due to inherited mutations in their genes. If so, they can test Rebecca to find out whether she has the particular variations of these genes that would increase her risk of getting cancer.
When Rebecca sees the genetic counselor, he asks how her grandmother, aunt, and uncle with cancer are related to her. She says that these relatives are all on her mother’s side — they are her mother’s mother and siblings. The genetic counselor records this information in the form of a specific type of family tree, called a pedigree, indicating which relatives had which type of cancer, and how they are related to each other and to Rebecca.
He also asks her ethnicity. Rebecca says that her family on both sides are Ashkenazi Jews (Jews whose ancestors came from central and eastern Europe). “But what does that have to do with anything?” she asks. The counselor tells Rebecca that mutations in two tumor-suppressor genes called BRCA1 and BRCA2, located on chromosome 17 and 13, respectively, are particularly prevalent in people of Ashkenazi Jewish descent and greatly increase the risk of getting cancer. About one in 40 Ashkenazi Jewish people have one of these mutations, compared to about one in 800 in the general population. Her ethnicity, along with the types of cancer, age of onset, and the specific relationships between her family members who had cancer, indicate to the counselor that she is a good candidate for genetic testing for the presence of these mutations.
Rebecca says that her 72-year-old mother never had cancer, nor had many other relatives on that side of the family. How could the cancers be genetic? The genetic counselor explains that the mutations in the BRCA1 and BRCA2 genes, while dominant, are not inherited by everyone in a family. Also, even people with mutations in these genes do not necessarily get cancer — the mutations simply increase their risk of getting cancer. For instance, 55 to 65 per cent of women with a harmful mutation in the BRCA1 gene will get breast cancer before age 70, compared to 12 per cent of women in the general population who will get breast cancer sometime over the course of their lives.
Rebecca is not sure she wants to know whether she has a higher risk of cancer. The genetic counselor understands her apprehension, but explains that if she knows that she has harmful mutations in either of these genes, her doctor will screen her for cancer more often and at earlier ages. Therefore, any cancers she may develop are likely to be caught earlier when they are often much more treatable. Rebecca decides to go through with the testing, which involves taking a blood sample, and nervously waits for her results.
Chapter Overview: Genetics
At the end of this chapter, you will find out Rebecca’s test results. By then, you will have learned how traits are inherited from parents to offspring through genes, and how mutations in genes such as BRCA1 and BRCA2 can be passed down and cause disease. Specifically, you will learn about:
- The structure of DNA.
- How DNA replication occurs.
- How DNA was found to be the inherited genetic material.
- How genes and their different alleles are located on chromosomes.
- The 23 pairs of human chromosomes, which include autosomal and sex chromosomes.
- How genes code for proteins using codons made of the sequence of nitrogen bases within RNA and DNA.
- The central dogma of molecular biology, which describes how DNA is transcribed into RNA, and then translated into proteins.
- The structure, functions, and possible evolutionary history of RNA.
- How proteins are synthesized through the transcription of RNA from DNA and the translation of protein from RNA, including how RNA and proteins can be modified, and the roles of the different types of RNA.
- What mutations are, what causes them, different specific types of mutations, and the importance of mutations in evolution and to human health.
- How the expression of genes into proteins is regulated and why problems in this process can cause diseases, such as cancer.
- How Gregor Mendel discovered the laws of inheritance for certain types of traits.
- The science of heredity, known as genetics, and the relationship between genes and traits.
- How gametes, such as eggs and sperm, are produced through meiosis.
- How sexual reproduction works on the cellular level and how it increases genetic variation.
- Simple Mendelian and more complex non-Mendelian inheritance of some human traits.
- Human genetic disorders, such as Down syndrome, hemophilia A, and disorders involving sex chromosomes.
- How biotechnology — which is the use of technology to alter the genetic makeup of organisms — is used in medicine and agriculture, how it works, and some of the ethical issues it may raise.
- The human genome, how it was sequenced, and how it is contributing to discoveries in science and medicine.
As you read this chapter, keep Rebecca’s situation in mind and think about the following questions:
- BCRA1 and BCRA2 are also called Breast cancer type 1 and 2 susceptibility proteins. What do the BRCA1 and BRCA2 genes normally do? How can they cause cancer?
- Are BRCA1 and BRCA2 linked genes? Are they on autosomal or sex chromosomes?
- After learning more about pedigrees, draw the pedigree for cancer in Rebecca’s family. Use the pedigree to help you think about why it is possible that her mother does not have one of the BRCA gene mutations, even if her grandmother, aunt, and uncle did have it.
- Why do you think certain gene mutations are prevalent in certain ethnic groups?
Attributions
Figure 5.1.1
Family Tree [all individual face images] from Clker.com used and adapted by Christine Miller under a CC0 1.0 public domain dedication license (https://creativecommons.org/publicdomain/zero/1.0/).
Figure 5.1.2
Rebecca by Kyle Broad on Unsplash is used under the Unsplash License (https://unsplash.com/license).
References
Wikipedia contributors. (2020, June 27). Ashkenazi Jews. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Ashkenazi_Jews&oldid=964691647
Wikipedia contributors. (2020, June 22). BRCA1. In Wikipedia. https://en.wikipedia.org/w/index.php?title=BRCA1&oldid=963868423
Wikipedia contributors. (2020, May 25). BRCA2. In Wikipedia. https://en.wikipedia.org/w/index.php?title=BRCA2&oldid=958722957
Created by: CK-12/Adapted by Christine Miller
Identical Twins, Identical Genes
You probably can tell by their close resemblance that these two young ladies are identical twins (Figure 5.2.1). Identical twins develop from the same fertilized egg, so they inherit copies of the same and have all the same genes. Unless you have an identical twin, no one else in the world has exactly the same as you. What are genes? How are they related to chromosomes? And how do genes make you the person you are? Let's find out!
Introducing Chromosomes and Genes
are coiled structures made of and . They are encoded with genetic instructions for making and . These instructions are organized into units called . There may be hundreds (or even thousands!) of genes on a single chromosome. Genes are segments of DNA that code for particular pieces of RNA. Once formed, some RNA molecules go on to act as blueprints for building proteins, while other RNA molecules help regulate various processes inside the cell. Some regions of DNA do not code for RNA and serve a regulatory function, or have no known function.
Human Chromosomes
Each species is characterized by a set number of chromosomes. Humans cells normally have two sets of chromosomes in each of their cells, one set inherited from each parent. Because chromosomes occur in pairs, these cells are called or 2N. There are 23 chromosomes in each set, for a total of 46 chromosomes per diploid cell. Each chromosome in one set is matched by a chromosome of the same type in the other set, so there are 23 pairs of chromosomes per cell. Each pair consists of chromosomes of the same size and shape, and they also contain the same genes. The chromosomes in a pair are known as .
All human cells (except gametes, which are sperm and egg cells) have the 23 pairs of chromosomes as shown in Figure 5.2.2.
https://www.youtube.com/watch?v=veB31XmUQm8&feature=youtu.be
Secrets of the X chromosome - Robin Ball, TED-Ed, 2019.
Autosomes
Of the 23 pairs of human chromosomes, 22 pairs are called autosomes (pairs 1-22 in the Figure 5.2.2), or autosomal chromosomes. are chromosomes that contain genes for characteristics that are unrelated to biological sex. These chromosomes are the same in males and females. The great majority of human genes are located on autosomes.
Sex Chromosomes
The remaining pair of human chromosomes consists of the sex chromosomes, X and Y (Pair 23 in Figure 5.2.2 and in Figure 5.2.3). Females have two X chromosomes, and males have one X and one Y chromosome. In females, one of the X chromosomes in each cell is inactivated and known as a . This ensures that females, like males, have only one functioning copy of the X chromosome in each cell.
As you can see from Figure 5.2.3, the X chromosome is much larger than the Y chromosome. The X chromosome has about two thousand genes, whereas the Y chromosome has fewer than 100, none of which is essential to survival. Virtually all of the X chromosome genes are unrelated to sex. Only the Y chromosome contains genes that determine sex. A single Y chromosome gene, called SRY (which stands for sex-determining region Y gene), triggers an embryo to develop into a male. Without a Y chromosome, an individual develops into a female, so you can think of female as the default sex of the human species.
Human Genes
Humans have an estimated 20 thousand to 22 thousand genes. This may sound like a lot, but it really isn’t. Far simpler species have almost as many genes as humans. However, human cells use splicing and other processes to make multiple proteins from the instructions encoded in a single gene. Only about 25 per cent of the nitrogen base pairs of DNA in human chromosomes make up genes and their regulatory elements. The functions of many of the other base pairs are still unclear, but with more time and research their roles may become understood.
The majority of human genes have two or more possible versions, called . Differences in alleles account for the considerable genetic variation among people. In fact, most human genetic variation is the result of differences in individual DNA base pairs within alleles.
Linkage
Genes that are located on the same chromosome are called . Linkage explains why certain characteristics are frequently inherited together. For example, genes for hair colour and eye colour are linked, so certain hair and eye colours tend to be inherited together, such as dark hair with dark eyes and blonde hair with blue eyes. Can you think of other human traits that seem to occur together? Do you think they might be controlled by linked genes?
Genes located on the sex chromosomes are called . Most sex-linked genes are on the X chromosome, because the Y chromosome has relatively few genes. Strictly speaking, genes on the X chromosome are , but the term sex-linked is often used to refer to them. The diagram below is called a linkage map: a linkage map shows the locations of specific genes on a chromosome. The linkage map below (Figure 5.2.4) shows the locations of a few of the genes on the human X chromosome.
Figure 5.2.4 Linkage Map for the Human X Chromosome. This linkage map shows the locations of several genes on the X chromosome. Some of the genes code for normal proteins. Others code for abnormal proteins that lead to genetic disorders.
5.2 Summary
- are coiled structures made of and proteinsno post that are encoded with genetic instructions for making and proteins. The instructions are organized into units called , which are segments of DNA that code for particular pieces of RNA. The RNA molecules can then act as a blueprint for proteins, or directly help regulate various cellular processes.
- Each species is characterized by a set number of chromosomes. The normal chromosome complement of a human cell is 23 pairs of chromosomes. Of these, 22 pairs are , which contain genes for characteristics unrelated to sex. The other pair consists of (XX in females, XY in males). Only the Y chromosome contains genes that determine sex.
- Humans have an estimated 20 thousand to 22 thousand genes. The majority of human genes have two or more possible versions, which are called .
- Genes that are located on the same chromosome are called . Linkage explains why certain characteristics are frequently inherited together. A linkage map shows the locations of specific genes on a chromosome.
5.2 Review Questions
- What are chromosomes and genes? How are the two related?
- Describe human chromosomes and genes.
- Explain the difference between autosomes and sex chromosomes.
- What are linked genes, and what does a linkage map show?
- Explain why females are considered the default sex in humans.
- Explain the relationship between genes and alleles.
- Most males and females have two sex chromosomes. Why do only females have Barr bodies?
5.2 Explore More
https://www.youtube.com/watch?v=M4ut72kfUJM
WACE Biology: Coding and Non-Coding DNA, Atomi, 2019.
https://www.youtube.com/watch?time_continue=3&v=jhHGCvMlrb0&feature=emb_logo
How Sex Genes Are More Complicated Than You Thought, Seeker, 2015.
Attributions
Figure 5.2.1
Twins5 [photo] by Bùi Thanh Tâm on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 5.2.2
Human_male_karyotype by National Human Genome Research Institute/ NIH on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original from the Talking Glossary of Genetics.)
Figure 5.2.3
Comparison between X and Y chromosomes byJonathan Bailey, National Human Genome Research Institute, National Institutes of Health [NIH] Image Gallery, on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 5.2.4
Linkage Map of Human X Chromosome by Christine Miller is used under a
CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
References
Atomi. (2019, October 27). WACE Biology: Coding and Non-Coding DNA. YouTube. https://www.youtube.com/watch?v=M4ut72kfUJM&feature=youtu.be
Seeker. (2015, July 26). How Sex Genes Are More Complicated Than You Thought. YouTube. https://www.youtube.com/watch?v=jhHGCvMlrb0&feature=youtu.be
TED-Ed. (2017, April 18). Secrets of the X chromosome - Robin Ball. YouTube. https://www.youtube.com/watch?v=veB31XmUQm8&feature=youtu.be
Long chains of hydrocarbons with a carboxyl group and a methyl group at opposite ends. Can be either saturated, containing mostly single bonds between adjacent carbons, or unsaturated, containing many double bonds between adjacent carbons.
A type of fat in which the fatty acid chains have all or predominantly single bonds.
A fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond.
A type of lipid consisting of a glycerol and three fatty acids. Triglycerides are a form of energy storage used in animals (fats) and plants (oils).
Image shows a Lego (TM) representation of Gregor Mendel with his plants.
Biological molecules that lower amount the energy required for a reaction to occur.
Amino acids are organic compounds that combine to form proteins.
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.
A substance that takes part in and undergoes change during a chemical reaction.
A substance that is formed as the result of a chemical reaction.
An expression that gives the identities and quantities of the substances involved in a reaction. A chemical equation shows the starting compound(s)—the reactants—on the left and the final compound(s)—the products—on the right, separated by an arrow.
The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Thus, the amount of matter cannot change.
The minimum energy required to cause a reaction to occur.
A chemical reaction that releases energy through light or heat.
Any reaction which requires or absorbs energy from its surroundings, usually in the form of heat.
The transformation of one molecule to a different molecule inside a cell.
The chemical processes that occur in a living organism to sustain life.
A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
The level of acid in a substance.
A scale used to specify how acidic or basic a water-based solution is. Acidic solutions have a lower pH, while basic solutions have a higher pH.