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Visualizing, Human Biology
Chapter Two
Everyday Chemistry of Life
Critical Thinking Study Questions and Answers
1. Radioisotopes are often used in medicine and biochemical experiments. For example, the
chemistry of photosynthesis was uncovered with radioactive carbon dioxide.
Photosynthesizing cells were exposed to radioactive carbon dioxide, and that radioactive
carbon was tracked through each step of glucose formation. Using this principle, how
might radioactive compounds be used in medical research? In treating a disease like
leukemia (cancer of the white-blood cells)? A. If the patient is given a source of
radioactive carbon, that carbon will be incorporated into newly synthesized proteins. The
more specific the original radioactive source, the more likely that source will be
incorporated into the pathway being studied. It might be that the medical researcher
wants to see what becomes of the carbon atoms in ingested glucose. Feeding the patient
radioactive glucose allows the researcher to trace that radioactivity as it moves through
the body and into the patient’s tissues. Radioactive compounds can be used to treat
cancer by introducing them to the body in such a way that the developing cancerous
tumor will pick them up. If the radioactivity is sequestered in the tumor, it will cause
mutations in the DNA of the cancerous cells, hopefully preventing them from
multiplying.
2. Choose two properties of water. Briefly describe the property, and show how it
contributes to a specific aspect of human life. A. 1. Water is a liquid at room
temperature. Most of the activities of the human body occur near room temperature, and
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require an aqueous environment. Water remains liquid through a wide range of
temperatures, allowing reactions to take place. 2. Water is a good solvent. Because of
its polarity, water molecules are able to pull apart the ionic bonds of many substances.
This allows micronutrients and minerals to be released from the foods we eat so they are
readily available for the necessary reactions of our bodies. 3. Water is cohesive and
adhesive. Water sticks to itself, allowing it to pull into tubes such as the veins. This in
turn allows blood to flow through the body. Water also sticks to other surfaces. This
ensures that there are no potentially fatal air bubbles floating in the blood stream, and that
the urinary system is always flowing. It also helps lubricate the digestive system and the
respiratory system. 4. Water holds a lot of heat without changing temperature (high
specific heat). Muscular movement generates heat, but the human body does not
spontaneously combust. Water absorbs that heat, and passes it to the surface where it can
be released to the environment. 5. Water releases a lot of heat when it evaporates (it has
a high heat of vaporization). When water is allowed to evaporate from the surface of the
body it takes with it a large amount of internally produced heat, maintaining a cooler
internal temperature. 6. Ice floats. Life in lakes and ponds would cease to exist in
winter if water sank when it froze. Thumbnail figure 2.8
3. Acid rain is caused when water in the atmosphere reacts with sulfur oxides to form
sulfuric acid. The acidity of typical acid rain is pH 3 to pH 5 (normal precipitation is pH
7 to pH 7.5). What is the mathematical relationship between the hydrogen-ion
concentrations at each of these pH levels? How could acid rain affect biological
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systems? A. With each single digit increase in pH, the hydrogen ion concentration
decreases 10-fold. Therefore a solution with a pH of 5 has 100 times fewer hydrogen
ions per milliliter than does a solution with a pH of 3. Normal rainfall has a pH of 7 to
7.5. When compared with normal rain, acid rain has 100 to 10,000 times more hydrogen
ions per volume. These hydrogen ions cause damage to proteins by altering the
environment in which they fold. Changing the pH causes alterations in the interactions
between adjacent and closely positioned amino acids. This in turn causes the protein to
unfold and re-fold in a different shape. Protein function is dependent on shape. Acid rain
deforms proteins, thereby damaging function. Thumbnail figure 2.20
4. Enzymes are proteins that serve as catalysts, speeding up reactions without getting used,
altered or destroyed. Enzyme function can be accelerated or slowed without damaging
the enzyme itself in a few ways. Review figure 2.24 to understand normal enzyme
functioning. What would happen to enzyme function if: Products build up in the cell?
Substrate concentration decreases? A second compound, similar to the substrate but
without its reactive properties, enters the enzyme's environment? Temperature rises
slightly? A. If product builds up in a cell, the product will dilute the available substrate.
The enzymatic reaction will slow down as the enzyme runs across fewer and fewer
substrate molecules in the surrounding “soup”
of substrate and product. Similarly, if substrate concentrations decrease the reaction will
slow down. The chance meeting of enzyme and substrate declines as the number of
substrate molecules with which to interact lessens. If a second compound is introduced
that fills the enzyme’s active site but does not react with the enzyme, the reaction will
again slow down. This time, the newcomer will be competing with the substrate for the
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binding site of the enzyme. Each time the new molecule bind, it removes that enzyme
from any potential reactions with its actual substrate. The enzyme remains out of
commission until the non-reactive molecule disassociates from the enzyme. Finally, an
increase in temperature will increase the rate of the enzymatic reaction, until the
temperature gets too high. Slight increases in temperature cause more movement of
molecules within the body. This results in more chance encounters of enzyme and
substrate. As temperatures increase, molecular movements increase. There will be a
point however, when temperatures get so high that proteins are denatured (cooked). A
cooked enzyme will not function. The protein will have unfolded with the excessive
heat, destroying the active site. Thumbnail figure 2.22
5. Although they serve different functions, DNA and ATP have common elements. What
structures are found in both molecules? What purpose do these structures serve in ATP?
In DNA? A. Both DNA and ATP include the nitrogenous base adenine. In ATP this
serves as the base from which the energy-carrying bond will extend. In DNA, adenine is
one of four different bases, used to carry the genetic code. A five carbon sugar is found
bound to the adenine in both macromolecules, however the sugar in DNA is missing one
oxygen as compared to that in ATP. In both macromolecules this sugar serves as a link
between the adenine and the phosphate ions. Both macromolecules also have phosphate
ions, one per adenine in DNA and three in succession in ATP. The phosphate ions in
ATP are where energy is stored. It takes a great deal of energy to hook a third highly
negative phosphate ion onto the already negative end of the macromolecule ATP. That
final bond is holding quite a bit of energy, which it will easily release. DNA does not
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have any high-energy bonds. In this case the phosphate is part of the backbone structure
of the molecule. Thumbnail figure 2.26
Additional Critical Thinking questions.
● In many science fiction novels, a new life form emerges that is not carbon based. These alien
life forms are often silicon-based. What is the relationship between carbon and silicon? Does
silicon form a different type of chemical bond than carbon? How would the physiology of these
organisms differ from your own physiology? What clues can you obtain from looking at the
periodic table?
● Lipids are always depicted as the dietary villain in weight loss plans. We are told to stay away
from them in our foods; we are told that lipids in our bodies comprise our fat stores; we are
warned against eating saturated fats. Are fats in foods really all that bad? List the types of lipid
found in the human body. Which is responsible for what we recognize as fat? Are any of the
lipid classes necessary components of a healthy body?
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