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AP Bio Ch 8

Terms in this set (33)

1. The analogy is made that a cell is a chemical factory. Explain why this might be an appropriate
analogy.
In its complexity, its efficiency, its integration & its responsiveness, the cell is peerless as a chemical factory. Bioluminesence and all other metabolic activities carried out by the cell are precisely coordinated and controlled.
2. What is metabolism?
The totality of an organisms chemical reactions.
3. Metabolism involves pathways. Describe what is meant by a metabolic pathway.
a. Contrast catabolic pathways with anabolic pathways. Give examples of each type.
i. Explain whether each type releases energy or stores energy.
A metabolic pathway begins with a specific molecule, which is then altered in a series of defined steps, resulting in a certain product.
a. Catabolic pathways release energy by breaking down complete molecules to simpler compounds. Anabolic pathways, in contrast, consume energy to build complicated molecules from simpler ones.
Ex 1: Catabolism = cellular respiration (glucose -> CO2 + H2O)
Ex. 2: Anabolism = the synthesis of a protein from amino acids.
4. How can catabolic and anabolic pathways work together?
Energy released from the downhill reactions of catabolism can be stored and used to drive the uphill reactions of the anabolic pathways.
5. Energy is the ability to cause change. Give an example that helps explain what this might mean
to life.
In everyday life, energy is important because some forms of energy can be used to do work -- that is, to move matter against opposing forces such as friction and gravity. For example, you expend energy to turn the pages of a book, and your cells expend energy in transporting certain substances across membranes
6. Contrast kinetic with potential energy.
a. What is a biological example of kinetic?
b. What is a biological example of potential?
Kinetic energy can be associated with the relative motion of objects. An object not presently moving may still posses energy, called potential energy; it is energy that matter has because of its location or structure.
a. The contraction of leg muscles pushes bicycle pedals
b. Molecules store energy because of the arrangement of their atoms
7. There are laws that govern energy and its transformations in matter. The study of these laws is
known as thermodynamics.
a. State the first law of thermodynamics and give a biological example.
b. State the second law of thermodynamics. Why does this explain that energy can't be
recycled?
a. The energy of the universe is constant -- energy can be transferred and transformed but not created or destroyed.
Example: by converting sunlight to chemical energy, a green plant acts as an energy transformer, not an energy producer.
b. Every energy transfer or transformation increases the disorder (entropy) of the universe. In the process of carrying out chemical reactions that perform various types of work, living cells unavoidably convert organized forms of energy to heat, thus losing energy.
8. Of what is entropy a measure? Use some examples to help explain.
a. How is spontaneity of a reaction related to entropy?
Entropy is a measure of disorder, or randomness. You can observe increasing entropy in the gradual decay of an old building. As a cheetah converts chemical energy to kinetic energy, it is also increasing the disorder of its surroundings by producing heat and small molecules that are the breakdown products of food.
a. For a process to occur spontaneously, it must increase the entropy of the universe.
9. Living organisms are an example of both low entropy (meaning high order) and high entropy
(meaning low order). Explain how both can be occurring in a living organism simultaneously.
Cells create ordered structures from less organized starting materials, like how amino acids are ordered into specific sequences of polypeptide chains. However, an organism also takes in organized forms of matter and energy from their surroundings and replaces them with less ordered forms. For example, an animal obtains starch, proteins, etc. from the food it eats, and as catabolic pathways break these molecules down, the animal releases CO2 and H2) -- small molecules that store less chemical energy than food did.
10. Since the world in getting more and more random, how can organisms be getting more and more
ordered?
Complex organisms evolve from simpler ancestors. The entropy of an organism may decrease, so long as the entropy of the universe increases. Thus, organisms are islands of low entropy of the universe.
11. How does the second law of thermodynamics explain the diffusion of a substance across a
membrane?
When a substance diffuses across a membrane, it goes from a high concentration to a low concentration, or high entropy to low entropy. Since this action requires energy, this helps to increase the entropy of the universe.
It also adds to the entropy of the destination.
12. Describe the forms of energy found in an apple as it grows on a tree; then falls and is digested by
someone who eats it.
As an apple forms, it has chemical energy, which, after an apple is eaten by a person, becomes potential energy that may become kinetic energy.
13. What is free energy?
a. How is it calculated?
Free energy measures the portion of a system's energy that can perform work when temperature and pressure are uniform through the system.
a. It is calculated by using this formula:
ΔH - TΔS = ΔG
ΔH = the change in the system's enthalpy (total energy)
T = temperature in kelvin
ΔS = change in the systems entropy
14. What does the value of ΔG help you predict?
a. If ΔG is negative =
b. If ΔG is positive =
c. Why do biologist care about ΔG?
a. If ΔG is negative = spontaneous
b. If ΔG is positive = non-spontaneous
c. Why do biologist care about ΔG? It gives them the power to predict which kind of changes can happen without help
15. How are free energy related to equilibrium?
As a reaction proceeds toward equilibrium, free energy of the mixture of the reactants and products decreases.
16. What type of reaction is shown in the diagram at right - exergonic or endergonic? Explain how you know.
a. Would this be a spontaneous or not?
b. In the body what type of reaction might this represent?
This is an exergonic reaction because it has a net release of energy, but then it proceeds to lose free energy.
a. spontaneous
b. could represent cellular respiration
17. What type of reaction is shown in the diagram at right - exergonic or endergonic? Explain how you know.
a. Would this be a spontaneous or not?
b. In the body what type of reaction might this represent?
Endergenic - it absorbs free energy over time.
a. non-spontaneous
b. the conversion of CO2 + H2O -> sugar + O2 (photosynthesis)
18. What types of work does a cell do? Give an example of each.
c. How does energy coupling help explain how a cell does its work?
Mechanical work: the contraction of muscle cells
transport work: the pumping of substances across membranes against the direction of spontaneous movement
Chemical work: the synthesis of polymers from monomes

c. It helps cells manage their energy resources to do work by using an exergonic process to drive an endergonic one.
19. ATP is the immediate source of the energy used to do work. Diagram a molecule of ATP and
explain where the energy is located in the molecule.
When the terminal phosphate bond is broken, a molecule of inorganic phosphate leaves ATP, which becomes ADP. This releases 7.3 kcal of energy per mole of ATP hydrolyzed.
20. How does ATP perform work? Give an example of the types of reactions that are powered by the hydrolysis of ATP.
With the help of specific enzymes, the cell is able to couple the energy of ATP hydrolysis directly to energenic processes by transferring a phosphate group from ATP to some other molecule, such as a reactant. The three types of cellular work - mechanical, transport and chemical -- are nearly always powered by the hydrolysis of ATP. Example: the synthesis of amino acid glutamine from glutamic acid and ammonia.
21. ATP is like a rechargeable battery. How does ATP get regenerated?
It can be regenerated by the addition of phosphate to ADP.
22. Just because a reaction is spontaneous doesn't mean that it will happen any time soon! Why not?
a. How is this related to activation energy?
It needs an initial investment of energy to start the reaction, called activation energy. (abbreviated Ea) To reach a contorted state where bonds can change, reactant molecules must absorb energy from its surroundings.
23. The diagram at right shows a chemical reaction as it takes place
without an enzyme and the same reaction with an enzyme.
a. label the Ea of the uncatalyzed reaction
b. label the Ea of the catalyzed reaction
c. label ΔG (the free energy).
d. Comparing the catalyzed to the uncatalyzed reaction explain
how the following change (and/or don't change): Ea and ΔG.
d. ΔG does not change since it is an exergenic reaction. The Ea (activation energy) provides a barrier that determines the rate of reaction, and it is higher without the enzyme.
24. What type of macromolecule is an enzyme?
Protein
25. How do enzymes recognize their substrate? How does this relate to "specificity"?
a. How are substrates held in active sites?
Enzymes are proteins which have unique 3-D shapes. The specificity of an enzyme results from its shape, which is a consequence of its amino acid sequence. This is how enzymes recognize their substrates.
a. The active site is typically a pocket or groove on the surface of a protein. There should be a comfortable fit between the shape of an enzyme's active site and the shape of its substrate.
26. Explain how an enzyme catalyzes a reaction. (study figure 8.17)
1. Enzymes enter active site; enzyme changes sides so its active side embraces the substrates (induced fit.)
2. Substrates held in active site by weak interactions such as hydrogen bonds and ionic bonds.
3. Active site (and R groups of its amino acids) can lower Ea and speed up reaction by (a) acting as a template for a substrate orientation, (b) stressing the substances and stabilizing the transition state, (c) providing favorable microenvironment, (d) participating directly in the catalytic reaction.
4. Substrates are converted into products
5. Products are released
6. Active site available for 2 new substrate molecules.
27. What is meant by "optimal temperature"? What happens to the rate of the reaction as the
temperature increases WITHIN the optimal range? What happens if the temperature is outside
(either too high or too low) the optimal range?
Optimal temperature = the temp at which an enzyme's reaction rate is the greatest. When the temperature increases within the optimal range, the reaction rate increases. If the temp is outside the optimal range, the enzyme denatures and reaction rate drops quickly.
28. What is meant by "optimal pH"? Is the optimal pH the same for all enzymes? Explain your
answer with examples.
Enzymes also have a pH at which it is most active. The optimal pH values for most enzymes fall within a range of 6-8, but there are some exceptions. For example, pepsin, a digestive enzyme, works best at pH 2.
29. Distinguish between cofactors and coenzymes. How are they different? How are they similar?
Many enzymes require non-protein helpers for catalytic activity called cofactors. If a cofactor is an organic molecule, it is called a coenzyme.
30. Contrast competitive with non-competitive inhibitors. Where does each bind? Do they turn the
enzymes "on" or "off"? Is it reversible or irreversible?
a. How does this relate to toxins and poisons?
A competitive inhibitor mimics the substrate, competing for the active site. It turns the enzyme on. A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. These can both be reversible if the bond is a weak bond, not a covalent one.
a. Toxins and poisons are often irreversible enzyme inhibitors.
31. Some enzymes have allosteric sites. What is an allosteric site?
a. Draw an enzyme and label the active site and allosteric site.
Allosteric = not the active site.
32. Contrast allosteric inhibition with allosteric cooperativity.
An allosteric inhibitor stabilizes an inactive form enzyme. Allosteric cooperativity amplifies the response or enzymes to substrates.
33. What is feedback inhibition? Why is it so useful for a cell?
Feedback inhibition: a metabolic pathway is switched off by the inhibitory binding of its end product that acts early in the pathway. Some cells use this pathway of 5 steps to synthesize the amino acid isoleucine from threonine, another amino acid.
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