biology Biomolecules and Enzymes

■. According to the figure, how many hydrogen bonds would there be in a DNA sequence of 10 base pairs in which there are five A-T and five C-G pairs? (図をみる）

25

10. Based on the diagram, what pH is necessary in order to achieve the maximum rate of both chymotrypsin and arginase activity in the same reaction?（図を見る

Answer: A pH of approximately 8.2

■4. Which curve of the graph represents a catalyzed reaction and which curve represents an uncatalyzed reaction?

Answer: The bottom curve (red) is catalyzed and the top (blue) is uncatalyzed.

9. Based on the diagram, what is the pH at which pepsin would exhibit the most activity?（図を見る）

Answer: pH = 2.0

■8. If product G inhibits enzyme 1, what type of regulation is in effect?

Feedback inhibition

■7. If end product E allosterically inhibits enzyme 1, what will be the result of a buildup of E in the cell?（図を見る）

Reduced production of E and G

■3. Explain why we refer to the ends of a nucleic acid molecule as 5ʹ and 3ʹ.（図を見る）

The 5ʹ end of a DNA strand is the end that contains the phosphate group of the first nucleotide. The phosphate in a nucleotide is attached to the 5ʹ carbon in the sugar (ribose or deoxyribose). The 3ʹ carbon in the sugar molecule is free to attach to the next nucleotide in the chain, with only a hydroxyl group bound at that position.

■2. The figure shows an important physical characteristic of DNA that helped lead to the discovery of the base pairing rules of A-T and C-G. What is this?

The consistent width of the double helix shows that any base pairing must be a purine with a pyrimidine, and not purine-purine or pyrimidine‒pyrimidine.

■5. What does the curve tell us about the change in energy of both reactions? What is the effect of the catalyst, if any?

The curve shows that the change in energy of both reactions is negative and that the change in energy is the same for both reactions. We also know that the presence of a catalyst lowers the activation energy.

14. Two complementary nucleotides are connected by _________ bonds. a. hydrogen b. ionic c. peptide d. phosphodiester e. covalent

a

15. In DNA, A pairs with T, and C pairs with G; these are examples of a specific type of reaction called a. complementary base pairing. b. a dehydration reaction. c. a reduction reaction. d. a hydrophobic reaction. e. a purine-purine reaction.

a

20. What accounts for the stability of the double-stranded DNA molecule? a. The hydrogen bonds between purines and pyrimidines b. Phosphodiester bonds between the nitrogenous bases c. Strong hydrogen bonds between the sugar and phosphate groups d. Its double-helix shape e. The direct bonding of the base to the phosphate molecule

a

30. A protein can best be defined as a polymer a. of amino acids. b. containing one or more polypeptide chains. c. containing 20 amino acids. d. containing 20 peptide linkages. e. containing double helices.

a

36. Which statement about the primary structure of a protein is false? a. It may be branched. b. It is held together by covalent bonds. c. It is unique to that protein. d. It determines the tertiary structure of the protein. e. It is the sequence of amino acids in the protein.

a

4. Ribose and deoxyribose are both found in nucleic acids. One difference between ribose and deoxyribose is that a. deoxyribose has one less oxygen molecule than ribose. b. ribose has one less oxygen molecule than deoxyribose. c. ribose is a pentose sugar, whereas deoxyribose is a hexose sugar. d. deoxyribose is found in RNA, whereas ribose is found in DNA. e. ribose binds a phosphate at the 3 position, whereas deoxyribose binds a phosphate at the 2 position.

a

51. The ability of an enzyme to change shape when it binds to its substrate is called a. induced fit. b. enzyme flex. c. the lock-and-key paradox. d. substrate-induced active site shaping. e. enzyme retrofit.

a

■40. Which protein structure is not destroyed by denaturation? a. Primary b. Secondary c. Tertiary d. Quaternary e. Both a and b

a

37. The shape of a folded protein is determined by a. its tertiary structure. b. the sequence of its amino acids. c. whether the peptide bonds have or linkages. d. the number of peptide bonds. e. the base-pairing rules.

b

41. The rate of a chemical reaction in a cell is the measure of how a. often the reaction occurs. b. quickly the substrates are converted to product. c. much energy must be added for the reaction to occur. d. much activation energy is required for the reaction to occur. e. easily the reaction is inhibited.

b

46. The enzyme sucrase increases the rate at which sucrose is broken down into glucose and fructose. Sucrase works by a. increasing the amount of free energy of the reaction. b. lowering the activation energy of the reaction. c. decreasing the equilibrium constant of the reaction. d. supplying energy to speed up the reaction. e. changing the shape of the active site.

b

49. The statement "enzymes are highly specific" means that certain a. enzymes are found in certain cells. b. reactions involving certain substrates are catalyzed by specific enzymes. c. enzymes require certain concentrations of substrates. d. enzymes are matched to reactions based on the activation energy level. e. concentrations of substrates work with certain enzymes.

b

53. In order for a reaction to occur, many enzymes require ATP and ADP, which temporarily bind to and then release from the substrate. ATP and ADP are therefore considered to be a. a side chain. b. coenzymes. c. substrates. d. a prosthetic group. e. cocatalysts.

b

58. Enzymes are highly sensitive to pH and temperature because a. changes in the environment raise their activation energy. b. changes in temperature and pH readily break their hydrogen bonds and can alter the enzyme shape. c. environmental changes affect their primary structure. d. at extreme temperatures and pH levels, coenzymes add chemical groups to the substrate. e. extremes of temperature and pH level change the ionization rate.

b

■13. The 5-carbon of deoxyribose in DNA is attached to a. adenine. b. a phosphate group. c. guanine. d. a pyrimidine. e. hydrogen.

b

■21. DNA carries genetic information in its a. helical form. b. sequence of bases. c. tertiary sequence. d. sequence of amino acids. e. phosphate groups.

b

■32. All proteins a. are enzymes. b. consist of one or more polypeptide chains. c. consist of three amino acids. d. have quaternary structures. e. are more soluble in nonpolar solvents than in water.

b

■43. An active site is a. the part of the substrate that binds with an enzyme. b. the part of the enzyme that binds with a substrate. c. the site where energy is added to an enzyme catalyst. d. the site where enzymes are found in cells. e. important in determining secondary structure.

b

■45. The molecules that are acted on by an enzyme are called a. products. b. Substrates. c. carriers. d. prosthetics. e. effectors.

b

■52. You are given a reaction and are told it is at "saturation." To determine if this is true, you should add _______________ and see if the reaction rate ___________. a. ATP; increases b. more substrate; increases c. a competitive inhibitor; decreases d. a downstream product; decreases e. a noncompetitive inhibitor; decreases

b

■55. An allosteric inhibitor a. decreases the concentration of an inactive enzyme. b. changes the shape of an enzyme. c. increases the concentration of a product. d. changes the shape of a substrate. e. increases the concentration of an enzyme-subs

b

■57. The process by which a final product acts as an inhibitor to the enzyme that catalyzes the commitment step in a metabolic pathway is called a. feedback activation. b. feedback inhibition. c. positive feedback. d. concerted activation. e. competitive inhibition.

b

■6. If enzyme 2 is inactive, which end product will be produced from the metabolic pathway? （図を見る）

b

■8. The sides of the "ladder" that makes up a nucleic acid molecule are made of a. nitrogenous bases. b. pentose sugars and phosphate groups. c. purines. d. pyrimidines. e. nucleosides.

b

1. A nucleotide consists of a pentose sugar, a phosphate group, and a(n) a. lipid. b. acid. c. nitrogen-containing base. d. amino acid. e. glycerol.

c

11. Which statement about DNA and RNA is true? a. DNA is single-stranded and RNA is double-stranded. b. DNA is only informational and RNA is only catalytic. c. DNA contains deoxyribose and RNA contains ribose. d. DNA is transcribed and RNA is replicated. e. DNA contains uracil (U) and RNA contains thymine (T).

c

16. According to the principle of complementary base pairing, purines always pair with a. deoxyribose sugars. b. uracil. c. pyrimidines. d. adenine. e. guanine.

c

2. A nucleotide in DNA is made up of a. four bases. b. a base plus a ribose sugar. c. a base plus a deoxyribose sugar plus phosphate. d. a sugar plus a phosphate. e. a sugar and a base.

c

23. Consider the following double-stranded DNA region: 5-TGCCAT-3 3-ACGGTA-5 If the lower strand is transcribed, which strand will result? a. 3-TGCCAT-5 b. 5-TCGGTA-3 c. 5-UGCCAU-3 d. 3-UGCCUA-5 e. 5-TCGGUT-3

c

39. A(n) _________ protein is a protein that has become nonfunctional due to the loss of its three-dimensional structure. a. permanent b. reversible c. denatured d. hydrolyzed e. environmentalized

c

42. Trypsin and elastase are both enzymes that catalyze hydrolysis of peptide bonds. But trypsin only cuts next to lysine and elastase only cuts next to alanine. Why? a. Trypsin is a protein, and elastase is not. b. Activation energy for the two reactions is different. c. The shape of the active site for the two enzymes is different. d. One of the reactions is anabolic and the other is catabolic. e. Hydrolysis of lysine bonds requires water, whereas hydrolysis of alanine bonds does not.

c

44. The active site of an enzyme a. never changes shape. b. forms no chemical bonds with substrates. c. determines, by its structure, the specificity of the enzyme. d. looks like a lump projecting from the surface of the enzyme. e. changes the energy of the reaction.

c

5. Which base is not found in DNA? a. Thymine b. Adenine c. Uracil d. Guanine e. Cytosine

c

50. Which of the following is an enzyme? a. Copper b. Heme c. Catalase d. Hydrogen peroxide e. Retinal

c

7. Nucleotides in RNA are connected to one another in the polynucleotide chain by a. covalent bonds between bases. b. covalent bonds between sugars. c. covalent bonds between sugar and phosphate. d. hydrogen bonds between purines. e. hydrogen bonds between any bases.

c

■18. DNA molecules can differ from one another in their a. physical shape. b. function. c. base sequences. d. hydrogen bonds. e. complementary base pairing.

c

■24. If there is an exposed purine during DNA replication, what will be joined to it? a. Any purine b. One specific purine c. One specific pyrimidine d. Any pyramidine e. A phosphate group

c

■26. A macromolecule isolated from the bone of dinosaurs is found to have primary chains of nitrogen-carbon-carbon repeats. It would be classified as what type of molecule? a. Polysaccharide b. Oligosaccharide c. Polypeptide d. Triglyceride e. Lipid

c

■27. Which solution is least likely to denature an enzyme? a. Urea b. Acetic acid c. Distilled water d. Boiling water e. Mercaptoethanol

c

■34. Theoretically, the number of different proteins that can be made from 50 amino acids is a. 5020. b. 20 × 50. c. 2050. d. 1050. e. 250.

c

17. What is the nucleotide sequence of the complementary strand of the DNA molecule 5-AATGCGA-3? a. 3-CCGTTAT-5 b. 3-AATGCGA-5 c. 3-GGCATAG-5 d. 3-TTACGCT-5 e. 5-AGCGTAA-3

d

19. The double-helix structure of DNA is the overall result of a. covalent base pairings. b. the covalent bonding of purines and pyrimidines. c. the phosphodiester bonds between deoxyribose and phosphate. d. hydrogen bonding of the two complementary polynucleotide strands. e. ionic bonding of base pairs.

d

47. The binding of substrate to enzyme creates a(n) a. transition state. b. activation groove. c. catalyst. d. enzyme-substrate complex. e. energy barrier.

d

■. Cytosine is a pyrimidine that forms three hydrogen bonds. Uracil is also a pyrimidine. Based on this information, one can conclude that uracil forms ______ hydrogen bonds and pairs with __________________. a. three; guanine (a two-bond pyrimidine) b. three; adenine (a three-bond purine) c. three; guanine (a three-bond purine) d. two; adenine (a two-bond purine) e. two; thymine (a two-bond pyrimidine)

d

■10. Which statement about the differences between DNA and RNA is false? a. DNA has thymine, whereas RNA has uracil. b. DNA usually has two polynucleotide strands, whereas RNA usually has one strand. c. DNA has deoxyribose sugar, whereas RNA has ribose sugar. d. DNA is a polymer, whereas RNA is a monomer. e. In DNA, A pairs with T, whereas in RNA, A pairs with U.

d

■29. Almost all enzymes are a. DNA. b. lipids. c. carbohydrates. d. proteins. e. amino acids.

d

■31. Which statement about proteins is true? a. They are insoluble in water. b. They are the structural units of glycogen. c. They possess glycosidic linkages between amino acids. d. Many function as enzymes. e. They are involved in information storage.

d

■33. Amino acids can be grouped according to the properties of their a. amino groups. b. hydrogen. c. carboxyl groups. d. R groups. e. carbon.

d

■48. The enzyme glucose oxidase binds the 6-carbon sugar glucose and catalyzes its conversion to glucono-1,5-lactone. Mannose is also a 6-carbon sugar, but glucose oxidase cannot bind mannose. The specificity of glucose oxidase is based on the a. free energy of the transition state. b. activation energy of the reaction. c. change in free energy of the reaction. d. three-dimensional shape and structure of the active site. e. rate constant of the reaction.

d

■9. The nucleotide sequence of DNA a. is the same in all organisms of a species. b. contains only information for translation. c. evolved before RNA. d. contains the four bases A, T, G, and C. e. All of the above

d

■５６. Which statement about the feedback inhibition of enzymes is false? a. It is usually exerted through allosteric effects. b. It is directed at the enzyme that catalyzes the commitment step in a metabolic pathway. c. It affects the rate of a reaction, not the concentration of the enzyme. d. It acts by permanently modifying the active site. e. It is an example of reversible inhibition.

d

12. RNA differs from DNA in that RNA a. contains uracil instead of thymine. b. is single-stranded, whereas DNA is double-stranded. c. is an intermediate in information transfer, whereas DNA encodes hereditary information. d. contains ribose, whereas DNA contains deoxyribose. e. All of the above

e

22. Which of the following depend(s) on complementary base pairing? a. DNA replication b. Transcription c. Translation d. Folding of an RNA molecule back on itself e. All of the above

e

28. When an egg is exposed to extreme heat it turns from a liquid substance into a solid substance. Even when the egg is allowed to cool, these changes are not reversible for a number of reasons. Which is not one of those reasons? a. Water has been removed from the egg proteins. b. Rapidly moving molecules have broken apart hydrogen bonds and hydrophobic interactions in the egg's proteins. c. Proteins in the egg have become denatured and lost secondary and tertiary structure. d. The denatured proteins have aggregated. e. Fats in the egg have become saturated and less fluid.

e

38. The amino acids of the protein keratin are arranged in an alpha helix. This secondary structure is stabilized by: a. covalent bonds. b. peptide bonds. c. glycosidic linkages. d. polar bonds. e. hydrogen bonds.

e

54. Enzymes are sensitive to a. temperature. b. pH. c. irreversible inhibitors such as DIPF. d. allosteric effectors. e. All of the above

e

6. The four nitrogenous bases of RNA are abbreviated as a. A, G, C, and T. b. A, G, T, and N. c. G, C, U, and N. d. A, G, U, and T. e. A, G, C, and U.

e

■3. Which statement about purines and pyrimidines is true? a. Purines include the bases of cytosine and thymine; pyrimidines include the bases of adenine and guanine. b. Pyrimidines are found in RNA, whereas purines are found in DNA. c. Purines consist of hydrogen, carbon, oxygen, and nitrogen, whereas pyrimidines have phosphorus, hydrogen, carbon, oxygen, and nitrogen. d. Purines have only single bonds in their structure, whereas pyrimidines have both single and double bonds. e. Purines are double-ring structures, whereas pyrimidines are single-ring structures.

e

■35. How many different types of tetrapeptides (molecules with four linked amino acids) can be made from the 20 common amino acids? a. 4 b. 80 c. 256 d. 8,000 e. 160,000

e