Chemistry 2B - Exam 3 (April 21, 1998)

Please answer the following questions, selecting the best answer. There is only one correct choice, although you can choose "all of the above" or "none of the above" for some questions. However, select only one correct answer. Each question is worth 2 points, for a total of 100 points on the exam.

1. The enzyme amylase might be expected to catalyze the hydrolysis of

(a) proteins

(b) starch

(c) nucleic acids

(d) fats

2. The region of the enzyme molecule to which the substrate binds is the

(a) binding site

(b) substrate site

(c) active site

(d) allosteric site

3. Which of the following does not apply to enzymes?

(a) The substrate binds at the active site.

(b) The common name always ends in suffix -ase.

(c) They may or may not contain a cofactor.

(d) They may be used in disease diagnosis.

4. A physiologic function of a peptidase is to break down

(a) fats

(b) carbohydrates

(c) proteins

(d) nucleic acid

5. Enzyme G has an optimum pH of 6; enzyme H has an optimum pH of 11.

(a) Both enzymes will be active at pH = 1.

(b) Enzyme G will function better in acidic environment.

(c) Enzyme H will function better in acidic environment.

(d) Neither enzyme will have enzymatic activity at pH 7.

6. The following can denature an enzyme:

(a) increase in temperature

(b) a decrease in pH

(c) an increase in pH

(d) all of these

7. Mercury(II) ions can be:

(a) enzyme cofactors

(b) tightly bound to enzymes

(c) enzyme activators

(d) all of these

8. The rate of an enzyme-catalyzed reaction is:

(a) unaffected by temperature

(b) measured in an assay

(c) not affected by substrate concentration

(d) independent of pH

9. A small molecule that binds to an enzyme at a site other than the active site and that activates the enzyme is called a:

(a) negative modulator

(b) coenzyme

(c) zymogen

(d) positive modulator

10. In the reaction sequence,

         Ea      Eb      Ec
      A ----> B ----> C ----> D, 

molecule D deactivates enzyme E_a. This process is known as:

(a) positive modulation

(b) negative modulation

(c) feedback inhibition

(d) zymogen activation

11. In order for a molecule to be a competitive inhibitor of an enzyme, it must:

(a) be an antibiotic

(b) carry a positive charge

(c) bind to the active site of the enzyme

(d) all of these

12. A polypeptide that becomes an active enzyme when a small peptide fragment is cleaved from the molecule is a(n):

(a) cofactor

(b) antigen

(c) antibody

(d) zymogen

13. When trypsinogen enters the small intestine it is activated to form

(a) chymotrypsin

(b) trypsin

(c) chymotrypsinogen

(d) pepsin

14. An endopeptidase enzyme would show specificity for:

(a) terminal peptide bonds of a peptide chain

(b) disulfide bonds of a peptide chain

(c) hydrogen bonds of a peptide chain

(d) interior peptide bonds of a peptide chain

15. A carboxypeptidase:

(a) is an endopeptidase

(b) catalyzes the hydrolysis of carbohydrates

(c) catalyzes the removal of the C-terminal amino acids

(d) all of these

16. The large soluble protein found in blood plasma and that may become a blood clot is:

(a) fibrin

(b) thrombin

(c) prothrombin

(d) fibrinogen

17. The components of a nucleotide are:

(a) base-sugar

(b) phosphate-base

(c) base-D-sugar-phosphate

(d) sugar-phosphate

18. This structure is:

(a) cytosine

(b) uracil

(c) adenine

(d) thymine

19. Nucleic acids contain:

(a) ester linkages

(b) purines

(c) pentoses

(d) all of these

20. The complementary base pairs in the DNA double helix are held together by

(a) phosphodiester bonds

(b) hydrogen bonds

(c) ionic bonds

(d) covalent bonds

21. Retroviruses are unique because

(a) their genetic code does not code for proteins

(b) they have no RNA

(c) their RNA is transcribed to DNA

(d) they use a completely different genetic code

22. The paths (central dogma) through which genetic information is transmitted and eventually expressed as protein are:

(a) RNA ---> RNA; RNA ---> DNA; DNA ---> protein

(b) DNA ---> RNA; RNA ---> RNA; DNA ---> protein

(c) DNA ---> DNA; DNA ---> RNA, RNA ---> protein

(d) DNA ---> DNA; RNA ---> RNA, RNA ---> protein

23. At the molecular level, a gene is a

(a) segment of mRNA that codes for a protein.

(b) segment of DNA that codes for a polypeptide or protein.

(c) three-letter base code that specifies one amino acid.

(d) all of these

24. Which of the following statements correctly describes DNA?

(a) the molecule contains two DNA strands

(b) the deoxyribose-phosphate backbones of the strands are wound in a double helix

(c) the DNA strands are antiparallel

(d) all of these

25. The process by which information contained in DNA is passed to mRNA is called:

(a) translation

(b) replication

(c) transcription

(d) protein synthesis

26. The enzyme required for transcription is

(a) intronase

(b) DNA polymerase

(c) unwinding protein

(d) RNA polymerase

27. The sequence of nucleotides in a DNA molecule, written 5' to 3', is dC-T-T-A-T-G. What is the complementary base segment, written 3' to 5' (anti-parallel to above sequence)?

(a) dC-A-T-A-A-G

(b) dC-T-T-A-T-G

(c) dG-A-A-U-A-C

(d) dG-A-A-T-A-C

28. In eukaryotic cells the amino acid that is always involved in the initiation step of protein synthesis is

(a) glycine

(b) methionine

(c) phenylalanine

(d) alanine

29. A tRNA molecule is activated by binding with its

(a) amino acid

(b) codon

(c) anticodon

(d) all of these

30. The triplet on messenger RNA that participates in translation of the genetic message is:

(a) tRNA

(b) a codon

(c) an anticodon

(d) a gene

31. Which of these must be present at the ribosome for protein synthesis to take place?

(a) mRNA

(b) tRNA

(c) rRNA

(d) all of these

32. The process by which information contained in mRNA is expressed as a protein is called

(a) replication

(b) translation

(c) peptide polymerizing

(d) transcription

33. A ribosome is:

(a) composed of DNA and lipoproteins

(b) the site of protein synthesis in the cell

(c) composed of RNA and DNA

(d) found in the nucleus of the cell

34. The genetic code is degenerate because

(a) it can be broken

(b) most amino acids have more than one code word (codon)

(c) it is defective

(d) all of these

35. Gene mutations in an organism:

(a) are always harmful

(b) may cause a molecular disease

(c) have nothing to do with evolution

(d) none of these

36. Recombinant DNA techniques:

(a) may insert a gene from another organism

(b) utilize RNA clipping enzymes

(c) utilize no enzymes

(d) have little use in industry

37. An aerobic cell

(a) requires glucose as an energy source

(b) requires oxygen for survival

(c) is only found in muscle tissue

(d) all of these

38. Carbohydrate digestion begins:

(a) and ends in the stomach

(b) in the mouth and is completed in the stomach

(c) in the mouth and is completed in the small intestine

(d) in the stomach and is completed in the small intestine

39. The products of the hydrolysis of fats include:

(a) glycerol and fatty acids

(b) bile salts

(c) glycerol and amino acids

(d) oil and water

40. Enzymes that catalyze the hydrolysis of fats are known as:

(a) proteases

(b) lipases

(c) ureases

(d) nucleotidases

41. The class of biological molecules that should provide the most energy for the body is:

(a) carbohydrates

(b) proteins

(c) nucleic acids

(d) fats

42. Examples of sources of complete proteins include all of the following except:

(a) eggs

(b) milk

(c) wheat

(d) liver

43. Vitamin K deficiency leads to:

(a) rickets

(b) scurvy

(c) impaired blood-clotting

(d) night blindness

44. In the body

(a) potassium ions are the principal cations of the blood

(b) sodium ions are found mostly outside cells

(c) sodium ions and potassium can replace one another

(d) potassium ions are found mostly outside cells

45. The formed elements of the blood include

(a) erythrocytes

(b) thrombocytes

(c) leukocytes

(d) all of these

46. Blood serum contains

(a) no formed elements and no clotting factors

(b) clotting factors but no formed elements

(c) formed elements and clotting factors

(d) formed elements but no clotting factors

47. Interferons are

(a) antiviral proteins

(b) produced using recombinant DNA technology

(c) effective at very low concentrations

(d) all of these

48. The nature of a buffer pair is such that when small amounts of an acid or base are added to a buffered solution:

(a) pH changes very little

(b) pH decreases a great deal

(c) pH increases a great deal

(d) none of these

49. The following occurs at the lungs

(a) hemoglobin molecules pick up protons

(b) red blood cells exchange carbon dioxide for oxygen

(c) white blood cells pick up antigens.

(d) red blood cells exchange oxygen for carbon dioxide

50. How many molecules of oxygen can be carried by two molecules of hemoglobin?

(a) 2

(b) 4

(c) 6

(d) 8

Answer Key to Chem 2b Exam 3

1. b

2. c

3. b

4. c

5. b

6. d

7. b

8. b

9. d

10. c

11. c

12. d

13. b

14. d

15. c

16. d

17. c

18. c

19. d

20. b

21. c

22. c

23. b

24. d

25. c

26. d

27. d

28. b

29. a

30. b

31. d

32. b

33. b

34. b