Question

CHEM 122 Exam 4 Fall 2008

1. The structural formulas of amino acids are the same except for the following groups: a. CO2H b. NH2 c. side group R d. H-bond e. all of these

2. H2NCH(CH3)CO2H side group is: a. polar b. hydrophobic c. acidic d. hydrophilic e. basic

3. The peptide bonds that combine amino acids in a protein are: a. ester bonds b. ether bonds c. sulfide bonds d. amide bonds e. glycosidic bonds

4. The 10 structure of a protein is: a. -helix b. –helix c. attractions of side groups d. sequence of amino acids e. none of these

5. The bonds which are important in the 20 structure of a protein are: a. H-bonds b. hydrophobic interactions c. disulfide bonds d. salt bridges e. peptide bonds

6. The 30 structure of a protein with R groups of -CH2COO- and –(CH2)4NH3+ would have the following interactions: a. disulfide bonds b. salt bridges c. H-bonds d. hydrophobic interactions e. peptide bonds

7. H2NCH2CO2H is an amino acid with: a. – charge b. + charge c. L-configuration d. D-configuration e. achiral

8. In a typical amino acid zwitterion, the CO2H group has: a. + charged b. - charged c. neutral d. none of these e. all of these

9. At a specific PH , known as a PI ( isoelectric point ) the over all charge is: a. 0 b. + c. - d. none of these e. all of these

10. At a PH < 5 , the zwitterion for alanine ( PI = 6 ), will have a net charge of: a. - b. + c. 0 d. none of these e. all of these

11. Denaturation of a protein: a. changes the 10 structure of a protein b. is always irreversible c. hydrolyzes peptide bonds d. change the R groups e. disrupts the 20 , 30 , and 40 strucures of a protein

12. The enzyme which catalyzes CH3COCOO - ----- CH3CH(OH)COO - is called: a. oxidoreductase b. transferase c. hydrolase d. lyase e. isomerase

13. Zymogene is: a. an inactive enzyme b. stored in an organ c. can be activated when needed d. can be activated by change of PH e. all of these

14. An enzyme: a. increases the reaction temperature b. is converted to a product c. catalyzes the reaction d. increases the reaction PH e. none of these

15. Compared to an uncatalyzed reaction, an enzyme-catalyzed reaction: a. uses less substrate b. produces different products c. occurs at a faster rate d. requires more energy e. requires an higher temperature

16. The general function of an enzyme in the body is to: a. catalyze chemical reactions b. maintain a neutral PH c. act as a reactant d. maintain body energy e. remove waste products

17. When a substance bonds to an enzyme for reaction, its place of binding is the: a. allosteric site b. secondary site c. tertiary site d. active site e. none of these

18. Urease catalyzes only the hydrolysis of urea. This limited activity is called a. moderate specifity b. noncompetitive specifity c. hyperspecifity d. absolute specifity e. no specifity

19. In the induced-fit model, the active site: a. stays the same shape during binding b. adapts to the shape of the substrate c. uses a cofactor to change substrate shape d. uses an inhibitor to change substrate shape e. none of these

20. A competitive inhibitor is one that: a. binds to the enzyme far from the active site b. destroys the substrate c. binds to the allostic site on an enzyme d. forms a complex with the substrate e. binds to active site in place of the substrate

21. Nitrogen-containing base and a sugar is: a. nucleoside b. purine c. pyrimidine d. nucleotide e. base pair

22. Nitrogen-containing base, a sugar, and a phosphate group is: a. nucleoside b. base pair c. nucleotide d. purine e. pyrimidine

23. Which of the following can not be found in a nucleotide of RNA: a. purine b. pyrimidine c. phosphate d. ribose e. deoxyribose

24. The process in which the DNA double helix unfolds, and each strand serves as a template for the synthesis of a new strand is : a. transcripition b. translation c. complementation d. replication e. restriction

25. The type of RNA which carries the gentic information for protein synthesis is: a. hRNA b. rRNA c. mRNA d. tRNA e. sRNA

Answer 1

1. The structural formulas of amino acids are the same except for the side group R.
2. H2NCH(CH3)CO2H side group is hydrophobic.
3. The peptide bonds that combine amino acids in a protein are amide bonds.
4. The 1o strructure of a protein is sequence of amino acids.
5. The bonds which are important in the 2o structure of a protein are H-bonds.
6. The 3o structure of a protein with R groups of -CH2COO- and -(CH2)4NH3+ would have the salt bridges. Explanation- Salt bridges are the weak ionic interaction between a positive and negative R groups. Due to their charge they can also interact with water so the ionic interaction between them is weak.
7. H2NCH2CO2H is an amino acid with achiral. Explanation - Glycine is the simplest amino acid and it has hydrogen atom as its side chain rather than a bulky side chain. So, it is achiral.
8. In a typical amino acid zwitterion, the CO2H group has negative (-) charge. Explanation- In zwitterion, the net charge of an amino acid is 0. The positive charge of NH2 group and negative charge of CO2H group neutralize each other.
9. At a specific pH, known as PI (isoelectric point) the overall charge is 0. Explanation -. At the PI, the amino acids exist as zwitterions.
10. At a pH<5, the zwitterion for alanine (PI=6), will have a net charge of a positive (+). Explanation - At low pH, the surrounding has maximum free protons, so they will interact with the molecules and the molecules will be protonated. In alanine the COO- accepts proton and becomes neutral similarly the -NH2 also accepts proton and becomes positive. Hence, at low pH the net charge is positive.
11. Denaturation of a protein disrupts the 2o, 3o and 4o structures of a protein. Explanation- Denaturation is not strong enough to break the peptide bond.
12. The enzyme which catalyzes CH3COCOO- -------- CH3CH(OH)COO- is called oxidoreductase.
13. Zymogen is an inactive enzyme, stored in an organ, can be activated when needed, can be activated by change of pH (all of these).
14. An enzyme catalyzes the reaction.
15. Compared to an uncatalyzed reaction, an enzyme-catalyzed reaction : occurs at a faster rate.
16. The general function of an enzyme in the body is to : catalyze chemical reactions.
17. When a substance bonds to an enzyme for reaction, its place of binding is the active site.
18. Urease catalyzes only the hydrolysis of urea. This limited activity is called absolute specifity.
19. In the induced-fit model, the active site adapts to the shape of the substrate.
20. A competitive inhibitor is one that binds to active site in place of the substrate.
21. Nitrogen containing base and a sugar is a nucleoside.
22. Nitrogen-containing base, a sugar and a phosphate group is a nucleotide.
23. Deoxyribose can not be found in a nucleotide of RNA. Explanation- RNA contains purine, pyrimidine, phosphate and a ribose sugar.
24. The process in which the DNA double helix unfolds, and each strand serves as a template for the synthesis of a new strand is replication. Explanation - During replication, the DNA is amplified where the double stranded DNA is unwound by helicase enzyme and each of the stand serves as template fo the synthesis of new daughter strands.
25. The type of RNA which carries the genetic information for protein synthesis is mRNA. Explanation - The information for protein synthesis is carried by mRNA from the DNA and the information is interpreted by tRNA with help of rRNA associated with ribosome.