2011 biochem midterm

Question 1

Which of the following is the last step in DNA synthesis?
A. removal of primers
B. primer binding
C. addition of nucleotide by polymerase
D. ligation of newly synthesized strands
E. separation of DNA strands

Answer 1

D. ligation of newly synthesized strands

Question 2

What is the biochemical role of vitamin C?
A. cross-linkage
B. collagen degradation
C. protein folding
D. hydroxylation of proline
E. glycosylation

Answer 2

D. hydroxylation of proline

Question 3

What happens to albumin in egg white when the egg is boiled?
A. degradation 
B. denaturation 
C. lipidation
D. oligomerization
E. hydroxylation

Answer 3

B. denaturation

Question 4

A competitive inhibitor was introduced to an enzyme catalyzed reaction. What is the effect of this on enzyme activity?
A. increase Vmax
B. decrease Vmax
C. no effect
D. decrease Km
E. Increase Km

Answer 4

E. Increase Km

Question 5

What is the effect of nucleotide analogs when they are administered?
A. inhibition of DNA synthesis
B. catalyze elongation 
C. degrade the DNA 
D. denaturation

Answer 5

A. inhibition of DNA synthesis

Question 6

Which one does NOT affect glycogen degradation in muscles?
A. ATP
B. AMP
C. glucagon
D. epinephrine
E. Glucose-6-phosphate

Answer 6

C. glucagon

Question 7

What is the function of copper in the collagen structure?
A. Cross-linking 
B. Hydroxylation 
C. Glycosylation
D. Amino acid removal
E. Degradation

Answer 7

A. Cross-linking

Question 8

What is a metaphasic chromosome?
A. naked DNA molecule without histones
B. single-stranded DNA
C. 4 DNA stands with histones
D. double-stranded DNA molecule with histones
E. uncompacted DNA

Answer 8

C. 4 DNA stands with histones

Question 9

What is the action of restriction enzymes?
A. degrading the DNA molecule
B. Cutting Fragments of DNA into nucleotides
C. Restricting the growth of bacteria
D. Cutting DNA at specific nucleotide sequences
E. Prevents the formation of the sugar-phosphate backbone

Answer 9

D. Cutting DNA at specific nucleotide sequences

Question 10

What is the significance of the annealing temperature in a PCR reaction?
A. degrading primers
B. elongation of DNA strands
C. binding of primers
D. separation of the DNA strands
E. denaturation of Taq DNA polymerase

Answer 10

C. binding of primers

Question 11

Glucosyl-transferase identifies what?
A. Misfolded sequences
B. Correctly folded proteins 
C. NH2 groups on proteins 
D. Hydrophilic amino acids

Answer 11

A. misfolded sequences

Question 12

What is the function of the leader sequence?
A. targeting to peroxisomes
B. targeting of nuclear proteins
C. targeting of proteins to mitochondria
D. limiting cytoplasmic proteins to specific regions
E. coupling of ribosomes to ER

Answer 12

E. coupling of ribosomes to ER

Question 13

A lysosomal protein has its leader sequence cleaved in ER, where does it end up?
A. plasma membrance
B. lysosome 
C. peroxisome 
D. nucleus
E. ER

Answer 13

B. lysosome

Question 14

What is the function of DNA polymerase?
A. ligation of DNA strands
B. stabilizing single-stranded DNA
C. removes primers
D. adding nucleotides
E. relaxing the double helix

Answer 14

D. adding nucleotides

Question 15

Which technique do we use to separate DNA molecules on the basis of size?
A. PCR
B. Gel electrophoresis 
C. DNA sequencing 
D. DNA probing
E. Hybridization

Answer 15

B. Gel electrophoresis

Question 16

What are proto-oncogenes?
A. genes involved in cell death
B. genes that restrict growth
C. genes involved in normal cell function and regulation
D. activated genes
E. cancer-causing genes

Answer 16

C. genes involved in normal cell function and regulation

Question 17

Where are proteins targeted if they have mannose-6-phosphate?
A. mitochondria 
B. peroxisomes 
C. lysosome
D. plasma membrane
E. cytoplasm

Answer 17

C. lysosome

Question 18

If an antibiotic binds to the 30s subunit, what will be inhibited?
A. elongation
B. initiation
C. translocation
D. termination
E. mRNA reading

Answer 18

B. initiation

Question 19

What is a structural feature of collagen?
A. heavily hydroxylated
B. beta sheets
C. made of tetrapeptide repeats
D. rich in phenylalanine

Answer 19

A. heavily hydroxylated

Question 20

What nucleotide modification is involved in the regulation of large chromosome regions?
A. methylation
B. lipidation
C. hydroxylation 
D. oligomerization 
E. glycosylation

Answer 20

A. methylation

Question 21

What is the difference between HbS and HbA?
A. S-S bonds
B. Covalent linkage 
C. Ionic attractions 
D. Primary structure 
E. Hydrogen bonds

Answer 21

D. Primary structure

Question 22

Relating temperature to enzyme activity, what is the reason behind decreased enzyme activity at higher temperatures?
A. Denaturation
B. Decreased ΔG
C. Substrates degrade
D. Decreased activation energy

Answer 22

A. Denaturation

Question 23

What is the effect of an allosteric effector on an enzyme?
A. interacting with the active site covalently
B. changing the protein configuration
C. always decreases enzyme activity
D. regulating enzyme activity reversibly via the active site
E. always increases enzyme activity

Answer 23

B. changing the protein configuration

Question 24

Which is most probably used to regulate a metabolic pathway?
A. regulating the first step that ends in the product
B. regulation of a step that branches
C. allosteric regulation of the fastest step in the pathway
D. regulating the step with ΔG=0
E. regulating the final step leading to the formation of the product

Answer 24

A. regulating the first step that ends in the product

Question 25

What is a feature of 5’ capping? A. the cap is added is a 5’-3’ direction B. it is catalyzed by RNA polymerase II C. It is made of a 7-methylguanosine D. The cap is added after polyadenylation and splicing E. It is added to the 20th nucleotide in the mRNA

Answer 25

C. It is made of a 7-methylguanosine

Question 26

What is a characteristic of hemophilia A? A. mutation is the immunosuppressive factor VIII B. deficiency in the immunosuppressive factor VIII C. excess of blood clotting factor VIII D. platelet abnormalities E. prolonged bleeding

Answer 26

E. prolonged bleeding

Question 27

``` In cystic fibrosis, which ion is transported by the transmembrane regulator protein? A. K+ B. Na+ C. Cl- D. Ca++ E. Mg+ ```

Answer 27

C. Cl-

Question 28

``` If one parent is normal and one is a carrier of cystic fibrosis, what is the % of children that will have cystic fibrosis? A. 0% B. 25% C. 50% D. 75% E. 100% ```

Answer 28

A. 0% | autosomal recessive trait

Question 29

``` What is the difference between the infectious prion protein and the normal prion protein in Creutzfeldt-Jakob disease? A. increased alpha helices B. disrupted covalent linkages C. S-S bonding deficient D. Increased beta sheets E. Ionic bonds ```

Answer 29

D. Increased beta sheets

Question 30

``` What is the substrate that is used by glycogen synthase to synthesize glycogen? A. UTP-glucose B. UDP-glucose C. Glucose-6-phosphate D. Glucose-1-phosphate E. D-glucose ```

Answer 30

B. UDP-glucose

Question 31

What is the difference between eukaryotic and prokaryotic translation? A. using less energy B. searching for the start codon in initiation C. using less initiation factors D. Tu delivers charged t-RNA E. Smaller ribosomes

Answer 31

B. searching for the start codon in initiation

Question 32

``` At what level does interferon regulation of gene expression occur? A. transcription initiation B. transcription termination C. polyadenylation and splicing D. mRNA stability E. global regulation ```

Answer 32

A. transcription initiation

Question 33

Why isn’t DNA synthesis in DNA sequencing PCR geometric? A. two primers used B. one primer used C. higher annealing temperature D. half the number of initial strands used E. because of using a slower polymerase

Answer 33

B. one primer used

Question 34

``` What characterizes RNA polymerase I? A. not sensitive to α-amanitin B. catalyzes t-RNA synthesis C. has a proofreading activity D. uses dNTP’s E. catalyzes mRNA synthesis ```

Answer 34

A. not sensitive to α-amanitin

Question 35

``` A defect in which repair system leads to HNPCC? A. base excision repair B. nucleotide excision repair C. 3’-5’ exonuclease activity D. DNA mismatch repair E. Dimer repair ```

Answer 35

D. DNA mismatch repair | HNPCC= Hereditary nonpolyposis colorectal cancer

Question 36

``` What group in ddNTP is responsible for termination in a PCR reaction? A. 1’OH B. 2’H C. 3’H D. 4’OH E. 5’OH ```

Answer 36

C. 3’H

Question 37

``` What are ribozymes? A. splicing RNA B. ribosome forming RNA C. catalytic RNA D. amino acid carrying RNA E. Protein synthesizing RNA ```

Answer 37

C. catalytic RNA

Question 38

``` What do chaperones bind to in a protein to assist in folding? A. buried hydrophobic amino acids B. exposed hydrophilic amino acids C. basic amino acids D. buried hydrophilic amino acids E. exposed hydrophobic amino acids ```

Answer 38

E. exposed hydrophobic amino acids

Question 39

``` An enzyme is stored as an inactive precursor. It is activated irreversibly by cleavage of a section of the polypeptide. What is this mechanism of activation called? A. allostery B. cooperativity C. covalent activation D. proteolysis ```

Answer 39

D. proteolysis

Question 40

``` What is the function of the BCR-ABL protein? A. Serine-threonine kinase B. tyrosine kinase C. transcription factor D. protein folding E. apoptosis regulation ```

Answer 40

B. tyrosine kinase