QUESTION NO. 1

Patients with the rare genetic disease xeroderma pigmentosum (XP) are very sensitive to light and are highly susceptible to skin cancers. The study of such patients has enhanced our knowledge of DNA repair because XP is caused by defective DNA repair nucleotide excision repair. (A variant, XP-V, is deficient in postreplication repair.) In nucleotide excision repair

A. removal of the damaged bases occurs on only one strand of the DNA.

B. only thymine dimers generated by UV light can be removed .

C. the excision nuclease is an exonuclease.

D. a single multifunctional enzyme carries out the repair process.

E. only the damaged nucleotides are removed.

QUESTION NO.2

Homologous recombination:

A. occurs only between two segments from the same DNA molecule.

B. requires that a specific DNA sequence be present.

C. requires one of the duplexes undergoing recombination be nicked in both strands.

D. involves a four-stranded intermediate (Holliday junction) which can be cut in either of two ways.

E. is catalyzed by transposases.

QUESTION NO. 3

The sigma (σ) subunit of prokaryotic RNA polymerase

A. part of the core enzyme.

B. binds the antibiotic rifampicin.

C. is inhibited by α-amanitin.

D. must be present for transcript ion to occur.

E. specifically recognizes promoter sites.

QUESTION NO. 4

Antisense nucleic acids

A. complementary to mRNA would enhance translation .

B. could result if a gene is inserted downstream of a promoter but in opposite direction to normal.

C. can have no clinical uses.

D. react only with DNA.

E. are necessary for recombinant DNA technology.

QUESTION NO. 5
There is a window in which the effect is primarily on viral replication since AZT is much less effective at competing with dTTP for incorporation by cellular DNA polymerases because of the proofreading ability of DNA polymerases. Proofreading activity co maintain the fidelity of DNA synthesis

A. occurs after the synthesis has been completed.

B. is a function of 3' co 5' exonuclease activity intrinsic to or associated with DNA polymerases.

C. requires the presence of an enzyme separate from the DNA polymerases.

D. removes mismatched bases in the interior of the chain.

E. does nor occur in prokaryotes.

QUESTION NO. 6

Topoisomerases

A. regulare the level of superhelicity of DNA in cells

B. always break only one strand of DNA.

C. can create but nor remove supercoils.

D. must hydrolyze ATP for their action.

E. of the subclass gyrases, introduce negative superhelices in eukaryotic DNA.

QUESTION NO. 7

Formation of mature insulin includes all of the following except

A. removal of a signal peptide.

B. folding into a three-dimensional structure .

C. disulfide bond formation.

D. Dremoval of a peptide from an internal region.

E. γ-carboxylation of glutamate residues.

QUESTION NO. 8
Interfering with topoisomerases is one way of inhibiting DNA replication. Certain antibiotics target DNA gyrase(type II topoisomerase) of E. coli inhibiting catalytic activity. Topoisomerase poisons prevent resealing of the phosphodiester bond, leaving covalent protein-DNA junctions. These compounds are used in treating infections and as chemotherapeutic agents. DNA gyrase

A. ATP subunits hydrolyze ATP to form new phosphodiester bonds.

B. removes negative supercoils.

C. swivelase subunits create and reseal transient nicks on both strands.

D. increases the linking number.

E. occurs in eukaryotes as well as prokaryores.

QUESTION NO. 9
Cystic fibrosis is a frequent generic disease of Caucasians. The CF gene codes for a protein called the cystic fibrosis transmembrane conductance regulator (CFTR) which functions as a cAMP-regulated chloride channel. The protein has two membrane-spanning domains, two domains that interact with ATP, and one regulatory domain. The most common defect is in the gene for one of the ATP binding domains. The result is a protein that does not fold correctly in the endoplasmic reticulum, is not properly glycosylated, and is nor transported to the cell surface. Rather, it is degraded in the cytosol within proteasomes. Drugs that foster chaperone interaction with the mutant protein are a potential therapeutic approach. Chaperones

A. are always required to direct the folding of proteins.

B. when bound to protein increase the rate of protein degradation.

C. usually bind to strongly hydrophilic regions of unfolded proteins.

D. sometimes maintain proteins in an unfolded state to allow passage through membranes.

E. foster aggregation of proteins into plaques.

Question

QUESTION NO. 1

Patients with the rare genetic disease xeroderma pigmentosum (XP) are very sensitive to light and are highly susceptible to skin cancers. The study of such patients has enhanced our knowledge of DNA repair because XP is caused by defective DNA repair nucleotide excision repair. (A variant, XP-V, is deficient in postreplication repair.) In nucleotide excision repair

A. removal of the damaged bases occurs on only one strand of the DNA.

B. only thymine dimers generated by UV light can be removed .

C. the excision nuclease is an exonuclease.

D. a single multifunctional enzyme carries out the repair process.

E. only the damaged nucleotides are removed.

QUESTION NO.2

Homologous recombination:

A. occurs only between two segments from the same DNA molecule.

B. requires that a specific DNA sequence be present.

C. requires one of the duplexes undergoing recombination be nicked in both strands.

D. involves a four-stranded intermediate (Holliday junction) which can be cut in either of two ways.

E. is catalyzed by transposases.

QUESTION NO. 3

The sigma (σ) subunit of prokaryotic RNA polymerase

A. part of the core enzyme.

B. binds the antibiotic rifampicin.

C. is inhibited by α-amanitin.

D. must be present for transcript ion to occur.

E. specifically recognizes promoter sites.

QUESTION NO. 4

Antisense nucleic acids

A. complementary to mRNA would enhance translation .

B. could result if a gene is inserted downstream of a promoter but in opposite direction to normal.

C. can have no clinical uses.

D. react only with DNA.

E. are necessary for recombinant DNA technology.

QUESTION NO. 5
There is a window in which the effect is primarily on viral replication since AZT is much less effective at competing with dTTP for incorporation by cellular DNA polymerases because of the proofreading ability of DNA polymerases. Proofreading activity co maintain the fidelity of DNA synthesis

A. occurs after the synthesis has been completed.

B. is a function of 3' co 5' exonuclease activity intrinsic to or associated with DNA polymerases.

C. requires the presence of an enzyme separate from the DNA polymerases.

D. removes mismatched bases in the interior of the chain.

E. does nor occur in prokaryotes.

QUESTION NO. 6

Topoisomerases

A. regulare the level of superhelicity of DNA in cells

B. always break only one strand of DNA.

C. can create but nor remove supercoils.

D. must hydrolyze ATP for their action.

E. of the subclass gyrases, introduce negative superhelices in eukaryotic DNA.

QUESTION NO. 7

Formation of mature insulin includes all of the following except

A. removal of a signal peptide.

B. folding into a three-dimensional structure .

C. disulfide bond formation.

D. Dremoval of a peptide from an internal region.

E. γ-carboxylation of glutamate residues.

QUESTION NO. 8
Interfering with topoisomerases is one way of inhibiting DNA replication. Certain antibiotics target DNA gyrase(type II topoisomerase) of E. coli inhibiting catalytic activity. Topoisomerase poisons prevent resealing of the phosphodiester bond, leaving covalent protein-DNA junctions. These compounds are used in treating infections and as chemotherapeutic agents. DNA gyrase

A. ATP subunits hydrolyze ATP to form new phosphodiester bonds.

B. removes negative supercoils.

C. swivelase subunits create and reseal transient nicks on both strands.

D. increases the linking number.

E. occurs in eukaryotes as well as prokaryores.

QUESTION NO. 9
Cystic fibrosis is a frequent generic disease of Caucasians. The CF gene codes for a protein called the cystic fibrosis transmembrane conductance regulator (CFTR) which functions as a cAMP-regulated chloride channel. The protein has two membrane-spanning domains, two domains that interact with ATP, and one regulatory domain. The most common defect is in the gene for one of the ATP binding domains. The result is a protein that does not fold correctly in the endoplasmic reticulum, is not properly glycosylated, and is nor transported to the cell surface. Rather, it is degraded in the cytosol within proteasomes. Drugs that foster chaperone interaction with the mutant protein are a potential therapeutic approach. Chaperones

A. are always required to direct the folding of proteins.

B. when bound to protein increase the rate of protein degradation.

C. usually bind to strongly hydrophilic regions of unfolded proteins.

D. sometimes maintain proteins in an unfolded state to allow passage through membranes.

E. foster aggregation of proteins into plaques.

Accepted Answer

Nucleotide excision repair (NER) is the main pathway used by mammals to remove bulky DNA lesions as…