29. Which of the following is NOT true about histone modifications and the enzym

Question

29. Which of the following is NOT true about histone modifications and the enzymes that generate them?

A. The enzymes responsible are often part of multiprotein complexes that include transcription factors.

B. The enzymes responsible can work with chromatin remodeling complexes to alter specific regions of chromatin in response to environmental signals. C. The modifications can be passed on by epigenetic inheritance. D. The enzymes responsible can create histone variants.

E. All of these choices are correct.

30. Researchers trying to determine the genetic basis of a rare metabolic disease have been examining the pedigrees of three families affected with the disease. For all of the families, the disease is coinherited with markers on chromosome 2 and chromosome 8. They later observe that family members show no disease if they have the defect on only chromosome 2 or on only chromosome 8. At this point the researchers could conclude:

A. the disease is caused by defects in two or more genes on different chromosomes.

B. the gene product of chromosome 2 combines with the product from chromosome 8 to form a defective protein.

C. family members with no disease have mutations that compensate for the defects on chromosome 2 or 8.

D. the same disease can be caused by defects in single genes on different chromosomes.

E. family members with a single defect have a predisposition for inheriting the disease.

32. The term "semidiscontinuous DNA replication" indicates:

A. implementation of multiple replication forks.

B. the insertion of DNA to replace the RNA primers during lagging-strand synthesis. C. the mechanisms of leading- (continuous) and lagging- (discontinuous) strand synthesis.

D. the mechanisms of leading- (discontinuous) and lagging- (continuous) strand synthesis.

E. the presence of several chromosomes that are replicated separately.

33. As DNA polymerase forms a new phosphodiester bond, all the following occur EXCEPT:

A. an amino acid residue accepts the H+ released from 3' hydroxyl of deoxyribose.

B. oxygen of 3' hydroxyl attacks a phosphoryl group of nucleoside triphosphate.

C. phosphate is displaced and protonated by an acidic amino acid residue.

D. hydrogen bonds between DNA strands help position nucleotides.

E. metal ions lower pl<a within the active site to facilitate activation of the 3' O- nucleophile.

34.

36. What is accomplished when ATP is hydrolyzed by DnaC?

A. Allows formation of the oriC/DnaB complex

B. Helps release DnaB helicase as it is loaded onto the DNA

C. Helps bind DnaB helicase to the clamp

D. Removes DnaC at termination of replication

E. Removes DnaA at termination of replication

35. A biochemist is purifying a new DNA helicase encoded by a pathogenic virus. The enzyme activity is readily detected after the first several purification steps that generate fractions a, b, and c, each with successively greater purity. The researcher then puts fraction c on an ionexchange column, and this process generates two new fractions, d and d'. The helicase activity cannot be detected in either of the new fractions. However, when fractions d and d' are mixed, the activity reappears. The most likely explanation for this is:

A. The helicase is present in both fractions; however, the low concentration results in no activity. Mixing the fractions yields a higher helicase concentration and then activity can be observed.

B. The helicase is present in one fraction; however, it has additional peptide sequences that must be removed in order for the helicase to assume an active form. An enzyme in the second fraction activates the helicase via proteolytic cleavage.

C. The helicase is present in one fraction and another protein or macromolecule required for helicase activity is present in the other fraction.

D. The helicase is present in one fraction; however, the helicase requires ATP, which is present in the other fraction. When the fractions arc mixed, the helicase becomes catalytic again.

E. All of the above are equally likely.

Explanation / Answer

29:Answer:- Option D.

Explanation:- The enzymes responsible can create histone variants. This is not true about histones and enzymes that geberate them.

30: Answer :- Option B

Explanation:- The gene product of chromosome 2 combines with the product from chromosome 8 to form a defective protein.

32:Answer:- Option C

Explanation:- The mechanisms of leading- (continuous) and lagging- (discontinuous) strand synthesis. This is called semi discontinuous replication.

34:Answer:- Option D

Explanation :- Removes DnaC at termination of replication and leaving Dna B to be loaded on DNA template strand.

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