Question 1

In the polymerization of DNA,a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which functional group of the last nucleotide in the polymer?

Accepted Answer

A) the 5' phosphate 
B) C₆ 
C) the 3' OH 
D) a nitrogen from the nitrogen-containing base 
E) the 5' OH

Question 2

In E.coli,there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin.Which of the following would you expect as a result of this mutation?

Accepted Answer

A) No proofreading will occur. 
B) No replication fork will be formed. 
C) The DNA will supercoil. 
D) Replication will occur via RNA polymerase alone. 
E) Replication will require a DNA template from another source.

Question 3

Which of the following help(s)to hold the DNA strands apart while they are being replicated?

Accepted Answer

A) primase 
B) ligase 
C) DNA polymerase 
D) single-strand binding proteins 
E) exonuclease

Question 4

E.coli cells grown on ¹⁵N medium are transferred to ¹⁴N medium and allowed to grow for two more generations (two rounds of DNA replication).DNA extracted from these cells is centrifuged.What density distribution of DNA would you expect in this experiment?

Accepted Answer

A) one high-density and one low-density band 
B) one intermediate-density band 
C) one high-density and one intermediate-density band 
D) one low-density and one intermediate-density band 
E) one low-density band

Question 5

What is a telomere?

Accepted Answer

A) the mechanism that holds two sister chromatids together 
B) DNA replication during telophase 
C) the site of origin of DNA replication 
D) the ends of linear chromosomes 
E) the RNA primer used during DNA replication

Question 6

Use the following information to answer the questions below.
The green algae Chlamydomonas is said to be GC rich.
-What does this mean?

Accepted Answer

A) There is a tendency for its DNA to recombine with G or C bases. 
B) The organism prefers an environment rich in GTP or cAMP. 
C) RNA primers only bind to GC pairs. 
D) There is characteristically more GC base pairs in the DNA sequence than in an average organism's DNA sequence. 
E) It has more mismatched pairs of GC bases than are found in the average organism.

Question 7

Heterochromatin is observed in

Accepted Answer

A) anaphase. 
B) metaphase. 
C) interphase. 
D) bacteria and archaea only. 
E) eukaryotes only.

Question 8

In a linear eukaryotic chromatin sample,which of the following strands is looped into domains by scaffolding?

Accepted Answer

A) DNA without attached histones 
B) DNA with H1 only 
C) the 10-nm chromatin fibre 
D) the 30-nm chromatin fibre 
E) the metaphase chromosome

Question 9

The images above are of DNA at various levels of coiling and folding.Use this image to answer the questions below.
-For a science fair project,two students decided to repeat the Hershey and Chase experiment,with modifications.They decided to label the nitrogen of the DNA,rather than the phosphate.They reasoned that each nucleotide has only one phosphate and two to five nitrogens.Thus,labelling the nitrogens would provide a stronger signal than labelling the phosphates.Why won't this experiment work?

Accepted Answer

A) There is no radioactive isotope of nitrogen. 
B) Radioactive nitrogen has a half-life of 100 000 years, and the material would be too dangerous for too long. 
C) Avery et al. have already concluded that this experiment showed inconclusive results. 
D) Although there are more nitrogens in a nucleotide, labelled phosphates actually have 16 extra neutrons; therefore, they are more radioactive. 
E) Amino acids (and thus proteins)also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

Question 10

Eukaryotic telomeres replicate differently than the rest of the chromosome.This is a consequence of which of the following?

Accepted Answer

A) the evolution of telomerase enzyme 
B) DNA polymerase that cannot replicate the leading strand template to its 5' end 
C) gaps left at the 5' end of the lagging strand 
D) gaps left at the 3' end of the lagging strand because of the need for a primer 
E) the "no ends" of a circular chromosome

Question 11

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?

Accepted Answer

A) sequence of bases 
B) phosphate-sugar backbones 
C) complementary pairing of bases 
D) side groups of nitrogenous bases 
E) different five-carbon sugars

Question 12

Which of the enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments?

Accepted Answer

A) helicase 
B) topoisomerase 
C) DNA ligase 
D) DNA polymerase I 
E) DNA polymerase III

Question 13

Grains represent radioactive material within the replicating eye.
-In an experiment,DNA is allowed to replicate in an environment with all necessary enzymes,dATP,dCTP,dGTP,and radioactively labeled dTTP (³H thymidine)for several minutes and then switched to nonradioactive medium.It is then viewed by electron microscopy and autoradiography.The figure above represents the results.
Which of the following is the most likely interpretation?

Accepted Answer

A) There are two replication forks going in opposite directions. 
B) Thymidine is only being added where the DNA strands are furthest apart. 
C) Thymidine is only added at the very beginning of replication. 
D) Replication proceeds in one direction only. 
E) Thymidine is not being incorporated into the DNA, but is associating with the DNA due to hydrogen bonding.

Question 14

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

Accepted Answer

A) The origins of replication occur only at the 5' end. 
B) Helicases and single-strand binding proteins work at the 5' end. 
C) DNA polymerase can join new nucleotides only to the 3' end of a growing strand. 
D) DNA ligase works only in the 3' → 5' direction. 
E) Polymerase can work on only one strand at a time.

Question 15

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

Accepted Answer

A) primase 
B) DNA ligase 
C) DNA polymerase III 
D) topoisomerase 
E) helicase

Question 16

After mixing a heat-killed,phosphorescent strain of bacteria with a living nonphosphorescent strain,you discover that some of the living cells are now phosphorescent.Which observations would provide the best evidence that the ability to fluoresce is a heritable trait?

Accepted Answer

A) DNA passed from the heat-killed strain to the living strain. 
B) Protein passed from the heat-killed strain to the living strain. 
C) The phosphorescence in the living strain is especially bright. 
D) Descendants of the living cells are also phosphorescent. 
E) Both DNA and protein passed from the heat-killed strain to the living strain.

Question 17

A biochemist isolates,purifies,and combines in a test tube a variety of molecules needed for DNA replication.When she adds some DNA to the mixture,replication occurs,but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long.What has she probably left out of the mixture?

Accepted Answer

A) DNA polymerase 
B) DNA ligase 
C) nucleotides 
D) Okazaki fragments 
E) primase

Question 18

In analyzing the number of different bases in a DNA sample,which result would be consistent with the base-pairing rules?

Accepted Answer

A) A = G 
B) A + G = C + T 
C) A + T = G + T 
D) A = C 
E) G = T

Question 19

Which of the following investigator(s)was/were responsible for the following discovery?
In DNA from any species,the amount of adenine equals the amount of thymine,and the amount of guanine equals the amount of cytosine.

Accepted Answer

A) Frederick Griffith 
B) Alfred Hershey and Martha Chase 
C) Oswald Avery, Maclyn McCarty, and Colin MacLeod 
D) Erwin Chargaff 
E) Matthew Meselson and Franklin Stahl

Question 20

What is meant by the description "antiparallel" regarding the strands that make up DNA?

Accepted Answer

A) The twisting nature of DNA creates nonparallel strands. 
B) The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. 
C) Base pairings create unequal spacing between the two DNA strands. 
D) One strand is positively charged and the other is negatively charged. 
E) One strand contains only purines and the other contains only pyrimidines.

Exam 16: The Molecular Basis of Inheritance