Chapter 14 The Molecular Basis of Inheritance

Question 0

What were the contributions of Griffith? Hershey and Chase? Watson and Crick? Rosalind Franklin?

Answer 0

Griffith discovered the genetic role of DNA. Hershey and Chase studied DNA as genetic material using T2 bacteriophages that infect E. Coli. Watson and Crick discovered the complete structure of DNA. Rosalind Franklin used X-Ray crystallography to determine that DNA was a double helix.

Question 1

What is meant by DNA replication?

Answer 1

The process by which a DNA molecule is replicated.

Question 2

What is the structure of DNA?

Answer 2

DNA is a double helix, has a sugar phosphate backbone, has a deoxyribose sugar group, and has nitrogenous bases.

Question 3

How do the nitrogenous bases pair together?

Answer 3

Adenine pairs with Thymine.

Cytosine pairs with Guanine.

Question 4

DNA is antiparallel. What does this mean?

Answer 4

This means that the sugar-phosphate backbones of the DNA double helix run in opposite directions.

Question 5

DNA replication is a semiconservative process. What does this mean?

Answer 5

This means that the replicated DNA double helix consists of one old strand and one newly made strand.

Question 6

What is the origin of replication?

Answer 6

Short stretches of DNA having a specific sequence of nucleotides.

Question 7

What is the replication fork?

Answer 7

A Y-shaped region where the parental strands of DNA are being unwound.

Question 8

What is the role of Helicase?

Answer 8

Enzymes that untwist the double helix at the replication forks, separating the two parental strands. Allow each parental strand to serve as a template.

Question 9

What is the role of single-strand binding proteins?

Answer 9

Prevent the unpaired strands from repairing (holds them apart while serving as a template).

Question 10

What is the role of topoisomerase?

Answer 10

Breaks, swivels, and rejoins the parental DNA ahead of the replication fork (relieve the strain caused by unwinding).

Question 11

What is the role of primase?

Answer 11

Synthesizes the addition of a short RNA chain (primer) to which complementary bases are added.

Question 12

What is the role of DNA polymerase?

Answer 12

Synthesizes the new DNA by adding nucleotides to a pre-existing chain.

Question 13

What is the role of DNA ligase?

Answer 13

An enzyme that joins the sugar phosphate backbones of all the Okazaki fragments into a continuos DNA strand.

Question 14

What is the role of nuclease?

Answer 14

DNA cutting enzyme.

Question 15

What is the leading strand of DNA?

Answer 15

The new complementary DNA strand synthesized along the template toward the replication fork in the 5’ to 3’ direction.

Question 16

What is the lagging strand?

Answer 16

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in the 5’ to 3’ direction away from the replication fork.

Question 17

What are Okazaki fragments?

Answer 17

A short segment of DNA replicated away from the replication fork.

Question 18

Sometimes errors occur during replication. One

Means of fixing an error is mismatch repair. What is meant by this?

Answer 18

Other enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors.

Question 19

What is nucleotide excision repair?

Answer 19

A repair system that removes and then replaces a damaged segment of DNA using the undamaged strand as a template.

Question 20

What are telomeres?

Answer 20

The randomly repetitive DNA at the end of a eukaryotic chromosomes DNA molecule.

Question 21

What is the function of telomeres?

Answer 21

Protect the organism’s genes from being eroded during successive rounds of replication.

Question 22

What happens to the telomeres during each round of replication?

Answer 22

They become shorter.

Question 23

What is the evolutionary significance of a change in the DNA nucleotide sequence during replication?

Answer 23

If an error occurs that is not corrected, the sequence change becomes permanent. If the change takes place in the DNA of a gamete then the mutation is passed onto an organisms offspring. Some of the changes have no effect, some are harmful, and a very small percent are beneficial. These changes are the source of genetic variation that natural selection acts on resulting in evolution.