Ch 13

Question 1

What is the relationship among DNA, a gene, and a chromosome?

Answer 1

A chromosome contains hundreds of genes, which are composed of DNA.

Question 2

A base substitution mutation in a gene sometimes has no effect on the protein the gene codes

Answer 2

some amino acids have more than one codon

Question 3

A researcher treats cells with a chemical that prevents DNA synthesis from starting. This treatment would trap the cells in which part of the cell cycle?

Answer 3

G1 Phase. The cells would be trapped in the G1 phase, unable to progress to the S phase
due to the inhibition of DNA synthesis.

G1 phase (Gap 1 phase): During this phase, the cell grows in size and prepares for DNA
replication.

S phase (Synthesis phase): This is the phase during which DNA replication occurs. By the end of
this phase, the cell has two full sets of chromosomes.

Question 4

What enzyme breaks apart the hydrogen bonds between two strands of DNA?

Answer 4

Helicase

Question 5

List and describe the three steps of DNA replication.

Answer 5

1. Initiation
   a. Start at speicific sites called origins of replication.
   b. DNA helicase unwinds the double helix, creating the replication fork
2. Elongation
   a. An RNA primer is laid down by primase, giving DNA polymerase a starting
   point.
   b. Leading Strand: Synthesized continously in the 5’ to 3’ direction.
   c. Lagging Strand: Made in fragments called Okazaki fragments. RNA primers are
   replaced with DNA, and fragments are linked togehter by DNA ligase.
3. Termination
   a. In prokaryotes, replication ends when two replication forks meet
   b. In eukaryotes, telomerase exteneds the ends (telomeres) of chromosomes to
   ensure no genetic material is lost.

Question 6

DNA polymerase III reads the parent strand in a ___ direction, synthesizing the new strand in a ___ direction.

Answer 6

3’ to 5’
5’ to 3’

Question 7

Describe how new nucleotides are added during DNA replication.

Answer 7

nucleotides attach via their phosphate binding to the 3’ –OH group

Question 8

During DNA replication, which of the following enzymes removes the RNA nucleotides
from the primer and adds equivalent DNA nucleotides to the 3’ end of Okazaki fragments?

Answer 8

DNA polymerase I

Question 9

correctly describes chromatin

Answer 9

Heterochromatin is mostly “silent” having few genes, whereas euchromatin contains the
majority of genes.