Chapter 16 Questions

Question 1

Is DNA replication similar or different between prokaryotes and eukaryotes?

Answer 1

DNA replication is similar in both prokaryotes and eukaryotes

Question 2

What location does replication begin?

Answer 2

special locations called origins of replication

Question 3

How many origins of replication do prokaryotes have? How many do eukaryotes have?

Answer 3

Prokaryotes only have one origin of replication, while eukaryotes have hundreds to thousands

Question 4

Know the role of each major protein and enzyme involved in replication

Answer 4

Proteins: DNA helicase, single-strand binding proteins, topoisomerase
Enzymes: DNA polymerase, primase, DNA ligase

Question 5

What is a replication “bubble” and how is it formed?

Answer 5

DNA helicase binds to the initiator proteins and begins separating double stranded DNA into single strands in a small area which forms a “replication bubble”

Question 6

What is a replication fork?

Answer 6

DNA helicase binds to the initiator proteins and begins separating double stranded DNA into single strands in a small area which forms two replication forks at each side of replication bubble

Question 7

Why is a primer needed for DNA replication?

Answer 7

It forms a 3’ end for DNA polymerase to attach to and initiate replication from

Question 8

What form does a nucleotide have prior to being added to a growing DNA strand?

Answer 8

nucleoside triphosphate

Question 9

What is the difference between a dNTP and a NTP?

Answer 9

DNA polymerase adds dNTPs to both strands of separated double stranded DNA in 5’ to 3’ direction
-RNA polymerase adds NTPs only to template DNA strand of separated double stranded DNA in 5’ to 3’ direction
(-The difference is in their sugars: dATP has deoxyribose while ATP has ribose)??

Question 10

What is released after a nucleotide is added to a growing DNA strand?

Answer 10

two phosphate groups as a molecule of pyrophosphate

Question 11

Describe the difference between the leading and lagging strands during DNA replication.

Answer 11

Leading - allows for DNA polymerase to continuously add DNA nucleotides since it runs in the same direction as the replication fork
Lagging - only allows DNA polymerase to add nucleotides in the direction going away from the replication fork

Question 12

How are Okazaki fragments formed?

Answer 12

Short segments from the discontinuous addition of DNA nucleotides

Question 13

How are Okazaki fragments connected?

Answer 13

connected together by DNA ligase to form a continuous strand

Question 14

Which direction are DNA nucleotides added to the template strand? (5’to3’ or 3’to5’?

Answer 14

5’ to 3’

Question 15

What does DNA proofreading refer to?

Answer 15

DNA polymerases “proofread” newly made DNA, replacing any incorrect nucleotides

Question 16

Which enzyme is responsible for proofreading?

Answer 16

DNA polymerase

Question 17

What are two common ways that DNA becomes damaged?

Answer 17

by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes

Question 18

What is the basic mechanism involved in DNA repair and which enzymes have roles in this process?

Answer 18

In nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA

Question 19

What does a chromosome mainly consist of?

Answer 19

DNA and Proteins

Question 20

What are the basic differences between bacterial and eukaryotic chromosomes?

Answer 20

• • Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein - DNA is precisely combined with proteins in a complex called chromatin
• • The bacterial chromosome is a double-stranded, circular DNA molecule associated with a small amount of protein - DNA is “supercoiled” and found in a region of the cell called the nucleoid

Question 21

What are the different levels of chromosome packaging?

Answer 21

• -DNA double helix (2nm diameter)
• -Nucleosomes (10nm fibers)- consists of a core of eight histones (DNA packaging proteins) with DNA wound twice around which forms a 10nm fiber
• -30nm fibers- 10nm fibers coil into 30nm diameter fibers
• -Looped domains (300nm fibers)- 30nm fibers form loops using scaffolding protein which forms fibers with 300nm diameter
• -Metaphase chromosome- 300nm fibers coil into 700nm chromatids

Question 22

What type of proteins play a major role in chromosome packaging?

Answer 22

Histones

Question 23

What are the two major forms of chromatin present during the cell cycle?

Answer 23

Heterochromatin and Euchromatin

Question 24

Which form of chromatin is the active form and which is the inactive form?

Answer 24

Heterochromatin - inactive

Euchromatin - active

Question 25

What causes the different levels of activity between the two types of chromatin?

Answer 25

How compacted and how transcribed it is

Question 26

What are Chargaff’s rules?

Answer 26

the ratios of A to T and G to C is 1:1

Question 27

Why is it impossible for pyrimidines to pair with pyrimidines and purines to pair with purines?

Answer 27

purine adenine can only bind with the pyrimidine thymine and the purine guanine can only bind with the pyrimidine cytosine

Question 28

Know how to calculate the percentage of DNA nucleotides if given the percentage of one nucleotide (example: What would the % G, % C, and %T be if the %A = 40)

Answer 28

?

Question 29

How many hydrogen bonds form between adenine and thymine?

Answer 29

2 ?

Question 30

How many hydrogen bonds from between guanine and cytosine?

Answer 30

3 ?

Question 31

Know the difference between the conservative and semi-conservative model for DNA replication and which one is the true model.

Answer 31

the conservative model (the two parent strands rejoin)
-semiconservative model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand