Chapter Thirteen

Question 1

What is the importance of Rosalind Franklin?

Answer 1

Rosalind Franklin prepared crystallographs from DNA samples and this suggested a double helix with 10 nucleotides per turn

suggested that the sugar phosphate backbone must be on the outside

Question 2

What was the importance of Watson and Crick?

Answer 2

Used model building (based on Franklin’s idea) and physical and chemical evidence to solve the DNA structure

Question 3

What are the four features of DNA structure?

Answer 3

1. DNA is a double stranded helix
2. DNA is right handed
3. Strands of DNA run antiparallel
4. The outer edges of the bases are exposed in major and minor grooves

Question 4

What is DNA made of?

Answer 4

DNA is made of four different nucleotides (deoxyribose, phosphate, and nitrogenous base) that are connected by phosphodiester linkages

Question 5

Where is DNA found in the cell?

Answer 5

Usually found in the nucleus, but can be found in organelles like the chloroplast and the mitochondria

Question 6

How are strands of DNA held together?

Answer 6

by hydrogen bonds and vanderwal’s forces

Question 7

What are the purines?

Answer 7

they are nitrogenous bases that are two rings fused and are Adenine and Guanine

Question 8

What are the pyrimidines?

Answer 8

they are single ringed nitrogenous bases and they include Cytosine and Thymine (and in RNA also Uracil)

Question 9

What nitrogenous bases pair with each other, DNA/DNA?

Answer 9

the A’s and T’s go together

and the C’s and G’s go together

Question 10

What nucleotides pair with each other DNA/RNA?

Answer 10

the C’s and the G’s still go together

but the A’s now go with the U’s

Question 11

What is Chargaff’s rule?

Answer 11

in all DNA the amount of purines is the same as the amount of pyrimidines

Question 12

What is DNA replication?

Answer 12

It is the process of making two identical DNA molecules originated from the original two strands

Question 13

What is meant by semi conservative?

Answer 13

Semi conservative is a mechanism by which DNA is replicated

Each parent strand is a template, and the new molecules receive one old molecule

this conserves one old template strand

Question 14

What are the two main steps of DNA replication?

Answer 14

1. the double helix is unwound, making two template strands
2. new nucleotides form complimentary base pairs with the template DNA strand and are linked by phosphodiester linkages

Question 15

When does replication start?

Answer 15

when the pre-replication complex of proteins bind to the origin of replication

Question 16

What is the origin of replication?

Answer 16

the ori or specific region of DNA that indicates the starting point of replication

Question 17

What are replication forks?

Answer 17

The two points at which the two strands of DNA are separated to allow replication of each strand

V shape when the zipper starts moving outward

Question 18

What is DNA helicase?

Answer 18

it is the enzyme that unzips the original strand into template strands and forms the replication fork

uses energy from ATP hydrolysis

Question 19

What are the single stranded binding proteins?

Answer 19

they work with the DNA helicase to keep the separate strands from folding back

Question 20

What does primase do?

Answer 20

it is an enzyme that synthesizes the primer

Question 21

What are primers?

Answer 21

the primer is a short starter strand, usually RNA, that is complementary to the DNA template so the polymerase can grab onto it

Question 22

What is DNA polymerase

Answer 22

it is the enzyme that adds nucleotides to the template strand at the three prime end of the template strand and is shaped like a right-handed palm

it can only add nucleotides in the five prime to three prime direction on the new strand

Question 23

What is the leading strand?

Answer 23

DNA polymerase can only add nucleotides in the 5 prime to 3 prime direction

So the leading edge is at an advantage because they get to add nucleotides in the direction that the helicase is going continuously

Question 24

What is the lagging strand?

Answer 24

Again the DNA polymerase can only add nucleotides in the 5 to 3 direction

the lagging edge is at a disadvantage because the nucleotides are added in the opposite direction of the helicase’s movement, so it becomes discontinuous

this results in the formation of Okazaki fragments

Question 25

What are Okazaki fragments?

Answer 25

they are small discontinuous stretches of new DNA, which each require its own primer

Question 26

What is DNA ligase?

Answer 26

it is the enzyme that catalyzes the anabolic reaction of the phosphodiester linkages on the lagging edge in order for the new strand to be complete

Question 27

What are the three DNA repair mechanisms?

Answer 27

1. Proofreading: DNA polymerase recognizes mismatched pairs and removes incorrectly paired bases