Topic 7: DNA structure and replication

Question 1

Before DNA structure was known, it was understood that it had the following properties(3):

Answer 1

1. Must allow for accurate replication- accurate replication of the genectic material is required at every replication
2. The instruction to encode the whole collection of proteins that are expressed in a particular organism
3. Must be able to change (rarely)- Genectic material is stable enough to be reliable (to enode an organism’s proteins), but on occasion, can change to result in hereditary changes/mutations

Question 2

The base in DNA all contain

Answer 2

nitrogen

Question 3

Purines:

Answer 3

Guanine and adenine

Question 4

Pyrimidines

Answer 4

thymine and cytosine, uracil

Question 5

nucleotide has at least

Answer 5

1 phosphate

Question 6

Deoxyadenosine contains:

Answer 6

Sugar+adenine

Question 7

In the deoxyribose sugar, a base attaches on the—– carbon and the phosphate attach on the —- carbon. The —- carbon has a —-

Answer 7

1. 1’
2. 5’
3. 3’
4. OH group

Question 8

DNA Base pairing (3):

Answer 8

1. Same amount of purine nucleotides as pyrimidine nucleotides (in dsDNA)
2. Same amount of A and T; Same amount of G and C
3. A+T is necessarilt equal to G+C

Question 9

There are — base pair in a full twist of DNA

Answer 9

10

Question 10

Nucleotides contain

Answer 10

• phosphate
• sugar
• base

Question 11

Nucleotides form DNA strands by

Answer 11

phosphodiester linkages

Question 12

Phosphodiester linkages (2)

what it does+what it includes

Answer 12

• Phosphate/sugar backbone
• links the 3’ carbon of one sugar to the 5’ carbon of aother via a phosphate

Question 13

The 2 sugar phosphate backbones are

Answer 13

antiparallel

one is 5’-3’ nd other is 3’-5’

Question 14

DNA strands are held together by — hydrogen bonds. AT has — and CG has—-

Answer 14

2 or 3
2
3

Question 15

Semi conservative replication (3)

what happens+ results in

Answer 15

1. 2 DNA strands unwinds from eachother
2. Each DNA strand acts as a template for the synthesis of a new complementary strand
3. Results in 2 double helices that are identical to the original

Question 16

Replication is catalyzed by—- which is—-

Answer 16

DNA polymerase which is an enzyme that adds nucleotides into a growing DNA chain

Question 17

Whate drives DNA synthesis or DNA polymerase?

Answer 17

Cleaving off pyrophohphate produces energy to help drie DNA synthesis

Question 18

In DNA replication, what does the OH hydroxyl group on the 3’ carbon do?

Answer 18

Forms a nucleophillic attack on alpha phosphorus. Cleaves off the 2 pyrophosphate which provides energy to drive the rxn.

Question 19

New nucleotides can only be added on the —- because it has to ——

Answer 19

1. 3’ end
2. have a free OH group to form the nucleophillic attack for new nucleotides

Question 20

DNA is synthesized in the

Answer 20

5’-3’ direction

Question 21

Replication is catalyzed by

Answer 21

DNA polymerase

Question 22

What drives the DNA synthesis?

Answer 22

Cleaving off the pyrophosphate (2) on the triphosphate base by 3’oh produces energy to help drive DNA synthesis

Question 23

New nucleotides can only be added on the

Answer 23

3’ end

Question 24

Where is the base attached in dna

Answer 24

1’ carbon of the deoxyribose sugar

Question 25

Where is the phosphate attached on the deoxy ribose sugar

Answer 25

the 5’ carbon

Question 26

DNA pol 3

Answer 26

Catalyzes DNA synthesis. Can extend a chain bit cant start a chain (5’-3’)

Question 27

Helicase

Answer 27

Distrupts the H0bonds between strands

Question 28

DNA gyrase

Answer 28

Relaxes supercoil DNA and rejoins the DNA strands

Question 29

SSDNA binding porteins

Answer 29

stabilizes unwound DNA

Question 30

4 steps for DNA replication

Answer 30

1. Primase synthesizes short RNA primers using DNA as a template
2. DNA polymerase III synthesizes DNA starting at the 3’ end of RNA primers
3. DNA poly 1 removes RNA primers and fills the gap
4. DNA ligase connects adjacent DNA fragments

Question 31

What type of bond does DNA ligase catalyze?

Answer 31

Phosphodiester bond