Biochem - DNA

Question 1

Chromatin

Answer 1

Condensed DNA w/ histones – nucleosome core (histone with DNA wrapped 2x) linked by H1

Question 2

Histone

Answer 2

H2A x2
H2B x 2
H3 x2
H4 x2

Question 3

Deamination of cytosine

Answer 3

Uracil

Question 4

Purines synthesis required substrates

Answer 4

“GAG”
Glycine
Aspartate - N
Glutamine – N

tetrahydroFolate
CO2

“cat PURRR until they GAG and Cough on Fur balls”

Question 5

Pyrimidine synthesis required substrates

Answer 5

Aspartate
CO2
Glutamine
ATP

Carbamyol phosphate

Question 6

CPS-2

Answer 6

Carbamoyl phosphate synthase 2

Rate limiting step of pyrimidine synthesis

Question 7

CPS1 vs CPS2

Answer 7

CPS1:
Urea cycle
In mitochondria
Ammonia source of nitrogen

CPS2:
Pyrimidine synthesis
Found in cytosol
Glutamine source of nitrogen

Question 8

Draw out prokaryotic DNA replication

Answer 8

Page 516

Question 9

Exonuclease activity of DNA polymerase

Answer 9

DNA polymerase I and III can add and remove nt from end of DNA strand

DNA polymerase III works 3’-5’

DNA polymerase I:
3’ – 5’ 1 nt at a time
5’ – 3’ 1-10 nt at a time

Question 10

Eukaryote DNA polymerase alpha

Answer 10

Makes own primer

Replicates 1st 20 nt

Question 11

Eukaryote DNA polymerase delta

Answer 11

Builds okazaki fragments on lagging strand

Question 12

Eukaryote DNA polymerase epsilon

Answer 12

Elongates leading strand

Question 13

Eukaryote DNA poly beta

Answer 13

DNA repair

Question 14

Eukaryote DNA poly gamma

Answer 14

mt DNA replication

Question 15

Silent mutation

Answer 15

Genetic code change, same aa

Final polypeptide unchanged

Question 16

Missense mutation

Answer 16

Change aa sequence

Polypeptide product different structural or functional properities

Question 17

Nonsense mutation

Answer 17

Base substitution leads to stop codon

Question 18

Frameshift mutation

Answer 18

Nt added or delated shifting reading frame

Downstream aa sequence completely different

Question 19

Pyrimidine dimer

Answer 19

2 pyrimidines on same strand of DNA get covalently bonded together
Ts
UV damage

Question 20

Mismatch repair

Answer 20

Wrong base added
Nick daughter strand up stream
Remove several bases and remake strand and fill in gap created

Question 21

Nucleotide excision repair

Answer 21

Damaged after creation
Remove entire nt and replace it
Recognizes large bulky areas of damaged DNA

Pyrmidine dimers

Endonucleases remove damaged nt
DNA polymerase fills in gap
DNA ligase joins fragments

Question 22

Base excision repair

Answer 22

Nonbulky damage just base damaged

Loss of amino group
Oxidized
Methylated

Glycosylase – recognized damaged base – removes damaged base

Lyase – cuts 3’ end of backbone

Endonuclease – cuts 5’ end, removes backbone

Type beta DNA polymerase fills in gaps

Ligase seals it

Question 23

Double strand repair

Answer 23

Nonhomologous end joining

Clean break in both strands of DNA, gluing back together

Use this if no overlapping segments of DNA

Question 24

Hereditary nonpolyposis colorectal cancer

Answer 24

Defective mismatch repair

Question 25

Xeroderma pigmentosum

Answer 25

AR

Defective nucleotide excision repair

Increased risk skin cancer, can’t repair UV damage

Extreme – avoid all sunlight

Question 26

Bloom syndrome

Answer 26

Mutation in helicase
-DNA replication and repair

hypersensitive to sunlight
increased susceptibility to leukemias and lymphomas 
-immunodeficiency
-infertility
-facial anomalies

Question 27

Ataxia-telangectasia

Answer 27

Defective repair of dsDNA breaks

• IgA deficiency
• Ataxia
• poor smooth pursuit of eyes
• high AFP after 8 mo
• sensitive to ionizing radiation

Question 28

BRCA ½

Answer 28

Defective repair of dsNDA breaks