Final Exam - DNA structure & replication

Question 1

topoisomerase I

Answer 1

enzyme that uncoils DNA before replication (relaxes supercoiled DNA)

Question 2

helicase

Answer 2

unwinds double helix & makes replication fork

Question 3

SSB (ssDNA binding) protein

Answer 3

stabilizes the ssDNA

Question 4

primase

Answer 4

makes RNA primer

Question 5

DNA polymerase III

Answer 5

synthesizes DNA from 5’ –> 3’

proofreads and repairs

Question 6

DNA polymerase I

Answer 6

removes RNA primer

replaces them w/DNA

Question 7

DNA ligase

Answer 7

connects the DNA Okazaki fragments

Question 8

DNA gyrase

Answer 8

compacts DNA & makes them supercoiled

Question 9

mismatch repair

Answer 9

DNA polymerase III proofreads the newly-made DNA; removes wrong bases & repairs (checks complementary base pairing); done during S phase

Question 10

Telomere repair or preservation

Answer 10

Telomerase (enzyme) helps prevent telomere from getting shortened after each cycle
- done during S phase

Question 11

excision repair

Answer 11

happens after cell divides, in the G1 or G2 phase

• over 50 enzymes monitor
• excise the damaged strand of DNA (by an endonuclease)
• make a new matching strand (by DNA polymerase & DNA ligase)

Question 12

3 types of RNA polymerases

Answer 12

1. RNA polymerase I - transcribes ribosomal RNA (rRNA)
2. RNA polymerase II - transcribes messenger RNA (mRNA)
3. RNA polymerase III - transcribes transfer RNA (tRNA)

Question 13

codon

Answer 13

mRNA base triplets
written in 5’ –> 3’ direction
each codon specifies which one (of 20) amino acids

Question 14

start codon

Answer 14

also Met (methionine)
AUG

Question 15

stop codons

Answer 15

UAA
UAG
UGA

Question 16

3 types of RNA polymerases

Answer 16

1. RNA polymerase I - transcribes ribosomal RNA (rRNA)
2. RNA polymerase II - transcribes messenger RNA (mRNA)
3. RNA polymerase III - transcribes transfer RNA (tRNA)

Question 17

codon

Answer 17

mRNA base triplets
written in 5’ –> 3’ direction
each codon specifies which one (of 20) amino acids

Question 18

start codon

Answer 18

also Met (methionine)
AUG

Question 19

stop codons

Answer 19

UAA
UAG
UGA

Question 20

TATA box

Answer 20

tells the RNA where to start transcription on the strand

Question 21

difference between prokaryotes and eukaryotes in RNA synthesis?

Answer 21

Prokaryotes

1. transcribe & translate simultaneously b/c no nucleus
2. polycistronic - transcription results in only mRNA that codes for more than one protein
3. only have one type of RNA polymerase
4. don’t go through any processing (poly A tail or intron removal) before translation

Eukaryotes

1. transcription in nucleus; translation in cytoplasm
2. monocistronic - one gene transcribed per transcription
3. contain introns that need to be removed
4. expressed regions, exons, are spliced during RNA processing