Exam 4 DNA Structure and Replication

Question 1

Polynucleotides or Nucleic acids of Cells

Answer 1

RNA and DNA

Question 2

DNA nucleotides

Answer 2

A, C, G, T
-> sugar deoxyribose

Question 3

RNA nucleotides

Answer 3

A, C, G, U
-> sugar ribose

Question 4

Purines

Answer 4

A & G
-> double ring base

Question 5

Pyrimidines

Answer 5

C, T, & U
-> single ring base

Question 6

Watson- Crick Model of DNA main features

Answer 6

1. Double Helix with sugar-phosphate backbone outside
2. Antiparallel strands
3. Strict base pairing of nucleotides (A:T & C:G)
4. Two strands held together by hydrogen bonding between bases

Question 7

DNA Replication simple definition

Answer 7

parental strand from double helix makes a daughter strand.
these are two double helices (“old” DNA strand paired with “new” DNA strand)

Question 8

Helicase

Answer 8

breaks hydrogen bonds between bases
-> enzyme that breaks the hydrogen bonds between nucleotides at the fork, making the bubble bigger and exposing new single stranded DNA

Question 9

Topoisomerase

Answer 9

relieves strain caused by helicase (overwound DNA)
-> works on the double helix in front of the fork, cutting the DNA to relieve strain created by the activity of helicase, then repairing the double helix once it relaxes

Question 10

Single Strand Binding Protein

Answer 10

prevents DNA strands from winding back together

Question 11

Primase

Answer 11

makes an RNA primer
-> makes a short RNA primer to the 3’-end. Each time a new single stranded DNA is exposed in the replication bubble, Primase will make a new primer - this results in the fragments on the lagging strand

Question 12

DNA polymerase III

Answer 12

extends the 3’ end of the primer to make a new DNA strand
-> will continue until it “runs into” another daughter strand

Question 13

DNA pol I

Answer 13

removes the RNA primer and replaces it with DNA nucleotides
-> happens where the 3’-end of one daughter strand meets the 5’-end of another daughter strand

Question 14

Ligase

Answer 14

links two DNA fragments together with a phosphodiester bond
-> between the 3’- and 5’-ends of two fragments, making a single daughter strand

Question 15

Where does DNA replication start?

Answer 15

DNA replication starts at origin of replication
-> proteins bind and separate DNA strands

Question 16

Replication Bubble

Answer 16

consists of two replication forks
-> move away from each other in opposite directions (antiparallel)
-> helices and topoisomerase unwind parental DNA together

Question 17

Leading Strand

Answer 17

the 3’-end of the daughter DNA is towards the fork, so DNA polymerase 3 follows helicase and make one long daughter strand

Question 18

Lagging Strand Process

Answer 18

the 3’-end of the daughter DNA is away from the fork, so DNA polymerase 3 goes the “wrong way”
Single stranded DNA is exposed by the the expanding bubble/fork, so primase will start the process over again by creating DNA fragments.