chapter 12

Question 1

semiconservative replication

Answer 1

only one sequence of bases can be specified by each template strand so the two DNA molecules built on the pair of templates will be identical to the original

• each of the original nucleotide strands are conserved

Question 2

conservative replication

Answer 2

the entire double stranded DNA molecule serves as a template for a whole new molecule of DNA and the original molecule is fully conserved during replication

Question 3

Dispersive replication

Answer 3

both nucleotide strands break down into fragments which serve as a template for the synthesis of new DNA

Question 4

Meselson and Stahl Experiment

Answer 4

using isotopes of nitrogen and spun in a centrifuge and demonstrated that DNA replication is semiconservative - each DNA strand serves as a template for the synthesis of a new DNA molecule

Question 5

how many origin of replication do bacterial chromosomes have

Answer 5

only one

Question 6

replication fork

Answer 6

the point of unwinding where the two strands separate from the double-stranded DNA helix

Question 7

bidirectional replication

Answer 7

if there are two replication forks, one at each end of the replication bubble, the forks proceed outward in both direction

Question 8

what happens in the process of replication

Answer 8

• dna molecule unwinds to expose the bases that act as a template strand
• in dna synthesis, nucleotides are added to the 3’ OH group of the growing nucleotide strand
  ‘ 3’OH group strand attacks the 5’ phosphate group of upcoming dNTP and two phosphate groups are cleaved and phosphodiester bond is created between two nucleotides

Question 9

what direction is DNA synthesis

Answer 9

5’ to 3’

Question 10

what is the new strand that undergoes continuous replication called

Answer 10

leading strand

Question 11

where does synthesis proceed in replication

Answer 11

exposed in the 5’ to 3’ direction and opposite of the unwinding

Question 12

what is the newly made strand that undergoes discontinuous replication called

Answer 12

lagging strand

Question 13

Okazaki fragment

Answer 13

shorter fragments of DNA produced by discontinuous fragments

Question 14

four stages of replication

Answer 14

initiation, unwinding, elongation and termination

Question 15

what happens during initiation

Answer 15

Initiator proteins bind to the origin of replication
- causes a short stretch of DNA to unwind
- the unwinding allows helicase and other single strand binding proteins to attach to the single stranded DNA

Question 16

what happens during unwinding

Answer 16

DNA synthesis requires double stranded DNA to be unwound; to be single strand

Question 17

DNA helicase

Answer 17

breaks the hydrogen bonds between the bases of the two nucleotide strands of DNA molecule
- initiator protein first separates DNA strands at origin and then helicase unwinds

Question 18

single-stranded binding proteins

Answer 18

attach tightly to the exposed single stranded DNA and protect the nucleotide chains and prevent structures from interfering with replication

Question 19

DNA gyrase

Answer 19

• a topoisomerase which reduces the torsional strain that develops as the two strands of dna unwins

Question 20

elongation

Answer 20

• single stranded DNA is used as template for synthesis of dna

Question 21

primase

Answer 21

synthesizes short RNA primers which provides 3’-OH group to which DNA polymerase can attach DNA nucleotides

• primers are later removed and replaced with DNA nucleotides

Question 22

DNA polymerase I

Answer 22

removes and replaces primers DNA repair; restarts replication after damaged DNA halts synthesis

Question 23

DNA polymerase III

Answer 23

elongates DNA by adding nucleotides to the 3’ end of growing DNA strand

Question 24

dna ligase

Answer 24

joins okazaki fragments by sealing breaks in the sugar phosphate backbone of newly synthesized dna

Question 25

termination

Answer 25

• occurs when two replication forms meet

Question 26

proofreading

Answer 26

incorrect positioning of a nucleotide strand allows the dna polymerase to remove the incorrectly paired nucleotide

Question 27

mismatch pair

Answer 27

corrects errors after replication is complete
- recognized by enzymes that excise the incorrectly paired nucleotide and use the original nucleotide strand to replace the incorrect nucleotide

Question 27

differences between eukaryotic dna replication and bacterial replication

Answer 27

• replication at multiple origins in eukaryotic
• eukaryotic chromosomes are linear and prokaryotic are circular
• dna template is with histone proteins in the form of nucleosomes and nucleosome assembly must follow dna replication

Question 27

what do nucleosomes do after dna replication?

Answer 27

new nucleosomes quickly reassemble on the two new molecules of dna

• they break down during replication and reassemble from new and old histones

Question 28

telomeres

Answer 28

• prevents the loss of genes as chromosome end wears
• “dna caps”
• consists of units of DNA sequence with the same SEQUENCE
• have single-stranded overhangs that is due to incomplete end replication
• binds to complementary strands to form loops

Question 29

Holliday junction

Answer 29

double stranded DNA molecule of two homologous chromosome align precisely
- strand invasion causes herteroduplex dna