DNA Replication

Question 1

what direction is DNA synthesised

Answer 1

DNA (+RNA) is always synthesised in the 5’ –> 3’ direction

- the parental strand goes 5’–> 3’

Question 2

how many bonds does A-T have, and C-G

Answer 2

A-T = 2
C-G = 3

Question 3

what are the 7 stages that is needed to make a DNA copy

Answer 3

• Progressive addition of new nucleotides
• a starting point for nucleotide addition
• unwinding of the helical double-stranded DNA
• release of tension generated by Unwinding the DNA helix
• Prevention of unwound double-stranded helical DNA
• Joining ends of newly synthesized fragments together
• removes RNA primer and fills gave with DNA nucleotides

Question 4

which enzyme is used to add new nucleotides

Answer 4

• DNA Polymerase 3

Question 5

which enzyme is used to make RNA primers

Answer 5

Primase enzyme

Question 6

which enzyme is used to unwind the DNA

Answer 6

Helicase

Question 7

which enzyme is used to nick and rejoin the DNA strand to release tension

Answer 7

Topoisomerase

Question 8

which protein prevents the DNA strand to wind back up

Answer 8

Single stranded DNA binding proteins (SSD)

Question 9

what enzyme is used to join the ends of the newly synthesised strands

Answer 9

DNA ligase

Question 10

which enzyme is used to remove RNA primers and fill the gaps

Answer 10

DNA polymerase 1

Question 11

what is the leading strand and the lagging strand

Answer 11

leading strand = continuously synthesised in it 5’ –> 3’ direction

lagging strand = discontinuously synthesised in its 5’ –>3’ direction as okazaki fragments

Question 12

what are the 7 proteins/enzymes that help with DNA replication

Answer 12

• helicase
• topoisomerase
• Ssbp (single stranded DNA binding proteins)
• primase
• DNA polymerase 3
• DNA polymerase 1
• Ligase

Question 13

describe the job of the enzyme Helicase

Answer 13

• it pulls the DNA strands apart

Question 14

describe the job of the enzyme topoisomerase

Answer 14

• moves ahead of the replication fork and cuts both strands which allows them to unwind completely/release the tension.
• then glues the 2 strands back together

Question 15

describe the job of the protein Ssbp

Answer 15

• when the DNA strands are apart, they bind to the single strands of DNA, which prevents the DNA going back together.
• they prevent the single strands of DNA from being degraded

Question 16

describe the job the enzyme Primase does

Answer 16

• has catalytic properties

- has 3prime hydroxyl group that it uses to ass a short stretch of RNA nucleotides

Question 17

describe the job the enzyme DNA polymerase 3 does

Answer 17

• It utilize the 3prime hydroxyl of the RNA primer and adds a DNA nucleotide to it.
• Adds 1 nucleotide at a time
• keeps extending the strand and kicks the Ssbp off when continuing the strand

Question 18

describe the job the enzyme of DNA polymerase 1 do

Answer 18

• it recognizes the RNA and DNA hybrid, it then removes the RNA component
• it then uses the 3 prime hydroxyl group in the Okazaki fragment that is next door to it, and it extends the okazaki fragments up to the other fragments
• this it moves along to the other RNA
• IT DOES NOT CONNECT THE OKAZAKI FRAGMENTS TOGETHER

Question 19

describe the job the enzyme Ligase does

Answer 19

• utilizes the 3 prime hydroxyl group that’s at the end of 1 fragment and the 5’ prime phosphate f the next door group/fragment and created a phosphors difate bond between the 2 fragments/nucleotides
• in the end you will have a continuous DNA strand

Question 20

when can DNA errors be repaired

Answer 20

• during = EXOnuclease

- after = ENDOnuclease

Question 21

describe what exonuclease are

Answer 21

are enzymes that cleave DNA sequences in a polynucleotide chain from other the 5’ or 3’ end. Only one at a time

Question 22

describe what endonuclease is

Answer 22

a group of enzymes that cleave the phosphodiester bond present within a polynucleotide chain

Question 23

what are the differences between endo and exonuclease

Answer 23

• exonuclease only take the incorrect nucleotide out of the DNA strand
• endonuclease takes a bulk of nucleotides and the incorrect one out of the DNA strand

Question 24

what is PCR

Answer 24

the Polymerase chain reaction

Question 25

what happens in the vitro method

Answer 25

• makes multiple DNA copies so that there is enough DNA material to work with