DNA replication

Question 1

DNA is?

Answer 1

(nucleic acid) is the genetic material

Question 2

What does DNA contain?

Answer 2

the genetic blueprint that directs the development of all your biochemical, anatomical, physiological and behavioural traits

Question 3

why do you resemble your parents?

Answer 3

because of precise replication of DNA and transmission from one generation to the next

Question 4

DNA and RNA are…

Answer 4

polymers of nucleotide monomers

Question 5

Nucleotides polymerize by what reaction?

Answer 5

Condensation reaction forming phosphodiester link between 3’ carbon and 5’ carbon

Question 6

polymerisation meaning

Answer 6

(adding a nucleotide) only at the 3’ end

Question 7

DNA secondary structure

Answer 7

double-helix with two anti-parallel nucleic acid strands

Question 8

antiparallel strands meaning

Answer 8

one runs 5’ to 3’ in one direction; and the other runs 3’ to 5’ in the opposite direction

Question 9

how is the double helix stabilized?

Answer 9

by hydrogen bonds between nucleotide bases

Question 10

what is the distance between two phosphate backbones?

Answer 10

2 nanometers (nm). only purine-pyrimidine pairings fit the space

Question 11

What does unwinding and separating the DNA do?

Answer 11

forms two template strands; then addition of appropriate, complimentary nucleotides forms (2) new, identical copies

Question 12

Where does the DNA start to separate

Answer 12

replication “bubbles” which form at the origin of replication = stretches of DNA with specific nucleotide sequences

Question 13

why do replication bubbles grow as replication proceeds?

Answer 13

because synthesis of new complimentary DNA strands is bidirectional

Question 14

what happens once a replication bubble opens?

Answer 14

a suite of enzymes initiates replication; this starts at the origin and moves towards replication fork

Question 15

topoisomerase function

Answer 15

breaks, swivels and rejoins DNA relieving strand of unwinding

Question 16

helicase function

Answer 16

unwinds and separates DNA strand

Question 17

primase function

Answer 17

synthesises RNA primer

Question 18

single-strand binding proteins

Answer 18

stabilizes unwound strand

Question 19

Direction of DNA synthesis is?

Answer 19

5’ to 3’ direction

Question 20

leading strand

Answer 20

nucleotides can be added to 3’ end of complimentary strand = continuous

Question 21

lagging strand

Answer 21

nucleotides added to 3’ end of complimentary strand in short segments away from replication fork = Okazaki fragments.

Question 22

what is the discontinuous part of the lagging strand?

Answer 22

nucleotides can be added at the 3’ end and the short segments are then joined together to complete lagging strand

Question 23

length of primer

Answer 23

is 5-10 RNA nucleotides long, base-paired to template strand

Question 24

DNA polymerase 3 movement?

Answer 24

moved along the DNA template strand by the associated “sliding clamp” protein

Question 25

How does DNA polymerase 3 catalyze synthesis of DNA?

Answer 25

by adding nucleotides to pre-existing chain at 3’ end (in 5’ to 3’ direction) at a rate of 50 per second

Question 26

DNA polymerase 3 function

Answer 26

adds nucleotides to form first Okazaki fragment away from replication fork at the 3’ end of the template strand

Question 27

initial pairing errors during DNA replication ratio

Answer 27

1:100,000

Question 28

mutations meaning

Answer 28

permanent errors occur 1:billion

Question 29

DNA polymerase function

Answer 29

fills in the gap by adding in missing complimentary nucleotides. Can also proofread correcting mistakes as it goes

Question 30

DNA ligase function

Answer 30

seals the free ends of the new DNA to the old DNA

Question 31

Nuclease enzymes function

Answer 31

detect and cut DNA removing damaged section

Question 32

How can genes be eroded away?

Answer 32

normal replication machinery provides no way to complete the 5’ end of lagging strands, so genes near the end of DNA could be eroded away

Question 33

telomeres meaning

Answer 33

repetitive, non-coding nucleotide sequences at the ends of DNA which protect genes (protective caps)

Question 34

How is the double helix opened and stabilized?

Answer 34

a battery of enzymes and other proteins converge on the point where the double helix opens and stabilize the separating single DNA strands

Question 35

Lagging strand during DNA replication summary

Answer 35

1) primase forms RNA primer
2) DNA poly 3 synthesizes first Okazaki fragments in 5’ to 3’ direction
3) Primase and DNA poly 3 synthesize second Okazaki fragment
4) DNA poly 1 removes RNA primer and replaces with DNA nucleotides
5) DNA ligase closes gaps in sugar-phosphate backbone