DNA Replication

Question 1

What examples are there of polymers

Answer 1

DNA

RNA

Question 2

Which of the nitrogenous bases are purines

Answer 2

Adenine

Guanine

Question 3

Which of the nitrogenous bases are pyrimidine

Answer 3

Cytosine
Uracil
Thymine

Question 4

What makes up a nucleoside

Answer 4

Sugar and base

Question 5

What makes up a nucleoside phosphate

Answer 5

Nucleoside (sugar and base) and phosphate

Question 6

Where does a covalent bond form

Answer 6

Between phosphate group of one nucleotide and 3’ carbon of sugar of another nucleotide

Question 7

Which bond is 5’-3’ and what are the characteristics

Answer 7

Phosphodiester
Very strong
Make backbone stable

Question 8

What causes the width to be the same between backbones

Answer 8

Purine always paired with a pyrimidine

Question 9

What must happen before DNA replication

Answer 9

Initiator protein binds to origin of replication (initiator protein recognises specific DNA sequence)

Question 10

What does DNA helicase do

Answer 10

Cause DNA to untwist, form Y shape
Break hydrogen bonds between bases
Forms two single-stranded template strands

Question 11

What is single-stranded DNA-binding (SSB)

Answer 11

Proteins bind to each single stranded DNA molecule, hold them in place, stop the strands rejoining

Question 12

How many nucleotides does single-stranded DNA-binding (SSB) bind to

Answer 12

32 nucleotides

Question 13

What is a tetramer

Answer 13

Four molecules joined together

Question 14

What does DNA topoisomerases do

Answer 14

Aid unwinding process - cuts DNA backbone

Question 15

What does DNA primase do

Answer 15

Synthesis short RNA primer (5-10 bases)

Attaches to 3’ end of template strand

Question 16

What does DNA polymerase do

Answer 16

Causes nucleotide addition to primer
Must be complementary to base on template
Catalyses phosphodiester bond formation between 3’ carbon of last nucleotide and 5’ phosphate of incoming nucleotide

Question 17

Where does the DNA polymerase read from

Answer 17

3’ to 5’

So new strand grows 5’ to 3’

Question 18

How is 5’ to 3’ polarity maintained

Answer 18

DNA synthesised in opposite directions on two template strands

Question 19

What is the leading strand

Answer 19

New strand made in same direction as movement of replication fork

Question 20

What is the lagging strand

Answer 20

The stand synthesised in opposite direction

Question 21

Where does DNA polymerase remove nucleotide

Answer 21

From end of DNA chain - exonuclease activity

Question 22

Which strand does DNA polymerase synthesise

Answer 22

New strand toward replication fork

Leading strand only needs single RNA primer for synthesis

Question 23

How is the DNA on the lagging strand synthesised

Answer 23

Discontinuously
Needs a series of primers
New primer attaches at replication fork - short second segment synthesised

Question 24

What is the name of short segments on lagging strand

Answer 24

Okazaki fragments

Question 25

How is the second new DNA strand made (from lagging)

Answer 25

Okazaki fragments have to be joined

Used DNA polymerase and DNA ligase

Question 26

How does DNA polymerase remove nucleotides - exonuclease activity

Answer 26

DNA polymerase reads RNA primer in DNA recognises not meant to be there - chops out nucleotides of RNA primer
Left with gap where DNA polymerase removed RNA primer, DNA ligase closes gap, form phosphodiester bond

Question 27

What is ‘proof reading site’

Answer 27

DNA polymerase reads what’s just been added to molecule, cuts out wrong nucleotides adds right base instead

Question 28

What is needed before DNA synthesis starts

Answer 28

RNA primer