DNA

Question 1

What makes up a nucleotide

Answer 1

1. nitrogenous organic base (A+T C+G)
2. sugar
3. phosphate

Question 2

Who discovered the double helix

Answer 2

Watson and crick in 1953

Question 3

what type of backbone is DNA

Answer 3

Sugar phosphate backbone

Question 4

what bonds hold the helix together

Answer 4

hydrogen bonds

Question 5

how are the subunits linked

Answer 5

covalently

Question 6

what are the purines

Answer 6

adenine and guanine

Question 7

what are the pyrimidines

Answer 7

uracil, thymine, cytosine

Question 8

where is uracil found

Answer 8

RNA

Question 9

when is DNA formed

Answer 9

condensation reaction

Question 10

what is polymerisation

Answer 10

subunit addition to the chain

Question 11

how does DNA encode infromation

Answer 11

in the order of sequences of base pairs in the DNA strand

Question 12

what do DNA strands form

Answer 12

Linear messages- they spell out the sequence of amino acids in proteins

Question 13

do the 2 woven strand mirror each other

Answer 13

yes, but they are antiparallel

Question 14

is DNA stable

Answer 14

yes but is bulky

Question 15

what groove does the double helix have

Answer 15

a major or minor groove

Question 16

can the 2 DNA strands be separated

Answer 16

they can be separated by melting or deannealing and they can be reannealled when in close proximity

Question 17

when can DNA form circular molecules

Answer 17

when their ends are joined e.g. bacteria or ribosomes

Question 18

what is the pros of the double helix

Answer 18

1. chemically stable
2. easily unwound for transcription
3. mirror imaging excellent for replication and repair

Question 19

what are the cons of the double helix

Answer 19

1. can only replicate 5’-3’ which causes difficulties
2. difficult to fold into nucleus- torsional effects

Question 20

what occurs in replication

Answer 20

1. 1 strand of the double helix acts as a template for the complementary strand
2. the double helix is opened by initiator protein
3. the newly synthesised strands have opposite polarity
4. 2 identical daughter duplexes are produced

Question 21

what are two DNA replication theories

Answer 21

conservative (2 different coloured strand)
semi-conservative (2 different coloured strands woven- contains one of the original strands)

Question 22

where does DNA replication start

Answer 22

at A=T rich regions called replication origins

Question 23

what is the function of DNA polymerase

Answer 23

adds new nucleotides and proofreads DNA

Question 24

what do the leading and lagging strands do

Answer 24

DNA strands can only extend in 5’-3’ direction so the lagging strand is made in small pieces (okasaki fragments) which are joined