Biochemistry of Nucleic Acid

Question 1

What is the genome

Answer 1

total DNA in each cell
carries genetic information which is stored in the nucleotide sequence
the sequence determines the amino acid sequence of polypeptide chain

Question 2

What is DNA

Answer 2

polymer

2 complimentary antiparallel helices that contain a sugar phosphate backbone on outside and bases on inside

Question 3

what elements is DNA composed of

Answer 3

C, H, N, O, P

Question 4

2 types of nucleotide shape

Answer 4

purines and pyrimidines - join together by hydrogen bonds

Question 5

where does transcription take place

Answer 5

nucleotide to nucleotide in nucleus formation of RNA from DNA
pre-mRNA formed then undergoes splicing to form RNA

Question 6

where does translation occur

Answer 6

nucleotide to amino acid
RNA to polypeptide chain
occurs in cytoplasm

Question 7

difference between DNA and RNA

Answer 7

RNA has a hydroxyl group on second carbon whereas DNA only has a hydrogen atom

Question 8

what is a nucleoside

Answer 8

base and sugar

Question 9

what is a nucleotide

Answer 9

nucleoside + phosphate group

Question 10

what bases occur in DNA

Answer 10

adenosine
cytosine
guanine
thymine

Question 11

what bases are pyrimidines

Answer 11

uracil
thymine
cytosine

Question 12

what bases occur in RNA

Answer 12

adenosine
cytosine
guanine
uracil

Question 13

what bases are purines

Answer 13

adenosine

guanine

Question 14

during polymerisation off DNA/RNA what is a phosphodiester bond formed between

Answer 14

a free 3’ OH group and 5’ triphosphate

consumes 2 high energy bonds

Question 15

what does each gene produce

Answer 15

number of different proteins

only small number of genes are expressed

Question 16

what does carbon 1 have attached

Answer 16

a base

Question 17

what does carbon 5 have attached

Answer 17

a phosphate

Question 18

where can new nucleotides only be added to

Answer 18

free 3’ OH group forming phosphodiester bond

Question 19

how do nucleotide analogies work as drugs

Answer 19

ZDV and AZT = retrovir
analogue of thymidine
incorporated into growing viral of DNA
Lachs 3’ OH group therefore chain elongation is terminated, prevents transcription

Question 20

How does ZDV work as a drug

Answer 20

reverse transcriptase has a higher affinity for ZDV than human DNA polymerase so turn RNA into DNA infecting host cell and uses DNA to make products which makes new viral cell

Question 21

why is DNA antiparallel

Answer 21

one 5’ to 3’

one 3’ to 5’

Question 22

what must take place before cell division/mitosis

Answer 22

DNA must replicate so daughter cells have complete compliment of genome
replication is semi-conservative

Question 23

what is DNA replication catalysed by

Answer 23

DNA polymerase

Question 24

what is the role of DNA polymerase

Answer 24

adds nucleotides to growing DNA strand
cannot start DNA synthesis on its own
requires an RNA primer to start replication

Question 25

why do eukaryotic genomes have many origins of replication

Answer 25

replication starts simultaneously at several points in genome bidirectional ensures replication can be finished in reasonable time

Question 26

why is DNA replication discontinuous

Answer 26

nucleotides can only be adde to the free 3' end therefore synthesising in a 5' to 3' direction

Question 27

what is the leading strand

Answer 27

always has a free 3' end

Question 28

what is the lagging strand

Answer 28

as DNA can only be added to 3' end the 5'end being replicated must be replicated in short segments called Okazaki fragments primer binds as DNA unwinds then nucleotides added as more template unwinds more primers bind and catch up with itself

Question 29

what is the role of helicase

Answer 29

unwinds DNA, stops It rewinding

Question 30

what is the role of DNA ligase

Answer 30

primers distend, then DNA ligase joins nucleotides by forming phosphodiester bonds between them in the lagging strand

Question 31

what is RNA primer synthesised by

Answer 31

primase

Question 32

what is the replication fork

Answer 32

unwound DNA leading template strand (3' to 5') lagging template strand (5' to 3')

Question 33

what are the building blocks for DNA replication

Answer 33

dATP, dTTP, dCTP, dGTP

Question 34

what do they 3 phosphates do

Answer 34

one phosphate group forms phosphdiester bond | leaves two phosphates as pyrophosphate - energy supply

Question 35

what can incorporation of the wrong nucleotide result in

Answer 35

can create mutations can be deleterious errors occur once every 10000-100000 base pairs

Question 36

what activity does DNA polymerase have

Answer 36

3' -> 5' exonuclease activity removes incorrect nucleotide improves error rate proofreads and repairs