Unit 2 - DNA replication

Question 1

what are the purines?

Answer 1

2 carbon-nitrogen rings

adenine/ guanine

Question 2

what are the pyrimidines?

Answer 2

1 ring

cytosine/ thymine/ uracil

Question 3

what does each nucleotide contain?

Answer 3

• five carbon sugar
• nitrogenous base
• phosphate group

Question 4

what are the four nucleotides found in DNA?

Answer 4

dAMP - deoxyadenosine monophosphate
dCMP - deoxycytidine
dGMP - deoxyguanosine
dTMP - deoxythymidine

Question 5

what are the four nucleotides found in RNA?

Answer 5

AMP - adenosine monophosphate
CMP - cytidine
GMP - guanosine
UMP - uridine

Question 6

what is the bond linking nucleotides between C3 and C5?

Answer 6

phosphodiester bonds

Question 7

what are primers and what are they needed for?

Answer 7

short piece of nucleic acid base-paired template

starting point for DNA replication - requires 3’ - OH group

Question 8

describe the DNA polymerase reaction

Answer 8

DNA partially unwound and RNA primers synthesised attach to the ends
DNA polymerase adds nucleotides to 3’ end
as the strand is further unwound the leading strand is synthesised continously but lagging strand synthesised as okazaki fragments
primers removed by nucleases and replaced with DNA

Question 9

what is the role of telomerase in DNA replication?

Answer 9

extends the ends of chromosomes so prevents shortening of chromosomes
- found in germ-line cells

Question 10

what attaches to the promoter region of gene?

Answer 10

RNA polymerase

Question 11

how is gene expression controlled? - explain any components involved

Answer 11

• controlling availability of regulatory proteins (transcription factors) that bind to promoters&enhancers
  (enhancers= DNA sequence in eukaryotes which varies in position and boosts transcription in nearby gene)
• controlling strength of interaction between DNA & histones (euchromatin/ heterochromatin)
• splicing

Question 12

what are the initiation and termination codons?

Answer 12

initiation: AUG

termination codons: UGA, UAG, UAA

Question 13

What are ribosomes composed of and what are its three tRNA binding sites?

Answer 13

protein/ ribosomal RNA

EPA - exit site/ peptidyl site/ aminoacyl site

Question 14

what are the three main repeated cycle within translation?

Answer 14

binding of aminoacyl-tRNA (requires GTP)
peptidyl-transferase reaction (formation of peptide bonds)
translocation (movement of ribosome one codon along mRNA) - also requires GTP

Question 15

which antibiotics inhibit peptidyl transferase reaction and translocation?

Answer 15

erythromycin/ clarithromycin

chloramphenicol

Question 16

what is the effect of ricin ?

Answer 16

removes base from rRNA (ribosomal nucleic acid)

Question 17

At the end of transcription what are the promoter regions and stop codons replaced with?

Answer 17

promoter - Gppp cap

stop codon - poly A tail