transcription and translation

Question 1

how is RNA different to DNA ?

Answer 1

single stranded
stem loop structure (one continuous strand)
contains uracil instead of thymine

Question 2

what are the three main classes of RNA ?

Answer 2

rRNA - combines with proteins to form ribosomes
tRNA - carries amino acids to be incorporated into the protein
mRNA - carries the genetic information

Question 3

which RNA is stable ?

Answer 3

rRNA
tRNA

Question 4

which RNA is unstable ?

Answer 4

mRNA

Question 5

describe the structure of tRNA

Answer 5

cloverleaf structure

Question 6

what are RNA polymerases ?

Answer 6

multi-subunit complexes
create rRNA

Question 7

how many RNA polymerases do prokaryotic cells and eukaryotic cells have ?

Answer 7

prokaryotic - 1 type
eukaryotic - 2 type ( Pol l, ll, lll )

Question 8

what synthesises all mRNA ?

Answer 8

Pol ll

Question 9

what are the steps of transcription ?

Answer 9

RNA polymerase binding
DNA chain separation
transcription initiation
elongation
termination

Question 10

Explain the steps of transcription

Answer 10

RNA polymerase binding
- detects initiation sites on DNA (promoters )
- requires transcription factors

DNA chain separation
-Unwinding of DNA

Transcription initiation
- Selection of first nucleotide of growing RNA
- Required additional general transcription factors

Elongation
- Addition of further nucleotides to RNA chain
- RNA synthesised in 5’ – 3’ direction

Termination
- Release of finished RNA

Question 11

what is TFIID ?

Answer 11

general transcription factor required for all Pol ll transcribed genes

Question 12

what is required for specific regulation of transcription ?

Answer 12

specific transcription factors

Question 13

what are coding and non-coding regions ?

Answer 13

exons - coding
introns - non-coding

Question 14

are exons and introns transcribed together ?

Answer 14

yes

Question 15

when and how are introns removed ?

Answer 15

before translation into the protein
removed by splicing

Question 16

describe the ends of mRNA ?

Answer 16

a “cap” of modified GTP is added
AAUAAA - sequence is recognised

Question 17

what do tRNA do during translation ?

Answer 17

anticodons of tRNA form base pairs with codons of mRNA

Question 18

how many combinations can be made from base pairs ?

Answer 18

64 possible combinations, 20 amino acids

Question 19

what is required for translation ?

Answer 19

amino acids
tRNAs
aminoacyl-tRNA synthetases
protein factors
ATP/GTP
ribesomes
mRNA

Question 20

what is the start codon for translation ?

Answer 20

AUG

Question 21

what are the steps of translation ?

Answer 21

Initiation
elongation
termination

Question 22

explain the steps of translation

Answer 22

Initiation
- GTP provides energy
- Ribosomal subunit binds to 5’ end of mRNA, moves
along until start codon found
- Initiator tRNA pairs to start codon
- Large subunit joins assembly and initiator tRNA is
located in P site

Elongation
- Elongation factor brings aminoacyl-tRNA to A site
- GTP is hydrolysed
- Second elongation factor regenerates the first to pick
up next aminoacyl-tRNA
- Peptidyl transferase catalyses peptide bond formation
between amino acids in P and A sites

Termination
- Occurs when A site of ribosome encounters a stop
codon (UAA, UAG or UGA)
- Finished proteins cleaves off tRNA

Question 23

Initiation

Answer 23

• GTP provides energy
• Ribosomal subunit binds to 5’ end of mRNA, moves
  along until start codon found
• Initiator tRNA pairs to start codon
• Large subunit joins assembly and initiator tRNA is
  located in P site

Question 24

elongation

Answer 24

• Elongation factor brings aminoacyl-tRNA to A site
• GTP is hydrolysed
• Second elongation factor regenerates the first to pick
  up next aminoacyl-tRNA

Question 25

Termination

Answer 25

• Occurs when A site of ribosome encounters a stop
  codon (UAA, UAG, UGA
• Finished proteins cleaves off tRNA