Topic 13.3: Translation

Question 1

how many rRNA and protiens do prokaryotes and eukaryotes have

Answer 1

prokaryotes - 3 rRNA and many proteins

eukaryotes - 4 rRNA and many proteins

Question 2

what subunits of ribosome are there in prokayrotes and eukaryotes

Answer 2

prokaryotes - 30S + 50S subunits = 70S ribosome

eukaryotes - 40S + 60S subunits = 80S ribosome

Question 3

what is required for translation

Answer 3

adaptor molecule = tRNA
template = mRNA
enzyme = rRNA in ribsomes
substrates = activated amino acids
SO tRNA with activated amino acids
initiation factors, elongation factors, release factors, and energy (GTP/ATP)

Question 4

what are some key features of genetic code

Answer 4

triplet code - 3 base pairs = amino acid
degenerate = more than one triplet code (codon) for same amino acid
non overlapping and ‘comma less’ - no gaps

Question 5

what is a key feature of translation

Answer 5

5 to 3 prime end template read through to produce N to C polypeptide chain extension

Question 6

what is the initiation codon

Answer 6

AUG

Question 7

what is the termination codon

Answer 7

UAA, UAG, UGA

Question 8

whjat is the role of tRNA

Answer 8

each tRNA can bind an amino acid to its 3 prime end (as it can be charged with an activated amino acid)
each tRNA has an anticodon to recognise a complementary codon in mRNA

Question 9

how do tRNA become charged and attached to activated amino acids

Answer 9

Aminoacyl-tRNA synthetase will recognize a specific amino acid and then binds to ATP to charge amino acid
the same enzyme will then recognize a specific tRNA using anticodon and binds specific amino acid to specific tRNA to form a charged tRNA with aminoa cid attached

Question 10

what happens during initiation of translation

Answer 10

mature mRNA has 5 prime CAP and initiation codon (AUG)

1. the cap is recognized by cap binding proteins, which along with initiation factors, small ribosome and energy, the tRNA-methionine (amino acid activated) become attached
2. the complex moves across mRNA until it reaches AUG which is recognized by the anticodon on P site of tRNA-amino acid complex (needs energy)
3. initiation factors are lost and a large subunit is being recruited (functional ribsoome subunit ready). so results in tRNA-methionine complex bound to AUG initiation codon and a functional ribosome assembled

Question 11

what results from initiation

Answer 11

80s initiation complex with tRNA-methionine in P site of ribosome on AUG on mRNA and empty A site on ribosome ready for elongation

Question 12

what are the sites called on functional ribosome

Answer 12

E, P, A from 5 to 3 prime end

Question 13

why is the A site empty

Answer 13

to receive the next tRNA-amino acids complex

Question 14

what happens during elongation of translation

Answer 14

1. the next codon can be recognized at empty A site where binding of aminoacyl-tRNA occurs with its cognate amino acid attached to it (GTP required)
2. peptide bond formation occurs catalysed by peptidyltransferase between first amino acid and second one and the first one is thus a uncharged tRNA which is in E site
3. translocation occurs - ribosome moves across mRNA (need GTP), one codon at a time from 5 to 3 end.
4. the peptidy- tRNA complex moved to P site and empty A site forms so new codon is being freed, the growing polypeptide is ‘pushed’ intp exit tunnel, elongation factors are involved

Question 15

what results from elongation

Answer 15

peptidyl-tRNA in P site and empty A site ready for next cycle
only 2 sites occupied of EPA

Question 16

what happens in termination

Answer 16

stop codon is recognise on mRNA by release factor and one water molecule is brought into ribosome which causes a hydrolysis reaction and the tRNA molecules becomes uncharged in P site and the peptide is free and exits in tunnel. the ribosomes then become dissociated into subunits

Question 17

What are the function of release factors

Answer 17

Release factors promote polypeptide chain termination

Question 18

What is translation

Answer 18

Ribosomes polymerise amino acids to form proteins

Question 19

Best chronological gene expression order

Answer 19

Promoter recognition
mRNA synthesis
Splicing
Methiontl-tRNA synthetase catalysed reaction
Recruitment of 60S subunit to form 80S initiation complex
Translocation
Ribosome dissociation
Protein folds into final 3D structure