Translation

Question 1

what types of RNA are involved in translation?

Answer 1

mRNA - messenger

tRNA - transfer

rRNA - ribosomal

Question 2

what is the role of mRNA , tRNA and rRNA in translation?

Answer 2

1. mRNA = template, encodes information to make the protein
2. tRNA - carrier, each amino acid brought to mRNA by a specific tRNA
3. rRNA - structural and functional roles in ribosomes
   4.

Question 3

what is the start codon on an mRNA?

Answer 3

AUG = methionine= typical 1st codon in protein

Question 4

at what point on mRNA do we start translating codons?

Answer 4

just after the 5’UTR region - whenever it comes across a start codon

Question 5

What is an open reading frame?

Answer 5

a set of codons that run continously bounded by an initiation codon and a termination codon = reading frame is determined by which base is chosen as the start of a codon

in protein synthesis usually only one open reading frame contains useful information

Question 6

is the genetic code universal?

Answer 6

yes - it applies to all species conserved from early stage of evolution

Question 8

what genetic change causes sickle cell anaemia?

Answer 8

it is due to a missense mutation in the beta globin gene - single nucleotide substitution (a to T) in the codon for amino acid 6 - converts a glutamic acid codon (GAG) to a valine codon (GTG) autosomal recessive

Question 9

what is the ‘Wobble exception to base pairing’?

Answer 9

wobble = flexible pairings

the wobble base is last 3’ base in codon on mRNA which binds with the first 5’ based in anticodon on tRNA - it allows felxibility/efficiency in use of tRNA - a single tRNA species carrying an AA can recognize 2 codons

so this is why different codons can produce the same AA

Question 11

what is the role of the ribosome?

Answer 11

they are the factories in which protein synthesis occurs - they are complexes of protein and rRNA - which is extensive secondary structuring stimilar to tRNA -

ribosome brings tRNA and mRNA together to translate nucleotide sequence of mRNA into amino acid of a protein

Question 12

what are the 2 parts to tranlation initiation?

Answer 12

1. assembly of components required for chain formation (tqo ribosomal subunits, mRNA, tRNA specified by the AUG codon, GTP, initiation factors to help ribosome recognise the sequence for the start of translation
2. recognition of the start codon by a tRNA methionine molecule

*initiator tRNA is in P site

Question 13

what are the 3 sites of the ribosome?

Answer 13

• A= aminoacyl site - accepts new tRNA
• P= peptidyl site - contains amino acid chain
• E= exit site - harbours deacylated tRNA on way out of ribosome

Question 14

describe the process of ‘elongation ‘

Answer 14

elongation involves the addition of amino acids to the carboxyl end of the growing chain - peptide bonds are formed between adjacent amino acids

ribosome moves along mRNA being translated - in 5’ to 3’ direction

1. tRNA delivered to A site
2. peptide bonds formed
3. growing amino acid chain now in A site
4. after bond formed, the ribosome is translocated 3 nucleotides to the next codon

Question 15

describe the process of termination in translation

Answer 15

occurs when one of three termination codons arrives in the A site

stop codon recognized by a release factor

release factor binds to A site which causes the newly synthesized protein to be released and dissasembly of the tRNA - ribosome- mRNA complex

Question 16

how are polypeptide chains modified post translation?

Answer 16

1. trimming - removal of part of the translated sequence
2. chemical alterations - attachment of a chemical group
3. degredation - marking a protein for destruction

Question 17

what chemical alterations are made of post-tranlated peptide chains?

Answer 17

• phosphorylation - catalysed by protein kinases and protein phosphatases
• glycosylation - used to target proteins to plasma membrane lysosome
• hydroxylation - extensive in collagen
• palmitoylation - serves as an anchor in cell membrane

Question 18

how are proteins degraded?

Answer 18

proteins are marked for destruction by ubiquitination - the attahcment of ubiquitin - which acts as a tag for proteosome