Molecular Genetics Translation

Question 1

tRNA

Answer 1

-Clover shaped RNA molecule

-Transfer RNA

-Functions as the delivery system of amino acids to ribosomes as they synthesize proteins

-Is very short, only 70-90 base pairs long

Question 2

Structure of tRNA

Answer 2

-3’ end of tRNA binds to specific amino acids

-Anticodon on tRNA complements mRNA codon

Question 3

tRNA activation

Answer 3

-RNA is made in the nucleus

-Amino acids float free in the cytoplasm

-Enzyme: aminoacyl-tRNA synthetase

-An amino acid is attached when needed as this takes energy

Question 4

Ribosomes

Answer 4

-2 subunits: small and large

-E site → exit site

-P site → polypeptide binding site

-A site → amino acid site

-Composed of proteins and rRNA

-3 tRNA binding sites

Question 5

Initiation

Answer 5

-mRNA, tRNA and small ribosomal subunit bind with P site at start codon

-Only the first tRNA binds to P at start codon

-Large subunit binds using energy from GTP

Question 6

Elongation

Answer 6

mRNA read 3 nucleotides at a time in codons

-tRNA brings corresponding amino acid into the A site of the ribosome

-Ribosome catalyzes dehydration synthesis reaction between amino acids in P site and A site

-Peptide bond is formed

-Growing polypeptide now attached to tRNA in A site

-Ribosome moves forward one codon

-Free tRNA in P site exits out the back of ribosome on the E site

-tRNA (with polypeptide) moves into P site

Question 7

Termination

Answer 7

-Elongation continues until reaching a stop codon

-There is no amino acid for stop codon, just STOP

-Release factor binds and hydrolyzes the bond between the last tRNA and its amino acid

-New protein is free

Question 8

Polyribosomes

Answer 8

• Many ribosomes may simultaneously translate from a single mRNA