B8 PROTEIN SYNTHESIS

What is the definition of transcription?

the production of mRNA from DNA

What is the definition of translation?

the production of polypeptides from the sequence of codons carried by mRNA

What occurs during transcription?

• DNA helicase attaches and unwinds DNA double helix

• hydrogen bonds between the 2 strands are broken and DNA strands separate

• one strand is used as a template

• free RNA nucleotides join with exposed DNA bases via complementary base pairing on the template strand

• RNA polymerase joins the free RNA nucleotides together to form mRNA

• mRNA formed is complementary to the DNA and is pre-mRNA

• introns are removed in splicing

• mRNA passes out via the nuclear pore

• mRNA associates with a ribosome

What occurs during translation?

• mRNA attaches to the ribosome at the start codon

• tRNA with the complementary anticodon to the codon binds to the mRNA

• a second tRNA with the complementary anticodon to the second codon binds to the mRNA next to the first one

• amino acids attached to the two tRNA molecules are close enough to form a peptide bond

• ribosome moves along the mRNA to include the next codon

• a third tRNA carrying its specific amino acid binds to the third codon on mRNA

• enzymes join the next amino acid forming another peptide bond

• the ribosome moves along the mRNA to include the next codon

• this repeats with the addition of one amino acid each time until the stop codon is reached

• the amino acids are now joined together to form a polypeptide chain

Why is ATP required in protein synthesis?

provides energy for the formation of peptide bonds between amino acids during translation and the joining of amino acids to the tRNA molecule