Protein Synthesis

Transcription

• This process takes place in the nucleus of a eukaryotic cell.
• The DNA double helix unwinds; the enzyme helicase is used to break the hydrogen bonds between the bases, allowing the 2 strands to partly separate.
• The sequence of 1 of the strands becomes the template / antisense strand and is used in the production of mRNA.
• mRNA is built from free RNA nucleotides which line up alongside the DNA template strand.
• Due to complementary base pairing e.g. U pairs with A and C with G, the order of bases on the DNA exactly determines the order of bases on the RNA strand.
• Every triplet code on the DNA creates a complementary codon on the mRNA.
• The individual mononucleotides are joined together by phosphodiester bonds.
• The completed mRNA molecules now leave the nucleus through pores in the nuclear envelope into the cytoplasm.
• The cytoplasm is where the 2nd stage of protein synthesis, translation, takes place.

Translation

• This takes place on ribosome's on endoplasmic reticulum in the cytoplasm.
• The mRNA attaches to the ribosome.
• A transfer RNA (tRNA) molecules carrying an amino acid molecule has 3 bases called an anticodon.
• These pair with complementary bases on the mRNA codon.
• The ribosome moves along the mRNA as it pairs up with the tRNA anticodons until it reaches the stop codon.
• Then the amino acids that the tRNA carry are joined by peptide bonds formed in condensation reactions to produce a polypeptide chain.