translation

Central Dogma of Molecular Biology

• DNA → RNA → Protein

• DNA to RNA is Transcription

• RNA to Protein is Translation

transcription review

• The biosynthesis of a messenger RNA (mRNA) from a DNA template

• Only about 1.5% of the genome actually codes for a protein

• Occurs in the nucleus (in eukaryotes)

• Uses RNA polymerase (RNApol)

  • Synthesizes in the 5’ to 3’ direction

  • Has helicase activity

  • Does NOT need a primer

• Only one of the two DNA strands is transcribed

  • The transcribed mRNA is complementary and uses A, U, G, C 

  • Only part of the DNA code is transcribed

amino acid structure

• monomer:

  • carboxyl group

  • amino group

amino acid polymers = polypeptides

RNA amino acids

1 base → aa 4 total 4^1

2 bases → aa 16 total 4²

3 base → aa 64 combos 4³

why only 20?

    degenerate = multiple 3-letter combos

tRNAs

• decoders that translate mRNA → proteins

• even tRNA is loaded with a specific amino acid at its 3’OH end

• anticodon loop of tRNA complimentary to the input codon

Loading tRNAs with anti codon

• ATP facilitates ester bond between the carboxyl group and the 3’ hydroxyl group (OH)

• the enzyme that does this is aminoacyl tRNA synthase

• difference amino acids are loaded by different aminoacyl tRNAs synthase

  • humans have 20 different aminoacyl tRNAs

During translation: polypeptide chain

• amino acid chain immediately start folding in cytoplasm

• primary - linear peptide strand

• secondary - alpha helices and the beta sheets

• tertiary - folds to make 3d shape

• 4th - complex of multiple proteins