synthesis

• how does RNA differ from DNA?

  • nucleotides form single polynucleotide chain, not two (single stranded)
  • sugar is ribose, not deoxyribose
  • base Uracil replaces Thymine, which binds with Adenine
• transcription?

  1. DNA unwinds, hydrogen bonds breaking between the bases, 2 strands start to separate.
  2. antisense strand is used as template
  3. free mRNA nucleotides pair with bases on template
  4. RNA polymerase joins mRNA nucleotides together via condensation reactions, phosphodiester bonds firming.
  5. mRNA produced has same sequence of bases as coding strand of DNA
  6. mRNA moves out nucleus through pore into cytoplasm and attaches to a ribosome for translation
• genetic code?

  • triplet code- three bases in DNA code for each specific amino acid and can be seen as start/stop signals
  • non overlapping- each base is only part of one triplet
  • degenerate- several triplets can code for the same amino acid
  • universal- code is the same in all living organisms
• translation?

  1. in the cyto, each aa is attached to own unique tRNA with unique anticodon.
  2. ribosome attaches to mRNA at start codon and moves along to read codons in mRNA
  3. tRNA bring specific aa to ribosome, tRNA with corresponding anticodon attaches by complementary base pairing
  4. ribosome joins aa together via peptide bonds
  5. one aa is attached to pp chain, tRNA is released
  6. when ribosome reaches stop codon, mRNA+pp chain released
  7. primary structure of protein ready for folding
• overall recap of transcription/translation?

  • transcription= mRNA copy of gene is made in nucleus and leaves via nuclear pore into cytoplasm.
  • translation= mRNA and tRNA used to join correct sequence of aa to build a new protein
• important note about bases !

  • 3 bases on DNA= triplet
  • 3 bases on mRNA= codon
  • 3 bases on tRNA= anticodon