8.1 - Genes & Genetic Code

• what are genes?

  a section of DNA that contains coded information for making polypeptides and functional RNA located on a particular position (locus) on a DNA molecule
• how do genes determine nature & development of organisms?

  they code for polypeptides which make proteins like enzymes Which control chemical reactions responsible for development & activities in an organism
• what is the genetic code?

  the set of rules by which the genetic information in DNA or MRNA is translated into proteins
• What's a codon?

  a three base sequence that codes for an amino acid or functional RNA
• What's the reasoning behind codons?

  there are 20 different, naturally occurring amino acids

  each amino acid must have its own code for bases but there are only 4 bases

  if each base coded for a different amino acid then only 4 amino acids would be coded for

  3 bases produce 64 codes(4^3) which satisfies 20 amino acids

  other 24 codons may also code for those 20 amino acids - that's why the genetic code is degenerate
• main features of the genetic code

  degenerate

  non-overlapping

  universal
• why is the genetic code degenerate?

  most amino acids are coded for by more than one codon
• What's the technical definition of degenerate?

  lacking some usual or expected quality
• why is the genetic code non-overlapping?

  each base is only part of one triplet and only read once

  each triplet codes for just one amino acid
• Why is the genetic code universal?

  each codon is the same in all organism with a few minor exceptions - direct link to evolution
• other features of the genetic code

  some amino acids are coded for by one codon, the rest by 2 to 6 each

  Start of a sequence of DNA that codes for a polypeptide is always the same - codes for methionine

  3 triplets don't code for amino acids & are when the polypeptide stops & RNA polymerase detaches from gene