The genetic code

• what is meant by the genetic code being 'universal'?

  everything has the same 4 bases
• how many bases are in one codon?

  3
• what is a base pair?

  • sets of hydrogen-linked nucleobases that make up nucleic acids, DNA and RNA
  • they consist of 2 complementary DNA nucleotide bases that pair to form a 'rung of the DNA ladder'
• what is a gene?

  a length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA
• what does degenerate mean?

  more than one codon can code for the same amino acid
• describe DNA

  • sugar - deoxyribose
  • bases - (C,G) , (A,T)
  • strands - double stranded
  • number of forms - 1
  • shape of polynucleotide - double helix
• describe RNA

  • sugar - ribose
  • bases - (C,G) , (A,U)
  • strands - single stranded
  • number of forms - 3 (t, m, r)
  • shape of polynucleotide - depends of type/form
• what are the 3 types of RNA?

  • Messenger RNA (mRNA) - carries code from nucleus to ribosomes in cytoplasm
  • Transfer RNA (tRNA) - binds to amino acids
  • Ribosomal RNA (rRNA) - what ribosomes are made of, reads mRNA
• what is mRNA?

  • gives instructions to ribosomes for synthesis of proteins
  • copied using DNA as a template (transcription)
  • is single stranded
  • has a variable length
  • bases grouped in threes - codons
• what is tRNA?

  • involved in protein synthesis as interpreters of mRNA
  • each tRNA associated with a different amino acid
  • complicated 3-D structure ('clover leaf')
  • anti-codons binds to codons on mRNA
  • anti-codons determine what amino acid is carried at binding site
• what is rRNA?

  • component of the ribosome (apparatus involved in protein synthesis)
  • what is reading mRNA
• what is a codon?

  a sequence of 3 bases on a messenger RNA molecule that codes for a single amino acid
• why is a codon 3 bases long?

  • allows for enough combinations of bases to code for all amino acids (20)
  • called the triplet code
• what are key feature of the genetic code?

  • codon is read in 5'-3' direction
  • start codon is usually AUG (methionine)
  • UAA, UAG, UGA are stop codons
  • codons are non-overlapping
  • universal
  • redundant (degenerate)
• how does one base mutating into another affect a protein?

  • effects primary structure and tertiary structure due to different R-groups which will effect the proteins bonding, structure and therefore function
  • this mutation only affect 1 amino acid if at all (degenerate quality)
  • could be beneficial, or damaging or unchanging
• how does the deleting or inserting mutation affect a protein?

  • would change the triplet codon - they couldn't be read properly as the whole protein would be changed
  • this is much more harmful than substitution
  • is less harmful at the end of the sequence