DNA structure

• what are the monomers of DNA?

  Nucleotides
• what are DNA nucleotides made of?

  • common sugar
  • Phosphate group
  • A T C G
• full names of the four bases in nucleotides

  • adenine
  • Thymine
  • cytosine
  • Guanine
• describe how nucleotides interact to form a molecule of DNA

  • sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
  • base connected to each sugar
  • complementary base pairs joined by weak hydrogen bonds
• explain how a gene codes for a protein

  • sequence of three bases in a gene forms a triplet
  • each triplet codes for an amino acid
  • order of amino acids determines the structure and function of protein formed
• why is the folding of amino acids important in proteins such as enzymes?

  determines the shape of the active site which must be highly specific to the shape of its substrate
• what is protein synthesis?

  formation of a protein from a gene
• two stages of protein synthesis

  1. transcription
  2. translation
• what does transcription involve?

  formation of mRNA from a DNA template
• outline transcription

  • DNA double helix unwinds
  • RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
  • RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
  • mRNA formation complete, mRNA detaches and leaves the nucleus
• what does translation involve?

  ribosome joins amino acids in a specific order dictated by mRNA to form a protein
• outline translation

  • mRNA attaches to a ribosome
  • ribosome reads the mRNA bases in triplets
  • Each triplet codes for 1 amino acid which is brought to the ribosome by a tRNA molecule (carrier molecule)
  • polypeptide chain is formed from the sequence of amino acids which join together
• what is a mutation?

  • random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variants of the protein
  • occur continuously
• describe the effect of a gene mutation in coding DNA

  if a mutation changes the amino acid sequence, protein structure and function may change (enzyme may no longer fits its substrate binding site or a structural protein may lost its strength)

  if a mutation doesn’t change amino acid sequence, there is no effect on protein structure or function
• what is non-coding DNA?

  DNA which doesn’t code for a protein but instead controls gene expression
• describe the effect of a gene mutation in non-coding DNA

  gene expression may be altered, affecting protein production and the resulting phenotype