DNA and Chromosome structure

• What are genes?


  DNA base sequence that codes for the amino acid sequence for the production of polypeptides and a functional RNA molecule.
• What is the locus?


  The fixed position a gene occupies on a chromosome
• What is an allele?


  An alternative from of a gene
• What is the structure of a chromosome?

  2 sister chromatids joined at the centromere

  23 pairs, 46 total in humans
• What are homologous pairs of chromosomes 


  2 chromosomes that carry the same genes, may be different alleles such as Aa or Bb
• What is DNA storage like in eukaryotes?

  Longer, Linear, Associated with histones
• What is DNA storage like in Prokaryotes?

  Shorter, circular and not associated with histones
• Describe how a gene is a code for the production of a polypeptide

  The base sequence in the triplet code determines the order of amino acid sequence (primary structure of polypeptides)
• How is a phosphodiester bond formed between two DNA nucleotides?

  1. Condensation reaction, which releases a water molecule
  2. Forms between deoxyribose and phosphate
  3. Catalysed by DNA polymerase enzyme
• Define "Non-coding base sequences and describe where they are positioned within the genome 


  These are introns which do not code for the production of polypeptides, and are positoned between genes
• Suggest one way the structure of chromosomes could differ along its length.

  Differences in the base sequences.