DNA, genes and chromosomes

• Similarities of DNA in eukaryotic and prokaryotic cells

  • Nucleotide structure is identical - deoxyribose attached to phosphate and a base
  • Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
  • DNA in mitochondria/chloroplasts have similar structure to DNA in prokaryotes - short, circular and not associated with proteins
• Differences of DNA in eukaryotic and prokaryotic cells

  • Eukaryotic DNA is longer
  • Eukaryotic DNA is linear, prokaryotic DNA is circular
  • Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
  • Eukaryotic DNA contains introns, prokaryotic does not
• What is a chromosome?

  • Long linear DNA associated with histone proteins
  • In the nucleus of eukaryotic cells
• What is a gene?

  A sequence of DNA (nucleotides) bases that code for:

  • The amino acid sequence of a polypeptide
  • Or a functional RNA
• What is a codon?

  Triplet/3 bases on mRNA or DNA that code for a specific amino acid
• What does it mean if the genetic code is universal?

  The same base triplets code for the same amino acids in all organisms
• What does it mean if the genetic code is non-overlapping?

  Each base pair is part of only triplet so each triplet is read as a discrete unit
• What does it mean if the genetic code is degenerate?

  An amino acid can be coded for by more than one base triplet
• What is an exon?

  Base sequence of a gene coding for an amino acid sequence (in a polypeptide)
• What is an intron?

  Base sequence of a gene that doesn't code for amino acids, in eukaryotic cells
• What is a homologous chromosome?

  Pair of matching chromosomes (one from each parent), with the same genes but can have different alleles
• What is an allele?

  A variation of a gene (one from mum and one from dad). Order of bases in each allele is slightly different, so they code for slightly different version of the same polypeptide
• What is the locus?

  The location of a particular gene or chromosome
• What is a diploid?

  Two copies of each chromosome
• What is a haploid?

  One copy of each chromosome