4- DNA and Chromosomes

• Eukaryotic cells


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotic cells


  Cells that lack a nucleus and membrane-bound organelles
• DNA in prokaryotes


  • Usually a circular molecule with no free ends
• DNA in eukaryotes


  • Linear molecules with two ends
• DNA in eukaryotes


  • Much longer than DNA in prokaryotes
• Chromatin


  DNA bound to histones in the nucleus of eukaryotic cells
• Chromosome replication


  1. Chromosome is copied

  2. Two copies (chromatids) remain attached at centromere
• Chromatids


  The two copies of a replicated chromosome
• Homologous chromosomes


  Chromosomes that contain the same genes but may have different alleles
• Locus


  The position of a gene on a chromosome
• Alleles


  Different versions of a gene
• Humans inherit one chromosome from each homologous pair from each parent
• Much of the DNA in chromosomes does not code for proteins
• Non-coding DNA includes repeating base sequences and introns within genes