3.1.5 Nucleic acids are information-carrying molecules

• Most of the DNA of a cell is found in the nucleus, with the rest in the mitochondria or chloroplasts.
• In a dividing cell (Mitosis) the DNA molecules are condensed into chromosomes. At other times (interphase) the DNA molecules extend throughout the nucleus as chromatin - the relaxed form of DNA.
• Thymine (T) and Cytosine (C) are pyrimidines.

  Adenine (A) and Guanine (G) are purines.
• DNA


  • Every single cell has its own copy except for red blood cells
  • Needs to be protected because it is the code for all the proteins in a cell
• Chromosome


  Tightly coiled DNA
• Histone proteins


  Proteins that DNA is wrapped around to prevent tangling
• Nucleosome


  Complex of DNA wrapped around histone proteins
• In prokaryotic cells, DNA is circular and not wrapped around histones
• Gene


  Short section of DNA that contains a code for making a polypeptide and functional RNA. The code is a specific sequence of bases.

  
  

  The polypeptides make proteins and so genes determine the proteins of an organism.
• Allele


  Different form/version of the same gene
• Locus


  Location of a gene on a chromosome
• Homologous pair


  Pair of chromosomes with the same genes
• Humans have 23 pairs of chromosomes
• The 23rd chromosome pair are the sex chromosomes (X and Y)
• Compacting DNA into chromosomes

  DNA is tightly coiled around histone proteins
• Function of histone proteins

  Allow DNA to be tightly coiled into chromosomes
• A homologous pair of chromosomes are a pair of chromosomes with exactly the same genes, but might have different alleles.
• similarities between mitochondrial, chloroplast DNA and Prokaryotic DNA

  -Short

  -Circular

  -not bound to histone proteins