DNA & Genome

• DNA - a polymer which carries genetic code and creates a double helix.
• Gene - is a small section of DNA in a chromosome which codes for a protein
• How genes code for protein:

  • So particular section of the chromosome (gene) codes for a specific sequence of amino acids.
  • Once these amino acids are combined a protein is made.
  • There are only 20 types of amino acids. But they can all be combined in different ways to create thousands of different proteins.
• The DNA in a cell determines which protein the cell produces, which will determine what type of cell it will be.

  For example, a red blood cell will need lots of the protein called haemoglobin.
• Genome - is all the genetic information in an organism.
• DNA is made up of many nucleotides (the monomer). Each nucleotide is made up of a pentose sugar, phosphate group (which are the backbone) and a organic base.
• Bases in DNA;

  • There are 4 types of bases - A,C,G,T.
  • These bases have complementary base pairings, which are A and T as well as C and G.
  • Each DNA molecule has two DNA strands, these strands are connected together by 2 bases (one on each strand).
  • Each group of 3 bases codes for an amino acid.
• There are also non-coding parts of DNA that don't code for protein. Some of these are responsible for switching genes on and off, i.e. controlling whether a gene is used to form a protein.
• Understanding the human genome helps because:

  1. We can identify genetic diseases by their genes.
  2. We can understand what the disease is caused by, so better/ more effective treatment can be developed.
  3. We can trace the migration of our ancestors.
• A human has 46 (23 pairs) of chromosomes in each cell.
• The 23 rd pair of chromosomes are known as the sex chromosomes, this is because they determine the sex of the person. The XX chromosomes will make them a women. While, XY chromosomes will make them a man.
• The main uses of proteins:

  • Enzymes
  • Hormones
  • Structural proteins
• Alleles - are a different version of a gene. (e.g. eye colour)
• Homozygous - 2 alleles which are the same
• Heterozygous - 2 alleles which are different
• Alleles can be dominant or recessive. For the dominant gene to be expressed there needs to be one allele. For recessive gene to be expressed there needs to be two alleles. Also dominant genes are shown with capital letters while recessive genes are shown by lowercase letters.
• Genotype - is the collection of allels we have
• Phenotype - the physical characteristics given by the genotype