DNA

• DNA stands for deoxyribonucleic acid, its the chemical that all of the genetic material in a cell is made up from, it is found in the nucleus or in chromones which come in pairs. DNA is a polymer and is made up of two strands coiled together in a double helix
• A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.
• genes tell cells in what order to put the amino acids together, DNA also determines what proteins the cell produces eg haemoglobin and keratin which determines what type of cell it is eg red blood cell, skin cell
• The genome of an organism is the entire genetic material of that organism. The whole human genome has now been studied and this will have great importance for medicine in the future.
• the genome:

  • allows scientists to identify genes in the genome that are linked to different types of disease
  • knowing which genes are linked to inherited diseases to help us to understand them better and develop effective treatments
  • trace migration of populations of people around the world
• DNA is a polymer made from four different nucleotides. Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar. The sugar and phosphate form the backbone to the DNA strands
• DNA contains four bases, A, C, G and T. A always pairs with T and C always pairs with G

  A sequence of three bases is the code for a particular amino acid. The order of bases controls the order in which amino acids are assembled to produce a particular protein.
• label structure of nucleotide ( a repeating unit of a DNA strand )

  A) phosphate group

  B) sugar

  C) base A C T G

  
• The long strands of DNA consist of alternating sugar and phosphate sections. Attached to each sugar is one of the four bases.

  The DNA polymer is made up of repeating nucleotide units.
• • proteins are made in the cell cytoplasm on ribosomes
  • by using the code in the DNA. DNA is found in the nucleus and cant move out of it as it is really big, so the cell needs to get the code from the DNA to the ribosome
  • this is done using a molecule using mRNA which is made by copying the code from DNA and acts as a messenger, carrying the code between the two
  • the correct amino acids are brought to the ribosomes in the correct order by carrier molecules
• The sequence of amino acids in the protein is determined by the sequence of nitrogenous bases in the mRNA, which is in turn determined by the sequence of nitrogenous bases in the DNA. Thus, the structure of DNA directly affects the sequence of amino acids in the proteins made during protein synthesis
• when a chain of amino acids has been assembled, it folds into a unique shape which allows the protein to perform the task its meant to do
• examples of types of proteins

  • enzymes - act as biological catalysts to speed up chemical reactions in the body
  • hormones - used to carry messages around the body eg insulin is a hormone released into the blood by the pancreas to regulate the blood sugar level
  • structural proteins - are physically strong eg collagen is a structural protein that strengthens connective tissues
• The unique amino acid sequence of a protein is reflected in its unique folded structure. This structure, in turn, determines the protein's function. This is why mutations that alter amino acid sequence can affect the function of a protein
• Proteins are synthesised on ribosomes, according to a template. Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order.

  (HT only) When the protein chain is complete it folds up to form a unique shape. This unique shape enables the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen.
• there are parts of DNA that dont code for proteins (non-coding) Some of these parts switch on and off so they control whether or not a gene is expressed (98.5 percent of DNA is non coding)
• name the structures that contain DNA in the nucleus of a cell

  chromosones
• what is a gene

  a small section of dna found on a chromosone that codes for a paticular sequence of amino acids that are put together to make a specific protein
• explain why the function of a protein may be affected by a gene mutation

  a mutation changes the amino acid coded for which can change the shape of the protein that the amino acids made up which can affect its function
• explain the relationship between DNA and the proteins produced by an organism

  DNA contains genes, each gene codes for a paticular sequence of amino acids which are put together to make a specific protein
• outline how the enzyme coded for by a disease gene would normally be synthesised within a cell

  code from disease gene copied by mRNA, code then carried to a ribosome, amino acids brought to the ribosome in the correct order by carrier molecules, the amino acids then joined together to create the correct enzyme
• explain how a mutataion could alter the actvity of the enzyme it codes for

  mutation changes sequence of DNA bases which would change the amino acid it codes for which changes the shape of the enzyme and its active site so would affect the ability of the substrate to bind to it, changing the enzymes activity