Genetics

• • A gene is a short length of DNA found on a chromosome​
  •  Each gene codes for a particular sequence of amino acids​
  •  These sequences of amino acids form different types of proteins​
  •  There are many different types of proteins but some example of these could be:​
  • structural proteins such as collagen found in skin cells​
  • enzymes​
  • Hormones​​
  •  Genes control our characteristics as they code for proteins that play important roles in what our cells do
• •  DNA is a polymer (a molecule made from many repeating subunits) – The monomer is a nucleotide​
  •  These individual subunits of DNA are called nucleotides​
  •  Each nucleotide consists of a common sugar (pentose) and phosphate group with one of four different bases attached to the sugar​
  •  Two nucleotides are joined by condensation reaction forming a phosphodiester bond
• DNA Structure:

  •  The genetic material in the nucleus of a cell is composed of a chemical called DNA​
  •  DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms​
  •  DNA is a polymer made up of two strands forming a double helix – remember this from large molecules!​
  •  DNA is contained in structures called chromosomes​
  •  Chromosomes are located in the nucleus of cells
• Role of RNA:

  •  Ribosomes use the sequence of bases contained within DNA to make proteins​
  •  DNA cannot travel out of the nucleus to the ribosomes (it is far too big to pass through a nuclear pore) so the base code of each gene is transcribed onto an RNA molecule called messenger RNA (mRNA)​
  •  mRNA can move out of the nucleus and attaches to a ribosome (the mRNA acts as a messenger between DNA and the ribosome)​
  • RNA transfers genetic information from DNA to the ribosomes were proteins are synthesised​
  • RNA molecules are relatively short single stranded polynucleotide chains
• DNA Pairs:

  •  The bases on each strand pair up with each other, holding the two strands of DNA in the double helix​
  •  The bases always pair up in the same way:​
  • Adenine always pairs with Thymine (A-T)​
  • Cytosine always pairs with Guanine (C-G)​
  •  This is known as ‘complementary base pairing’
• DNA Double Helix:

  • The phosphate and sugar section of the nucleotides form the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder​
  • It is this sequence of bases that holds the code for the formation of proteins
• RNA - Adenine, Cytosine, Guanine, Uracil