DNA and the genome

• what is DNA

  • the genetic material in the nucleus of the cell is composed of a chemical called deoxyribonucleic acid. DNA is a polymer made p of two strands forming a double helix.
• what is a gene?

  • 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.
• what is the genome?

  • a 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
• structure of DNA

  • 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 four bases are A,C,T,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.
• DNA

  • the long strands of DNA consist of alternating sugar and phosphate sections. Attached to each sugar is one of four bases.
  • DNA is a polymer made up of repeating nucleotide units.
• why do scientists want to understand the human genome?

  • to search for genes linked to different types of disease
  • understanding and treatment of inherited disorders
  • use in tracing human migration patterns
• what is protein synthesis?

  The DNA code for the protein remains in the nucleus, but a copy, called mRNA, moves from the nucleus to the ribosomes where proteins are synthesised in cytoplasm. The protein produced depends on the template used, if sequence changes a different protein will be made. Carrier molecules bring specific amino acids to add to the growing protein in the correct order.Each protein molecule has hundreds, or thousands of amino acids joined together in a unique sequence.
• in the complementary strands, a C is always linked to a G and an A is always linked to a T
• stages of protein synthesis

  • transcription - base sequence of the gene is copied into a complementary template molecule mRNA which is a single stranded molecule
  • the mRNA now passes out of the nucleus and into the cytoplasm
  • translation - mRNA attaches to the ribosome and amino acids are brought to the ribosome on carrier molecules (tRNA)
  • The ribosome reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order
  • once complete the chain folds into its unique shape
• how are proteins useful in the body?

  • enzymes
  • hormones
  • structural proteins such a collagen
• 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, when the protein chain is complete, it folds up to form a unique shape. this unique shape enables the proteins to do their jobs as enzymes, hormones or forming structures in the body such as collagen.
• how do mutations occur?

  • mutations occur continuously. most do not alter the protein, or only alter it slightly so that its function and appearance are not changed.
  • a few mutations code for an altered protein with a different shape. an enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.
• what do non-coding parts of DNA do?

  • non-coding parts of DNA can switch genes on or off, so variation in the areas of DNA may effect how genes are expressed