DNA genes and protein synthesis

• gene

  a gene is a section of DNA that codes for a protein.

  it codes for:

  amino acid sequence of a polypeptide

  functional RNA including tRNA and mRNA.
• Degenerate code 


  redundancy in codons can be described as degenerate because most amino acids are coded for by more than one triplet.

  20 different amino acids

  more than one codon codes for an amino acid

  this is described as redundancy.
• Non-overlaping


  each base in the sequence is only read once.

  123,456 not 124,234

  the genetic message once initiated of a fixed point is read in a definite frame in a series of three letter words.

  the framework would be disturbed as soon as detection or addition of more bases.
• Universal 


  Genetic code found in all organisms from bacteria to man.

  may have developed 3 billion years ago with the first bacteria and changed very little throughout the evolution of living organisms.
• Introns and exons 


  Introns are part of genes that do not directly code for proteins.

  exons are parts of DNA that are converted into mature mRNA.
• The genetic code 


  three Bases code for each amino acid.

  20 different amino acids regularly occur in proteins.

  each three bases are called a triplet there are 64 possible triplets.
• Chromosome structure 


  Only visible as distinct structures during cell division.

  each chromosome is formed by two threads called chromatids.

  the length of DNA is highly coiled (about 2M every human cell)
• Prokaryotic DNA

  • DNA molecules are shorter
  • form a circle
  • no chromosomes
• Eukaryotic DNA

  • Form a line and are longer
  • occur with protéines called histones to form chromosomes
  • chloroplasts contain DNA like prokaryotes
• Homologous chromosomes 


  Egg (maternal) and sperm (paternal) known as homologous pairs.

  the number is now diploid.

  a homologous pair always has two chromosomes that carry the same genes but not necessarily the same alleles of genes
• Genome 


  The complete set of genes in a cell including those in mitochondria or chloroplasts.
• Proteome


  The full range of proteins produced by the genome, this is sometimes called the complete proteome.
• Allele

  one of an alternative forms of a gene.

  each individual inherits one allele from each parent those two alleles may be the same or different.
• RNA


  A single stranded polymer

  each RNA nucleotide consists of:

  • pentose sugar
  • phosphate group
  • base
• mRNA


  Used to transfer the DNA code from the nucleus to the cyptoplasum complementary to DNA.

  small so can leave nuclear pores

  used to determine sequence of amino acid during protons synthesis easily broken down and only exists whilst needed to maifacture protein
• tRNA 


  Small molecule

  single stranded and folded into a clover leaf shape.

  longer section is attached to an amino acid
• Transcription 


  Healicase acts on a region of DNA to break the hydrogen bonds between bases.

  RNA polymerase makes along one of the two DNA strands.

  RNA polymerase matches up complementary RNA nucleotides

  as the RNA nucleotides join together pre-mRNA is formed

  the DNA regions join together behind the RNA polymerase

  when RNA polymerase reaches a stop codon the chain is terminated
• Translation 


  mRNA attaches to the ribrosome at the start codon

  tRNA with the complementary anti-codon attaches to the mRNA

  this tRNA is attached to an amino acid

  the ribrosome moves along the mRNA bringing in 2 tRNA molecules at any one time an enzyme and ATP are used to join the amino acid with a peptide bond

  the first tRNA is released and can be collect another amino acid

  this process is repeated until a stop codon is reached.