Genes + protein synthesis

• What is a gene?

  A section of DNA that codes for one polypeptide
• What is an allele?

  They code for different versions of the same gene
• What does DNA carry

  The genetic code to allow the cell to make proteins
• How many bases code for one amino acid ?

  Three bases

  (Triplet)
• The code is non-overlapping - what does this mean

  each base is part of only 1 triplet code
• Why is the code degenerate

  Most amino acids are coded for by more than one triplet

  E.g

  ATT,ATC & ATA ) code for Ile

  64 did triplet codes only 20 amino acids
• How does the gene code info

  -specific sequence of bases on 1 strand of DNA controls sequence of amino acids (primary structure)

  
  

  -therefore tertiary structure and function of that protein
• What does a mutation result in?

  Non-functional proteins

  -mutation changes DNA base sequence

  -different sequence of amino acids in protein

  -different tertiary structure
• Ribosomal RNA


  -rRNA + proteins forms ribosomes

  -the site of protein synthesis and mRNA translation

  
  

  -coded for by numerous genes in many dif chromosomes
• Messenger RNA


  -may consist of thousand of nucleotides in single linear strand

  -formed by transcription of a gene of DNA in nucleus

  -complementary to DNA

  -coded for by a triplet of bases- codon

  -unpaired bases so easily broken down
• Transfer RNA

  -small molecule ( made of around 80 nucleotides)

  
  

  -single strand that folds back on itself

  
  

  -forms hydrogen bonds within complementary sections of the molecule -stable

  
  

  -sequence of 3 bases at base of molecule-anticodon

  
  

  Uracil
• What does Eukaryotic DNA contain?

  introns- non coding sections
• What are differences between DNA structure in prokaryotes and eukaryotes

  Prokaryote DNA Euk DNA

  -DNA circular- plasmids -no plasmids

  -no introns -has introns

  -no chromosomes -chromosmes

  -no proteins histones associated. -associated
• What is a genome?


  the complete set of genes in a cell, including those in mitochondria and/or chloroplasts
• What is a proteome?

  The full range of proteins that a cell is able to produce
• What is a complete proteome


  full set of proteins that can be made by an organism
• Where does transcription occur?

  nucleus of a cell
• Where does translation occur?

  ribosomes in the cytoplasm
• Describe the process of transcription


  -H bonds between DNA bases break -seperating 2 strands

  of DNA

  -one strand of DNA acts as template strand

  -Free RNA nucleotides are attracted to exposed DNA bases and align by complementary base pairing

  -RNA polymerase joins RNA nucleotides via phosphodiester bonds

  -introns spliced out of pre-mRNA
• Describe the process of translation

  -mRNA attaches to ribosomes

  
  

  -tRNA anticodons bind to mRNA codons by complementary base pairing

  
  

  -each tRNA brings a specific amino acid

  
  

  -2 tRNA molecules are held at a ribosome at any one time

  
  

  -peptide bond forms between adjacent amino acids -ATP

  
  

  -tRNA molecules released after their aa have been joined

  
  

  -ribosomes move along the mRNA until stop codon reached
• Give an advantage of mRNA being broken down relatively quickly

  -mRNA used in protein production

  -protein only needs to be produced when it is needed

  -MRNA breaks down once , used and is made again where protein production is required