DNA and protein synthesis

• What is a genome 


  The complete set of genes present in a cell
• what is the proteome 


  full range of proteins that a cell is able to produce

  usually larger than the genome of an organism
• structure of RNA and mRNA 


  contain phosphate group

  contain ribose sugar

  contain nitrogenous bases adenine guanine cytosine and uracil

  is a polynucleotide made up of nucleotides

  single stranded unlike DNA

  short chains
• Structure of tRNA 


  Has sugar phosphate backbone

  clover leaf shape

  as a amino acid binding site

  as specific anticodon on molecule complimentary to specific codon on mRNA molecule

  folded so hydrogen bonds form between complimentary bases
• stages of protein synthesis

  Transcription : DNA us transcribed and an mRNA molecule produced

  Translation: mRNA is translated into amino acid sequence
• process of transcription 


  DNA molecule unwinds and unzips as hydrogen bonds between complimentary base pairs broken by DNA helicase

  exposes gene to be transcribed

  free complimentary RNA nucleotides pair up on template strands via hydrogen bonding

  sugar phosphate backbone of RNA strand catalysed by RNA polymerase

  when gene transcribed hydrogen bonds between mRNA and DNA strands break down and DNA molecule re forms

  mRNA molecule leaves nucleus via pores in envelope
• what happens before mRNA leaves nucleus

  splicing occurs in pre mRNA and intron sections removed and exons joined together forming mRNA
• what is alternate splicing

  exons in genes can be spliced in many different way to produce different mature mRNA

  means single eukaryotic gene can code for more than one polypeptide chain

  why proteome larger than genome
• process of translation 


  occurs in cytoplasm of cell

  mRNA molecule attaches to a ribosome

  free molecules of tRNA in cytoplasm with complimentary anticodon to specific amino acids

  tRNA binds to amino acid and bring them to mRNA molecule on ribosome

  codons of bases on each tRNA molecule pairs with complimentary codons on mRNA molecule

  two tRNA molecules can fit on ribosome at one

  peptide bond formed between two amino acids by condensation reaction and molecule removed

  process continues until stop codon and amino acid chain complete leaves ribosome and then forms polypeptide
• difference between triplet and codon 


  triplet is sequence of 3 DNA bases that code for specific amino acid

  codon is sequence of three mRNA bases that codes for specific amino acid
• what is anticodon 


  sequence of three tRNA bases complimentary to a codon