Topic 8A

• Degenerate code: amino acids can be coded for by more than one dna triplet
• 5-bromouracil is a base analog that substitutes for thymine, it can bind with guanine - causes substitution mutation
• uncontrolled cell divison = tumour
• tumour- mass of abnormal cells
• Cancer- tumours that invade and destroy surrounding tissues
• two genes controlling cell division:

  • tumour suppressor genes
  • proto-oncogenes
• Tumour suppressor genes:

  • slow cell division by producing proteins to stop cell division or cause apoptosis

  if mutation in TSG occur:

  • gene inactivated
  • protein not produced
  • cell divides uncontrollably = tumour
• Proto-oncogenes:

  • stimulate cell division by producing proteins that make cells divide

  if mutation in P.O occurs:

  • can become overactive
  • stimulates cell to uncontrollably divide
  • mutated prot-oncogene = oncogene
• tumour cells:

  • larger & darker nucleus + can have more than 1
  • have irregular shape
  • dont produce all proteins for function
  • different antigens on surface
  • divide by mitosis more frequently
• causes of tumour growth:

  • abnormal methylation of DNA
  • INCREASED EXPOSURE TO OESTROGEN
• Abnormal methylation:

  • adding methyl group (-CH3) to DNA
  • Methylation of DNA important for regulating gene expression - it controls whether a gene is transcribed and translated

  hypermethylation or hypomethylation:

  • causes growth of tumours
  • hypermethylation of TSG
  • hypomethylation of PO
• role of Oestrogen in breast cancer:

  • oestrogen can stimulate some breast cells to divide and replicate
  • if cells become cancerous, rapid division of breast cells stimulated by oestrogen helps tumours form quickly
  • oestrogen my be able to introduce mutations directly to DNA of certain breast cells
• transcription factors:

  • move from cyptoplasm to nucleus
  • in nucleus bind to specific DNA sites; promoters - found near start
  • control expression by controlling rate of transcription
  • activators stimulate or increase rate of transcription- help RNA polymerase bind to target gene
  • repressors - prevent RNA Polymerase from binding to activate transcription
• Oestrogen can affect transcription by bn
• Oestrogen can affect transcription by binding to transcription factor called oestrogen receptor, forming oestrogen-oestrogen receptor complex
• the oestrogen- oestrogen receptor complex moves from the cyptoplasm into the nucleus where it binds to specific DNA sites near start of the target gene

  • can act as either an activator or repressor
• epigenetics: whether a gene is expressed - determined through the attachment or removal of epigenetic marks - alter how easy it is for proteins to transcribe and interact with DNA
• increased methylation of DNA:

  • Methyl group attached to cytosine by enzyme methyltransferase
  • increased methylation alters DNA structure - transcriptional machinery cannot interact with gene - gene switched off
• Decreased Acetylation of Histones:

  • how condensed chromatin is affects how accessible DNA is and if it can be transcribed
  • addition or removal of acetyl groups (-COCH3)
  • if histone acetylated = less condense - can be transcribed
  • without acetyl groups - more condensed - histone deacetylase
• • in vivo gene cloning: gene copies are produced in a living organism
  • in vitro gene cloning: gene copies made outside of living organism using polymerase chain reaction
• In vivo cloning:

  • insert DNA fragment into vector DNA
  • vector DNA then isolated and restriction endonuclease and DNA ligase stick DNA fragment and Vector DNA together
  • ligation: sticky ends of Vector DNA and DNA fragment joined by DNA ligase = recombinant DNA