6.1 Cellular Control

• What is a difference in mutations that occur in mitosis vs in meiosis

  • in mitosis it is somatic - it is not passed to the offspring
  • meiosis - may be inherited
• How do cancer cells come about?

  Mutations that occur in somatic cells can often result in cancers
• What is a frame shift?

  Something that causes a change in the way the amino acid sequence is read
• what are the three point mutations?

  • silent - mutations to the base end up coding for the same amino acid - no change to the amino acid sequence
  • missene - mutation to the base triplet alters the secondary and tertiary structure - changed shape can no longer carry out function
  • nonsense - mutations code for a termination/stop amino acid which results in a truncated protein
• Indel - what is it?

  • insertion or deletion of amino acids
• how does an indel mutation work

  • base triplets (NOT IN 3s) are inserted or deleted which causes a frameshift
  • Thalasemia
  • if alterations are too large, then it can no longer carry out its function and will degrade within the cell
  • if its in 3s it is ADDITION OR LOSS
• Why are operons useful?

  the genes that code for proteins (in a specific pathway) can all be switched on or off
• How do bacteria, such as E. coli respire in the absence of glucose?

  Use lactose (disaccharide of glucose and galactose) which requires different proteins compared to the metabolism of glucose and these are only produced when glucose is absent and lactose if present in order to conserve resources
• What is the lac operon?

  the operon where the genes that code for the proteins involved in lactose metabolism are loacted
• What are Lac Z, Y and A?

  Structural genes that code for the proteins
• Label the diagram

  answers

  A) LacI

  B) Promoter Region

  C) Operator region

  D) LacZ

  E) LacY

  F) LacA

  
• What is the promoter region?

  section of DNA where the RNA polymerase binds to begin transcription
• What does lacI do?

  codes for the proteins that prevents transcription of the structural genes. called a repressor protein
• What is the operator region?

  the section of DNA where the repressor protein binds to to prevent transcription
• What are tumor suppressor genes?

  Genes that help regulate cell growth and prevent the formation of tumors.
• What other things can tutor suppressor genes do?

  • repair dan that had been damaged by mutagens (chemicals that cause mutations)
  • if DNA can't be repaired, they instruct cells to die in a process called apoptosis (better for cell to die then divide and pass errors on)
• What happens if a tumour suppressor gene is damaged?

  • Becomes inactive
  • cell division is no longer inhibited and cells divide at an increased rate
  • mutations accumulate
  • Uncontrolled cell growth (cancer)
• Example of a tutor suppressor gene

  p53 codes for transcription factor p53
• What are transcription factors?

  • Regulate gene expression at transcriptional level
  • DNA folded around histone proteins to create nucleosome complexes
  • Methylation of DNA and histone causes DNA to pack tightly preventing transcription factors from binding to DNA
  • Histone acetylation loose packing of DNA - gene can be expressed
  • RNA polymerase bind to promoter region initiating transcription
• What are post transcriptional changes?

  • when a newly synthesised strand of mRNA (pre-mRNA or primary mRNA) is modified
  • key modifications are the removal of introns and the rearrangement of of exons
• How and why are introns removed?

  • removed as they do not code for amino acids in the primary structure of the polypeptide being made
  • removed by a protein called spliceosomes
• What is alternative splicing?

  • exons are reordered and some removed to allow a single gene result in the creation of the multiple genes
• What are some post-translation changes?

  • non protein groups can be added to the protein (lipids, carbohydrates)
  • cAMP activates or inactivates proteins in the cell - low glucose levels, cAMP accumulates and binds to positive regulator catabolite activator protein binds to promoter region increasing transcription of genes
• What is morphogenesis?


  The process of development and formation of an organism's shape and structure.
• What are homeobox genes?

  sequences of genes of 180 base pairs that plays a role in body plan development. highly conserved across animals plants and fungi - little variation in DNA sequence
• What are Hox genes?

  type of homeobox genes. genes that control the body plan of an organism in animals. code for proteins that act as transcription factors.
• What genes are responsible for producing proteins that initiate the cell cycle?

  proto-oncogenes
• When does apoptosis occur?

  • error in cell
  • too old to function
  • apoptosis occurs (cell death) - resources are recycled
• How is mitosis and apoptosis controlled?

  in response to internal and external stimuli

  • internal; mitosis inhibited by proteins until all DNA replicateed
  • External - oxidative stress can cause the onset of apoptosis