Topic 8

• Gene mutation:

  • change in base sequence of DNA
  • occurs during DNA replication
  • includes addition, deletion, substitution, inversion, duplication and translocation of bases
• Mutagenic agents: chemical or radiation that increases mutation rate

  
• Addition mutation:

  • One extra base is added to the DNA sequence
  • causes all subsequent codons to be altered (frameshift)
• Deletion mutation:

  • One base is deleted in the DNA sequence.
  • causes all subsequent codons to be altered (frameshift)
• Substitution mutation:

  • One base in the DNA sequence is changed
  • no frameshift
  • only one codon changes
  • may have no impact due to degenerate genetic code
• Frameshift:

  • A change in all the codons after the point of mutation
  • each base shifts left or right one position
• Inversion mutation:

  • A section of bases detach from the DNA sequence and re-join inverted
  • results in different amino acids being coded for in this region
• Duplication mutation:

  • One base is duplicated at least once in the sequence
  • causes a frameshift to the right
• Translocation of bases mutation: A section of bases on one chromosome detaches and attaches to a different chromosome
• Non-functioning protein:

  • a protein with a different primary and tertiary structure
  • therefore the shape is changed
  • it cannot carry out its function
• Tumour:

  • a mass of cells as a result of uncontrolled cell division
  • can be benign or malignant
• Benign tumour:

  • non-cancerous tumour
  • grows large but at a slow rate
  • produce adhesive and are surrounded by a capsule so they cannot spread

  
• Malignant tumour:

  • cancerous tumour
  • grows rapidly
  • can become unspecialised
  • can metastasise
  • grow projections
  • develop own blood supply

  
• Cancer: Malignant tumours that form due to uncontrolled cell division
• Metastasis:

  • cancer cells breaking off from the tumour
  • spreading to form secondary tumours in different tissues or organs
• Oncogene:

  • a mutated version of a proto-oncogene
  • results in constant initiation of DNA replication and mitotic cell division
  • causes tumour formation
• Tumour suppressor genes: genes that produce proteins to slow down cell division and cause cell death if DNA copying errors are detected
• Epigenetics:

  • the heritable change in gene function
  • without changing the DNA base sequence
  • caused by changes in the environment
  • can inhibit transcription
• Hypermethylation:

  • an increased number of methyl groups attached to a gene
  • results in the gene being deactivated
  • results in cancer if happens to a tumour suppressor gene
• Methylation of DNA:

  • inhibits transcription
  • methyl groups attach to the cytosine base on DNA
  • prevents transcriptional factors from binding
  • condenses the DNA-histone complex
• How can oestrogen increase the risk of breast cancer?

  • Oestrogen is a steroid hormone
  • it binds to a receptor site on a transcriptional factor
  • causing a change in shape
  • so it can bind to the DNA to initiate transcription
  • can result in uncontrolled cell division
• Stem cell: undifferentiated cells that can continually divide and become specialised
• Totipotent stem cell:

  • can differentiate into any body cell
  • occur for a limited time in early mammalian embryo
• Multipotent stem cell:

  • can differentiate into a limited number of cells
  • found in mature mammals e.g in bone marrow
• Unipotent stem cell:

  • can differentiate into one type of cell
  • found in mature mammals
• Induced pluripotent stem cell:

  • produced from adult somatic cells
  • using protein transcriptional factors
  • overcomes ethical issues of using embryonic stem cells
• What is a vector? a DNA molecule used as a vehicle to carry a DNA fragment e.g. plasmids/viruses
• Acetylation of histones:

  • Decreased acetylation inhibits transcription
  • removing acetyl groups makes the histones more positive
  • this attracts the negative phosphate group on DNA
  • making it harder for the transcriptional factors to bind
• RNA interference:

  • inhibition of the translation of mRNA
  • the mRNA gets destroyed so it cannot be translated
• siRNA:

  • small interfering RNA
  • destroys mRNA molecules to prevent translation
• Recombinant DNA technology:

  • combining different organisms’ DNA
  • enable scientists to manipulate and alter genes to improve industrial processes and medical treatment
• Sequencing projects:

  • Reading the full genome of organisms
  • provides opportunities to screen DNA to identify potential medical problems
• How can you create a DNA fragment?

  • Reverse transcription with reverse transcriptase
  • restriction endonucleases
  • gene machine
• Reverse transcriptase: An enzyme that makes cDNA single-stranded copies of DNA from mRNA
• Restriction endonulceases:

  • Enzymes that cut up DNA to create fragments
  • cut at specific recognition/restriction sequences
  • results in sticky ends
• In vivo cloning:

  • Creating DNA fragments using bacteria
  • involves restriction endonulcease enzymes
• In vitro cloning: Using PCR to create a large number of copies of a DNA fragment
• Describe the PCR process:

  1. increase temperature to 95C to break hydrogen bonds & split DNA into single strands
  2. temperature is decreased to 55C so primers can attach
  3. DNA polymerase joins complementary nucleotides & makes a new strand
  4. temperature increased to 72C (optimum for Taq DNA polymerase)
• Uses of genetic fingerprinting:

  • Forensic science
  • medical diagnosis
  • plant/animal breeding
  • paternity tests
• What is gel electrophoresis:

  • Separation of DNA samples using an electrical voltage
  • different lengths of DNA VNTRs are separated