TOPIC 8 - CONTROL OF GENE EXPRESSION

• Gene mutation

  • change in base sequence of DNA
  • occurs during DNA replication 
  • includes addition, deletion, substitution, inversion, duplication and translocation of bases
• Mutagenic agents


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• 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


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• Malignant tumour


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• 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 embryos
• Pluripotent stem cell

  • can differentiate into almost any body cell
  • occur in embryos
• 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
• Transcriptional factor


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• 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

  • mall 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
• Gene machine

  • creates DNA fragments using a computerised 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


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• In vitro cloning

  • Using PCR to create a large number of copies of a DNA fragment