Genetics of living systems

• Each amino acid in a protein is coded for by a sequence of 3 nucleotide bases on mRNA called a codon.
• How would you describe the genetic code ?

  Degenerate

  Non-overlapping

  Universal
• How is the genetic code degenerate ?

  More than one codon codes for each amino acid
• How is the genetic code non-overlapping ?

  Each base sequence is only read once.
• How is the genetic code universal ?

  The same codons code for the same amino acid in all organisms.
• Name 3 types of genetic mutation ?

  Substitution

  Deletion

  Insertion
• What is a genetic mutation ?

  A change in the DNA sequence.
• Name 3 types of substitution mutations ?

  Nonsense

  Missense

  Silent
• What is a nonsense mutation ?

  When the result of the mutation is one of the 3 stop codons
• What is the result of a missense mutation ?

  A different amino acid sequence is coded for.
• What is the impact of a silent mutation ?

  No impact as the same amino acid is coded for.
• Insertion mutation = an extra nucleotide is added
• Deletion mutation = a nucleotide is removed.
• What causes a frame shift ?

  Deletion or insertion of nucleotides
• What is the impact of a frame shift ?

  All codons are impacted even the start/stop codons.
• Name some causes of genetic mutation ?

  X-rays

  High energy radiation

  Chemicals in cigarette smoke and caffine

  UV light
• What is the impact of a neutral mutation ?

  Normal functioning protein is still synthesised as the phenotype of the organism is unchanged.
• What is the impact of a harmful mutation ?

  Proteins not synthesised or non-functional so the phenotype is negatively affected
• What is the impact of a beneficial mutation ?

  Proteins synthesised with a new and useful characteristic in the phenotype.
• Distinguish between a codon and anti-codon ?

  A codon is a triplet of bases that codes for an amino-acid while an anti-codon is a triplet of bases that is complementary to a codon.
• Every cell with a nucleus contains the entire genome of an organism, but not every gene needs to be turned on. Cells being able to turn on and off genes enables them to become specialised.
• When are genes switched on and off ?

  Transcriptional

  Post-transcriptional

  Translational
• What type of molecule are transcription factors?

  Protein
• Name 2 types of transcription factors and their function ?

  Activators, start transcription

  Repressors, stop transcription
• What is a transcription factor ?

  A protein that binds to DNA and switches genes on or off by increasing/decreasing the rate of transcription.
• Where does transcription factors bind to in eurkaryotic cells?

  Specific sites near the start of target genes
• Explain how hormones can activate transcription factors ?

  Transcription factor may be blocked by an inhibitor, when a hormone binds to the transcription factor it causes a conformational change on the transcription factor. The conformational change releases the inhibitor and the transcription factor can now bind to the DNA.
• What is an operon ?

  A group of genes that are expressed at the same time and share the same regulatory system.
• What is the lac operon an example of ?

  Regulatory mechanisms at transcriptional level.
• What does lac operon control ?

  The production of lactase and two other structural proteins.
• What is the function of lactase ?

  Breaks down lactose so that it can be used as an energy source in bacterial cells.
• Why is lactase an inducible enzyme ?

  It is only synthesised when lactose is present.
• Describe the structure of lac operon ?

  Regulatory genes

  Promotor for structural genes

  Operator

  Structural genes
• Name 2 structural genes in lac operon and what they code for ?

  LacZ codes for lactase

  lacY codes for permease
• Describe how the lac operon is turned off ?

  Repressor protein binds to the operator region.

  This blocks the binding of RNA polymerase to the promotor.

  Therefore there is no transcription of the structural genes.
• Describe how the lac operon gene is turned on ?

  Lactose binds to the repressor protein, causing a conformational change so it can no longer bind to the operator region.

  RNA can bind to the promotor region allowing transcription of structural genes.
• Describe the process of splicing ?

  Spliceosome cause the introns to form a loop shape.

  The introns are excised and the exons are then spliced together.
• How could gene expression be controlled at post-translational level ?

  Activation by cyclic AMP
• How can gene expression be regulated after transcription ?

  Splicing

  Activation by cAMP
• Describe how proteins can be activated by cAMP ?

  Some molecules (sugar or hormones) bind to the cell surface membrane and trigger the production of cAMP inside the cell.

  cAMP then activates the proteins inside the cell by altering their 3D structure.