Cellular control

• What are the different types of Point mutation?

  > In Silent mutations, changes to the base triplet sequence doesn't alter tertiary structure of protein as original amino acid is coded.

  > In Missense mutations, changes to the base triplet sequence alters tertiary structure of protein as a different amino acid is coded from mutation.

  > In Nonsense mutations, changes to the base triplet sequence results in coding a termination triplet resulting in a truncated protein.
• What are the different types of indel mutation?

  insertion, deletion, expansion
• Why are Indel mutations harmful?

  > Insertion/deletion of nucleotides cause a frameshift which alters the tertiary structure of the protein

  > Expanding triple nucleotide sequences increase in meiosis changing the tertiary structure of protein

  cause of Huntington disease
• What is a frameshift mutation?

  genetic mutation that shifts reading frame of DNA, resulting in change of amino acid sequence of protein
• What is the Lac Operon?

  A regulatory length of DNA in prokaryotic cells 6000 base pairs long.

  >Bacterium E.Coli metabolises glucose as a respiratory substrate.

  If this is absent then it uses the disaccharide Lactose which induces production of enzymes.
• How does E.Coli metabolise in the absence of Lactose?

  >Regulatory gene, which codes for a repressor protein, is expressed.

  > Gene binds to Operator region preventing RNA Polymerase from binding to Promoter.

  > Structural genes Lac Z and Lac Y are not transcribed into mRNA, so enzymes for lactose metabolism are not made.
• How does E.Coli metabolise in the presence of Lactose?

  > Lactose binds to repressor protein, producing an inducer-repressor complex.

  > This changes the shape of Lac I repressor protein, so it can't bind to the Operator.

  > RNA Polymerase can then bind to Promoter region and transcribe structural genes in mRNA which will be translated into two enzymes needed to break down lactose.
• What does IPOZY on Lac Operon represent?

  I: Regulatory gene that codes for a repressor protein (Lac I).

  P: Promoter region binds to RNA Polymerase to transcribe structural genes Lac Z and Y.

  O: Operator region.

  Lac Z: Codes enzyme B-galactosidase which hydrolyses Lactose to Glucose and Galactose.

  Lac Y: Codes enzyme Lactose Permease which allows lactose to enter bacterial cell.
• What are transcription factors?


  > Short non-coding pieces of RNA/proteins in nucleus that regulate gene expression.

  > They slide along DNA molecules binding to specific Promoter regions and aid attachment of RNA Polymerase activating gene transcription to produce DNA.

  Example: Tumour suppressor genes help regulate cell division via transcription factors.
• Post-transcriptional level of gene regulation:

  >Introns are Non-coding regions of DNA.

  >Exons are coding regions of DNA

  All DNA of a gene is transcribed into primary mRNA which is edited aided by endonuclease, by removing RNA introns through splicing and joining mature exons together.

  This length of DNA with both exons and introns will encode for more than one protein.
• In the Post-transcriptional level, how are proteins activated by cAMP?

  >Signalling molecule binds to receptor on plasma membrane of target cells activating a transmembrane protein which activates a G protein.

  >G protein activates adenyl cyclase enzymes catalysing the formation of cAMP molecules from ATP through phosphorylation.

  > cAMP molecules activate Protein Kinase A (PKA) which catalyses phosphorylation of proteins, activating enzymes in cytoplasm.

  PKA may phosphorylate CREB protein which enters nucleus acting as a transcription factor regulating gene expression.
• What are Homeotic genes?

  genes that control the anatomical development of an organism and contain homeobox sequences.
• What are Homeobox sequences/genes?

  Subset of Homeotic genes containing 180 DNA base pairs, encoding a 60 amino acid sequence (Homeodomain sequence) within a protein.
• Why are Homeobox genes highly conserved and crucial?

  Found in animals, plants and fungi.

  Homeobox sequence in mouse was similar in fly suggesting sequences are crucial for development in organisms.

  Similar homeobox sequence was found in species from millions of years ago, indicating they have given rise to previous ancestors and have been conserved since.
• What are Hox genes?

  > Subset of homeotic genes controlling body plan of organisms.

  > They are found only in animals and regulate development of embryos along anterior-posterior axis.

  > They encode Homeodomain-containing Proteins that act as transcription factors in nucleus of cell, switching on a cascade of gene activations for mitotic cell division and apoptosis.
• What signalling molecules are released by cells as genes involved in cell cycle and apoptosis respond to internal/external stimuli like stress?

  Cytokines from the immune system

  Hormones

  Nitric oxide
• How does Nitric oxide induce apoptosis?

  >Inner mitochondrial membranes become more permeable to protons. >This removes the gradient so proteins are released into cytoplasm to bind to apoptosis inhibitor proteins which induces apoptosis.
• Why is Apoptosis crucial in body development?

  It causes digits of limbs/ fingers to separate

  It removes ineffective T-lymphocytes in immune system

  Lack of apoptosis can lead to Tumour formation
• What is apoptosis?

  Programmed cell death
• What are the stages of Apoptosis?

  1> Enzymes break down cytoskeleton

  2> Cytoplasm becomes dense with tightly packed organelles

  3> Blebs form, protruding from cell surface membrane

  4> Chromatin condenses, nuclear envelope breaks and DNA breaks into fragments

  5> Cell breaks into vesicles which are ingested by phagocytes so there is no damaged tissue