Cellular Control

• Mutation

  An alteration to the DNA base sequence
• Mutations often arise spontaneously during DNA replication
• Addition and deletion mutations

  • Where one or more nucleotides (bases) are either inserted or deleted from the DNA sequence
  • More likely to be either harmful or beneficial, due to frame shift which means the entire amino acid sequence will be different
• Substitution mutation

  • When a nucleotide in the DNA sequence is replaced by another
  • More likely to be a neutral mutation, meaning no change occurs in the amino acid sequence
• Transcriptional regulation of gene expression

  Transcription factors - proteins that can either initiate or inhibit the transcription of genes, so that only certain parts of the DNA are expressed
• Function of the lac operon in low lactose concentrations

  1. E.coli can use lactose as a respiratory substrate, via use of an enzyme

  2. When lactose concentration is low, the lac operon binds to the gene that makes this enzyme and inhibits its expression
• Function of the lac operon in high lactose concentrations

  Lactose binds to the operon, causing it to change shape and unattach from the gene. Allows RNA polymerase to bind and the gene to be expressed
• Post-transcriptional regulation of gene expression

  Splicing - Primary mRNA contains both coding regions (exons) and non-coding regions (introns). The introns are removed to produce mature mRNA ready for translation
• Post-translational regulation of gene expression


  Activation of proteins, such as adrenaline. When adrenaline binds to a receptor, adenylyl cyclase is activated which converts ATP to cyclic AMP. Prompts further enzyme reactions, which activates the protein kinase A.
• Homeobox genes

  Code for transcription factors that activate genes when they're needed during development of a zygote. Their sequences are similar in plants, animals, and fungi
• Mitosis and development

  Mitosis (cell replication) is the primary mechanism of growth. Genes regulating mitosis respond to various stimuli, both internal and external, in order to control rate of growth
• Apoptosis and development

  Programmes the death of cells. It is highly controlled and keeps cell division at a constant rate so as to prevent cancer