3. Regulation of transcription and translation

Cards (36)

  • How transcriptional factors work once bound
    1. Each factor is complementary/ binds to different base sequences
    2. Once bound they allow RNA polymerase to begin transcription
    3. Allows for the creation of an mRNA molecules for that gene
    4. mRNA then travels to the ribosome to become translated into a protein
  • Examples of transcriptional factors

    • Steroid hormone, Oestrogen
  • How do transcriptional factors control the process of transcription?
    1. A protein from the cytoplasm enters the nucleus and binds to DNA in the nucleus
    2. Once bound to target genes, transcription begins resulting in the creation of an mRNA for that gene which can go on to be translated in the cytoplasm at the ribosome
  • Types of transcriptional factors and their affect on gene expression
    • Activators - stimulate or increase the rate of transpiration
    • Repressors - inhibit or decrease the rate of transcription
    • Without the binding of any factor, the gene becomes inactive and protein is not made
  • Oestrogen
    • Steroid hormone
    • Initiates transcription
  • Steroid hormone properties
    • Lipid soluble
    • Can simply diffuse through cell surface membrane
  • Oestrogen and it's role in initiating transcription
    1. Binds to oestrogen receptor site on the transcriptional factor
    2. Once it binds, causes it to change shape making it complementary and able to bind to DNA
    3. Enters nucleus through nuclear pores and attaches to DNA
    4. Once bound RNA polymerase attaches but only when transcriptional factor attaches
    5. Intiates transcription and allows for the production of an mRNA molecule
  • Epigenetics
    • The heritable change in gene functions
    • Without changing the DNA base sequence
    • These changes are caused by the environment
    • Can inhibit transcription - one way in which gene expression is controlled in eukaryotic organisms
  • Epigenetic tags
    Chemical tags/ changes in DNA structure that can control gene expression in eukaryotes
  • Factors which increase the numbers of chemical tags
    • Diet
    • Stress
    • Toxins
  • Epigenome
    • Single layer of chemical tags on DNA
    • Impacts the shape of DNA-histone complex
    • Whether it's tightly wound or unwound
  • Heterochromatin
    Tightly wound DNA-histone complex
  • Effect of tightly wound DNA-histone complex on the binding of transcriptional factors
    Transcriptional factors can-not bind to gene
  • Chromatin
    Unwound DNA-histone complex
  • Effect of unwound DNA-histone complex on the binding of transcriptional factors
    Transcriptional factors can bind
  • Increased methylation of the DNA
    • The addition of methyl groups of DNA
    • On the cytosine base
  • Increased methylation of the DNA leads to
    Heterochromatin - tightly wound DNA-histone complex's
  • The effect of increased methylation on transcription

    Inhibits transcription
  • How does increase methylation of the DNA inhibit transcription?
    1. Prevents the binding of transcriptional factors
    2. Causes the tight coiling and condensation of DNA-histone complex - heterochromatin
    3. Because methyl group is positively charged and DNA is negatively charged they attract and coil together
  • Decreased acetylation of associated histones

    The decreases binding of acetyl groups to histone proteins in DNA
  • Decreased acetylation of associated histones leads to

    Heterochromatin - tightly wound DNA-histone complex's
  • The effects of decreased acetylation of associated histones on transcription
    Inhibits transcription
  • How does a decrease in acetylation of histones inhibit transcription?
    1. Acetyl group has negative charge which repels the negative change of DNA (phospate group) - results in chromatin
    2. However, when they are removed increases positivity of histones which is now attracted to the negative phosphate group on DNA
    3. DNA more condenses/ tightly packed - heterochromatin
    4. Harder for transcriptional factors to bind
  • Changes to DNA-histone structure which result in chromatin and promotes transcription

    • Decreases methylation of the DNA
    • Increases acetylation of associated histones
  • Changes to DNA-histone structure which result in heterochromatin and inhibited transcription
    • Increased methylation of the DNA
    • Decreased acetylation of associated histones
  • Tumour suppressor genes
    • Genes which produce proteins that slow don cells division
    • Cause cell death in cells when DNA copying errors are detected
  • The effect of hypermethylation of tumour suppressor genes on the development of cancer

    • An increased attachment of methyl groups to tumour suppressor genes
    • Cause heterochromatin - transcriptional factors unable to bind to gene
    • Genes become turned off and inactive
    • Lack of control of mitosis and excess cell growth which can lead to the formation of cancerous tumours
  • Oncogenes
    Genes that create proteins which trigger mitosis
  • The effect of hypomethylation of oncogenes on the development of cancer

    • Reducing number the number of methyl groups attaches to oncogenes
    • Causes chromatin - transcriptional factors able to bind easily to genes
    • Gene is permanently switched on
    • Mitosis will continue to occur even when not needed - leads to uncontrolled cell division and the development of cancerous tumours
  • How can translation of mRNA be inhibited?
    1. When an mRNA molecules that has already been transcribed gets destroys before it can be translated into a polypeptide chain
    2. Conducted by small interfering RNA (siRNA)
  • How siRNA is made?
    1. In the cytoplasm
    2. Double standed RNA is cut into small sections of RNA and made single stranded
    3. Done by multiple enzymes
  • siRNA-enzyme complex
    1. Also in cytoplasm siRNA bind to another enzyme
    2. Forming an siRNA-enzyme complex
  • The binding of siRNA-enzyme complex to mRNA
    1. The siRNA-enzyme complex binds to mRNA which had just been transcribed
    2. Via complemenary base pairs
  • What happens when the two bind?
    1. The enzyme attached to siRNA cuts mRNA
    2. So it can no longer be translated
    3. mRNA pieces are degraded in a processing body
  • Transcriptional factors
    • Proteins which stimulate or inhibit the transcription of certain genes
    • They can turn on/ off genes so only certain proteins are produced in a particular cell
    • This allows them to be specialised
  • Why does the RNA polymerase only bind once the transcriptional factor and oestrogen attach to DNA?
    • RNA polymerase as a tertiary structure enzyme is complenmtary to both the transcriptional tactor and oestrogen together.