Mammalian cell biology 3

• What colour does DAPI stain the nucleus

  blue - only stains DNA
• what is the function of the nucleolus

  • up to 25% of nuclear volume
  • synthesis of ribosomal RNA and ribosome assembly
• what is the nucleoplasm

  fluid that fills the nucleus 
• what are cajal bodies

  structures of 0.2-1.0 um size that concentrate RNA processing factors needed in the nucleus 
• what are splicing speckles

  irregular structures that contain mRNA splicing factors 
• what are the granular component of nucleolus

  ribosome assembly site 
• what are fibrillar centres of nucleolus

  rRNA transcription
• heterochromatin

  • remains packed with histones after mitosis
  • transcriptionally inactive
  • 10% of DNA
• euchromatin

  transcriptionally active 
• characteristics of DNA

  • 2nm diameter
  • negatively charged
• charactersitics of histones

  • positively charged proteins
  • H2A, H2B, H3, H4
  • small protein of 100 amino acids
• characteristics of nucleosomes

  • most of the time DNA is organised in nucleosomes
  • loosens during transcription
  • diameter 30nm
• 30nm looped fibre characteristics

  interaction between DNA and histones (including an additional histone H1) results in a higher degree of package
• 30nm looped fibre domains characteristics

  DNA is further packed around a scaffold that contains specialised proteins 
• metaphase chromosomes characteristics

  genes are always at the same position 
• what is transcription

  the process of transcribing DNA nucleotide sequence information into RNA sequence information 
• RNA polymerase I

  ribosomal RNA
• RNA polymerase II

  messenger RNA
• RNA polymerase III

  transfer RNA
• RNA polymerase IV

  siRNA’s required for heterochromatin formation 
• which RNA polymerases are in plants

  IV
• Process of transcription

  1. numerous transcription factors bind to TATA box in the promoter
  2. RNA polymerase binds to the template strand and synthesises the exact copy of the coding strand (T replaced by U)
  3. RNA is released, further processed and released from the nucleus (bound to RNA-binding proteins)
• difference in transcription between prokaryotes and eukaryotes

  prokaryotes

  • transcription and translation in the same compartment
  • many genes on one mRNA

  eukaryotes

  • transcription and translation are compartmentalised
  • one mRNA for one gene
• what connects compartments of the endomembrane system

  transport vesicles that serve material exchange
• what is a compartment

  • a membrane surrounded space in the cell
  • if it has a specialised function it is an organelle
• what do secretory vesicles do

  mediate exchange of materials between the cell and the environment
• how can vesicle trafficking be visualised

  using GFP-fusion proteins