Mammalian cell biology 2

• What type of contacts do epithelial cells establish?

  Tight lateral and basal contact
• What is the function of tight junctions?

  • They act as a diffusion barrier - seperates blood from CSF (blood-brain barrier), prevents diffusion of proteins within epithelial cell
  • holds cell together
  • consists of plasma membrane proteins that interact (claudin, occludin)
• What is the role of adherens junctions?

  • consist of claudin and catenin
  • appeae to be involved in controlling actin organisation in epithelial cells
• What do catenins link to in adherens junctions?

  Actin cytoskeleton
• What is the function of gap junctions?

  • They allow passage of ions and small molecules
  • supports exchange between the cytoplasm of adjacent cells
• What are desmosomes specialized for?

  • contain specialised catherin proteins that interact with each other and with intermediate filaments
  • resist shear force in epithelia and in muscle
• What is the role of the extracellular matrix?

  Holds tissue together and provides strength, directing cell migration
• How do cells sense their environment?

  By recognizing pathogens and signals
• What are the two major signaling mechanisms?

  Phosphorylation of proteins and GTP-binding proteins
• What is the role of G-proteins?

  They act as molecular switches
• What activates G-proteins?

  Guanine nucleotide exchange factor (GEF)
• What do small monomeric G-proteins do?

  Receive signals from many receptors
• What do large trimeric G-proteins interact with?

  G-protein-coupled receptors
• What does adenylyl cyclase produce?

  Cyclic AMP
• What is a kinase?

  An enzyme that transfers phosphate groups

  
• What is the function of phosphatases?

  They remove phosphate groups from proteins
• What percentage of human proteins carry a phosphate group?

  30%
• How many kinases are in the human genome?

  520 kinases
• How many protein phosphatases are in the human genome?

  150 protein phosphatases
• What is Brownian motion?

  Random motion of particles in a medium
• What affects diffusion in the cytoplasm?

  Size of the molecule/organelle
• What is the Svedberg unit (S)?

  A measure of sedimentation behaviour - measure of how fast a particle settles
• What are ribosomes composed of?

  Proteins and ribosomal RNA
• What is the function of ribosomes?

  Translate mRNA into proteins
• What is a polysome?

  A structure with multiple ribosomes on mRNA
• What is the diameter of the nucleus?

  2-10 µm
• What are nuclear pores

  • Multi-protein complexes
  • have an eight fold symmetry
  • numerous proteins build the pore and control nuclear transport
• What do nuclear pores control?

  Transport in and out of the nucleus
• What is the function of the nuclear lamina?

  Protects the nucleus and organizes pores
• What happens to the nuclear envelope during mitosis?

  It disassembles

  
• What is required for nuclear transport?

  Small GTPase and soluble receptors

  
• what do cadherins do

  bridge between cells
• what are gap junctions made of

  connexions
• What are the functions of hemidesmosomes

  • contains many proteins including integrins that interact with the extracellular matrix
  • in skin epithelial cells
  • anchor the epithelia cell to the basal lamina, probably also involved in signalling
  • the extracellular matrix underneath the epithelium
• what is the extracellular matrix composed of

  • fibres of secreted proteins
  • collagen, matrix proteins, glycoproteins
• what inactivates G-proteins

  GTPase-activating protein (GAP)
• What technique was developed by Svedberg

  analytical ultracentrifugation and seperated pure proteins from each other
• What is molecular ratchet

  conformational change in the ribosome might help walking along the mRNA in order to synthesise a protein
• What is the process of protein translation

  1. matching tRNA to mRNA codon
  2. release of elongation factor TU
  3. formation of peptide bond
  4. elongation factor G triggers a forward movement of ribosome
• How many nucleoporin proteins make the nuclear pore


  30