Mammalian cell biology 4

• what is the endoplasmic reticulum

  • membraneous synthesis and transport organelle that is an extension of the nuclear envelope
  • membrane sacs and branched tubules make -50% of all membranes in the cell
• functions of smooth ER

  • calcium storage for cell signalling
  • lipid synthesis (at cytosolic face)
  • detoxification (drugs/poisons)
  • metabolism of carbohydrates
• functions of rough ER

  • processing of secretory proteins
  • ribosomes attached
• process of cotranslational translocation into the ER

  1. ribosome assembles and binds mRNA
  2. if polypeptide contains a signal sequence it is targeted to the ER membrane
  3. the signal peptide is cleaved off and the protein is translated into the ER lumen where it is folded and further processed
  4. cytosolic proteins can contain signal sequences that target them to other organelles

  
• how many hydrophobic amino acids do ER proteins usually consist of

  5-10 at the N-terminus
• types of integral membrane proteins inserted at the ER


  i

  
• what is Golgi apparatus

  disc-shaped stack of membranes 

  
• what are glycoproteins

  membrane proteins that are linked to sugar residues
• functions of glycoproteins

  • provide protection against pathogens - mucus coat on epithelia
  • serves in cell-cell recognition and signalling
  • marks progression of the protein
  • helps folding and interaction with other proteins
• formation of proteoglycans

  1. cis Golgi network - phosphorylation of oligosaccharides on lysosomal proteins
  2. cis cisterna - removal of Man
  3. medial cisterna - removal of Mal, addition of GlcNAc
  4. trans cisterna - addition of Gal, addition of NANA
  5. trans golgi network - sulfation of tyrosines and carbohydrates
• how are oligosaccharides linked to proteins

  1. about 50% of all eukaryotic proteins are glycosylated (bound with a sugar)
  2. N-glycosilation already in prokaryotes
  3. Oligosaccharides can be linked to Asparagine (N-linked) or Threonine (O-linked)
• phagocytosis

  large particles, forms phagosome
• pinocytosis

  uptake of liquid, no receptor, forms vesicle 
• process of membrane trafficking along the endocytic pathway

  1. formation of a vesicle at the plasma membrane
  2. fusion of vesicle with early endosome
  3. decision - degradation or recycling
  4. recycling via recycling endosomes
  5. maturation of early endosome to late endosome
  6. recycling of late endosomes to golgi
  7. maturation of late endosome into lysosome
• what are lysosomes

  • waste-recycling plant of the cell
  • vacuolar H+ ATPase serves as a proton pump acid environment
• what is autophagy

  • enclosure of cytosol and organelles into an autophagosome
  • organelles have a limited life time
  • autophagy recycles the organelle
  • under starvation the cell recycles cytosol by autophagy