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2010-10-12 10:23:20
Biomolecular Science

Cell Biology- Organelles
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  1. Three Classes of Membrane Lipids in animal cells:
    Phospholipids, Cholesterol (15%), Glycolipids (5%)
  2. Fatty Acid structure consists of...
    head made of...
    tail made of...
    • Hydrophillic head- carboxyl croup
    • Hydrophobic tail- Hydrocarbons
  3. Saturated vs. unsaturated (benefits...)
    • ~saturated means there is no double bonds in the hydrocarbon tail, there is as many H atoms present as possible to allow free rotation.
    • ~unsaturated means there is one or more double bonds present in the hydrocarbon tail, double bond creates a kink/rigidity, and also fewer H atoms.
  4. 4 Major Phospholipids (including +/-/=, and which side of membrane it is)
    5th phoshpolipid:
    • 1) Phosphotidylethanolamine (+)
    • 2) Phosphotidylserine (-) cytosolic side
    • 3) Phosphoytidylcholine (=) cystolic side
    • 4) sphingomyelin (=)
    • 5)Phosphatidylinositol (located in the inner half of plasma membrane ONLY, small amounts- important in cell signaling/hormones)
  5. Glycolipid structure:
    Carbohydrate, serine, carboxyllic tails
  6. glycolipids location and function
    • exclusively found on the extracellular portion of bilayer
    • form a carbohydrate coat (glycocalyx)
  7. glycocalyx
    cell coat fromed from glycolipids to protect the cell from injury and create cell adhesion
  8. Cholersterol (function and location)
    • provides cell membrane regidity
    • large quantities in cell membrane (between hydrophobic tails)- very small in size
  9. Membrane fluidity:
    • dynamic fluid like structures
    • lateral movement
    • rotational movement
    • NO flip-flop (rare)
    • shorter phospholipids provide more fluidity
    • kinks give more fluidity (packed less effectively- more unsaturated= more fluid)
    • more cholesterol= more rigid
  10. symmetry of membrane??
    assymetrical due to the two faces of bilayer being very different (ex: glycolipids are extra cellular only!!!)
  11. Assymetry is important for function b/c:
    • ~cytosolic proteins bind to specific phospholipid head groups
    • ~cell death
  12. Membrane proteins:
    • ~myelin membrane (electrical insulation of nerve axon <25%)
    • ~mitochondrial membrane (ATP synthesis >75%)
    • ~proteins can have carbohydrate chains attached (i.e. glycoproteins on glycolipids)
  13. 3 ways proteins attach to membrane:
    • 1) transmembrane (integral)
    • 2) Lipid Linked (integral)
    • 3) Protein linked (peripheral)
  14. Transmembrane Proteins:
    Extend through the bilayer, consist of both hydrophobic and hydrophilic domains
  15. Lipid Linked Proteins:
    Located entirely on the outside, covalently attached to lipid/glycolipids
  16. Protein Linked:
    Bound indirectly to either face of the membrane by weak interactions (peripheral proten) (weak and break off readily)
  17. Function of Membrane Proteins:
    • ~Transport (e.g. glucose transporter protein)
    • ~Enzymes (e.g. adenylate cyclase- plasma membrane bound enzyme)
    • ~Receptor (e.g. insulin receptor)
    • ~Recognition (e.g. Cell-cell recognition, immune recognition)
    • ~adhesion (e.g. cell adhesion proteins linkage to the ECM)
  18. movement of membrane proteins:
    rotation diffusion and later diffusion- no flip flop
  19. Example of cells confining lipids and proteins to particular domains of the membrane:
    • gut epithelium- membrane proteins restrict to particular omains of the plasma membrane
    • apical membrane/gut lume has protein A exclusively to transport nutrients from the gut
    • basal membrane has protein B exclusively to aid in transport to tissue/bloodstream
  20. Traffick across membranes:
    • plasma membrane is a barrier to most hydrophilic molecules
    • permeable to small non-polar molecules (O2 and CO2), and water molecules readily cross lipid bilayers
    • impermeable to ions and charged molecules
    • (~specialized transport systems are required to transport ions, sugars, aminoacids, nucleotides, etc.)
  21. Diffusion:
    molecules to pass through the membrane directly (H2O, CO2)
  22. Facilitated transport:
    • membrane proteins transport down a concentration gradient (e.g charged ions- Na+. Cl-)
    • glucose transport in rbcs
  23. active transport:
    • membrane proteins require energy (ATP)
    • can transport up or down a concentration gradient (e.g. Na+/K+ pump)
  24. Endocytosis vs. exocytosis
    • Endocytosis: invagination of membrane--> fusion of membrane to form vesicles (within the cell)
    • Exocytosis: vesicles bud off ER or Golgi --> fusion of vesicle with membrane

    (membrane will remodel)
  25. Cytosol: (4 facts)
    • area outside organelles
    • 50% of cell content
    • metabolic processes take place
    • contains cytoskeleton
  26. Cytoskeleton
    (3 types of filament and function)
    • Provides shape, cell movement, movement of organelles, mitosis
    • ~Microtubules usded for division
    • ~actin filaments for structure
    • ~intermediate filaments for the inbetween stages
  27. Describe the structure of the cell!!!
    Extracellular fluid, Cytoplasm, Glycoprotein, glycolipid, cholesterol, carbohydrates, peripheral proteins, integral proteins, etc.
  28. Major Organelles:
    Nucleolus, nuclear membrane, mitochondria, ribosomes, smoothe Endoplasmic Reticulum, plasma membrane, golgi apparatus, golgi vessicle, rough ER, Lysosomes
  29. Protein Trafficking:
    • Process of directing each newly made polypeptide to a particular destination
    • most proteins are encoded by nuclear DNA (except mitochondrial DNA) and synthesized on ribosomes in the cytosol
    • distributed to correct destination via action of sorting signals
  30. Signal Sequences:
    • signal or sorting sequences direct delivery of proteins to specific organelles- if no sorting signal will remain in cytosol.
    • receptor proteins on organelle surface recognize specific signal/sorting seq. in the new protein
    • Must be a particular set of sequence to be transported/sorted/etc.
  31. Nucleus (4 facts):
    • present in all cells in body except RBC
    • contains DNA (site of mRNA synthesis)
    • enclosed by two membranes with nuclear pores
    • houses genetic material
  32. (sub-organelle) Nucleolus (2 facts)
    • site of synthesis of ribosomal RNAs (rRNA)
    • rRNA comples w/ proteins to form ribosomes
  33. Examples of Macromolecules traffick between nucleus and cytosol:
    • RNA and DNA polymerases and histones go to nucleus send mRNAs and ribosomal proteins to cytosol which in return send RNA and DNA pol back to nucleus.
    • (Nuclear localisation signal directs protein from the cytosol to the nucleus)
  34. Ribosomes (4 facts)
    • site of protein synthesis
    • large complex of proteins and ribosomal RNAs
    • Eukaryotic ribosomes consist of 2 subunits (40s and 60s= 80s)
    • can be bound or free
  35. Endoplasmic Reticulum (3 facts)
    • Netweork of membrane enclosed tubules and sacs (cistemae) extend from nuclear membrane throughout the cytoplasm
    • rough ER is covered by ribosomes on outer surface- site of protein synthesis
    • smooth ER is not associated with ribosomes involed in lipid metabolism
  36. Proteins syntesised on Rough ER (KNOW THESE!!!!)
    • Proteins destined for secretion (Hormones, digestive enzymes)
    • Plasma membrane proteins (final destination- integral p)
    • proteins destined for the golgi or lysosomes
  37. Proteins synthesised on free ribosomes
    • destined for cytosol
    • proteins destined for: nucleus, peroxisomes, mitochondria
    • (glycolysis, anything not going to membrane)
  38. Steps to synthesis on Rough ER
    • ALL protein start synthesis on free ribosomes
    • if has ER signal sequence the ribosome attaches to ER
    • as polypeptide chain grows it passes through the ER membrane into the lumen
    • newly synthesised proteins accumulate in the lume or embedded in the ER membrane
  39. Rough ER Post translation Modifications (KNOW THESE)
    • Formation of disulfide bonds (isuline)*
    • Proper folding *
    • Addition and processing of carbohydrates (glycocalyx)
    • specific proteolytic cleavages (digestion)
    • assembly into multimeric proteins*
    • *occur exclusively in the RER
  40. Proper Folding (post translational modification)
    • chaperone proteins direct the folding of proteins into their proper 3-D structure
    • Needs energy
  41. Misfolded proteins:
    if misfolded they are usually exported to cytoplasm and degraded
  42. Proteosome
    A multiprotein protease complex where degradation takes place
  43. cystic fibrosis
    caused by mutation in membrane protein, result in incorrect folding, and protein is retained in the ER
  44. function of the smooth ER
    • detoxification of drugs/toxins
    • synthesis of lipids and carbohydrates
  45. Golgi Apparatus (4 facts)
    (proteins synthesised on the RER are further packaged in the Golgi apparatus)
    • Membrane bound
    • flattened stacks of smooth membranes or vesicles
    • located close to the nucleus
    • modifies/processes proteins and directs them to plasma membrane or internal organelles
  46. Export of proteins from the ER to the golgi complex
    • p synthesised on RER exit in transport vesicles
    • vesicles fuse with the cis-golgi comples
    • p migrate through the golgi cisternae to the trans-golgi
    • p are again packaged in vesicles
    • w/in the golgi p undergo further modifications (add of carbohydrate groups, proteolytic cleavage)
  47. export from golgi to the plasma membrane
    Exocytosis by vesicle budding and fusion
  48. summarize intracellular protein trafficking pathway:
    RER--> Golgo--> Transport vessicles (may be directed to lysosoles next or)--> plasma membrane--> secretion
  49. Mitochondria
    • Consists of 2 seperate membranes (inner and outer) and an inter membrane space
    • inner membrane is highly convoluted- cisternae
    • harness energy to produce ATP
    • metabolic processes (oxidative phophorylation, electron transport)
  50. traffick proteins into mitochondria
    • mitochondria have own DNA (30)
    • most mito proteins are encoded by nuclear DNA (synthesised of free ribosomes)
    • specific signal allows entry to mitochondria
    • p are unfolded and transported across membrane (chaperone proteins assist to help and protein refold... required energy)
  51. Lysosomes
    • membrane bound small vessicles
    • degrade components of the cells
    • contain degradative enzymes (nuclleases, proteases, phosphatases)
  52. traffick of proteins into lysomsomes (4 steps)
    • synthesised in the ER
    • thransported through golgi to the trans-golgi
    • while in ER and cis-golgi the p become tagged (mannose 6 phosphate)
    • allows recognition by appropriate receptor allows deliver to the lysosomes (mannose 6 phosphate receptor)
  53. Peroxisomes
    • membrane bound small vesicles
    • contain oxidases
    • oxidise organic substances- generate highly toxic hydrogen peroxide (H2O2)
    • traffic of proteins into peroxisisomes not well understood
  54. Summary of Intracellular protein trafficking pathways:
    • rough ER-->Golgi-->transport vesicles-->lysosomes or plasma membrane-->secretion
    • free ribosomes-->cytosol or nucleus or mitochondria