Cytology-Lecture 1and 2 Flashcards
Composition of plasma membrane?
PECIS Proteins ( transmembrane ) Phospholipids - 20-30% Extrinsic proteins Cholesterol 50-60% Intrinsic proteins Sugars - glycolipids glycoproteins
List function of plasma membrane?
Import export molecules Allow expansion change of shape Movement Communication Support Selectively permeable
Size of phospholipid bilayer
Head - 2nm
Both tails - 3.5nm
Cytoplasmic head - 2nm
What do phospholipids form in water?
Phospholipid bilayer
Round Micelle
Liposome
Main phospholipids in membrane? 4 main
Phosphatidylcholine Phosphatidylserine Phosphatidylethanolamine Sphingomyelin Compose 50-60% of total membrane lipid Glycolipids and cholesterol 30-40% of total membrane lipid
What is the closure of the phospholipid bilayer like when exposed to water?
Spontaneous and forms a separate compartment : explains how different metabolic rates of molecules outside compared to inside
How do we know composition of cell membrane?
Add water sol and lipid sol substances.
Form a lipid coat around cell.
What is meant by the fluid mosaic model?
Proteins move within membrane
Mosaic - patchwork of proteins found in phospholipid bilayer.
Name 5 Factors which effect fluidity and how
Directly proportional - temp and unsaturated fatty acid (kinks in tails allows for greater fluidity)
Indirectly proportional - cholesterol, proteins, length of phospholipid.
What is meant by intrinsic proteins?
They completely span the phospholipid bilayer.
Features of cell membrane? DFAF
Discontinuous, fluidity, asymmetry, freeze-fracture membrane -> 1:1 lipid proteins ratio. In nervous cells 4:1 lipid protein ratio.
Gycocalyx composition?
Oligosaccharide side chains linked covalently to proteins and lipids of the plasmalemma. Contains proteoglycans (GAGs links to proteins)
Glycocalyx functions (8)
Attach to extracellular matrix components
Cell to cell adhesion and recognition
Prevent cell damage by avoid touch with inappropriate substances
Receptor molecules for cell signalling
Prevent enzyme and receptor cleavage
Bind antigen and enzyme to cell surface
Supports t cells and antigen presenting cells in aligning with each other
Blood vessels reduces friction
Lipid rafts?
Special micro-domain in membrane
Less fluid, and bulge due to extra cholesterol, proteins, glycosphingolipids.
Function in cell signalling. Specific lipid rafts maybe function in specific cell signalling sequences.
Maybe present in some golgi and lysosomes.
Function of SER
Ca2+ and other ion storage in muscle cells
Detoxification in liver - add OH groups therefore favour elimination
Synthesis of steroid hormones and lipids in adrenal glands and gonads
Glycogen met.
Synthesis of phospholipids for membrane
Synthesis of phospholipids
SER enzymes facing bilayer
Lipids inserted onto inner leaflet of bilayer
What is meant by amphipathic and give an example?
Consist of both polar and non-polar groups.
Eg Phospholipids.
What are ribophorins?
Receptors on RER ribosomal units bind
Function of RER
Protein synthesis of export proteins - (secretion,lysosomal,membrane).
Post-translational modification of proteins.
RER sac closest to golgi - no ribosomes - transfer vesicles - “transitional element”.
Proteins retained in RER marked by KDEL sequence - LUS-Glu-Arg-Leu located at C terminus ( end of amino acid chain )
Ribosome structure
Large and small subunits cont rRNA and numerous proteins
Free ribosomes synthesise (2)
Cytoplasmic proteins
Peripheral proteins.
Post-translational function of RER (3)
Proteolysis, glycosylation, phosphorylation.
Name of active site of protein synthesis
Polyribosome (polysome)
Additional functions of RER (3)
Hydroxylation of proline and lysine in tropocollagen.
Folding of secondary structure. Form quaternary structure and polypeptides.
Start protein glycosylation - completed in golgi apparatus
Functions of golgi apparatus? (6)
Finish glycosylation of proteins. Glycosylation of lipids.
Form vesicles cont macromolecules.
Activation/Deactivation of proteins via proteolysis and phosphorylation.
Syn. GAGs and mucin.
Production of lysosomal enzymes.
Formation of acrosome vesicle in spermatozoa.
How do proteins pass via golgi (2)
Vesicles
Cisternae maturation
Importance if acrosome in sperm head?
Contain hydrolytic enzymes therefore greater chance of fertilisation inti ovum
Destination of proteins after pass thru golgi? (4)
RER
remain in golgi
Lysosomes
Exocytosis
Fate if proteins passed thru golgi body? (3)
RER - KDEL sequence on C terminus Luc glu arg leu
GOLGI - Specific sequence therefore remain bound to membrane
Lysosomes - Mannose-6-phosphate marker added during Golgi body therefore bind to M6P receptor on lysosome membrane.
Cell injury and the plasma membrane?
Give example of 2 poisons that relate to this.
Plasma membrane, morphological changes, formation of PM blebs, detachment of actin filaments from cell cytoskeleton.
Poisons : phalodin, cytochalasin B.
Describe vesicle transport
Vesicles form by budding off the PM.
Endo/exo-cytosis
How vesicles move?
Move via cytoskeleton
Microtubules (motor proteins) dyenin + kinesin -
Atp for active transport
How vesicles are recognised on PM.
Transmembrane proteins.
V-snare on vesicle bind to T-snare on membrane.
Form complex.
Allows vesicle to fuse with membrane and budding initiates.
Name 4 types of vesicle coats and 1 membrane phosopholipid that has an essential part in membrane transport?
Clathrin, COP (1&2), caveolin, retromer-coated
Phosophlipid: Inositol phospholipids (important in membrane transport)
Clathrin coated vesicles. Structure.
Hexameric, 3 small and 3 large chain polypeptides form triskelion.
36 triskelion form lattice around vesicle
Adaptins (4types-a,b,sigma, u) help form coat and vesicle curvature.
Dynamin (gtp binding protein) form around neck of budding vesicle - form free clathrin coated vesicle.
Clathrin coated vesicles - function (2)
a)Formed receptor mediated endocytosis.
Vesicles enter lysosomal degradation pathway.
Clathrin coat removed.
Recycled to PM.
b)regulated transport if proteins from TGN to secretory granules OR late endosome-lysosome pathway.
Clathrin adaptin removed, naked vesicle binds to granule.
Coat reused in vesicle transport.
Coatomer coated vesicles - structure
Large protein consist of monomer coat protein subunits COPS.
ADP-Ribosylation factor binds gtp, activated, binds to coatomer sub-units.
COPS Function
COP 1 - Transport vesicles from Golgi to RER
COP 2 - Transport vesicles from RER to Golgi
Uses transmembrane proteins v/t snare mechanism with help of : NSF (n-ethylmaleimide sensitive fusion) and SNAP ( Soluble NSF attachment protein) - fusion of vesicle to specific target membrane.
Caveolin coated vesicles. Structures where found? and function
Structure : found in smooth muscle, endothelial cells. Invaginations in PM, distinct coat formed by protein Caveolin.
Function : cell signalling, transport eg transcytosis and endocytosis
Retromer-coated vesicles. Structure and function.
4 protein subunits.
Return cargo from Endosomes to TGN.
2 prerequisites:
Cargo receptor protein available for binding.
Cargo membrane contains inositol phospholipid : phosphoinositide(PIP)
What enzymes do lysosomes contain?
Acid hydrolases. Active at ph < 5.0
How is the acidity of lysosomes maintained?
H+ pump, active transport from cytosol.
What protects lysosomes from the acidic enzymes? (3)
Glycoproteins in lysosomal membrane.
Rich in cholesterol.
Lysobiphosphatidic acid - prevent enzyme digestion of lysosome.
How are lysosomes formed?
Fusion of vesicle containing lysosomal enzymes and late endosome.
Describe lysosomal formation pathway (Early endosome)?
-Early endosome
Contain ligands from receptor mediated endocytosis
Ph PM.
Ligands -> Late endosome.
Describe lysosomal formation pathway (Late endosome/Intermediate compartment)?
-Late endosome (intermediate compartment)
Acidity ph<5.5
Contain M6P receptors
Contain inactive acid hydrolases/phosphatases. + lysosomal membrane proteins.
Receive enzymes from Golgi with M6P.
Received all enzymes from golgi therefore lysosomal enzyme degradation commences.
How are lysosomal membrane proteins and proenzymes formed?
RER - enzyme contain signal
GOLGI COMPLEX for processing - signal folded in specific manner therefore M6P binds to vesicle.
Via vesicles to Late endosomes (contain mp6 receptors)
Name 3 types of lysosome and how they are formed?
Multivesicular bodies - early endosome fuses with late endosome
Phagosome - phagocytic vacuole fuses with late endosome
Autophagolysosome - autophagic vacuole fuses with late endosome/lysosome.
How are autophagolysosomes formed?
RER membrane engulfs dead organelles/cytoplasmic components.
Autophagic fuses with late endosome/lysosome.
What are residual bodies?
Post lysosomes. No more degradation.
Contain lipofusin or hemosiderin.
Excreted from cell
Extra lysosome points? (3)
Involved in biosynthesis, phagocytosis, digestion.
Abundant in WBCs ( neutrophiles, macrophages).
In skin - melanocytes - melanin - stored in lysosomes ( melanosome) - internalised into keratinocytes.
Extra cellular digestion function of lysosomes?
Osteoclasts, spermatozoa, embryonic development - destruction of cells, digestion of inferior organelles.
Autophagy benefits
Cell differentiation
Cell organelle turnover
Where lipofucins are common?
Neurons, cardiac and skeletal muscle.
Difference in vesicles coated by COPs and Clathrin?
COPS
non specific, continuous, immediate secretion
E,g, hepatocytes, lymphocytes, fibroblasts, cell membrane replacement
CLATHRIN
Specific, receptor mediated, molecules buildup in vesicles until stimulated. Receptor binds -> Released by exocytosis
Name 4 types of endocytosis
Receptor mediated, pinocytosis, phagocytosis, autophagy
Receptor medicated endocytosis and give example
Specific stimulus.
Clathrin mechanism involving adaptin and dynamin (gtp binding protein).
Eg LDL receptors
Pinocytosis explain? 2 types and visible at…
Non specific, continuous.
2 types macro/micro-pinocytosis
Micro visible at TEM
Phagocytosis, explain?
Phagocytes engulf bacteria, dust, pathogen. Require ATP polymerisation of actin filaments form pseudopods(phagosome).
1) recognise and adsorption
2) internalise of particle
Entrapment - form vacuole - fuse with late endosome - form lysosome - particle digested - residual body - excreted by the cell.
Autophagy explain?
Cell turnover and differentiation.
Eg
Dead mitochrondria - RER membrane engulfs - form autophagic vacuole - fuses with late endosome/lysosome - form autophagolysosome - digested - residual body - lipofuscin excreted by cell.
Peroxidase function
Function in defense and met pathways
4 enzymes: d-amino acid oxidase, oxidase, catalase, urate oxidase (bacteria)
Oxidase- Beta oxidation of long chain fatty acids - smaller fatty acids.
Toxic byproduct h2o2.
Catalase- convert hydrogen peroxide to oxygen and water
Urate oxidase(located in nucleiod) - purines to urea
Proteins for peroxisomes?
Specific peroxisomal sequence on the Terminus C
Disease associated with peroxisomes?
Zellwegers syndrome - mutation in peroxisome receptor. terminus c peroxisomal protein not recognised.
Peroxisomes and CNS
P located in oligodendrocytes(support and insulation to axons.)
Damage to P, loss of axonal support.
Demyelation.
Peroxisomes additional functions
Synthesis of cholesterol, bile
Remove toxic compounds
Remove free radicals.
