Term
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Definition
| Part of cell membrane. Sugar chains attached to proteins and lipids on outsides. Have various functions. |
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Term
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Definition
| Both hydrophilic (charged, or uncharged & polar) and hydrophobic (uncharged, nonpolar) |
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Term
| What is on both leaflets and for structural integrity? |
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Definition
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Term
| What is only on the extracellular leaflet ? |
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Definition
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Term
| What are the rigid membrane? |
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Definition
Saturated fatty acid tails
Long chains
Lower temperature
High cholesterol
Cholesterol fills in gaps when lipids are too fluid |
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Term
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Definition
Unsaturated fatty acid tails (inc cis-dbl bond kinks)
Short chains
High temperature
Low cholesterol
Inner Leaflet = more unsat therefore is more flexible than the Outer Leaflet |
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Term
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Definition
| Circular arrangement of fatty acids |
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Term
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Definition
Circular arrangement of phospholipid bilayer
Phospholipid bilayer contains amphipathic membrane lipids
Leaflets held together via van der Waals interactions
Different phospholipids do not interdigitate |
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Term
| How are leaflet's held together? |
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Definition
Van der Waals interactions. Weak bonds between the hydrophobic tails.
(Membranes are self-healing and fluid) |
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Term
| What is membrane fluidity essential for? |
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Definition
Exocytosis
endocytosis
membrane trafficking and biogenesis |
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Term
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Definition
Faces extracellular matrix
Has glycolipids and glycoproteins
Contains cholesterol |
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Term
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Definition
Faces cytoplasm
In a non-apoptotic cell, has phosphatidylserine
Leaflets are asymmetric |
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Term
| What does the melting temperature depend on? |
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Definition
Lipids
unsat:sat fatty acids |
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Term
| What is an example of fillinf in gaps when lipids are too fluid? |
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Definition
| Steroid rings imoobilize PL hydrocarbon chains: reduces phospholipid movement |
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Term
| What happens when you increase the cholesterol in the cell membrane? |
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Definition
Increased cholesterol:phospholipid ratio gives a distorted cell shape Acanthocytes (“Spur Cells”
Associated with chronic liver disease and alcoholism
Excess cholesterol transferred to outer leaflet
Increased surface area of cell membrane makes red blood cells LESS deformable
Decreased deformability = Destruction by Spleen
Results in Hemolytic Anemia (High Reticulocyte Count) |
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Term
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Definition
| Acanthocytes (“Spur Cells”) |
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Term
| What is spur cell anemia? |
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Definition
distorted cholesterol balance in plasma and RBC membrane.
Immenent death
The anemia causes blood to be very rigid. So the RBCs are being prematurely destroyed in the spleen. |
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Term
| What are Oesophageal varices? |
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Definition
| esophageal varices are extremely dilated sub-mucosal veins in the lower esophagus. They are most often a consequence of portal hypertension, commonly due to cirrhosis; patients with esophageal varices have a strong tendency to develop bleeding. |
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Term
| Acanthocytosis/ Spur Cell Anemia |
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Definition
Inc cholesteroal in RBC membranes.
Assoc with chronic liver disease.
- abnormal lipoproteins with high cholesterol content and high plasma cholestestorl levels.
- xs cholesterol transferred to outer leaflet
Formation of flat, scalloped cells with projections, increase surface area of outer bilayers less deformable.
Decrease deformability leads to sequestration and destruction by spleen which then leads to hemolytic anemia. |
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Term
| What is the asymmetry of the cell membrane maintained? |
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Definition
| By flippases which are enzymes that selectively flip particular phospholipid across membrane. |
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Term
| What is the functional importance of flippases? |
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Definition
| Example is of phosphatidyl serin flipped to our leaflet signal apoptosis. |
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Term
| Describe the movement within one plane of bilayer. |
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Definition
| There is laterial diffusion, flexion and rotation. Flip=flop rarely occurs. |
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Term
| What does flip-flop require? |
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Definition
Flipases which are phospholipid specific and move these to outer leaflet.
Scrambalases. Which give non-specific scrambling. In ER membrane: mix up newly synthesised PLs.
EX: ER outer gets made first then flips inside |
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Term
| What are GLycolipids used for and where are they found? |
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Definition
Surface of all PMs
Only on outer leaflet, preferentially in lipid rafts
Cell-cell recognition
Protection (only on exposed
apical surface of epithelial cells)
Nerve conduction
GM1 Ganglioside :
= Receptor for Cholera toxin, found on
intestinal epithelial cells |
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Term
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Definition
- Butter Islands in Oil
Rich in cholesterol & glycosphingolipids
(long saturated tails)
→ less fluid, thicker
Stick out of membrane:
Longer & straighter lipid tails
Contain integral & peripheral membrane proteins : Clustering enables proteins to function together / for transport into endocytic vesicles
GPI: glycosylphosphatidylinositol anchor
= glycolipid that attaches proteins to PM |
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Term
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Definition
| Most PM proteins = glycosylated (outer leaflet): glycoproteins |
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Term
| What do does the variability in the ratio related to function of membrane tell us? |
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Definition
Most PMs= 1:1 lipid:protein ratio (by weight)
~ 50 phospholipids/protein (proteins larger & heavier than lipids)
Variability of ratio related to function of membrane
Myelin membrane: 25% protein
Mitochondrial membrane: 75% protein
Structural integrity : integral proteins bound to actin cytoskeleton
Determine characteristic functional properties of membranes |
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Term
| What are the functions of membrane proteins? |
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Definition
Transport (nutrients, metabolites, ions across bilayer)
Anchor membrane to macromolecules on either side
Receptors: signal transduction
Enzymes (lactase in apical membrane of GI epithelial cells)
Cell identity markers: MHC |
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Term
| What are Integral transmembrane proteins (30% total proteins, amphipathic) |
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Definition
Single/ multipass proteins
often a-helical in secondary protein structure
Receptors (signalling & adhesion), channels, transporters/pumps |
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Term
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Definition
located entirely outside but associated with inner / outer leaflet by noncovalent (often electrostatic) interactions
part of cytoskeleton, cytochrome C |
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Term
| Lipid-anchored (peripheral) proteins |
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Definition
located either side of bilayer, have lipid group that inserts into bilayer
signaling & adhesion proteins |
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