This summary document contains all the required information from 5 weeks of biological membranes lectures.
The lecture topics covered are as follows:
- Membranes and signalling
- Membrane synthesis
- Moving proteins into membranes
- Protein targeting
- Vesicular traffic
- Mitochondrial Elect...
BIOL2210 Weeks 1-5 Revision (Ponnanbalam, Baker 1, Harrison 1-2)
Membranes and Signalling
3 functions of cell membranes:
1. Keep toxic substances out cells
2. Allow molecules pass between organelles and cell to external environment
3. Separate metabolic processes within organelles
Lipids = any hydrophobic molecule insoluble in water but soluble in organic solvents.
1. Phospholipids – major component of cell membranes
2. Cholesterol – stops membranes becoming stiff & provides stability
3. Glycolipids – located on cell surface membranes, important for cell recognition
Membrane proteins:
1. Peripheral – connected to membranes by interactions with other proteins
2. Integral – inserted into and pass through membranes single or multiple times
3. Lipid-linked – attached to membranes via lipid linker
Nucleus:
Two membranes, with perinuclear space separating inner and outer membranes
Outer nuclear membrane consistent with rough ER
Role -> protection of genetic material/control of entry molecules through pores
Mitochondrion:
Outer membrane covers organelle, inner membrane folds/creates layered cristae
Intermembrane space -> important for oxidative phosphorylation
Types of phospholipids (decreasing in abundancy):
Phosphatidylcholine (PC) = choline bound to phosphate head
Phosphatidylethanolamine (PE) = ethanolamine attached at head; small head size
makes easier for proteins to position on membrane
Phosphatidylserine (PS) = typically confined to inner membrane; dying cells have on
outer membrane to signal macrophages to digest them
Phosphatidylinositol (PI) = can be phosphorylated forming signalling molecules
, 06/03/22
Sphingolipids => phospholipids with amide bond between a fatty acid and sphingosine
2 key functions in cell membranes:
1. Structural: protect cell from harmful environmental factors
2. Signalling: sphingolipid metabolism creates role-playing products
Cholesterol – modified sterol essential for membrane structural integrity & fluidity
Fluidity allows cells to change shape rapidly
Lipid composition affects membrane properties:
Pure SM bilayers thicker than PC bilayers
Cholesterol enhances thickness of PC bilayer through lipid ordering
Cholesterol has less effect on SM bilayers as they are more ordered
Membrane Synthesis
Membranes originate from the smooth endoplasmic reticulum (SER)
Produces cholesterol & membrane phospholipids using membrane-bound enzymes
SER RER
Lacks ribosomes Studded with membrane-bound ribosomes
More prominent in lipid-producing cells More prominent in protein-producing cells
1st stage FA synthesis: use of Acetyl-CoA as a building block
Catalysed by fatty acid synthase (FAS), with it taking place in cytoplasm
2nd stage FA synthesis: acetyl-CoA conversion to malonyl-CoA
Catalysed by acetyl-CoA carboxylase (ACC)
Malonyl-CoA provides 2 carbons to FAs, results in synthesis of 16C palmitate
Palmitate is precursor for other long-chain FAs, can be lengthened to form longer
saturated fatty acids.
To yield unsaturated FAs, desaturase enzymes remove two Hs from a FA
Phospholipid synthesis in ER membrane:
1. Two FAs esterified to phosphorylated glycerol phosphate backbone.
2. Phosphatase converts phosphatidic acid into diacylglycerol.
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