3 features of plasma membrane
Limiting structure
Selectively permeable barrier
Keeps internal env separate from external environment
PM is semipermeable and selectively permeable for which molecules
Semipermeable - mols that can pass through lipid bilayer
Selectively permeable - mols that cannot pass through
Role of P.M
Signal transduction (surface receptors)
Cell division
Cell to cell recognition
Chemical composition of PM. Which cell is suitable to study composition. How are the composition arranged
Protein, carbohydrates, lipids
Mature RBC
The composition varies according to the function of the cell. RBC has 49 P, 43 L, 8 C . Mitochondria has 80P, 18L, 3 C because of the electron transport chain where more protein is required for transporters. Myelin sheath has more lipids because no transportation occurs, it only acts as a insulation covering
What are lipids?
They are amphipathic molecules with a polar head (polyhydroxy group) and non polar tail (fatty acyl chain - hydrocarbon chain)
Membrane lipids cover how much in the membrane. What are their types?
50%. Phospholipids, glycolipids, cholestrol
Types of phospholipids, glycolipids, sterols
Which sterols are collectively called phytosterols
Campesterols sitosterol stigmasterol
Sterol found in yeast and bacteria
Ergasterol
Hopanoids - sterol like substance present in bacteria
Most common polyhyrdoxy alcohol present in membrane lipid
Glycerol
Fatty acyl chain is a hydrocarbon chain. Relationship between chain length and non polarity. How many fatty acyl chains are attached to the polar head. What is the bond between them called.
Chain length increases, non polarity increases.
2 fatty acyl chains therefore
2 Ester bonds
Types of fatty acids
Saturated
Unsaturated
Saturated fatty acid. Explain
The hydrocarbon chain has only single bonds. It has straight hydrocarbon chain
Unsaturated fatty acid explain
Hydrocarbon bond has double bond. It is of 2 type
Cis unsaturated- it forms a kink/bending in H-C chain.
Trans unsaturated - looks like saturated fatty acid. No bending.
Function of lipids
Provide fluidity of the membrane due to movement of lipid molecules
Transition temperature (Tm) of fatty acids. Definition. Tm is affected by
Temp at which 50% of lipids are present in gel form and 50% are present in solution form.
Affected by-
1.chain length increases, Tm increases.
2. The degree of double bond increases, Tm decreases
How is Tm measured
Differential scanning calorimetry
In a caloriemetry , temp is increased slowly and a peak of heat absorption marks the gel to fluid transition temp. What does it mean? Which factor greatly affects the Tm
It means membrane can remain in quasi fluid state at 28° temp. But at 10° as gel form and 50° as solution form.
The degree of unsaturation ( double bond) greatly reduces the Tm.
Which type of fatty acid can be kept in lower temperature.
Unsaturated fatty acids(double bonds) has low Tm value therefore it can remain in quasi fluid state in lower temp. Saturated fatty acids have high Tm value, therefore it will become solid on exposure to low temp.
What are phospholipids and its types
Lipid+ phosphate. Phospholipids are 2 types - glycerol based and sphingosine based.
Glycerol+ fatty acid =
Phosphate+ Glycerol + F.A=
Diacylglycerol (DAG) most common in plasma membrane. Helps in signalling.
Phosphotydic acid - can add bulky groups to increase polarity.
Adding bulky groups to phosphotydic acid increases
Polarity
Triacylglycerol forms what?
Formation of fat droplets -glycerolomosomes (present in adipose tissues)
Phosphatidylethanolamine
Abundant in bacteria PM
Present toward cytoplasmic phase
