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Lipids-1a

1a. Membrane

1b. Fluid mosaic model

Membrane proteins

Erythrocyte

2a. Transport across membrane

2b. Lipid molecules

2b. Lipid metabolism

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Membrane

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Freeze etching of membrane

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Freeze etching of membrane

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5Membrane contains several molecules

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One of the embedded

molecules is an integral

protein molecule

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Hydrophobic

tail

Lipid molecules are oriented in water

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a. Single tailed lipid, with tapered van der Walls envelopeb. Spheroidal micelle

c. More than optimal number of lipids will form unfavorable

water filled center

d. Such micelles flatten to collapse the hollow center, butdevelop water filled spaces

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a. Cylindrical van der Waals envelop of phospholipids

b. Forms extended disklike micelles, described as lipid bilayers

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10Transverse movement of lipid molecules is very rare

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11Temperature controls lipid molecules

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Membrane contains

several small lipidmolecules also

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Membrane Properties

Lipid bilayer with transmembrane proteins

These proteins decide the membrane function

Each living cell and organelle will have its own function

Structure of the membrane is also unique

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Composition of Membrane

Membrane Protein Lipid Carbohydrate

Mouse liver cells 46 54 2-4

Human erythrocyte 49 43 8

Mitochondrion

Outer membrane 52 48 2-4Inner membrane 76 24 1-2

Gram-positive bacteria 75 25 10

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Functions of Membrane

1. Delineation and compartmentalization2. Organization and localization of functions

3. Transport

4. Signal detection

5. Cell-to-cell communication

1

2

3

4

5

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a. Delineation and compartmentalization

Membrane acts as a barrier for hydrophilic molecules

Keeps essential substances inside the cell and keeps the

undesirable substances out

Intracellular membranes serve to compartmentalizefunction within eukaryotic cells

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b. Organization and Localization of Function

Inner membranes of mitochondrion role in respiration

Thylakoid membranes of chloroplast role in photosynthesis

Endoplasmic reticulum site of synthesis of biomolecules

(protein, lipids)

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c. Transport

Regulate movement of substances into and out of the cell

and organelles

Different types of transport (active transport, passive

transport, endocytosis, exocytosis)

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d. Cell-to-Cell Communication

In animal cells gap junctions

In plant cells - plasmodesmata

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e. Signal Detection

Electrical and chemical signal received at cell outer surface

Plasma membrane plays a key role in signal transduction

(through ligand-receptor interaction and followed by

events on the inner surface of the membrane)