Understanding Biological Membranes: Phospholipids, Proteins, Cholesterol, Carbohydrates - , Study notes of Biology

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The Dynamic Cell

Membrane

• Major components of biological

membranes:

• Phospholipids
• Membrane proteins
• Cholesterol (animal cells)
• Carbohydrates - Glycoproteins - glycolipids

Figure 3.20 Phospholipids (A)

Repeat Fig 3.20A here

Artificial bilayers can be made

in the laboratory.

Lipids maintain a bilayer

organization spontaneously

—helps membranes fuse

during phagocytosis, vesicle

formation, etc.

Membranes may vary in lipid

composition

Phospholipids vary—fatty

acid chain length, degree of

saturation, phosphate

groups

Membranes may be up to 25

percent cholesterol

Membranes contain proteins,

the number of proteins

varies with cell function

Some membrane proteins

extend across the lipid

bilayer—with hydrophobic

and hydrophilic regions or

domains.

The proteins and lipids in the

membrane are independent

and only interact noncovalently.

Figure 5.4 Interactions of Integral Membrane Proteins

Transmembrane proteins

may have different domains

on either side of the

membrane.

The two sides of the

membrane can have very

different properties.

Membranes are dynamic and

are constantly forming,

transforming, fusing, and

breaking down.

Figure 5.5 Dynamic Continuity of Membranes

Figure 5.1 The Fluid Mosaic Model

Cells arrange themselves in

groups by cell recognition

and cell adhesion.

These processes can be studied

in sponge cells—the cells are

easily separated and will

come back together again.