Page 15 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

Carbohydrate
Glycoprotein
Glycolipid
Globular Hydrophilic
protein heads
Protein
channel
(Transport
2 protein) Phospholipid
bilayer
Cholesterol

Phospholipid
molecule
Peripherial protein
Globular protein Surface protein Alpha-Helix protein
(integral protein) Filaments of cytoskeleton (Intergral protein)
Figure 2.7 The fluid-mosaic model of the cell membrane

Exam Tips 3. The basic membrane structure consists of a bimolecular
phospholipid fluid layer with globular protein units floating in it,
Remember the structure,
functions of membrane forming a mosaic pattern.
based on the fluid-mosaic
model of Singer and 4. The heads of the phospholipids are hydrophilic, pointing outwards
Nicholson and the roles into the aqueous medium on both sides of the membrane.
of component molecules.
(STPM 2009 essay on the 5. The tails of phospholipids are hydrophobic, facing each other
role of carbohydrate)
forming a non-polar interior in the middle of the membrane.
6. The structure is dynamic where each lipid molecule can move within
its own monolayer and so is each of the protein unit. Some protein
units however, are immobilised by microfilaments in the interior of
the cell.
7. The fluidity of the membrane depends on the length of the fatty
acid chains, their saturation and the amount of cholesterol in them.
Fluidity affects permeability, membrane enzyme activities, reception
to molecules and with which membranes it will fuse.

8. Cholesterol with its hydrophilic head and hydrophobic tail fits neatly
within the phospholipid layer. It functions to control mechanical
stability, flexibility and permeability of the membrane, especially in
reducing leakage of small polar molecules.
9. The proteins are embedded in the phospholipid layer like mosaic,
either in only one monolayer or span the bilayer. These are integral
or intrinsic proteins, fitted neatly because of their corresponding
non-polar properties of their surfaces. The peripheral or extrinsic
ones are attached on the outer polar layers of phospholipid.

10. The proteins function as carriers or channels for polar molecules
to cross the membrane, as structural components, enzymes,
receptors and electron carriers for respiratory or photosynthetic
phosphorylations.

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