B2 Fluid mosaic model, Compartmentalisation and organelles SL

SL

Glycolipids

Amphipathic carbohydrate molecules found within the cell membrane that result from the covalent bonding of carbohydrates to lipids. The carbohydrate groups of these molecules are polar and extend into the extracellular environment, whereas the non-polar lipid component lies embedded in the bilayer. They contribute to membrane stability as they form hydrogen bonds with the water molecules surrounding the cell.

Glycoglycerolipids

A group of glycolipids that are glycerol-based.

Glycosphingolipids

A group of glycolipids that are sphingoshine-based.

Glycoproteins

Amphipathic carbohydrate molecules found within the cell membrane that result from the covalent bonding of oligosaccharides to protein molecules. The hydrophilic carbohydrate groups of these molecules often protrude into the extracellular environment. These molecules have hydrophobic membrane-associated or core protein regions.

Functions of glycoproteins

1. Cell recognition: they act as markers on the surface of cells and help cells of the body recognize each other. They also help the immune system to recognize foreign cells.

2. Cell adhesion: they help cells adhere to each other to form tissues. For example, CAMs.

3. Cell signalling: they act as receptors for enzymes and other molecules helping in cell signalling, i.e. receiving and transmitting chemical signals.

Cell-adhesion molecules (CAMs)

Cell-surface glycoproteins that play an important role in cell adhesion.

Glycocalyx

The sticky layer formed by the carbohydrate groups of the glycolipids and glycoproteins that protrude from the cell surface. It helps in cell signalling, cell adhesion, cell-cell recognition, and protection of the cell surface.

Organelles

Structures within a cell that perform specific functions and are involved in metabolic processes.

Compartmentalisation

The organization of different functions and processes within specific areas or structures within the cell that are separated by plasma membranes; for example, membrane-bound organelles. It allows for the development of specialized structures such as the chloroplasts and mitochondria.

Parts of the cell that are not considered to be organelles

Cytoskeleton, cell wall, and cytoplasm.

Advantages of compartmentalisation of the nucleus form the cytoplasm

• Allows post-transcriptional changes to occur before translation.

• Allows the cytoplasm to send signals to the nucleus.