The document discusses the structure and components of the cell membrane. The phospholipid bilayer forms the basic structure of the membrane, with a hydrophilic phosphate head and hydrophobic lipid tails. The tails face inward to form a double layer with the heads facing outward. This bilayer forms a fluid mosaic, allowing phospholipids to move freely. Membrane proteins, such as integral and peripheral proteins, are embedded within the bilayer and provide functions like transport and structure. Cholesterol is also a key component that reduces membrane fluidity and permeability.

1. MEMBRANE STRUCTURE
Presented by IB Screwed

2. PHOSPHOLIPID BILAYER
What is a phospholipid?
Phospholipids are molecules. They have a hydrophilic phosphate head and two hydrophobic lipid tails.
What is a bilayer?
The phospholipids form a double layer, with
the tails on the inside and the heads facing outwards.
The hydrophilic heads are in contact with the cytoplasm and extracellular matrix

3. FLUID MOSAIC MODEL
The phospholipids form a fluid mosaic.
The membrane is in a fluid state, allowing the phospholipids to move and rearrange.
In electron micrographs, the phospholipids forms a mosaic pattern.

4. HYDROPHILIC VS. HYDROPHOBIC
Hydrophilic–‘water loving’: polar or charged molecules which are attracted to water. For example:ions, alcohols
Hydrophobic–‘water repelling’: non-polar molecules which are not attracted to water. For example: fats and oils
Amphipathic–Both hydrophobic and hydrophilic parts; polar and non-polar ends

5. MEMBRANE PROTEINS
The cell membrane contains many proteins which are used for structure and transport
There are three main types:
Integral proteins –often transport proteins. They span across the whole membrane
Peripheral proteins –sit on the surface of the membrane. Usually for shape.
Glycoproteins–used for cell recognition and signalling, hormone receptors

6. FUNCTION OF MEMBRANE PROTEINS
Since the inner part of the membrane is hydrophobic, necessary molecules like ions, proteins, etccannot cross without the membrane protein channels. They can provide facilitated diffusion or active transport (using ATP)
Other membrane proteins can be enzymes.
Some proteins are electron carriers.

7. CHOLESTEROL
In the media, cholesterol gets a bad name for its role in heart problems.
However, cholesterol is critical to animal plasma membrane structure. It reduces membrane permeability to some solutes. It also reduces the fluidity of the membrane.