Biological Membranes - the Fluid Mosaic

What are some characteristics of membranes?

• separate different areas

• Control the exchange of material across them

• Acts as an interface for communication

• Are partially permeable

• Use diffusion osmosis and active transport

• Formed from a biolayer of phospholipids

What is the structure of a phospholipid?

Only has 2 fatty acids and where the 3rd phosphate should be, there is a phosphate ion instead

Why is the phospholipids amphipathic?

• phosphate ions polar and therefore are soluble in water → hydrophilic

• Fatty acids are non-polar and therefore insoluble in water → hydrophobic

What does amphipathic mean?

Contains both hydrophilic and hydrophobic parts

What happens to phospholipids in the presence of water?

They form monolayer and bilayers

What shape do phospholipids make when mixed or shaken in water?

They form spheres called micelle

In a micelle phospholipid which way are the hydrophilic and phobic parts facing In water?

Hydrophilic phosphate head - faces outwards

Hydrophobic fatty acid tails - face inwards on each other

What is the fluid mosaic model?

It explains how biological molecules are arranged to form cell membranes

Why are cell membranes fluid?

Because the phospholipids and proteins usually move around sideways via diffusion

Why is it called a guild mosaic?

The patterns produced by the distribution of proteins

What are glycolipids?

Lipids with carbohydrate chains attached, projecting outwards

What are glycoproteins?

Proteins with carbohydrate chains attached, projecting outwards into the extra-cellular space

What part of the fluid mosaic do phospholipids make up?

The bilayer

What part of the fluid mosaic is cholesterol found only in eukaryotes?

Fit in between the phospholipid molecules

Which part of the fluid mosaic spans over both layers of the membrane?

Transmembrane proteins

What is cholesterol for?

• It regulates the fluidity of the membrane by preventing the phospholipids from packing too close together

• Allows membranes to be impermeable to ions, increasing strength and stability

When do membranes become less fluid?

• when there are more saturated fatty acid chains

• Lower temperatures

Why do more fatty acid chains cause the cell membrane to become less fluid?

They pack more closely together and there are a higher number of intermolecular forces between the chains

Why do lower temperatures cause the cell membrane to become less fluid?

The molecules have less energy and do not move as freely, becoming closely packed

When do cell membranes become more fluid?

• with more unsaturated fatty acid chains

• Higher temperatures

Why do more unsaturated fatty acid chains cause the cell membrane to become more fluid?

They pack together less tightly, less intermolecular forces between the chains

Why do higher temperatures cause the cell membrane to become more fluid?

The molecules have more energy and can more more freely so the structure becomes more fluid

What are glycolipids and glycoproteins for?

• they can act as receptor molecules by binding to the substance at the cell’s surface

• Can also act as cell markers or antigens for cell-to-cell communication

What are the 3 main receptor types?

• signalling receptors for hormones and neurotransmitters

• Receptors involved in endocytosis

• Receptors involved in cell adhesion and stabilisation

What are the two substances that receptors help bind to the cell membrane?

Drugs and hormones

What are transmembrane transport proteins for?

They create hydrophilic channels, allowing ions and polar molecules to pass through

What are the two types of transport proteins?

• channel proteins

• Carrier proteins

What is the correlation between the amount of transport proteins and the rate of diffusion in a membrane?

The more transport proteins, the faster the rate of diffusion