Plasma Membrane

Question 1

What happens when phospholipids are exposed to water

Answer 1

• A phospholipid bilayer is composed of two phospholipid layers, each with hydrophillic head and hydrophobic tail
• When exposed to water, hydrophlillic head has a natural tendency towards the water, a polar molecule, and so the hydrophillic head of both membranes will turn towards the water
• This leaves the hydrophobic tails of both layers to form the interior of the bilayer as they do not have a tendancy for polar molecules such as water
• This then forms the phospholipid bilayer

Question 2

Structure of Cell Membrane

Answer 2

• Phospholipid bilayer with protein molecules weaving in between
• Phospholipid made of hydrophilic head facing the aqueous environment and hydrophobic tail facing inwards
• Phospholipid layers connected by weak covalent bonds
• Hydrophobic tails can by unsaturated (with kinks), or saturated (without kinks).
• Different types of proteins embedded in cell membrane and their fucntions:
• Integral proteins: - penetrate hydrophobic interior layer
- transmembrane proteins (span entire memmbrane)
• Transport proteins: provide channel through which ionic and non polar molecules can move through (by changing shape), and in some cases, or just carry non-polar molecules
• enzyme proteins: some carry out multiple steps in the metabolic process
• signal protein (signal transduction): contains a receptor that fits a certain chemical messenger. Messenger causes the protein to change shape to allow message into the cell
• glycoproteins (cell to cell recognition): contain identification flags which membrane proteins of other cells recognise for binding of two cells
• Peripheral proteins: not on inside of cell membrane, loosely bound to it
• Cholesterol: - steroid which keeps stability of plasma membrane
- resists changes in membrane fluidity (fluidity buffer)
- maintains membrane fluidit