3A Introduction to Plasma Membrane

Question 1

Structure of plasma membrane

Answer 1

Structurally:
- a phospholipid bilayer embedded with proteins + carbohydrates + proteins
- Stable (amphipathic nature) (two fatty acid tails repel from water whereas phosphate head attracted to water)
- Fluid (molecules that make up the membrane are not
held static in one place + Mosaic (many different types of molecules are embedded in the
plasma membrane) (Fluid Mosaic Model)

1. Phospholipids = structurally comprised of a
   - Phosphate Head (glycerol + phosphate group) (negatively charged + hydrophilic + polar)
   - Two Fatty Acid Tails (long chains of carbon + hydrogen) (uncharged + hydrophobic + non-polar)
2. Proteins

• Integral proteins (permanent part of membrane)
• Transmembrane proteins (integral proteins that span the entire bilayer)
• Peripheral proteins (are temporarily attached to the plasma membrane)

3. Carbohydrates

• Usually in chains extending outside the cell + rooted in the membrane to lipids/proteins known as - Glycolipids/Glycoproteins

4. Cholesterol

• Lipid steroid embedded between the fatty acid tails of the plasma membrane in animal cells

Question 2

Function of Plasma Membrane

Answer 2

Functionally
- Selectively permeable (controls what enters and exists the cell) + separates the intercellular environment from the extracellular environment = Specialised internal environment

Proteins:
- Transport (controls what enters and exists the cell through channels/pumps = Selectively permeable plasma membrane)
- Catalysis (speeds up chemical reactions using an enzyme)
- Communication (receives signals/recognises cells/molecules) = often attached to cytoskeleton
- Adhesion (stick to other cells/extracellular matrix/cytoskeleton

Carbohydrates:
- Helps with (cell communication + signalling + recognising self or foreign molecules + adhesion)

Cholesterol:

• Regulates fluidity of membrane (High Temps = keeping phospholipids bound together whereas Low Temps = keeping phospholipids from becoming solid boundary)