Cell Membrane

Question 1

Cell Surface Membrane

Answer 1

• The plasma membrane that surrounds a cell
• Boundary between the cell cytoplasm and the environment of the cell

Question 2

Plasma Membrane

Answer 2

All membranes within (organelles) and around a cell

Question 3

Phospholipid Structure

Answer 3

• Hydrophilic heads are water soluble
• Hydrophobic tails are water insoluble

Question 4

Phospholipid Function

Answer 4

• Phospholipid bilayer acts as a barrier to most water soluble molecules
• Non polar, fatty acid tails stop polar molecules and ions passing across the membrane
• Allow lipid soluble molecules in and out of the membrane
• Make the membrane more flexible

Question 5

Micelles

Answer 5

• Form when phospholipids are submerged in water
• Form in a circle to ensure all the hydrophilic heads are facing outwards

Question 6

Cholesterol

Answer 6

• Formula - C27H46O
• Controls membrane fluidity
• More cholesterol = less fluidity and less permeability
• Hydrophobic to prevent leakage of water and dissolved ions from the cell
• Keeps the membrane stable at body temperature or it would burst

Question 7

Integral (Intrinsic/Transmembrane) Proteins

Answer 7

• Span the whole width of the membrane
• Carrier molecules or channels
• Helps transport substances that can’t diffuse through the membrane (amino acids, ions, sugars, etc)
• Other integral proteins are receptors for hormones and neurotransmitters

Question 8

Peripheral (Extrinsic) Proteins

Answer 8

• Confined to the inner or outer surface of the membrane
• Can be free on the membrane surface or bound to integral proteins
• Extracellular peripheral proteins act as receptors for hormones or neurotransmitters
• Cytosolic proteins are involved in cell recognition
• They dissociate from the membrane and move into the cytoplasm