Topic 1.3 Membrane Structure

Question 1

Phospholipid Molecule Structure

Answer 1

Phosphate head is hydrophillic and fatty acid tails are hydrophobic

Question 2

Proteins in the Plasma Membrane

Answer 2

Integral proteins
Peripheral proteins
Glycoproteins

Question 3

Functions of Membrane Proteins

Answer 3

T- Transport: Protein channels (facilitated) and protein pumps (active)
R- Receptors: Peptide-based hormones (insulin, glucagon, etc.)
A- Anchorage: Cytoskeleton attachments and extracellular matrix
C- Cell recognition: MHC proteins and antigens
I- Intercellular joinings: Tight junctions and plasmodesmata
E- Enzymatic activity: Metabolic pathways (e.g. electron transport chain)

Question 4

Cholesterol

Answer 4

It makes the phospholipids pack more tightly and regulates the fluidity and flexibility of the membrane.

Question 5

Why is membrane fluidity important?

Answer 5

Membranes need to be fluid enough that the cell can move

Membranes need to be fluid enough that the required substances can move across the membrane

If too fluid however the membrane could not effectively restrict the movement of substances across itself

Question 6

Falsification of Davson-Danielli model

Answer 6

Freeze fracturing revealed irregular rough surface inside the phospholipid bilayer. Globular structures were interpreted as trans-membrane proteins