Biological Membranes

Question 1

Hydrophobic vs Hydrophilic

Answer 1

Main component of membrane: phospholipids (spontaneous bilayer cuz of hydrophilic head & hydrophobic tail) - photo

Sphingolipids: another component in membrane (polar head & nonpolar tails)

Question 2

Membrane Fluidity (consistency of oil)

Answer 2

Phospholipids & proteins: weak interactions
- move freely with membrane (except if anchored to cytoskeleton)
Photo

Fluid mosaic model (membrane: many things that move around)

Question 3

Movement within membrane (4) - photo

Answer 3

1) Swinging (vibrating -most frequent cuz easiest movement)
2) Rotation
3) Lateral Diffusion (movement within one side of membrane -hydrophilic only)
4) Transversal Diffusion (polar crosses hydrophobic membrane - least frequent cuz hardest movement) polar interact w/ non polar

Question 4

Lipids saturation

Answer 4

Unsaturated fatty acids (double bonds = bends, kinks (take space, can’t be tightly packed, low m.p.)

Trans fat (Hs of double bond)
Cis=repulsion (kink, low m.p.), Trans=no repulsion (no kink, higher m.p.)

Question 5

Membrane fluidity & fats

Answer 5

Composition of membrane =fluidity
Level of saturation =level of fluidity

Cholesterol maintains membrane fluidity

Animals: cholesterol fills spaces left kinks by phospholipids = less fluid (too much = too rigid membrane =bad)

Cholesterol=50% membrane (20% of weight cuz small)

Organisms without cholesterol (maintain membrane fluidity):
Bacteria in cold environ. - fatty acid desaturases (introduced double bonds into fatty acid, counteract freezing)

Low m.p., high movement at low T, high fluidity

Question 6

Components of biological membrane

Answer 6

1. Phospholipid bilayer (everything else attached to or embedded in)
   1) Animal membrane (cholesterol), Plants (sterols)
   2) selectively permeable membrane
   3) matrix (area of attachment) for proteins
   4) No water soluble molecule in nonpolar interior
2. Interior protein network
   1) proteins inside cell w/ membrane (peripheral membrane proteins)
   2) Reinforce membrane shape
3. Cell-surface markers
   1) lipids & proteins + polysaccharides=
   Glycolipids & glycoproteins (golgi complex to membrane)
   2) affect exterior of cell (Cell-to-cell adhesion)
   3) Determine cell type, foreign organisms
4. Transmembrane protein
   1) Carriers, channels (protein transport) receptors (cell signalling) -implanted into membrane

Question 7

Anchoring of transmembrane proteins

Answer 7

Anchored to lipid: inserts into membrane by covalently attaching to lipid anchor inserted into membrane

Lipid anchor: produced in rough ER, modified hydrophobic region (inserts into membrane)

Spans the membrane: All or part of protein embedded in bilayer by going through bilayer

Question 8

Integral membrane protein

Answer 8

Hydrophobic regions (transmembrane domains)
Stay anchored in membrane

Domains: generally alpha-helices (1or up to 7) photo

Question 9

Protein channels (transmembrane domain)

Answer 9

Pores, holes in membrane
Beta-pleated sheets (beta-barrels)
NOT alpha-helices

Question 10

Functions of membrane associated proteins

Answer 10

Proteins: Transport or Cell-to-cell signaling

1. Transporters: let specific molecules in or out of cell (channels or carriers)
2. Enzymes: carry out chem rxn (anchored in membrane)
3. Cell surface receptors: bind to molecules outside of cell (hormones) & transmit signal to inside
4. Cell-surface identity marker: identify cells within body (proteins & glycoproteins); ex: natural killer cell
5. Cell to cell adhesion molecules: cells attach to one another (short lived or strong)
6. Attachment to cytoskeleton: cell attach to cytoskeleton