The Phospholipid Bilayer

Question 1

Describe some of the general functions of biological membrane ?

Answer 1

A continuous, highly selective permeability barrier, control of the enclosed chemical environment, communication, recognition and signal generation with response to stimuli

Question 2

What is the membrane compostion of the bilayer?

Answer 2

40% lipid, 60% protein and 1-10% carbohydrate

Question 3

What are the range of polar head groups available on the phsopholipids?

Answer 3

Choline, amines, amino acid and sugars.

Question 4

What are the sturural features of synaptomyelin?

Answer 4

No glycerol backbone, and the replacement of a phospocoline molecule with a sugar,

Question 5

What is the difference between cerebrosides and ganlgiosides?

Answer 5

Cerebrosides have a head group sugar monmener whereas ganlgiosides have a head group olgiosaccharide

Question 6

What are some of the sturctural features of cholestrol?

Answer 6

Polar head group, rigid polar steriod ring structure, non polr hydrocarbon chain

Question 7

What are the paradoxyl affect on chain motion of the cholesterol molecule?

Answer 7

Reduced phoshlipid chain motion causes reduced fuidity, whereas reduced phospholipid packing increases fluditiy

Question 8

What are the different restrictions on the phospholipid chain motility?

Answer 8

Aggergates, tethering, interaction with other cells, lipid mediated effects, and membrane protein assoications

Question 9

What is the difference between integral and peripheral membrane proteins?

Answer 9

Periphral are bound to the surface by electrostatic and hydrogen bond interactions and can be removed by changes in pH or ionic strength, whereas integral interact extensively with the hydrophobic domains, and cannot be removed by the manipulation of ionic strength but are removed by agents that compete for polar interactions

Question 10

What are some of the features of the erthycyte membrane?

Answer 10

Cytoskelton is a network of spectrin and actin moelcules, and a and B subunits work together to produce n antiparallel hererteriamer, which is attached to the membrane via the adapter proteins

Question 11

What are some of teh features of heredrity sephrocytosis.

Answer 11

Levels of spectrin may be depleted 40-50% shortened lifespan and the inability of cells to compensate leads to a heamolytic anaemia.

Question 12

What are some of the features of heredity elliptocytosis?

Answer 12

A spectrin molecule which is unable to form heterotetamers resulting in some fragile elliptoid cells.

Question 13

What are some of the features of the stop transfer sequence?

Answer 13

18-22 amino acids long, followed by charged amino acids which span the bilayer in hydrophobic form

Question 14

How is a membrane protein orientated into the membrane?

Answer 14

Signal sequence is recognised by the SRP, which locks the ribosome complex and prevents further elongation in the cytoplasm, recognised by a SRP receptor or docking protein, and the growing chain goes throught he pore, stop transfer sequence stops it within the pore, and a lateral gating mechanism releases it into the bilayer.

Question 15

What are some of the molecules that can pass directly through the bilayer?

Answer 15

Hydrophobic moecules such as O2, CO2 N2 and benzene, which are small unchardged and non polar, as well as small unchardged polar molecules such as H20, urea glycero

Question 16

What are some of the different types of membrane channels?

Answer 16

Ion channels, ligand gated ion channels, voltage gated ion channels, gap junction

Question 17

What is a gap junction?

Answer 17

Closed when the cellular concentration rises above 10um or the cell becomes an acid

Question 18

What is the intracellular and extracellular concentration of sodium?

Answer 18

Intracellular= 12mM 
Extracellular= 145mM

Question 19

What are the intracellular and extracellular concentration of K+?

Answer 19

Intracellular= 155mM, and extracellular= 4mM

Question 20

What are the intracullar and extracellular concentration of Ca2+?

Answer 20

Intracellular= 10-7 M whereas extracelluar is 1.5mM

Question 21

What are the intra and extracellular concentrations of Cl-?

Answer 21

Inratcellular 4.2mM, and extraellular= 123 mM

Question 22

What is a uniport?

Answer 22

Where a solute molecule is transported from one side of a membrane to another

Question 23

What is a symport?

Answer 23

Where the transport of a molecule depends on the simultnous and sequential transfer of a solute in the same direction

Question 24

What is a antiport?

Answer 24

Where the transfer of one moleucle depends on the simultaneous and sequentilal transport of a molecule in the opposite direction

Question 25

What are some of the features of the Na+/K+/ATPase pump?

Answer 25

There is an a subunit which contains the K+, Na+ and oubain binding sites, the B subunit has a glycoprotein role that directs the pump to the surgace,