Foundations 4

Question 1

membrane lipids form ___ in water - why?

Answer 1

bilayers: can’t make micelles because of having two fatty acyl tails. forms because of hydrophobic effect; spontaneous.

Question 2

bilayer vesicle: stability?

Answer 2

non covalent but very stable: will spontaneously reseal in aqueous environments

Question 3

membrane fluidity is critical in?

Answer 3

the activity of membrane bound enzymes, phagocytosis, cell growth and death

Question 4

melting temperature: aka? def?

Answer 4

transition temperature: empterature of its transition from an ordered crystalline state to a more fluid state

Question 5

below or above the transition temperature, what happens?

Answer 5

below: acyl chains pack together in van der waals contact, in a gel like state. above: lipid molecules and their acyl chains move freely and rapidly

Question 6

cholesterol: where in the membrane? role?

Answer 6

almost entirely buried among hydrophobic tails of membrane lipids. increases fluidity by disrupting vdw interactions between acyl tails

Question 7

integral membrane proteins are folded____ than cytosolic globular proteins?

Answer 7

differently: hydrophobic residues are on the outside of transmembrane domains

Question 8

what can or can’t cross the lipid bilayer?

Answer 8

small molecules via simple diffusion like CO2, O2, benzene, ethanol. water crosses very slowly. large/polar are excluded like glucose, amino acids, ions.

Question 9

aquaporins: what?

Answer 9

integral membrane proteins: for the large scale rapid movement of water

Question 10

how are aqua porins selective for water (3)

Answer 10

size restriction. electrostatic repulsion. water dipole reorientation

Question 11

transporter proteins: aka? do what?

Answer 11

carriers. catalyze movement of specific substances across membrane by binding specific ligands at specific sites

Question 12

GLUT transporters: what type?

Answer 12

passive: uptake of glucose from blood stream into cells

Question 13

two examples of linked active transporters

Answer 13

sodium potassium pump. sodium glucose transporter (secondary active symport both go into cell)

Question 14

3 major steps in signalling

Answer 14

binding of signal molecule to receptor. transduction: pathway of intracellular signalling reactions. responses.

Question 15

intracellular/cytosolic receptor vs. cell surface/membrane receptor

Answer 15

intracellular: bind steroid hormones which are hydrophobic and will diffuse across the lipid bilayer - receptor hormone complex binds to DNA to regulate gene expression. cell surface receptors: integral membrane proteins which bind ligands that can’t cross membrane

Question 16

phosphodiesterase: what? inhibition?

Answer 16

enzyme that hydrolyzes cAMP. inhibited by caffiene

Question 17

G protein cycle

Answer 17

basal trimer state +CDP. receptor activation, G protein releases GDP and binds GTP. dissociation into alpha and beta-gamma subunits. GTPase activity of alpha subunit –> GDP now back into trimer state= inactive.