cell membranes

Question 1

function of a plasma membrane

Answer 1

to act as a barrier - separate cellular components

Question 2

what are plasma membranes properties ?

Answer 2

flexibility and deformability
permeability barrier
fluidity yet structure
receptors
transporters
enzymes
association with cytoskeleton
adhesion proteins linking cells together

Question 3

what are the components of a plasma membrane

Answer 3

complex lipids
proteins
glycoproteins
glycolipids

Question 4

definition of amphipathic

Answer 4

dual affinity eg.
plasma membrane phospholipids are amphipathic as they are both hydrophilic and hydrophobic

Question 5

how do phospholipids arrange in fluids?

Answer 5

in a bilayer as they have a cylindrical shape so a bilayer is the most favourable arrangement

Question 6

what affects the structure of fatty acids ?

Answer 6

they have different structures due to chain lengths and double bonds
the double bonds kink the chain, changing the structure and therefore the packaging of the lipid ( increase SA ) so lower melting point and so more fluid

Question 7

what do seven span receptors do ?

Answer 7

( in plasma membrane ) transduce signals from molecules like glucagon, adrenaline, noradrenaline
effects vary between tissues depending on receptor type
hence why drugs aim to interfere with these receptors

Question 8

what are the 3 classes of membrane transport proteins?

Answer 8

transporters, ATP powered pumps, channel proteins

Question 9

what are ATP powered pumps?

Answer 9

ATPases that use energy from ATP hydrolysis to move ions across their conc. gradient
Na+/K+ pump in glucose and amino acid co transport

Question 10

what is a transporter?

Answer 10

protein that only binds to one substrate at a time and transports it passively down its conc. gradient

Question 11

what is a channel protein?

Answer 11

water filled pores in the bilayer which open allowing charged molecules (ions) to move down their conc. gradient

Question 12

what is the membrane potential of an animal cell? how is it created?

Answer 12

between -20mV and -200mV
Na+ molecules are pumped out and K+ are pumped in, more Na+ ions are pumped out than K+ pumped in so it creates a negative charge within the membrane

Question 13

what is a uniporter ?

Answer 13

moves one molecule down its conc. gradient at once
involved in facilitated diffusion

Question 14

what is an antiporter ?

Answer 14

moves two molecules at once , one down its conc. gradient while the other is transported against its conc. gradient - co transport

Question 15

define facilitated diffusion

Answer 15

passive movement of a molecule down its concentration gradient with use of a protein channel

Question 16

define active transport

Answer 16

active movement of a molecule against its concentration gradient using energy in the form of ATP and with the aid of protein carriers

Question 17

explain the relationship of permeability the membrane has with different molecules

Answer 17

hydrophobic molecules eg. oxygen, CO2, nitrogen and benzene can diffuse straight through the membrane
small uncharged polar molecules eg. H20, urea and glycerol are transported via facilitated diffusion
large uncharged polar molecules eg. glucose and sucrose are actively transported
ions are usually involved in pump systems and have specific protein channels for each ion

Question 18

define simple diffusion

Answer 18

when a molecule can pass straight through - must be lipid soluble ( hydrophobic molecules )