membrane Transport

Question 1

methods of membrane transport ?

Answer 1

SIMPLE DIFFUSION
A. Through Lipid Bilayer
B. Osmosis

CARRIER-MEDIATED TRANSPORT
A. Facilitated Diffusion
B. Primary Active Transport
C. Secondary Active Transport

VESICULAR TRANSPORT
A. Endocytosis
B. Exocytosis

Question 2

Cellular processes driven by energy stored in ion gradients across membranes ?

Answer 2

chemiosmotic - uptake/efflux of metabolites, nutrients and salts
osmotic volume regulation- h2o follows ions
chemical - H(Na) driven ATP synthesis
cell homeostasis- pH regulation/efflux .. removal and storage of toxic solutes
signal transduction - Ca entry and action potentials
mechanical- H+ Driven ,, flagellar rotation

Question 3

simple diffusion ?

Answer 3

non polar and lipid soluble

diffuse directly through lipid bilayer

Question 4

frick’s first law of diffusion

Answer 4

J=-DA * [(change in C)/(change in X)]
J=flux/rate of diffusion per time unit
D=diffusion coefficient 
A = area across which the diffusion is occurring
C= con. gradient
X=distance along which diffusion occurs

Question 5

diffusion coefficient

Answer 5

D= -kT/6πrn
k- boltzmann's coefficent 
T- Temp in K
r=radius
n=viscosity of medium

Question 6

6 factors that affect the rate of diffusion through a cell’s membrane

Answer 6

lipid solubility
con gradient
cell membrane thickness 
molecule size 
mem surface area
comp of lipid bilayer

Question 7

Passive Processes: Facilitated Diffusion has certain lipophobic molecules that use

Answer 7

use carrier proteins or channel proteins,

Question 8

what are characteristics of carrier proteins or channel proteins Facilitated Diffusion

Answer 8

Exhibit specificity

• Are saturable; rate is determined by number of carriers or channels
• Can be regulated in terms of activity and quantity

Question 9

2 types of channel proteins

Answer 9

leakage ; always open

gated : controlled by chemical/electrical signaling

Question 10

osmolarity

Answer 10

The measure of total concentration of solute particles

Osmolarity = Concentration x Number of dissociable particles

Question 11

osmosis can occur when

Answer 11

Osmosis can occur when a membrane separates unequal solutions of a non-penetrating OR penetrating solute.
Osmosis can occur when a membrane separates pure water from a solution of a non-penetrating solute.

Question 12

osmotic pressure equation

Answer 12

π=nCRT
n = number of dissociable particles per molecule
C = total solute concentration (in molarity, i.e., mol/L)
R = gas constant
T = temperature in degrees Kelvin.

Question 13

Facilitated diffusion is the same as simple diffusion except

Answer 13

the diffusing substance is attached to a lipid soluble membrane carrier protein or moves through a channel

Question 14

symport vs antiport examples

Answer 14

both Na dependent
sym: Na with glucose , aa, Bile salts, choline uptake (in nerves)and NT

anti- Na with H+ or Ca2+

Question 15

exocytosis

Answer 15

i. Usually seen with hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes.
ii. TRANS face -side where the vesicle comes in.
iii. CIS face - side where the vesicle leaves.

Question 16

endocytosis

Answer 16

i. Transcytosis – transport into, across, then out of cell
ii. Involve formation of protein-coated vesicles
iii. Usually receptor mediated, so it’s very selective.

Question 17

phagocytosis

Answer 17

– pseudopods engulf solids in pods (aka phagosomes) and bring them into cell’s interior.

i. Usually done to macrophages and some WBCs.
ii. Combine them with a lysosome for digestion.
iii. Undigested contents remain in the vesicle or are ejected by exocytosis.

Question 18

pinocytosis

Answer 18

– fluid-phase endocytosis where the plasma membrane infolds, bringing extracellular fluid and solutes into interior of the cell.

i. Done for nutrient absorption into the small intestine.
ii. No receptors are used, so process is non-specific.

Question 19

receptor mediated endocytosis

Answer 19

i. Uptake of enzymes low-density lipoproteins, iron and insulin.
ii. Extracellular substances bind to specific receptor proteins in regions of coated pits.
iii. Contents can either be released inside the cell or bound to a lysosome for digestion.