Transport Mechanisms

Question 1

Permeability Characteristics of Cell Membrane

Answer 1

Highly permeable to: H2O, Lipid-soluble substances, dissolved gases (O2,Co2), small uncharged particles

Less Permeable to: larger molecules, charged particles

Impermeable to: very large molecules

Question 2

Integral Proteins

Answer 2

closely associated with phospholipids, mostly cross the membrane (transmembrane)

Question 3

Peripheral Proteins

Answer 3

more loosely associated, mostly on the cytoplasmic side

Question 4

Glycocalyx

Answer 4

Carbohydrates and glycoproteins on outer side of membrane

Question 5

Functions of plasma Membrane

Answer 5

Selective transport channel, enzyme, cell surface receptor, cell surface identity marker, cell adhesion, attachment to the cytoskeleton

Question 6

Membrane Proteins Functions

Answer 6

1. Transport specific molecules into and out of the cell
2. Act as enzymes that catalyze membrane associated reactions
3. Serve as receptors for receiving and transducing chemical signals form the cell environment
4. Cell surface identity markers
5. Cell- Cell adhesion
6. Attachment to cytoskeleton

Question 7

Passive

Answer 7

1. Diffusion
2. Carrier-mediated
   Facilitated Diffusion
3. Osmosis

Question 8

Active Transport

Answer 8

1. Carrier-mediated
   Active Transport
   a. Primary
   b. Secondary

Question 9

Fick’s Law of Diffusion

Answer 9

Rate of diffusion can be calculated:

J = PA (Co -Ci)

J = Net Flux: net movement of molecules across a membrane

P = Permeability (or diffusion) coefficient: a constant based on the ease with which a molecule moves through a membrane

A = Surface area of the membrane

Co - Ci = Concentration gradient of the diffusing molecule across the membrane

Question 10

Diffusion of particles may penetrate either by

Answer 10

a. Dissolving in the lipid component )for non-polar molecules) e.g. O2, CO2, fatty acids
b. Diffusing through channels(for ions)

Question 11

Ion channels may consist of

Answer 11

• a single protein or more often, of clusters of proteins.

- Ion channels show selectivity based on their diameter as well as on the distribution of charges lining the channel

Question 12

3 ways that channels can be gated

Answer 12

a. Ligand-gated
b. Voltage-gated
c. Mechanically-gated

Question 13

Characteristics of Carrier-mediated transport

Answer 13

a. Specificity
b. Saturation
c. Competition

Question 14

Secondary Active: Counter trasport Mechanisms

Answer 14

Na+/H+ exchanger
Na+/Ca2+ exchanger
Cl-/HCO3- exchanger

Question 15

Secondary Active: Cotrasport Mechanisms

Answer 15

Na+-glucose cotransporter

Na-amino acid transporter+

Question 16

Endocytosis

Answer 16

cell membrane invaginates, forming a channel, the end of which pinches off to form a vesicle

Question 17

Exocytosis

Answer 17

an intracellular vesicle fuses with the cell membrane and its contents are released into the ECF

Question 18

Pinocytosis

Answer 18

ingestion of dissolved materials by endocytosis. The cell membrane invaginates and pinches off placing small droplets of fluid in a pinocytic vesicle. The liquid contents of the vesicle is then slowly transferred to the cytosol.

Question 19

Phagocytosis

Answer 19

ingestion of solid particles by endocytosis. The cell membrane invaginates and pinches off placing the particle in a phagocytic vacoule (phagosome). The phagocytic vacoule then fuses with lysosomes and the material is degraded.

Question 20

Clathrin-dependent receptor-mediated endocytosis

Answer 20

-involves pinching off of “clathrin-coated vesicles” that often fuse with endosomes where the vesicles contents are sorted

Question 21

Potocytosis

Answer 21

• type of clathrin-independent receptor-mediated endocytosis
• involves the pinching off of tiny vesicles called “caveolae” that deliver their contents to the cell cytoplasm via channels or carriers.

Question 22

Osmotic Pressure

Answer 22

• the pressure required to prevent the movement of water across a semi-permeable membrane
• pressure is equal to the difference in hydrostatic pressures of the two solutions

Question 23

Van’t Hoff Equation for Osmotic Pressure

Answer 23

P = nRT/V

n= # of particles
R= gas constant
T = abs. Temp
V = Voume

Question 24

Osmolarity(Osm)

Answer 24

-total solute concentration of a solution

1 osmol = 1 mol of solut particles

Question 25

Isosmotic

Answer 25

solutions which have the same number of osmotically active particles as normal extracellular solutions

Question 26

Hypoosmotic

Answer 26

solutions which have a lower number of osmotically active particles

Question 27

Hyperosmotic

Answer 27

solutions which have a higher number of osmotically active particles

Question 28

Hypertonic solution

Answer 28

solution has a conc. of nonpenetrating solute particles greater than 300 mOsm, water will leave the cell and the cell will shrink

Question 29

Hypotonic

Answer 29

solution has a conc. of nonpenetrating particles less than 300 mOsm, water will enter the cell and the cell will swell.

Question 30

Isotonic

Answer 30

solution has a conc. of 300 mOsm of nonpenetrating solute particles, there will be no net shift of water.

Question 31

Capillary wall

Answer 31

-a single layer of flattened endothelial cells and a supporting basement membrane.

Question 32

Bulk flow

Answer 32

-flow of molecules subjected to a pressure difference causing redistribution of extracellular solution

Question 33

Filtration

Answer 33

-bulk flow across a porous membrane (which acts as a “seive”, withhold some particles).