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Flashcards in Transport Mechanisms Deck (33):
1

Permeability Characteristics of Cell Membrane

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

2

Integral Proteins

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

3

Peripheral Proteins

more loosely associated, mostly on the cytoplasmic side

4

Glycocalyx

Carbohydrates and glycoproteins on outer side of membrane

5

Functions of plasma Membrane

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

6

Membrane Proteins Functions

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

7

Passive

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

8

Active Transport

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

9

Fick's Law of Diffusion

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

10

Diffusion of particles may penetrate either by

a. Dissolving in the lipid component )for non-polar molecules) e.g. O2, CO2, fatty acids

b. Diffusing through channels(for ions)

11

Ion channels may consist of

-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

12

3 ways that channels can be gated

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

13

Characteristics of Carrier-mediated transport

a. Specificity
b. Saturation
c. Competition

14

Secondary Active: Counter trasport Mechanisms

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

15

Secondary Active: Cotrasport Mechanisms

Na+-glucose cotransporter
Na-amino acid transporter+

16

Endocytosis

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

17

Exocytosis

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

18

Pinocytosis

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.

19

Phagocytosis

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.

20

Clathrin-dependent receptor-mediated endocytosis

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

21

Potocytosis

-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.

22

Osmotic Pressure

-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

23

Van't Hoff Equation for Osmotic Pressure

P = nRT/V

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

24

Osmolarity(Osm)

-total solute concentration of a solution

1 osmol = 1 mol of solut particles

25

Isosmotic

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

26

Hypoosmotic

solutions which have a lower number of osmotically active particles

27

Hyperosmotic

solutions which have a higher number of osmotically active particles

28

Hypertonic solution

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

29

Hypotonic

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

30

Isotonic

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

31

Capillary wall

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

32

Bulk flow

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

33

Filtration

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