Chapter 2 The Living Cell Part 2

Front 1

Membrane Transport

Back 1

Human cells are selectively (differentially) permeable.
*Nutrients enter cells but not other potentially harmful substances
*Waste products exit cell but not proteins required for normal cellular function

Front 2

Movement across plasma membranes

Back 2

1. Passive
*No energy required by cell
2. Active
*ATP from cell required

Front 3

Passive Processes

Back 3

1. Diffusion: All cells
2. Osmosis: Diffusion of water
3. Filtration:
*Cells of capillary walls
*Kidney
*Cerebrospinal fluid production

Front 4

Simple Diffusion

Back 4

1. Uses kinetic energy
2. Net movement of particles (ions, molecules, etc) from an area of their higher concentration to an area of their lower concentration, that is, along their concentration gradient.
3. EX: Movement of fats, oxygen, carbon dioxide through the lipid portion of the membrane.

Front 5

Facilitated Diffusion

Back 5

1. Uses kinetic energy
2. Same as simple diffusion, but the diffusing substance is attached to a lipid-soluble membrane carrier protein or moves through a membrane channel.
3. EX: Movement of glucose and some ions into cells

Front 6

Osmosis

Back 6

1. Uses Kinetic energy
2. Simple diffusions of water through a selectively permeable membrane.
3. EX: Movement of water into and out of cells directly through the lipid phase of the membrane or via membrane pores (aquaporins).

Front 7

Filtration

Back 7

1. Is a passive process
2. Uses hydrostatic pressure
3. Movement of water and solutes through a semipermeable membrane (either through the plasma membrane or between cells) from a region of higher hydrostatic pressure to a region of lower hydrostatic pressure, that is, along a pressure gradient.
4. EX: Movement of water nutrients, and gases through a capillary wall; formation of kidney filtrate.

Front 8

Flick's First Law of Diffusion

Back 8

*Diffusion across cell membranes tends to equalize the concentrations on the two sides of the membrane.
*The diffusion rate across a membrane is proportional to the area of the membrane and to the difference in concentration of the diffusing substance on the two side of the membrane.
***J=DA9difference in C/C)
J= net rate of diffusion in moles or grams per unit time
D= diffusion coefficient of the diffusing solute in the membrane
A= The area of the membrane
*Difference in C= concentration difference across the membrane
X= thickness of the membrane

Front 9

The magnitude of the net flux is:

Back 9

Directly proportional to the difference in concentration across the membrane, the surface area of the membrane, and the membrane permeability coeffiecient.

Front 10

Diffusion Rate

Back 10

1. The great the difference in concentration (or electrochemical gradient) between the two sides of the membrane, the higher the rate of diffusion.
2. The higher the temperature, the faster the rate of diffusion.
3. the larger the membrane surface area, the faster the diffusion rate.
4. the shorter the distance, the faster the diffusion (the greater the distance that the solute had to travel, the slower the diffusion rate).
5. the smaller the mass of the solute, the faster its diffusion rate.

Front 11

Simple Diffusion Examples

Back 11

--Nonpolar and lipid-soluble substances.
*Oxygen
*Carbon Dioxide
*Fat soluble vitamins
*Alcohol
*Steroids
*Nitrogen
*Ammonia

Front 12

Facilitated Diffusion Examples

Back 12

--Best know example is glucose
--Insulin primarily affects the type of glucose transporters in the plasma membranes of muscle and adipose tissue.
--Insulin increases the number of glucose transporters in those sites.
*also other sugars, amino acids, and ions.

Front 13

Diffusion through channels

Back 13

-Transmembrane proteins create the channels.
-the channels are water filled.

Channels can be:
*Always open or gated
*Some have binding sites for molecules,
*Some are selective related to size or charge of molecule to pass.
(Leakage channels are always open)
(Gated channels can open and close due to binding of hormones, neurotransmitters or drugs)
--EX: Ligand gated channels
some open due to a change in the membrane's charge (voltage gated channels)

Front 14

Diffusion through Ion Channels

Back 14

*Integral proteins that form channels
1. Can be a single protein
2. More often, several proteins aggregate to form the channel.
3. Diameter is usually only slightly larger than the ion
(prevents larger molecules from passing through the channel)

Front 15

Leakage Channel

Back 15

1. Important to the generation of the resting membrane potential.
2. More potassium leakage channels than sodium leakage channels.
3. More potassium leaves the cell (loss of positive charges at inner surface of cell) compared to sodium entering cell.
4. Net result is negative charge at inner membrane surface.

Front 16

Gated Channels

Back 16

--Some function such that protein shape keeps the channel closes; a conformational change in the protein will then open the gate and allow ion flow. The channel alternates between open and closed positions.

Front 17

Osmosis

Back 17

1. Is polar covalent- movement of water across a semi-permeable membrane.
2. Water is polar but is able to cross plasma via gaps in the phospholipid tails and membrane proteins called aquaporins.
3. Net diffusion of water is osmosis.
4. The greater the solute concentration the lower the water concentration. 9the number of the solute particles is what is important, no the chemical nature of the solute)

Front 18

Hydrostatic Pressure

Back 18

Pressure exerted on a membrane by a liquid.

Front 19

Equilibrium

Back 19

Results when the hydrostatic and osmotic pressure balance

Front 20

Osmotic Pressure

Back 20

The force exerted on a membrane by a solution containing solute particles that cannot cross the membrane.

1. The higher the concentration of the solute particles that can't cross the membrane, the higher the osmotic pressure.

The technical definition is: the pressure that prevents water movement across a membrane that is permeable to water but not he solutes.

Front 21

Tonicity

Back 21

A measure of the solution's ability to change the volume of a cell by altering the water content.
--The key is sodium

Front 22

Isotonic

Back 22

1. the concentration of the solutes on both sides of the membrane are the same
2. There is no net flow of water
3. the cell stays the same size
Ex: 0.9% NaCl solution- normal saline.

Front 23

Osmolarity and Tonicity

Back 23

Osmolarity: Depend\ds only on the number of solutes in the solution.

Tonicity: Depends on solute concentration as well as:
a. Solute permeability across the plasma membrane.
b. affects cell size.
c. Clinically relevant

Front 24

Hypotonic

Back 24

A solution that has a lower than normal number of solutes;
Water moves into the cell and the cell increases in size (can actually rupture; lyse)
Ex: pure water

Front 25

Hypertonic

Back 25

The solution has a higher than normal solute concentration;
Water exits the cell and moves into the extracellular space.
The cell shrinks (crenation)
Ex: 2% NaCl