13.transport across membrane

8/9/2019 13.Transport Across Membrane

1/5


2/5

6/3/2009

2

Fluid Mosaic

Model of the cell

membrane

CELL MEMBRANE TRANSPORT

Importance:

Allows entry of glucose for respiration to generateATP

Allows excretion of waste product

Allows secretion of enzymes

Maintain ionic balance

Use several methods namely

Passive transport: no ATP

Active transport: use ATP from cell

PASSIVE TRANSPORT

1. Simple diffusion

Net movement of particles from high conc to low

conc

Does not require ATP

Will continue until equilibrium is reached

Eg. of particles: O2, CO2, steroids

PASSIVE TRANSPORT

Factors affecting rate of diffusion

Surface area of membrane

Difference of concentration across the membrane

Thickness of membrane

Temperature

Size of particles

Simple Diffusion PASSIVE TRANSPORT

2. Facilitated diffusion

Diffusion assisted by transport protein

molecules embedded in membrane

Transport proteins has some properties of

enzyme

Down concentration gradient

No ATP required

Useful for ions and hydrophilic molecules

Eg: Na, Ca, K, Cl, glucose


3/5

6/3/2009

3

PASSIVE TRANSPORT

Transport proteins:

Channel protein

Water-filled pore in the membrane

For hydrophilic substances

Can open and close like gates

Carrier protein

Has binding sites for substances to bind

Can change shape

Useful for large polar molecules such as amino acidsand sugars

PASSIVE TRANSPORT

3. Osmosis

Net movement ofwater molecules from region

with high water potential to lower water

potential through a partially permeable

membrane

Move across via hydrophilic pores

Maintain tonicity: Hypotonic, Isotonic,

Hypertonic

Osmosis

Solution = Solvent (water) + Solute (NaCl)

Red Blood Cell (99.1% water and 0.9% NaCl)

A CB

100% water

0% NaCl

99.1% water

0.9% NaCl

90% water

10% NaCl

Hypotonic HypertonicIsotonic

Shrink and

crenateSwell and lysisNo net gain or loss

SOLUTE AND WATER POTENTIAL

Solute potential

The potential of a solution to gain water.

The lower the solute potential, the higher the

tendency to gain water

Water potential

The tendency for water molecules to leave the

solution by osmosis


4/5

6/3/2009

4

OSMOSIS Osmotic Pressure

Amount of hydrostatic pressure needed to

stop or prevent osmosis (movement of waterfrom high to low concentration areas).

OP is due to the presence of non-diffusiblesolute particles in the solution.

The greater number of solute particles in thesolution, the greater the osmotic pressure ofthat solution.

ACTIVE TRANSPORT

Movement of particles from against

concentration gradient by means of specific

transport protein (protein pumps) and

requires energy from cell.

Occurs in one direction. Importance:

Allows cell to take up more nutrients

Enables to excrete waste products

ACTIVE TRANSPORT

Evidence that ATP is required for active

transport:

AT only takes place in living, respiring cells

Factors that influence rate of respiration also

influence rate of active transport Large numbers of mitochondria

Cyanide can stop active transport

ACTIVE TRANSPORT

Faster than diffusion.

1. Substances bind to binding site.

2. Protein carrier changes shape.

3. Requires ATP.

4. Substances are released.

ACTIVE TRANSPORT

Protein pumps: pumps molecules against

concentration gradient

Sodium-potassium pump

Proton pumps in mitochondria

Ions uptake from soil into root cells

Uptake of sodium and glucose from nephron

tubule into surrounding cells


5/5

6/3/2009

5

Vesicular Transport Transport of large particles and macromolecules

across plasma membranes

Exocytosis: moves substance from the cell interiorto the extracellular space. Vesicles fuse withmembrane.

Endocytosis: enables large particles andmacromolecules to enter the cell Phagocytosis pseudopods engulf solids and bring them

into the cells interior Pinocytosis small amount of fluids is taken into cell

EXOCYTOSIS

ENDOCYTOSIS

13.transport across membrane

Documents