TRANSPORT THROUGH

PLASMA MEMBRANE

Discussion Matter

1. INTRODUCTION

2. BASIC MECHANISM OF TRANSPORT

3. PASSIVE TRANSPORT

4. SPECIAL TYPE OF PASSIVE TRANSPORT

5. ACTIVE TRANSPORT

6. SPECIAL TYPE OF ACTIVE TRANSPORT

7. MOLECULAR MOTORS

8. APPLIED PHYSIOLOGY

INTRODUCTION

- Through the transport mechanism across cell membrane:

+ The cell in the body must be supplied with essential substances.

+ Must get rid many unwanted substances.

- Essential: water, nutrients, electrolytes, etc.

- Unwanted: waste products, CO2, etc.

Who is the actors for this transport?

LIPID & PROTEIN

BASIC MECHANISM

PASSIVE TRANSPORT MECHANISM

ACTIVE TRANSPORT MECHANISM

PASSIVE TRANSPORT MECHANISM

High Concentration

Region

Low Concentration

Region

Passive transport?

- The transport of substances along the concentration gradient OR electrical gradient OR BOTH (electrochemical gradient).

- Higher concentration lower concentration

- Does not need energy

- Downhill movement/ diffusion.

2 Diffusion

1. Simple Diffusion

- Simple diffusion through lipid layer

- Simple diffusion through protein layer

2. Facilitated Diffusion

- Facilitated or carrier-mediated diffusion

Simple Diffusion Through Lipid Layer

- Directly proportional to the solubility of substances in lipids.

- Lipid layer of the cell membrane is permeable only to lipid soluble substances. (O2, CO2, alcohol)

Simple Diffusion Through Protein Layer

- Electrolytes diffuse through protein layer

- Protein layer is permeable to water-soluble substances.

1. Protein Channel/Ion Channel

- Pores

lined up by the integral protein molecules.

hypothetical pores.

Form the channel for diffusion of water.

Continuation

2. Type of Protein/Ion Channel

- The channel are named after the ions which diffuse through this channel.

- Ex: sodium channel, potassium channel, etc.

WHY?

The characteristic features of protein channel is selective permeability. Each

channel can permit only 1 type ion pass through it.

Continuation…

3. Regulation of the Channels

- Ungated channels -> continuously opened channels

- Gated channels -> closed channels

3 types -> voltage-gated channels

-> ligand-gated channels

-> mechanically gated channels

Continuation…

a. Voltage gated channels -> open whenever there is a change in the electrical potential. Ex: neuromuscular junction

b. Ligand gated channels -> open in the presence of some hormonal substances (ligands).

c. Mechanical gated channels -> opened by some mechanical factors. Ex: receptor cells.

Facilitated or Carrier-Mediated Diffusion

The type of diffusion by which the water soluble substances having larger molecules are transported through the cell membrane with the help of carrier protein.

Faster

For glucose and amino acid?

Factors Affecting Rate of Diffusion

Permeability of the Cell Membrane

Temperature

Concentration Gradient/Electrical Gradient of the Substances across the Cell Membrane

Solubility of the Substance

Thickness of the Cell Membrane

Size of the Molecules

Size of the Ions

Charge in the Ions

SPECIAL TYPE OF PASSIVE TRANSPORT

Bulk Flow -> diffusion of large quantity of substances : high pressure region low pressure region.

Ex: exchange gases across the respiratory membrane in lungs.

Filtration -> movement of water & solutes: high hydrostatic pressure area low hydrostatic area.

Osmosis -> movement of water/any other solvent: lower concentration area high concentration solute.

Continuation…

- Osmosis through semipermeable membrane.

- Osmotic Pressure -> pressure created by the solutes in a fluid.

- Reverse Osmotic Pressure -> process in which water/other solvent flows in reverse direction.

- Colloidal Osmotic Pressure -> osmotic pressure exerted by colloidal substances.

- Oncotic Pressure -> osmotic pressure exerted by colloidal substances (protein) of the plasma. It is about 25mm Hg.

2 type osmosis:

1. Endosmosis -> movement of water into the cell.

2. Exosmosis -> movement of water out the cell.

ACTIVE TRANSPORT

The movement of substances against the chemical/electrical/electrochemical gradient.

It is uphill transport.

It is required energy

Active Transport vs Facilitated Diffusion

Active Transport Facilitated Diffusion

Carrier protein need energy Carrier protein does not need energy

The substances are transported against the concentration/ electrical/ electrochemical gradient

The substances are transported along the concentration/ electrical/ electrochemical gradient

Carrier Protein of Active Transport

Uniport

- Carries only 1 substances in a single direction.

- Uniport pump.

Symport or Antiport

- Symport ->transport 2 different substances in the same direction.

- Antiport -> transport 2 different substances in opposite direction.

Mechanism of Active Transport

Substances:

Comes near the cell membrane

Combines with the carrier protein

Forms substances-proteins complex

Complex moves towards the inner surface of the cell membrane

Released from the carrier proteins

Same protein moves back to outer surface to transport another substances.

Substances Transported

Ionic Non-ionic

Sodium Potassium Calcium Hydrogen Chloride Iodide

Glucose Amino acid urea

2 Types Active Transport

Primary Active Transport

Secondary Active Transport

PRIMARY ACTIVE TRANSPORT

Type of transport mechanism in which the energy is liberated directly from the breakdown of ATP.

Sodium-Potassium Pump

Sodium 7potassium transported across the cell membrane.

Na+-K+ ATPase pump

Transport sodium: insideoutside cells

Transport potassium: outsideinside cells

Present in all cells of the body

Responsibility -> distribution of sodium & potassium ions across the cell membrane

-> development of resting membrane potential

Sodium-potassium pum

Transport of Calcium Ion

Actively transported from inside to outside of the cell by calcium pump.

Operated by a separate carrier protein.

Energy from ATP by the catalytic activity of ATPase.

Also present in some organelles. For move calcium into organelles.

Transport of Hydrogen Ions

Actively transported by hydrogen pump.

Energy from ATP.

The pump present in Stomach & Kidney.

SECONDARY ACTIVE TRANSPORT

Transport of substance with sodium ion.

When sodium is transported, another substance also transported. Either in same direction or opposite.

2 type: Cotransport & Counter transport

Sodium Cotransport

Substance is transported by symport along with sodium.

Movement energy from breakdown of ATP.

Released energy utilized form movement another substance.

Substances: glucose, amino acid, chloride, iodine, iron, urate.

Sodium cotransport

Sodium Counter Transport

Substances are transported in exchange for sodium ion by antiport.

Various counter transport:

+ sodium-calcium counter transport

+ sodium-hydrogen counter transport

+ other counter transport system

Sodium counter transport

SPECIAL TYPE OF ACTIVE TRANSPORT

Endocytosis

Exocytosis

transcytosis

Endocytosis

Mechanism by which macromolecules enter the cell.

It cannot pas the membrane by passive or active transport mechanism.

3 types:

pinocytosis-> cell drinking, by which macromolecules like bacteria and antigen are taken into cells.

Mechanism?

Phagocytosis-> Cell eating, particle larger than macromolecules are engulfed into the cells.

Larger bacteria, larger antigen, other larger foreign body.

Mechanism?

Receptor-mediated Endocytosis-> transport of macromolecules with the help of a receptor protein.

->clathrin: receptor protein in surface od cell membrane

-> receptor-coated pit: clathrin + pits cell membrane.

Mechanism?

Exocytosis

Process by which the substances are expelled out from the cell.

The substances are extruded from cell without passing through the cell membrane.

Role of Calcium? Calcium ion enter the cell and cause exocytes.

Mechanism?

Transcytosis

Extracellular macromolecule enters through 1 side of a cell, migrates across cytoplasm of the cell and exits through the other side.

Mechanism?

MOLECULAR MOTOR

Protein based molecular machine that perform intracellular movement in response to spesific stimuli.

Function:

-transport of synaptic vesicle containing neuro transmitter from the nerve cell body to synaptic terminal.

-role in cell division by pulling the chromosomes

Transport of viruses & toxins to the interior of the cell for its own detriment.

Type of molecular motor:

- Kinesin

- Dynein

- Myosin

APPLIED PHYSIOLOGY

Abnormalities of sudium-potassium pump:

Cause cardiac failure

Hypertension

Ion channel diseases (caused by gen mutation that encode the ion channels)

sodium channel diseases : muscle spasm, Liddle’s symdrome.

Potassium channel disease: heart disorder, inherited deafness, epileptic seizures in new born.

Chloride channel diseases: renal stone, cystic fibrosa