OSMOSIS AND DIFUSSION OF THE CELL MEMBRANE

CHARACTERISTIC OF CELL MEMBRANE

Composed of phospholipid, cholesterol, proteins & chains of oligosaccharides

Range of thickness : 7.5 nm – 10 nm

Visible only in the electron microscope

STRUCTURE OF CELL MEMBRANE

FUNCTIONS OF CELL MEMBRANE

Selective Permeability• Size, charge, chemical properties

of atoms / molecules determine whether the success in getting through the membrane

Physical Barrier• Separates substances inside and

outside of the cell

Act As Communicator • Communication between cells & its

environment can occur because it contains receptors that recognize & respond to molecular signals

Allows Intercellular Connection• Establish a flexible boundary, protects

cellular contents and also supports cell structure

Transport Across The Cell

Membrane

Passive Transport

Simple Diffusion

Facilitated Diffusion Osmosis

Active Transport

Primary Secondar

y

Vesicle Transport

Endocytosis Exocytosis

SIMPLE AND FACILITATED DIFFUSION

Passive transport Goes down the concentration gradient From high concentration to low concentration

of solute Does not require energy (ATP)

SIMPLE DIFFUSION ACROSS A PLASMA MEMBRANE

Movement of small molecule through phospholipid bilayer.

Lipid soluble molecule due to hydrophobic characteristic of the bilayer.

FACILITATED DIFFUSION ACROSS A PLASMA MEMBRANE

Diffusion of large molecules Requires carrier protein Each carrier protein is specific for one

molecule Example – Potassium diffusion.

Facilitated Diffusion of Potassium ions through a Gated

K + Channel

OSMOSIS – HYPOTONIC

HYPERTONIC

ISOTONIC

ACTIVE TRANSPORT

The movement of substances across the plasma membrane against the concentration gradient

Molecules or ions move from a region of lower concentration to higher concentration

Requires the use of both carrier protein and cellular energy to transport molecules

Carrier protein involved in active transport are often called pumps

The most known pumps is Sodium-Potassium pumps

Active Transport

Primary

Na-K pumps

Proton pumps

Secondary

Na-glucose co-

transport

Na-Ca exchange

PRIMARY ACTIVE TRANSPORT

SODIUM-POTASSIUM PUMPPROTON PUMP

Secondary active transport

SODIUM-GLUCOSE CO- TRANSPORTER

SODIUM-CALCIUM EXCHANGER

VESICULAR TRANSPORT

A means for transport of large sized molecules (e.g. proteins) across cell membrane.

It represents a specialized function of cell membrane.

Requires energy.

2 types;

ENDOCYTOSIS

Divided into 3 parts:

1.Phagocytosis

-cell eating (uptake of large molecules)

2.Pinocytosis

-cell drinking (uptake of solutes)

3.Receptor-mediated

-cytoplasm membrane folds inwards

and form coated pits.

1.PHAGOCYTOSIS

2.PINOCYTOSIS

3.RECEPTOR-MEDIATED

EXOCYTOSISThe excretion of waste material from the cell to its

outer environment.

Large waste product which requires the formation of vesicles

Molecules excreted includes:

Cell DebrisWaste productsMembrane

proteins + lipids which are bound to become part of the actual membrane

EXOCYTOSIS

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