CHAPTER TWO

The Plasma MembraneBy

Bilal Javed

Learning ObjectivesLearning Objectives

1. Understand the role of the plasma membrane in– Structure – Identification– Membrane transport

• Understand the mechanisms of various membrane transport mechanisms- Diffusion - & osmosis- active transport - &bulk transport

1. Understand the role of the plasma membrane in– Structure – Identification– Membrane transport

• Understand the mechanisms of various membrane transport mechanisms- Diffusion - & osmosis- active transport - &bulk transport

Plasma membranePlasma membrane• Controls entry and exit of dissolved substances into

and out of cell• Comprises a phospholipid bilayer with embeded

proteins and glycoprotein's• Some of the proteins act as antigens helps in

identification (i.e. glycoprotein's). While others as protein channels.

• Too thin to be resolved with the light microscope• Apart from phospholipid there are Other lipids, eg.

Cholesterol • this is known as the “Fluid mosaic model”

• Controls entry and exit of dissolved substances into and out of cell

• Comprises a phospholipid bilayer with embeded proteins and glycoprotein's

• Some of the proteins act as antigens helps in identification (i.e. glycoprotein's). While others as protein channels.

• Too thin to be resolved with the light microscope• Apart from phospholipid there are Other lipids, eg.

Cholesterol • this is known as the “Fluid mosaic model”

Fluid Mosaic model of plasma membraneFluid Mosaic model of plasma membrane

Identification/ or Recognising cells:self and non-self

Identification/ or Recognising cells:self and non-self

• Antigens are displayed on the outer surface of the plasma membrane. They are usually made of proteins combined with carbohydrates (i.e. glycoproteins)

• Are Molecules that act as labels on the outside of cells, & serve the purpose of identification or recognition.

• For example: - Antigens from two different organisms/ or individual differ. - Immune system checks antigens

- If “self” antigens displayed: OK - If “non-self” antigens displayed:

DEFEND!

• Thus the immune system uses cells and chemicals to kill any “non-self” cells

• Antigens are displayed on the outer surface of the plasma membrane. They are usually made of proteins combined with carbohydrates (i.e. glycoproteins)

• Are Molecules that act as labels on the outside of cells, & serve the purpose of identification or recognition.

• For example: - Antigens from two different organisms/ or individual differ. - Immune system checks antigens

- If “self” antigens displayed: OK - If “non-self” antigens displayed:

DEFEND!

• Thus the immune system uses cells and chemicals to kill any “non-self” cells

Membrane transportMembrane transport

• Plasma membrane is semi-permeable– Only some dissolved substances can pass through

• Membrane transport process can be passive or active

• Passive membrane transport processes:– Don’t require energy– With concentration gradient

• Active membrane transport processes:– Requires energy– Against concentration gradient

• Plasma membrane is semi-permeable– Only some dissolved substances can pass through

• Membrane transport process can be passive or active

• Passive membrane transport processes:– Don’t require energy– With concentration gradient

• Active membrane transport processes:– Requires energy– Against concentration gradient

• Solute: type of molecule dissolved in another type of substance; that substance is called a…

• Solvent: substance that dissolves the solute

• Solute: type of molecule dissolved in another type of substance; that substance is called a…

• Solvent: substance that dissolves the solute

Understanding important terms solute and solvent...

Understanding important terms solute and solvent...

Some Examples Some Examples • Put one tablespoon of sugar

into a glass of water and stir. • Solute = sugar Solvent = water Or• Examples Fish use gills to

extract oxygen dissolved in seawater

• Solute = oxygen Solvent = water

What is Concentration Gradient ??What is Concentration Gradient ??

• Water and solutes move according to their concentration gradient.

• Everything naturally moves away from where it is concentrated and towards where it is less concentrated.

• This natural movement is called “diffusion”.• i.e. Concentration gradients form when there is a

difference in concentration between two places and Diffusion takes place until the concentration reaches “equilibrium”

• Water and solutes move according to their concentration gradient.

• Everything naturally moves away from where it is concentrated and towards where it is less concentrated.

• This natural movement is called “diffusion”.• i.e. Concentration gradients form when there is a

difference in concentration between two places and Diffusion takes place until the concentration reaches “equilibrium”

Diffusion Diffusion • Diffusion is the net movement of molecules from a region of high

concentration to a region of low concentration.

• It is random, passive movement. Which tries to equalize concentration and water solutes.

• Two types:- Simple: very small molecules such as O2, CO2 and H2O can pass freely through the lipid bilayer. Also, lipophilic molecules such as alcohol, anaesthetic and DDT- Facilitated: requires the assistance of a membrane

protein; “channel mediated” and “carrier mediated”. Types of substances transported include sugars and ions.

NB: both types require NO energy

• Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration.

• It is random, passive movement. Which tries to equalize concentration and water solutes.

• Two types:- Simple: very small molecules such as O2, CO2 and H2O can pass freely through the lipid bilayer. Also, lipophilic molecules such as alcohol, anaesthetic and DDT- Facilitated: requires the assistance of a membrane

protein; “channel mediated” and “carrier mediated”. Types of substances transported include sugars and ions.

NB: both types require NO energyhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Passive membrane transport - diffusion

Passive membrane transport - diffusion

• Simple diffusion • Net movement of a

substance from a region of high concentration to a region of low concentration

• Moves through phospholipids – no carrier/channel protein used

• Lipophilic compounds

• Simple diffusion • Net movement of a

substance from a region of high concentration to a region of low concentration

• Moves through phospholipids – no carrier/channel protein used

• Lipophilic compounds

Passive membrane transport – channel mediated diffusion

Passive membrane transport – channel mediated diffusion

• Facilitated Diffusion • Substances that cannot

pass through phospholipid bilayer easily– Hydrophilic– Size

• Pass through a protein channel– Always open

• Facilitated Diffusion • Substances that cannot

pass through phospholipid bilayer easily– Hydrophilic– Size

• Pass through a protein channel– Always open

Passive membrane transport – carrier mediated diffusion

Passive membrane transport – carrier mediated diffusion

• Facilitated diffusion• Substances that cannot

pass through phospholipid bilayer easily

• Pass through a protein carrier– Changes shape for

passage to occur

• Facilitated diffusion• Substances that cannot

pass through phospholipid bilayer easily

• Pass through a protein carrier– Changes shape for

passage to occur

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

OSMOSIS – A Special Diffusion Case !!!OSMOSIS – A Special Diffusion Case !!!

• Definition: The net movement of solvent from a region of low concentration of solute to a region of high concentration of solute through a partially-permeable membrane.

• NB: This is a movement of water through a semi-permeable membrane that blocks solutes from moving,

(i.e. Salts or sugars cannot get through the bilayer, but only water can).

• Definition: The net movement of solvent from a region of low concentration of solute to a region of high concentration of solute through a partially-permeable membrane.

• NB: This is a movement of water through a semi-permeable membrane that blocks solutes from moving,

(i.e. Salts or sugars cannot get through the bilayer, but only water can).

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Hypertonic Vs Hypotonic Hypertonic Vs Hypotonic • Hypertonic Solutions• Hypertonic: means higher

concentration of solutes.• Thus a cell placed in a

hypertonic environment will lose water and shrink (i.e. disfigure) .

• For example Plant cells plasmolyse when placed in very salty water and animal crenate

• Hypertonic Solutions• Hypertonic: means higher

concentration of solutes.• Thus a cell placed in a

hypertonic environment will lose water and shrink (i.e. disfigure) .

• For example Plant cells plasmolyse when placed in very salty water and animal crenate

• Hypotonic Solutions • Hypotonic means lower

solute concentration• thus a cell placed in

hypotonic environments if animal cells, can rupture, lyses or burst WHY? Because animal cells have no cell walls.

• However plant cells are protected from rupturing HOW? by their strong cell walls. i.e. turgid

• Hypotonic Solutions • Hypotonic means lower

solute concentration• thus a cell placed in

hypotonic environments if animal cells, can rupture, lyses or burst WHY? Because animal cells have no cell walls.

• However plant cells are protected from rupturing HOW? by their strong cell walls. i.e. turgid

Plant Cell Animal CellHypertonic

Condition: cells suspended in very salty water

Result: will lose water and shrink

Hypotonic

Condition: cells suspended in pure water (i.e. net flow of water molecules into cells)

Results: the cell will swell and burst.

plasmolysed crenated

turgid lysed

Isotonic SolutionsIsotonic Solutions

• Isotonic means balanced.• Cells in an isotonic

environment experience no net flow of water due to osmosis.

• The water flowing in is balanced by the water flowing out

• Isotonic means balanced.• Cells in an isotonic

environment experience no net flow of water due to osmosis.

• The water flowing in is balanced by the water flowing out

Active transportActive transport

• Net movement of dissolved substances into or out of cells “against” the concentration gradient.

• “Requires energy” (in the form of ATP)

• Also requires a different carrier protein for each different type of substance

• Net movement of dissolved substances into or out of cells “against” the concentration gradient.

• “Requires energy” (in the form of ATP)

• Also requires a different carrier protein for each different type of substance

Example of Active Transport...Example of Active Transport...

• Needs energy in the form of ATP

• Needs a different carrier protein for each different type of substance

Comparison Comparison

• This is for solid particles that are too large to move through the lipid bilayer or protein channels.

• It may involve the uptake of large molecules or small cells.• It may involve the output of large molecules that will function outside the

cell (secretion).• Includes: endocytosis: into cells

exocytosis: out of cells– “Secreted” if compound is made by cell for export– “Voided” if compound is a waste product

• This is for solid particles that are too large to move through the lipid bilayer or protein channels.

• It may involve the uptake of large molecules or small cells.• It may involve the output of large molecules that will function outside the

cell (secretion).• Includes: endocytosis: into cells

exocytosis: out of cells– “Secreted” if compound is made by cell for export– “Voided” if compound is a waste product

Bulk transportBulk transport

ExocytosisEndocytocis

There are two types of EndocytosisThere are two types of Endocytosis

• phagocytosis• Definition: from the

Greek language, phago = ‘eating’ and cyto= ‘cell’

• When the material being transported is a solid food particle.

• Not so common.

• phagocytosis• Definition: from the

Greek language, phago = ‘eating’ and cyto= ‘cell’

• When the material being transported is a solid food particle.

• Not so common.

• pinocytosis• Definition: from the

Greek language, pinus = ‘drinking’ and cyto= ‘cell’

• When the material is in the solution being transported into cell

• Most common in eukaryotic cells

• pinocytosis• Definition: from the

Greek language, pinus = ‘drinking’ and cyto= ‘cell’

• When the material is in the solution being transported into cell

• Most common in eukaryotic cells

Thank you