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
Top Related