Download - Plasma/Cell Membrane
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ABOUT AUTHOR
GUL MUNEERS/O ABDUL RAZZAQUE
BIOCHEMISTRY
BS PART IIUNIVERSITY OF SINDH
2K10/BCH/23
PROUD TO BE BIOCHEMIST
WE EXPLORE THE SECRETS OF LIFE
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PLASMA MEMBRANE
By GUL MUNEER
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What is plasma membrane?
Outermost layer (animal) Thickness is 5-8 nm Selectively permeable Serve as outer boundary Allows some substances to cross more easily than others Made of Phospholipids, proteins & conjugated molecules Separate and protect cell from external environment Provide connecting system b/w cell & its environment Also called cell membrane
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How could you define plasma membrane?
An outermost envelope surrounding the cell that separates and protects the cell from the external environment and provides a connecting system B/w the cell and its environment is called plasma membrane.
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STRUCTURE OF PLASMA
MEMBRANE
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Structure of the Plasma Membrane
The plasma membrane is composed of two layers of phospholipids back-to-back.
Phospholipids are lipids with a phosphate attached to them.
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Phospholipids Fatty acid tails
hydrophobic Phosphate group head
hydrophilic Arranged as a bilayer
Fatty acid
Phosphate
Phospholipids, glycolipids, cholesterol are amphipathic lipids containing hydrophobic and hydrophillic ends
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Phospholipid bilayer
polarhydrophilicheads
nonpolarhydrophobictails
polarhydrophilicheads
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Sandwitch model OR
Danielli- Davson Model
Proposed by Davson and Danielle in 1935“Cell membrane is lipid bilayer sandwitched
B/w two monomolecular protein layers”
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Fluid mosaic model
In 1972, S.J. Singer & G. Nicolson proposed Fluid
mosaic model.
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What is Fluid mosaic model?
“Cell membrane is lipid bilayer in which proteins are partially
embeded like Floating iceburgs in sea”
The fluid mosaic model describes the plasma membrane as a flexible boundary of a cell. The phospholipids move within
the membrane.
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OVERVIEW
Lipid molecules are present in a fluid state capable of rotating and moving.
The proteins occur as a ‘mosaic’ of discontinuous particles that penetrate deeply into and even through the lipid
sheet.Globular proteins are irregularly
embedded in the lipid bilayer.
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Membrane proteins
Membrane proteins are categorized into two groups:
1- Extrinsic (peripheral) membrane proteins2- Intrinsic (integral) membrane proteins
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Extrinsic membrane protein
Proteins loosely associated with membrane surface Located entirely outside of the lipid bilayer Either on the extracellular or cytoplasmic surface Also called Peripheral membrane proteins: Example: Cytochrome C of Mitochondria Cell surface identity marker (antigens)
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Intrinsic membrane proteins
Directly incorporated within the lipid bilayer Tightly bound to lipid bilayer Provides channel for the water-soluble substances Also called Integral membrane proteins Example: Transmembrane protein Transport proteins Channels, permeases (pumps)
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Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid
bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembraneproteins
Filaments ofcytoskeleton
Peripheralprotein
Glycoprotein
Phospholipids
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Proteins domains anchor molecule Within membrane
nonpolar amino acids
hydrophobic anchors protein
into membrane
On outer surfaces of membranepolar amino acids
hydrophilicextend into
extracellular fluid & into cytosol
Polar areasof protein
Nonpolar areas of protein
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NH2
H+
COOH
Cytoplasm
Retinalchromophore
Nonpolar(hydrophobic)a-helices in thecell membrane H+
Porin monomer
b-pleated sheetsBacterialoutermembrane
proton pump channel in photosynthetic bacteria
water channel in bacteria
function through conformational change = shape change
Examples
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Classes of amino acidsWhat do these amino acids have in
common?
nonpolar & hydrophobic
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Classes of amino acidsWhat do these amino acids have in
common?
polar & hydrophilic
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Association of membrane proteins with the lipid bilayer Transmembrane Proteins
1. A single α-helix2. Multiple α-helices3. Rolled up β-sheet
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4.α- helix (hydrophobic face) embedded in lipid bilayerthe.
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Cytoplasmic side
5. Protein covalently attaches lipid chain– fatty acid chain or prenyl group(cytoplasmic side)6. Protein attaches phosphatidylinositol viaan oligosaccharide linker7, 8. Noncovalent interaction betweenproteins
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Plasma Membrane : Membrane ProteinsFunctional classificationTransmembraneProteins
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Plasma Membrane : Membrane ProteinsFunctional classification Transmembrane Proteins
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Plasma Membrane : Membrane ProteinsFunctional classification Peripheral Proteins(only one side of the membrane)
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Chemical composition
Composed of Lipids, Proteins and Carbohydrates. Actual components differs from tissue to tissue.
Lipids of cell membrane are Phospholipids Glycolipids Sterol Cholesterol
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Why carbohydrates are not inserted into the biological membrane?
The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.
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Membrane carbohydrates Play a key role in cell-cell
recognitionability of a cell to distinguish one cell
from anotherAntigens (MHC)
important in organ & tissue development
basis for rejection of foreign cells by immune system
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Four major phospholipids found in mammalian plasma membraneThere are many ‘minor’ phospholipids exists, too.
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CholesterolUnique to plasma membraneStabilize membrane
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CholesterolUnique to plasma membraneStabilize membrane
Cholesterol
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Movement across the
Cell Membrane
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Many Functions of Membrane Proteins
Outside
Plasmamembrane
Inside
Transporter Cell surfacereceptor
Enzymeactivity
Cell surface identity marker
Attachment to thecytoskeletonCell adhesion
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Transport proteins allow needed substances or waste materials to move through the plasma membrane.
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Aquaporins Water moves rapidly into & out of
cells evidence that there were water
channels
1991 | 2003
Peter AgreJohn Hopkins
Roderick MacKinnonRockefeller
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Diffusion 2nd Law of Thermodynamics
governs biological systems universe tends towards disorder (entropy)
Diffusion movement
fromhighlowconcentration
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Diffusion Move from HIGH to LOW
concentration“passive transport”no energy needed
diffusion osmosis
movement of water
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Diffusion through phospholipid bilayer What molecules can get through directly?
fats & other lipids
inside cell
outside cell
lipid
salt
aa H2Osugar
NH3
What molecules can NOT get through directly?
polar molecules H2O
ions salts, ammonia
large molecules starches, proteins
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Channels through cell membrane Membrane becomes semi-
permeable with protein channels specific channels allow specific
material across cell membrane
inside cell
outside cell
sugaraaH2O
saltNH3
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The diffusion of water across a selectively permeable membrane is called osmosis.
Osmosis: Diffusion of WaterOsmosis: Diffusion of Water
Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.
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Managing water balance Cell survival depends on balancing
water uptake & loss
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Passive TransportPassive TransportWhen a cell uses no energy to move particles across a membrane passive transport occurs.
Concentration gradientPlasma
membrane
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Passive Transport by proteinsPassive Transport by proteins
Passive transport of materials across the membrane using transport proteins is called facilitated diffusion.
Plasma membrane
Channel proteins
Concentration gradient
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Facilitated Diffusion
Diffusion through protein channels channels move specific molecules across
cell membrane no energy needed
“The Bouncer”
open channel = fast transport
facilitated = with help
high
low
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Passive transport by proteinsPassive transport by proteins
The movement is with the concentration gradient, and requires no energy input from the cell.
Concentration gradient
Plasma membrane
Step 1 Step 2
Carrier proteins
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Active TransportActive Transport
Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell.
Plasma membrane
Concentration gradient
Carrier proteins
Cellular energy
Step 1 Step 2
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Active Transport Cells may need to move molecules against
concentration gradient shape change transports solute from
one side of membrane to other protein “pump” “costs” energy = ATP
“The Doorman”
conformational change
ATP
low
high
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Active transportMany models & mechanisms
ATP ATP
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Getting through cell membrane Passive Transport
Simple diffusion diffusion of nonpolar, hydrophobic molecules
lipids high low concentration gradient
Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel
high low concentration gradient Active transport
diffusion against concentration gradient low high
uses a protein pump requires ATP
ATP
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Transport summarysimplediffusion
facilitateddiffusion
activetransport
ATP
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How about large molecules? Moving large molecules into & out
of cell through vesicles & vacuoles Endocytosis ( 2 Types)
1. phagocytosis = “cellular eating”2. pinocytosis = “cellular drinking”
exocytosis
exocytosis
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ENDOCYTOSIS
- Cell membrane surrounds the substances by infolding in the form of vacuole or forms a vesicle.
Two Types of Endocytosis
Phagocytosis – engulf solid particles
Pinocytosis – engulf liquid material
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Transport of Large ParticlesTransport of Large Particles
Endocytosis is a process by which a cell surrounds and takes in material from its environment.
Endocytosis Exocytosis
Digestion
Nucleus
Wastes
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Transport of Large ParticlesTransport of Large Particles
Exocytosis is the expulsion or secretion of materials from a cell.
Endocytosis Exocytosis
Digestion
Nucleus
Wastes
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THE END
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THANK YOU