Dr Pradeep Kumar Professor, Physiology KGMU. The Plasma Membrane – a Phospholipid Bilayer.
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Transcript of Dr Pradeep Kumar Professor, Physiology KGMU. The Plasma Membrane – a Phospholipid Bilayer.
Components of Plasma Membrane
Lipids Proteins
1) Phospholipids
2) Cholesterol
3) Glycolipds
1) Peripheral (Associated)
2) Integral (Membrane Spanning)
3) Glycoproteins
~50% ~50%
(75%)
(20%)
(5%)
Isolate the cell’s contents from the external environment
Regulate traffic in and out of the cell
Communicate with other cells
The phospholipid bilayer
1. Impermeable to water-soluble and polar molecules, ions
2. Permeable to small and nonpolar molecules
3. Lipids oriented with polar heads facing out
hydrophobictails
hydrophilicheads
hydrophilicheads
extracellular fluid(watery environment)
cytoplasm(watery environment)
phospholipid
bilayer
Membranes are “fluid mosaics” with proteins embedded in or attached to the membrane
Proteins can move within the fluid lipid bilayer
extracellular fluid (outside)
cytoplasm (inside)
protein filaments
recognition protein receptor protein transport protein
binding site
phospholipid bilayer
phospholipid cholesterol
carbohydrate
1. Transport proteins
◦ regulate the movement of water-soluble molecules across the membrane
Ion Channel proteins, Pumps, Receptors
Carrier proteins, Enzymes, Cell adhesion Molecules
2. Receptor Proteins
◦ trigger cellular response when specific molecules bind to them
Nervous system
Endocrine system
Passive transport is a function of molecular size, lipid solubility, and size of the concentration gradient
1. Simple diffusion
1 A drop of dye is placed in water.
2 Dye molecules diffuse into the water; water molecules diffuse into the dye.
drop of dye
pure water
3 Both dye molecules and water molecules are evenly dispersed.
(a) isotonic solution (b) hypertonic solution (c) hypotonic solution
10 micrometers
equal movement of waterinto and out of cells
net water movement out of cells
net water movement into cells
ions
(b) facilitated diffusion through a channel
channelprotein
proteins formingpermanenthydrophilic channel
(extracellular fluid)
(cytoplasm)Carrier protein has binding site for molecule.
amino acids,sugars,
small proteins
(c) facilitated diffusion through a carrier
carrier protein
Molecule enters binding site.
Carrier protein changesshape, transporting moleculeacross membrane.
Carrier protein resumes original shape.
Energy-requiring transport
1. Active transport • Ion gradients and energy
production
2. Endocytosis
3. Exocytosis
(extracellular fluid)
Transport protein binds ATP and Ca2+.
Transport protein uses energy from ATP to change shape and moveion across membrane.
Transport protein resumes original shape.
(cytoplasm)
transport protein
ATP binding
site
recognitionsite
ATP
Ca2+
(extracellular fluid)
(cytoplasm)
food particle
particle enclosed in vesicle
phagocytosis
vesicle containing extracellular fluid
cell
pseudopod
pinocytosis
(a)
(b)
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