Structure and Function of Plasma membrane Flashcards
What are the 4 Major components of a Eukaryotic Cell?
Plasma Membrane
Nucleus
Membrane-Bound organell
Cytoskeleton
What does the Plasma membrane do?
Defines boundaries of the cell
Why must the Plasma membrane physically seperate the interior of cell from surrounding enviroment?
For regulation and to keep desirable substances in the cell
What are the 6 functions of The Plasma Membrane?
Barrier - entry/exit of substances Site Metabolic Activities - mitochondria Ion transport - nerve impulses Cell signalling - communication Cell shape - eg erythrocytes Cell-Cell interaction - adhesion molecules
What are the 3 identities of the Existence of Plasma membrane?
1) Cell swelling (hypotonic less concentrated) & Shrinking (hypertonic more concentrated)
2) Escape of Cell contents (if ruptured)
3) Compartments (most internal organelles, chemical activities)
Who and When discovered the PM?
Robertson in 60’s - Unit membrane
Who and What model discovered in the 70’s?
Singer and Nicholson - Fluid Mosaic Model
How was the Unit membrane found by Robertson?
Used Osmium to stane the membrane and found railroad track structure
Describe Robertsons Railroad track structure?
Trilaminer consisting of 2 Dark lines (outer inner layer) containing polar head group
Seperated by Central Light space containing hydrophobic tail of lipid molecules
What did Electron Microscopy studies find?
Cells are seperated by thin PM that retains cell contents
What does Fluid Mosaic Model consist of?
2 Fluid layers of lipid and Proteins within or on Lipids
Describe the Structure of the Plasma Membrane?
Lipid molecules 50% of mass, Asymmetrically distributed, Amphiphilic with hydrophilic head and hydrophobic tail
What are the 3 Common types of Membrane Lipid Fluids?
Phospholipids
Glycolipids
Sterols
Describe Structure of Phospholipids?
2 Hydrocarbon tails - fatty acids
Tails differ in length between 14-24 carbon
Cis-double bonds in 1 tail creating Kink
Why do Phospholipid Molecules Aggregate?
Keep Hydrophobic tails in the interior and Expose Hydrophilic heads to water
What are the 2 types of Aggregation styles?
Cone shaped
Cylinder shaped
Describe Cone shaped aggregation?
Lipid molecules in a single chain form micelles
Describe Cylinder shaped aggregation?
Phospholipid molecules (double tailed) form bilayer
What is a Glycerol Based Phospholipid called?
Phosphoglyceride
What are the 4 Main types of Phosphoglycerides in PM?
Phosphatidylcholine
Phosphatidylethanolamine
Phosphatidylserine (-)
Phosphatidylinositol
Why is Phosphatidylserine Negative?
Activates certain enzymes with negative charge during apoptosis so PM modify and express on outer of membrane so macrophages recognize and remove out of system
What is the Main type of Sphingolipid in PM?
Spingomyelin
Describe the Phospholipid structure?
Polar head (such as choline, ethanolamine, serine, inositol)
Lipid backbone
Glycerol or Spinogosine based
How are Glycolipids formed?
By the Addition of a CHO group to lipids
What is a Glycerol based glycolipid called?
Glycolipid
What is a Spingosine based glycolipid called?
Spingolipid
What is a combination of glycerol and sphinogosine based glycolipids called?
Glycosphingolipids
What are the 2 most Common Glycosphingolipids?
Cerebrosides
Gangliosides
Describe Function of Cerebrosides?
Act as Antigens
Describe Function of Gangliosides?
Determine ABO blood group system
Where are cerebrosides and gangliosides more prominent?
Nervous System
Describe Glycolipid Structure?
Carbohydrate head group
Lipid backbone
Glycerol or sphingobased
What do Sterols in the Eukaroytic PM store large amounts of?
Cholesterol
What does Sterols affect?
PM Fluidity, increases permeability barrier properties
What does Sterols Maintain?
Stability and Integrity of PM
What does the Lipid Bilayer depend on?
Composition (type of phospholipid)
and Temperature
Describe the Composition of the Lipid Bilayer?
- Shorter chain lengths (reduces tails interaction with opposition monolayer)
- Cis double bonds (produce kinks in hydrocarbon chains, make difficult to pack together)
Describe Temperature of Lipid Bilayer?
The movement decrease when the temperature drops and Increases as it rises
What kind of Movements are they of Phospholipid molecules in the membrane?
- Rotation its long axis
- Lateral diffusion by exchanging places with neighbouring molecules in same layer
- Transverse diffusion or flipflop to opposite layer
What are the 3 Capable kinds of movements of Phospholipid molecules in the Membrane?
Flexion
Rotation
Lateral Diffusion
What are the classes of Proteins?
Integral
Peripheral
Lipid Anchored
Where are Integral proteins?
Embedding within bilayer
What are the Regions within Integral Proteins?
Hydrophobic segments have affinity for interior, Hydrophilic regions extend outwards to aqeous phase
Where are Peripheral Proteins located?
Surface of PM linked to polar head of phospholipids, more hydrophilic lack hydrophobic segment
Where are Lipid Anchored Proteins?
Attached to lipid molecules in bilayer, hydrophilic on surface of membrane
What are Lipid Rafts?
Transient clusters of lipids and proteins within membrane
What do Lipid Rafts do?
Increase function efficiency - existence is controversial
What are the Functions of the Plasma Membrane?
Barrier and Transport and Signal detection
Describe the Barrier function of PM?
Allow nutrients to enter and keep out harmful
Defines boundaries of cell and compartments
Seperates organelles into discrete regions
Describe the Transport function of PM?
Controls the passage of substances in/out of cells, selective permeable, proteins in bilayer act as pore channels
What are the Main transport Proteins of the PM?
Transporter proteins
Ion Channel proteins
Describe Signal detection of the PM?
Cells receive info from enviroments via signals, chemical signals bind to specific receptor proteins
What does a Signal and Receptor create?
Molecular event inside
Give an example of protein for Liver and Muscle PM?
Insulin - insulin binds to liver and muscle cells to facilitate uptake of glucose
