Plasma Membranes

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  • Created by: Aleena
  • Created on: 16-04-19 13:21
Plasma Membrane?
Is a partially permeable barrier consisting of a phospholipid bilayer and various other proteins.It controls the entry & exit of molecules in and out of the cell
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Roles of Membrane?
1)separate cell contents from outside environment 2)segarate cell contents within cytoplasm(compartmentalisation) 3)Regulate transport of molecules in & out of cell 4)Cell recognition/signalling e.g.hormones
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example of compartmentalisation
Holding reactants of metabolic pathways(reactions) in place
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Features of the phospholipid bilayer?
the hydrophilic phosphate heads face outwards-so that they can interact with the aqueos cell/ outside environment.The inner core consists of hydrophobic fatty acid tails-that act as as barrier to many molecules e.g.large polar/ionic molecules
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What is fluid mosaic model?
It decribes the features of a plasma membrane.It is 'fluid' because the phospholipids are free to move within the bilayer and its 'mosaic' because the proteis/lipids embedded in the bilayer vary in shape/size/position-like tiles in mosaic
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Glycolipid?
Lipids with carbohydrate chains attatched.These are called cell markers/antigens-used by immune system cells to recognise foreign/non-foreign cells.
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Cholesterol?
A lipid with a hydrophobic & hydrophobic end and it regulates the fluidity of the membrane
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How does Cholesterol help maintain the stability of membrane?
Cholesterol binds to phosphate heads & fatty acid tails due to its hydrophobic & hydrophillic ends-which pulls the phospholipids together
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How does Cholesterol help maintain the flexibility of membrane?
As Cholesterol molecules bind to the phospholipids, the presence of the cholestrol between the fatty acid tails prevents the membranes becoming too solid by stopping the phospholipids from grouping too closely & crystallising
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What are the 2 types of membrane proteins?
Intrinsic and Extrinsic Proteins
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Intrinsic Proteins?
transmembrane proteins embedded through both layers of a membrane.They have amino acids with hydrophobic R-groups on their external surface.
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2 types of Intrinsic proteins?
Channel proteins & Carrier Proteins
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Channel Proteins
provide a hydrophilic channel that allows passive movement of polar molecules/ions down a concentration gradient through the membrane
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How are channel proteins held in place in the membrane?
the hydrophobic R groups on the outside of the protein interact with the hydrophobic core of the the membrane
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Roles of Glycoprotein?
1) Cell adhesion 2)Receptors for chemical signals-so when the chemical(e.g.hormones or drugs) binds to the glycoprotein, this stimulates a response from the cell
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An example of cell signalling?
When receptors(glycoproteins) on the nerve cell synapses bind to the neurotransmitters triggers/prevents an electrical impulse in the next neurone
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Carrier proteins
Important role in both passive & active transport into cells-this involves shape of protein changing
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Extrinsic (or Peripheral) Proteins
Proteins only present in 1 side of the bilayer & normally have hydrophilic R-groups on outside-so interact with phosphate heads of phospholipids or intrinsic proteins
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Types of Extrinsic Proteins?
Glycoproteins and Enzymes
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Glycoprotein?
Embedded in the plasma membrane with a carbohydrate chain attatched to it.
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Card 2

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Roles of Membrane?

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1)separate cell contents from outside environment 2)segarate cell contents within cytoplasm(compartmentalisation) 3)Regulate transport of molecules in & out of cell 4)Cell recognition/signalling e.g.hormones

Card 3

Front

example of compartmentalisation

Back

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Card 4

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Features of the phospholipid bilayer?

Back

Preview of the front of card 4

Card 5

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What is fluid mosaic model?

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