Which membrane model is the one now thought to be correct?
Fluid Mosaic model
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What are integral proteins?
Proteins embedded in the phospholipid bilayer
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What are peripheral proteins?
Proteins attached to the outer surface of a membrane
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What are glycoproteins?
Proteins with sugar (carbohydrate) units attached to the outer surface of the membrane
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Which part of a phospholipid is a) hydrophobic b) hydrophilic?
a) Hydrocarbon chains b) Phosphate head
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Are phospholipids hydrophobic or hydrophilic?
Neither! They are amphipathic
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They hydrocarbon chains are actually what...
Fatty acid chains
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What happens when phospholipids are mixed with water?
They arrange into bilayers with the hydrophobic tails facing inwards and the hydrophilic heads in contact with the water
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Why are these membranes very stable?
The attraction between the hydrophobic tails in the centre and between the hydrophilic heads with the water makes it stable
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Why is cholesterol able to fit between phospholipids in the membrane?
It is mainly hydrophobic but has a hydrophilic end like phospholipids so can fit between them
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What does cholesterol do to phospholipid molecules?
Restricts their movement
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What does cholesterol do to membranes?
Reduces the fluidity and the permeability of the membrane to hydrophilic particles in order to maintain concentration differences so diffusion can be restricted
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Name seven functions of membrane proteins
Cell - to - cell communication; cell adhesion; hormone binding sites; pumps for active transport; immobilised enzymes; electron transport; channels for passive transport
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What sort of protein is used for cell-to-cell communication?
Glycoproteins
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What type of protein is an insulin receptor?
Integral
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Give an example of an integral protein used for cell adhesion
Cadherin
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Give an example of a protein used for electron transport?
Cytochrome C
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What type of protein is Cytochrome C?
Peripheral
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Give the name of an immobilised enzyme?
Cytochrome oxidase
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What sort of protein is cytochrome oxidase?
Integral
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Give two functions of nicotinic acetylcholine receptors?
A receptor for a neurotransmitter and a channel for facilitated diffusion of sodium ions
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What sort of protein is nicotinic acetylcholine?
Integral
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What is the function of a calcium pump?
To transport calcium ions by active transport
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What sort of protein is a calcium pump?
Integral
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Name two ions that are hydrophilic
Hydrogen and sodium
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What is the main function of cell membranes?
To act as a barrier which ions and hydrophilic molecules cannot easily pass through
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Are integral proteins hydrophobic or hydrophilic?
Hydrophobic on part of their surface to embed them in the bilayers but the hydrophilic parts project out the phosphate heads
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Are peripheral proteins hydrophobic or hydrophilic?
Hydrophilic so are not embedded in the bilayer
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Is the attachment between peripheral proteins and integral proteins reversible?
Yes
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How else do peripheral proteins anchor themselves into the membrane?
A single hydrocarbon chain attaches to them and inserts into the membrane
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What sort of membranes have the highest protein percentage?
The membranes of chloroplasts and mitochondria
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What is the protein content of plasma membranes?
50%
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Give an example of a membrane with small protein percentages
Myelin sheath membranes around nerve fibres - 18%
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Do plant cells contain cholesterol?
No
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What is cholesterol?
A type of lipid - a steroid
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Exactly which part of a cholesterol molecule is hydrophilic?
Hydroxyl group
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What state of matter do hydrocarbon tails behave like?
Liquid
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What state of matter do phosphate heads behave like?
Solid
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Why is a membrane fluid?
Because the components are free to move
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How does cholesterol prevent phospholipids crystallising and behaving like a solid?
Disrupts the regular packing of hydrocarbon tails
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How does cholesterol help in the formation of vesicles during endocytosis?
Cholesterol can help membranes curve into a concave shape due to cholesterol's shape
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Other cards in this set
Card 2
Front
What are integral proteins?
Back
Proteins embedded in the phospholipid bilayer
Card 3
Front
What are peripheral proteins?
Back
Card 4
Front
What are glycoproteins?
Back
Card 5
Front
Which part of a phospholipid is a) hydrophobic b) hydrophilic?
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