Cell membranes

What’s a plasma membrane
A membrane at the surface of a cell
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Functions of a plasma membrane
Partially permeable barrier, cell recognition and cell communication
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Functions of membranes within cells
Compartmentalisation, form vesicles, site of chemical reactions and controlling what goes in and out of organelles
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What’s compartmentalisation
Separating of membrane-bound areas
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Describe the fluid mosaic model
The phospholipids are free to move within the layer
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Functions of the phospholipid bilayer
Centre of the bilayer is hydrophobic so doesn’t allow water soluble substances e.g. ions through
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Functions of cholesterol
Interacts with hydrophilic and hydrophobic components pulling them closer together so adding stability
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Functions of channel proteins
Hydrophilic channel for passive movement of polar molecules down a concentration gradient
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Functions of carrier proteins
Transport of molecules by both active transport and facilities diffusion
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What are glycoproteins
Intrinsic proteins with carbohydrate chains attached
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Functions of glycoproteins
Cell adhesion and receptors for cell signalling
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Description of cell signalling/cell communication
A chemical e.g. a hormone binds to the complimentary receptor which elects a respons from the cell
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Antigens - recognised by the immune system as self of non-self
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Examples of cell signalling
Drugs e.g. antihistamines and hormones e.g. glycagon binds to liver cells causing release of glucose
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Affect of temperature on membrane permability
Increasing the temperature - phospholipids gain kinetic energy do move more and the membrane becomes more fluid increasing permeability and proteins will also be denatured
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Affect of solvents on membrane permeability
Organic solvents -dissolve lipids in membrane and some non-polar molecules enter the membrane disrupting the structure therefore increasing permeability
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Diffusion definition
Net movement of particles from an area of higher concentration to and area of lower concentration down a contraction gradient
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Passive transport methods
Diffusion and facilitated diffusion
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Factors affecting simple diffusion (without a barrier)
Temperature - higher temp, particles have more kinetic energy so move faster increasing the rate of diffusion. Concentration difference - greater concentration gradient causes larger overall movement so increase rate of diffusion
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Factors affecting diffusion across membranes
Surface area - larger surface area means a faster rate of diffusion. Thickness of membrane - thinner the exchange surface the faster the rate of diffusion
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Facilitated diffusion definition
Diffusion across a membrane through channel proteins
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Facilitated diffusion involving carrier proteins
Molecules binds to the protein causing it to change shape
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Definition of selectively permeable
Protein channels and carrier proteins are specific to on molecule or ion
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Active transport definition
Movement of molecules from a region of lower concentration to a region of higher concentration up a concentration gradient
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Requirements for active transport
Energy (supplied by ATP) carrier proteins
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Process of active transport
1. Molecule binds to receptor in channel of carrier protein. 2. Inside the cell ATP binds to the carrier protein and is hydrolysed to ADP and phosphate. 3. Binding of the phosphate molecule causes the protein to change shape, releasing the molecule
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Bulk transport definition
A form of active transport for very big molecules like enzymes and hormones
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Transport of materials into cells
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Transport of solids by endocytosis
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Transport of liquids by endocytosis
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Process of endocytosis
1. Membrane invaginates (bends inwards). 2. Membrane enfolds the material until it fuses to for a vehicle
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Bulk transport of materials out of cells
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Process of exocytosis
1. Vesicles forming by the Golgi apparatus fuse with the cell surface membrane 2. The contents of the vehicle are released outside the cell
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Osmosis definition
Diffusion of water across a partially permeable membrane down a water potential gradient
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Water potential definition
Pressure exerted by water molecules as they collide with a membrane/container
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Measuring water potential
Measured in pascals, pure water has the highest possible water potential of 0 kPa
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Hydrostatic pressure definition
Pressure created by water in an enclosed system
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Definition of cytolysis
Bursting of an animal cell due to increased hydrostatic pressure
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Definition of crenation
Reduction in volume of a animal cell due to a decrease in hydrostatic pressure
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Definition of turgid
When water enters a plant cell by osmosis the me,brand is pushed against the cell wall (turgor pressure)
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Definition of plasmolysed
When water is lost from a plant cell by osmosis the volume of the cytoplasm is reduced, pulling the cell surface membrane away from the cell wall
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Other cards in this set

Card 2


Functions of a plasma membrane


Partially permeable barrier, cell recognition and cell communication

Card 3


Functions of membranes within cells


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Card 4


What’s compartmentalisation


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Card 5


Describe the fluid mosaic model


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