Cell membrane and transport

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  • Created by: lridgeway
  • Created on: 25-11-18 13:32
What are cell membranes made of?
phospholipids and proteins
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What happens to phospholipids in cell membranes?
Form bilayers, and as phospholipids have hydrophillic and hydrophobic ends they allow lipid soluble not water soluble substances through as the hydrophobic regions are on the inside of the membrane
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What is the model for cell membranes called and why?
fluid mosaic model because; individual molcues can move within a layer within relation to one another and proteins are embedded in bilayer in various shapes sizes and patterns
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What substances are lipid-soluble?
vitamin A, small molecules oxygen and carbon dioxide
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How do these travel through the cell membrane?
dissolve through the membrane
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What substances are water soluble?
glucose, polar molecules and ions
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How do these travel through the cell membrane?
pass through intrinsic protein/water filled channels
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What evidence is there for moving proteins in the cell membrane?
take cell membranes from two different animals red blood cells and put them together and over time they will move and mix
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What is glycocalyx and what does it do?
extra proteins or lipids attached to the membranes. some act as hormone receptors, some have roles in cell to cell recognition
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What are extrinsic proteins and what do they do?
proteins are on either side of the cell membrane but not all the way through. they provide structural support and act as cell recognition sites
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What are intrinsic proteins and what do they do?
proteins that extend across the entire membrane and act as carriers for water soluble substances
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What do channel proteins do?
allow active transport to occur as the proteins have a gap in them
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Define diffusion?
movement of substances from an area of high concentration to an area of low concentration
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What other things are there to know about diffusion?
passive and occurs through membrane. it happens due to random motion of particles
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What affects the rate of diffusion?
temperature, thickness of membrane(diffusion pathway), large concentration gradient, permeability, surface area and molecule size and nature
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What is the calculation for diffusion?
concentration gradient x surface area / diffusion pathway
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Define facilitated diffusion
movement along a concentration gradient assisted by a carrier protein
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What molecules use facilitated diffusion?
charged particles, ions and large lipid insoluble molecules
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Other facts about facilitated diffusion
uses intrinsic proteins, passive process (down conc grad) and it increases rate of diffusion without ATP
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What are some features of channel proteins?
pores lined with polar groups to allow charged ions through, hydrophillic so water soluble substances can pass through, only allow one specific ions through and some are gated so open and close to cells needs
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Explain how carrier proteins work
allow large polar molecules through as the molecule binds to binding site on the protein which forces the protein to change shape and releases the molecule across the membrane
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Explain co-transport
A passive process in which two molecules must be present at once in order for both of them to be transported across the membrane simultaneously, this works with a mechanism like a carrier protein
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give an example of co-transport
glucose and sodium into intestine
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Define active transport
net movement of molecules against a concentration gradient
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What does active transport require?
ATP
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4 facts about active transport
active process, uses carrier proteins, rate is limited by protein availability and uptake is affected by respiratory inhibitors due to reliance on ATP
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Explain how active transport works
molecule binds on outside of cell membrane and ATP on the inside. ATP hydrolyses and releases a phosphate changing the protein shape and releasing the molecule. Phosphate them recombines to from ATP again and the protein returns to its original shape
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Define exocytosis
process by which substances leave the cell
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Explain exocytosis
contents travel through cell in a vesicle and then attach to cell membrane. Contents is expelled into the outside of the cell. this requires energy
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Define and explain endocytosis
material engulfed by cell membrane extensions which surround it to make a vesicle. it is an active process and there is two types. the cell changing shape is called invagination
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Define phagocytosis
uptake of solids too large for other processes
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Define pinocytosis
uptake of liquids into cell
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Define osmosis
net movement of water molecules from a region of negative water potential to an area of more negative water potential across a partially permeable membrane
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Define water potential
measure of the free energy water molecules have (tendency to move) measured on kPa
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What is special about pure water?
no tendency to move so has a water potential of 0
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What happens to pure water if you add solutes?
solutes pull water with in inwards force as molecules of water become weakly bonded to the solute this decreases the water potential
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Define pressure potential
pressure exerted on the cell wall by the cells contents (plants only)
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Define solute potential
a measure of osmotic strength of a solution
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What is the water potential equation?
water potential = solute potential + pressure potential
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Define hypertonic solution
has lots of solutes and little water so low water potential and water leaves cell if a cell was placed in the solution
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Define isotonic solution
same water potential inside and outside cell so no net movement of water molecules
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Define hypotonic solution
has lots of water and little solutes do high water potential and water enters a cell if a cell is placed in the solution
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Explain osmosis in animal cells
no cell wall so rely on solute potential
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What happens when water enters an animal cell?
it swells and bursts called lysis
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What happens when water leaves an animal cell?
it shrivels and shrinks the plasma sticking to itself called crenation
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Explain how plant cells become turgid
cytoplasm pushed against a cell wall, pressure potential increases until it has equal and opposite force to one solute is having, no water can enter the cell
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Explain what incipient plasmolysis is
cytoplasm beginning too pull away from cell wall. the cell exerts no pressure so water potential equals solute potential meaning water potential can be found
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Explain how plant cells become plasmolysed
cytoplasm completely pulled away from cell wall which would cause a plant to wilt and there is no pressure potential so water potential is greater than the solute potential
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Other cards in this set

Card 2

Front

What happens to phospholipids in cell membranes?

Back

Form bilayers, and as phospholipids have hydrophillic and hydrophobic ends they allow lipid soluble not water soluble substances through as the hydrophobic regions are on the inside of the membrane

Card 3

Front

What is the model for cell membranes called and why?

Back

Preview of the front of card 3

Card 4

Front

What substances are lipid-soluble?

Back

Preview of the front of card 4

Card 5

Front

How do these travel through the cell membrane?

Back

Preview of the front of card 5
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