Membranes - Spec

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  • Created by: rachel
  • Created on: 06-03-13 16:24
What are the roles of membranes at the surface of cells?
They separate cell content from the outside environment. Cell recognition & signalling. Regulating the transport of materials into or out of cells.
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What are the roles of membranes within cells?
Form organelles, isolate contents of an organelle & so metabolic pathways. They are site of attachment for enzymes & ribosomes & provide selective permeability - control what goes in & out. Also, creates concentration gradients or specific environmen
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What are plasma (cell surface) membranes described as?
Partially permeable barriers.
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Describe the fluid mosaic model of membrane structure.
A bilayer of phospholipid molecules forms main structure. Various proteins are studded in the bilayer. Some are partially embedded (extrinsic) & some completely span the membrane (intrinsic).
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Describe the roles of phospholipids.
Have hydrophobic head & fatty acid tail. Form a bilayer separating cell from outside. Fluid so components can move around freely. They act as a barrier, selecting what goes in & out of the cell. permeable (small & non polar mol.) impermeable (large).
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Describe the role of cholesterol in cell membranes.
Gives membranes stability by siting between fatty acid tails & therefore making the barrier more complete, preventing molecules like water & ions from passing through membrane.
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Describe what Glycolipids are and what their role is.
They are phosophlipid molecules that have a carbohydrate part attached. They are used for cell signalling, cell surface antigens & cell adhesion.
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Describe the role of proteins in cell membranes.
Channel proteins allow the movement of some substances, such as large molecules of sugar into and out of the cell as they cant travel directly through the cell surface membrane. Carrier proteins actively move substances across the cell surface membra
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Describe what Glycoproteins are.
They are protein molecules with a carbohydrate part attached.
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Describe the role of Glycoproteins in cell membranes.
Act as antigens. Enable identification of cells (self or non-self). Cell signalling. Act as receptors/binding sites to hormo. Specific shape thats complementary to communicating mol. that binds to receptor. Acts as receptors on trans. proteins - move
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What do glycoproteins do with cell adhesion & stabilising membranes.
Glycoproteins allow cell adhesion to hold cells together in a tissue. & Attach to water molecules to stabilise the membrane.
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Explain the effect of changing temperature on membrane structure & permeability.
> in temp means molecules have more kinetic energy. > in movement makes membrane leaky (mols that shouldn't do so move inn & out) Membrane structure is disrupted as phospholipid bilayer melts. Membrane & carrier proteins denatured - more permeable
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Explain the term cell signalling.
Process that leads to communication&coordination between cells. e.g. hormones binding to their receptors on cell surface membrane to trigger a response or reaction inside cell. Allows for cell recognition & the coordination of the action inside cell
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Explain the role of membrane bound receptors as sites where hormones & drugs can bind.
Hormones are used in cell signalling. target cells have a receptor which is complementary to hormone, meaning that it can bind to receptor cells, triggering desired internal response. Some drugs bind to receptor molecules on cells
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What is passive transport?
The transport of a molecule without using energy.
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What's the definition of Diffusion?
The net movement of molecules from a region of high concentration of the molecule to an area of low concentration of the molecule down a concentration gradient.
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What's the definition of facilitated diffusion?
Where proteins pay a key role in relating transport across membranes.
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What are the purposes of channel proteins?
They allow small polar molecules & ions to diffuse across membranes. Channel proteins form pores in the bilayer which are shaped to allow one type ion through. These are often gated (can be opened/closed).
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What are Aquaporins?
They are channel proteins that allow water through.
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Describe how carrier proteins are specific & how they transport by changing shape.
They are shaped to fit a specific molecule (like glucose). Once this fits in, the carrier changes shape to allow the molecule to slide through the other side.
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What's the definition of Active transport?
The movement of molecules/ions across membranes, using ATP to drive 'protein pumps' within the membrane. Moves molecules & ions against a concentration gradient.
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GIve a few examples of active transport.
(1) mineral ions being moved into root hair cells. (2) H+ions being moved out of companion cells. (3) mineral ions being moved across the endodermis. (4) movement of sucrose out of sieve tube at sink.
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What is endocytosis?
Active transport of large quantities of material into a cell forming a vesicle. Uses ATP.
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What is exocytosis?
Active transport of large quantities of material out of a cell from a vesicle. Uses ATP.
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Explain what is meant by osmosis in terms of water potential.
The movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
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What would happen to an animal cell which is surrounded by pure water with a high water potential?
The water would move into the cell & the cell would burst - haemolysed.
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What would happen to an animal cell surrounded by a solution with a negative water potential?
Water moves out & the cell is crenated.
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What would happen to a plant cell if it is surrounded by solution with a high water potential?
Water moves in & cell is turgid.
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What would happen to a plant cell surrounded by solution with a negative water potential.
Water moves out of the cell. Cell is plasmolysed.
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Card 2

Front

What are the roles of membranes within cells?

Back

Form organelles, isolate contents of an organelle & so metabolic pathways. They are site of attachment for enzymes & ribosomes & provide selective permeability - control what goes in & out. Also, creates concentration gradients or specific environmen

Card 3

Front

What are plasma (cell surface) membranes described as?

Back

Preview of the front of card 3

Card 4

Front

Describe the fluid mosaic model of membrane structure.

Back

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Card 5

Front

Describe the roles of phospholipids.

Back

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