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27 Cards in this Set
- Front
- Back
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What are the three functions of phospholipids in the cell membrane? |
•To allow lipid-soluble substances to enter and leave the cell •To prevent water-soluble substances entering and leaving the cell •To make the membrane flexible and self-sealing |
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What are the two ways that proteins are embedded in the phospholipid bilayer? |
•Extrinsic- only partially span the membrane and are there to give mechanical support or, in conjunction with glycolipids, act as receptors •Intrinsic- completely span the membrane. Some of these are protein channels which form water-filled tubes that allow ions to diffuse across. Others are carrier proteins that bind to molcules such as glucose then change shape to move them across the membrane |
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What is a glycolipid made up of? |
A coarbohydrate covalently bonded with a lipid |
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What are the three functions of cholesterol in the membrane and why is it suited for these? |
•Pulls together the fatty acid tails of the phospholipid molecules, reducing the lateral movement of them and other molecules while retaining flexibility •Make the membrane less fluid at high temperatures •Prevent leakage of water and dissolved ions from the cell as it is very hydrophobic |
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What are the 6 functions of proteins in plasma membranes? |
•To provide structural support •To act as channels transporting water-soluble substances across the membrane •To allow active transport across the membrane through carrier proteins •To form cell-surface receptors for identifying cells •To help cells adhere together •To act as receptors, e.g for hormones |
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What are the three functions of glycolipids in the membrane? |
•To help cells attatch to each other and so form tissues •To help maintain the stability of the membrane •To act as recognition sites- the carbohydrate portion extends outside the cell where it acts as a cell surface receptor for certain chemicals (this is how the ABO blood system works) |
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What are glycoproteins? |
Carbohydrate chains which are attatched to extrinsic proteins on the outside of the membrane to act as cell surface receptors for hormones and neurotransmitter |
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What are the three functions of glycoproteins in the cell membrane? |
•Act as recognition sites for hormones and neurotransmitters •Help cells to attch to each other and form tissues •Allow cells to recognize each other (e.g lymphocytes can recognize own cells) |
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What are 5 functions of membranes within cells? |
•To control the entry and exit of materials into each organelle •To seperate organelles from cytoplasm so specific metabolic reactions can take place within •To provide an internal transport system e.g ER •To isolate enzymes which might damage the cell e.g lysosomes •To provide surfaces on which reactions can occur e.g protein synthesis using ribosomes on rough E.R |
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Why do the majority of molecules not diffuse freely across the cell membrane? |
They might be: •Not lipid soluble- can't pass through phospholipid bilayer •To large to pass through the protein channels •Of the same charge as the protein channels so are repelled •Polar so cannot pass through the non-polar hydrophobic tails of the bilayer |
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Why is the cell membrane's arrangement known as the fluid-mosaic model? |
•Fluid- the individual phosphate molecules can move relative to each other so the membrane is flexible •Mosaic- the proteins embeddid in the membrane vary in size and shape like mosaic tiles |
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Define diffusion |
The net movement of molecules or ions from a region of high concentration to a region of low concentration until they are evenly distributed |
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Why does diffusion happen? |
Due to the kinetic energy of all particles, they move around randomly and are constantly bouncing off each other and the walls of their vessel. This means they will naturally spread out |
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How does active transport differ from passive transport (4 ways) |
•Metabolic energy in the form of ATP is needed •Substances are moved against their cencentration gradient •Carrier proteins acting as 'pumps' are used •The process is very selective and only specific substances are transported |
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Why can glucose not be transported from the ileum to the blood by diffusion only? |
As diffusion would only result in equal concentrations between the blood and the ileum, so active transport is required to transport all of the glucose |
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Why is there a greater concentration of glucose and amino acids in the ileum than the blood? |
Glucose and amino acids are constabtly being digested so their concentration is high in the ileum. In the blood, they are being removed by the cells for respiration constantly. |
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What are the two types of proteins which carry out facilitated diffusion? |
Protein channels and carrier proteins |
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How do protein channels work? |
They are filled with water and allow specific water-soluble ions to diffuse through. The ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens it to the other side. |
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How do carrier proteins work? |
When a molecule which is specific to the protein is present, it binds with the protein, causing it to change shape in such a way that the molecule is released to the outside of the membrane. |
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Define osmosis |
The passage of water from an area of higher water potential to an area of lower water potential through a selectively permeable membrane. |
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What is the water potential of a solution of pure water? |
0 kpa |
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Does adding a solute to water raise or lower the water potential? |
Lowers it- it makes it more negative |
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If the solution on the left of a membrane has a water potential of -20 kpa and on the right it is -30kpa, which way will the water move? |
To the right- as this is a region of lower water potential (so lower water concentration) |
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Define active transport |
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carroer proteins |
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Describe the process of active transport |
The carrier proteins spanning the molecule have binding sites which the molecule or ions to be transported binds to. Inside the membrane, ATP binds to the protein causing it to split into ADP and a phosphate, and the energy released causes the protein to change shape, releasing the molecule. Then the phosphate is released, changing the protein's shape back again. |
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Why is active transport needed to transport glucose and amino acids into the ileum? |
Diffusion will only result in equal concentrations at best across the membrane. This would mean that not all the available glucose would be absorbed. |
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Describe the mechanism of co-transport of glucose or amino acids in the ileum |
•The sodium-potassium pump actively transports sodium ions out of the epithelial cells into the blood, resulting in the lumen of the intestine having a much higher sodium ion concentration than the blood. •Sodium ions diffuse down this conc. gradient into the cell through co-transport carrier proteins in the cells membrane, carrying either amino acids or glucose with them •The glucose then diffuses into the blood using another type of protein carrier |
