Plasma Membranes
- Created by: maddiecorfield
- Created on: 29-10-16 18:56
What is compartmentalisation?
Containing reactions in separate compartments of the cell so that the conditions can be specific to the reaction.
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What is the role of membranes?
Partially permeable barrier, site of chemical reactions, site for cell communication (cell signalling)
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Give examples of the chemical reactions that may take place on the plasma membrane.
Inner membrane of mitochondria for respiration, thylakoid membranes of grana in chloroplasts for photosynthesis
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How are membranes structured?
phospholipid bilayer, hydrophilic phosphate heads form inner and outer surface, shielding the hydrophobic fatty acid tails
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Why are membranes suited to an aqueous environment?
Cells normally live in aqueous environment, along with cytoplasm and organelles, hydrophilic heads can react with water
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Why is the fluid mosaic model named so?
Fluid represents freedom to move and membrane flexibility, mosaic as proteins are diff size and shapes embedded, similar to a mosaic. Model is a simple visual representation
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What do membranes contain?
phospholipids, glycolipids, glycoproteins, intrinsic proteins, extrinsic proteins, cholesterol
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What are channel proteins?
Intrinsic proteins, hydrophilic channel allows passive movement of polar molecules and ions down conc gradient
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How are channel proteins held into position?
by interactions between the hydrophobic core of the membrane and the hydrophobic R-groups on the outside of the proteins
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What are carrier proteins?
Passive and active moment into cells, often involving shape of protein changing
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What are glycoproteins?
Intrinsic proteins embedded in the plasma membrane with attached carbohydrate chains of varying lengths and shapes. Play a role in cell adhesion and are receptors.
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What are glycolipids?
Similar to glycoproteins, lipids with attached carbohydrate chains. Cell markers or antigens, can be recognised by cells in the immune system as self or non-self.
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What are extrinsic proteins?
Present on one side of bilayer, normally have hydrophillic R-groups on outer surfaces and react with polar heads of the phospholipids or with intrinsic proteins, can be present in either layer and some move between layers.
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How is cholesterol structured and what is its main function?
A lipid with a hydrophillic end and hydrophobic end, it regulates fluidity of membranes.
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How does cholesterol carry out its main function?
They're positioned between phospholipids, hydrophillic end interacting with the heads and hydrophobic end interacting with the tails, pulling them together. It adds stability to the membrane without making them too rigid, prevents crystallisation
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What happens if a membrane loses its structure?
they lose their ability to regulate movement in and out of the cell, and therefore cell processes will be disrupted. This affects their permeability, meaning more molecules can pass through them.
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What happens to a membrane with a temperature below 0?
decreased energy in the phospholipids, making the structure very rigid. The cold denatures channel/carrier proteins and makes the membrane more permeable. Ice crystals may pierce through the membrane.
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What happens to a membrane with a temperature between 0 and 45?
Phospholipids can move around more and aren't as tightly packed, so the membrane is partially permeable. As temp increases, phospholipid kinetic energy increases, therefore move around and increase permeability.
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What happens to a membrane with a temperature above 45?
phospholipid bilayer begins to melt (break down) which increases permeability. Water in the cell expands, putting pressure on the membrane. Channel and carrier proteins begin to denature.
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What are examples of organic solvents?
alcohols less polar than water, benzene that is non polar
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What do organic solvents do to the membrane?
dissolve cell membranes, disrupting cells. Solvent interacts with hydrophobic core of membrane (fatty acid tails) causing structure of membrane to change. Bilayer only arranges normal water,when the water is replaced, the bilayer is disrupted
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What do solvents with a low concentration do to the membrane?
insert into membrane and disrupt structure
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What do solvents with a high concentration do to the membrane?
dissolve membrane
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What is active transport?
requires metabolic energy (ATP) to transport molecules (active and bulk transport)
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What is passive transport?
no external energy, energy from natural motion of molecules is used for transport (diffusion and facilitated diffusion)
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What is diffusion?
Net, overall movement of particles (atoms, molecules and ions) from a region of high concentration to an area of low concentration
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When will diffusion stop?
until there is a concentration equilibrium between the two areas. Particles are still moving but the movement is equal in both directions.
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Why does diffusion happen?
Diffusion happens because particles in a gas or liquid have their own kinetic energy which is random, causing an unequal distribution of particles to eventually become equal.
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Why is diffusion over small distance fast and long distance slow?
When particles are moving, they constantly collide. This slows down the rate of diffusion,
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Why does diffusion rate explain why cells are microscopic?
Movement of particles within the cell relies on diffusion, and a large cell would lead to slow rates of diffusion – reactions would not get the substrates they need quickly enough or ATP would be supplied too slowly to energy-requiring processes.
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How does temperature affect diffusion?
higher the temperature, higher rate due to inc. Kinetic energy, movement at higher speeds.
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How does concentration difference affect diffusion?
greater difference in concentration between two areas, faster the rate of diffusion because the overall movement will be larger.
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What can pass through diffusion by a membrane?
if the membrane is complimentary to the particle – non polar (no charge)/lipid soluble molecules such as O2 can diffuse freely down a concentration gradient.
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Why can only those particles pass through diffusion by a membrane?
any particle that has a charge cannot interact with the hydrophobic core of the membrane, so can't easily pass through, apart from small polar molecules, such as water. These can diffuse through at a very slow rate,makes membranes partially permeable
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How does surface area affect diffusion across a membrane?
larger the exchange surface, the higher the rate of diffusion
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How does thickness of membrane affect diffusion across a membrane?
thinner the exchange surface, higher the rate of diffusion
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What is facilitated diffusion?
Polar molecules and ions passing the membrane through channel and carrier proteins
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What do channel proteins let through?
aqueous channel for ions and large polar molecules
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What do carrier proteins let through?
a conformational change in shape of protein has to occur to allow the molecule or ion to pass through.
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What does the rate of facilitated diffusion depend on?
temperature, concentration gradient, surface area, membrane thickness, number or channel/carrier proteins
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How do you create a concentration gradient?
particles must be moved up a concentration gradient faster than they move down it. This requires metabolic energy, ATP, from respiration.
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How is active transport carried out?
uses carrier proteins, (which are selective/ specific proteins to specific substances, and span both layers of phospholipid bilayer) that act as specific 'pumps.'
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What is bulk transport?
bulk or big molecules too big to go through proteins so must be moved in and out using vesicles - active
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What is phagocytosis?
Solids
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What is pinocytosis?
Liquids
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What is endocytosis?
cell surface membrane invaginates (bends inwards) when it comes into contact with the material. The membrane enfolds until the membrane fuses, forming a vesicle. Vesicle pinches and moves into cytoplasm, transferred to sites of further processing
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Give an example of endocytosis.
bacteria are engulfed by phagocytes and move towards lysosomes to be broken down.
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What is exocytosis?
reverse of endocytosis. Vesicles made by golgi body move towards and fuse with the cell surface membrane, the contents are then removed out of the cell.
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How is ATP needed in exocytosis and endocytosis?
ATP is needed to move vesicles along the cytoskeleton and for the changing of the membrane.
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What is osmosis?
the diffusion of water across a partially permeable membrane. It is a passive process and requires no metabolic energy.
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What is a solvent?
able to dissolve other substances
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What is a solute?
substance dissolved in a solvent.
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What is the concentration?
The amount of solute in a certain volume of aqueous solution is the concentration, which affects the water potential.
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What is water potential?
Water potential is the pressure exerted by water molecules as they collide with a membrane, which is affected by concentration.
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What are the units for water potential?
pascal (pa) kilopascals (kPa)
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What is pure waters conc and pa?
Pure water has the potential of 0kPa at standard temperature (25oC) and atmospheric pressure (100kPa).
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What happens to solute in water?
Solute in water lowers potential, therefore all solutions have negative water potential. The more concentrated the solution, the more negative the water potential will be.
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Where do molecules move in osmosis?
The molecules move from higher to lower as they are passive, and move to where there are less free water molecules.
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What happens when wo solutions with a different concentration are separated by a partially permeable membrane?
there will be a net movement of water from the area of high water potential (lower concentration to the lower water potential (higher concentration).
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What happens to animal cells if water potential of external solution is equal to cell solution?
normal cells, water is constantly entering and leaving cells, but at equal rates.
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What happens to animal cells if water potential of external solution is higher than cell solution?
aters moves in, increasing the hydrostatic pressure. Since the plasma membrane is so thin, it can't stretch and withstand pressure, so cytolysis occurs.
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What is cytolysis?
the break of the cell, where the contents of the cell, including haemoglobin are released.
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What happens to animal cells if water potential of external solution lower than cell solution?
Water will move out of cell into solution, so the volume of the cell will decrease and cell surface membrane will 'pucker'. Crenation occurs, haemoglobin will be more concentrated in the cell, giving it a darker appearance.
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How do multicellular organisms prevent cytolysis or crenation?
red blood cells found in aqueous solution plasma. This has the same water potential as the cell solution, known as isotonic.
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What is isotonic?
if the intracellular fluid has the same water potential as the extracellular fluid
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What happens to a plant cell if water potential of external solution equal to cell solution?
water is constantly entering and leaving the cells, but at equal rates
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What happens to a plant cell if water potential of external solution is higher than cell solution?
water moves into cells, increasing hydrostatic oressure, pushing membrane against rigid cell wall, increasing turgor pressure. As this increases, it resists entry of more water and the cell is said to be turgid
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What happens to a plant cell if water potential of external solution lower than cell solution?
water will move out of the cell into solution,and the volume of the cytoplasm will decrease, pulling the cell surface membrane away from the cell wall, meaning it is plasmolysed.
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Other cards in this set
Card 2
Front
What is the role of membranes?
Back
Partially permeable barrier, site of chemical reactions, site for cell communication (cell signalling)
Card 3
Front
Give examples of the chemical reactions that may take place on the plasma membrane.
Back
Card 4
Front
How are membranes structured?
Back
Card 5
Front
Why are membranes suited to an aqueous environment?
Back
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