Biological Membranes Flashcards
What do Plasma Membranes do?
-Plasma Membranes keep cellular components inside of the cell
-form separate membrane bound areas in a cell(compartmentalisation)
- it is a site of cellular reactions and allows the cell to change shape.
What is compartmentalisation?
Formation of separate membrane bound areas in a cell.
What does compartmentalisation do?
Metabolism includes many different and often incompatible reactions. Compartmentalising reactions allows efficiency of reactions and prevents dangerous molecules from being released in the cell.
What components are in the membrane structure?
Phospholipids, Cholesterol, Channel proteins, Carrier proteins, Glycoproteins and Glycolipids.
What is the fluid mosaic model?
The structure of a plasma membrane where proteins occupy various positions in the membrane. It named because the phospholipids are free to movie in a layer and the proteins embedded in the membrane.
What do phospholipids do?
They create a phospholipid bilayer which acts a barrier to most substances
What are features of a cholesterol?
It has a hydrophilic end and hydrophobic end
What do cholesterol do?
Helps regulate fluidity as cholesterol’s hydrophilic ends interact with the phospholipid heads and hydrophobic end interacts with the tails which stop the phosopholipids from crystalising.
What are the features of a channel protein?
Hydrophilic channel which is held in position b interactions of the hydrophobic core and hydrophobic R groups.
What do channel proteins do?
A channel that allows passive movement(diffusion) of polar molecules(water) and ions down a concentration gradient.
What are features of carrier proteins?
The shape is always changing.
What do carrier proteins do?
Allows passive transport and active transport into cells.Allowing large molecules to be brought up and down the membrane.
What are the features of a glycoprotein?
It is embedded into cell surface attached by a carbohydrate chain.
What do glycoproteins do?
Contributes to cell adhesion( cells joining together to form tight junctions) and being a receptor for chemical signals.
How does cell signalling work?
The chemical binds to the receptor and brings out a response or sets off events inside the cell.
What are examples of cell signalling
Receptors for neurotransmitters-> acetylcholine at nerve synapses
Receptors for peptide hormones( insulin and glucagon) which affects the storage and intake by cells
What are features of glycolipids?
Lipids that are attached to cell membranes with carbohydrate chains.
What do glycolipids do?
They are cell markers or antigens and can be recognised as self/ non- self of the organism by cells of the immune system.
What are intrinsic proteins?
Amino acids with hydrophobic R groups on external surfaces which interact with the hydrophobic core which keeps it in place.
Where are intrinsic proteins located?
(integral proteins)Embedded through both layers of the membrane.
What are extrinsic proteins?
Hydrophobic R groups on their outer surfaces and interact with the polar heads of the polar heads of the phospholipids/intrinsic proteins.
Where are extrinsic proteins located?
(peripheral proteins) present on one side of the bilayer or some move between layers.
What is membrane fluidity used for?
-Diffusion of substances
-membranes to fuse
-cells to move and change shape
What are examples of Extrinsic proteins?
Cholesterol
What are examples of Intrinsic proteins?
-Carrier/channel proteins
-glycoproteins
-glycolipids
What effect does heat have on plasma membranes permeability?
If heat increases so does the kinetic energy of phospholipids. The membrane will be more fluid and loose its structure this will make it easier for particles to cross it.
What effect does heat have on channel/carrier proteins?
The proteins will denature. As these are used for transport membrane permeability will be increased.
What effect does water have on membranes?
Water helps with stability of phospholipid bilayer( as the hydrophilic heads turn towards the water)
What effect does less polar organic solvents have on membranes?
Less polar organic solvents will dissolve membranes( eg alcohol will dissolve bacteria membranes and kill them)
What is the average thickness of a plasma membrane?
5-10nm
What are the uses of membrane fluidity? (3)
-Diffusion of substances in and out
-Membranes to fuse
-Cells to move and change shape
What does heat do to plasma membranes structure?
Increases membrane permeability.
As the temperature increases the kinetic energy of the phospholipids increase. The membrane becomes more fluid + lose structure( able to break down completely)
What does heat do to carrier/channel proteins?
Will be denatured at high temperatures- membrane permeability will be effected.
What does water have on membrane structure?
Essential in forming phospholipid bilayer and creating stability. As the non polar tails are oriented away from water which produces hydrophobic core and hydrophilic heads turn towards water.
What effect does organic solvents less polar than water (eg. alcohol) on membranes?
They will dissolve membranes which will disrupt cells.(eg. alcohol is used in destroying bacteria to reduce infection)
What effect does pure/strong alcohol solutions do on membranes?
Destroy cells in body as they are toxic.
What effect does less concentrated solutions of alcohol(alcoholic drinks) have on membranes?
They do not dissolve membranes but they cause damage
What effect does non polar alcohol molecules have on plasma membrane?
The presence of the molecules between the phospholipids can disrupt the membranes.
What happens when the membrane is disrupted? + example
The membrane becomes more fluid and more permeable. Some cells need a intact membrane to function- neurons transmitting nerve impulses can no longer be transmitted as normal.
What effect does temperature below freezing have on membranes?
The phospholipids do not move and are tightly packed together so the membrane is less permeable and rigid.
Ice crystals are able to pierce the membrane and slightly increase permeability
What state is the membrane at temperatures of 0- 45 degrees Celsius ?
Phospholipids are able to move and are not packed which makes the membrane permeable
What state is the membrane at temperatures above 45 degrees Celsius?
-Phospholipids start to melt
-Water inside the cell puts pressure on membranes
-proteins denature
All these increase permeability
Definition of Diffusion?
The net movement of particles from a high concentration to a low concentration.
What is Fick’s Law?
Rate of diffusion is proportional to:
(SA x conc. diff.) / length of diffusion path
What are examples of small non polar molecules and how do they diffuse across the membrane?
Eg. oxygen and carbon dioxide
They rapidly diffuse across a membrane
What are examples of small polar molecules and how do they diffuse across the membrane?
Eg. Water and Urea
They diffuse slowly across the membrane
What molecules are unlikely to diffuse across a membrane?
Charged ions ( eg. sodium and chloride)
What molecules use simple diffusion to pass through the membrane?
Small non-polar molecules.
What are examples of simple diffusion?
Carbon dioxide is small enough to diffuse through the phospholipids and lipid based molecules can pass through hydrophobic reigons.
What molecules use facilitated diffusion?
Polar or large molecules
What is facilitated diffusion?
When carrier/channel proteins help polar/very large molecules diffuse across a membrane.
What are Channel proteins used for in facilitated diffusion?
To help water(osmosis) and ions transport across membrane. Aquaporins(channel protein) help water transport
What are carrier proteins used for in facilitated diffusion?
To help bigger molecules( eg glucose) transport across cell
What effects the rate of facilitated diffusion?
-Temperature
-Number of channel Proteins present
-Concentration gradient
-membrane thickeness and area
How does temperature effect facilitated diffusion?
higher temperature-> higher rate of diffusion
Does concentration gradient effect facilitated diffusion
Yes a greater concentration gradient means a more higher rate of diffusion
How does membrane thickness and area effect facilitated diffusion?
Larger surface area means a faster rate of diffusion. Thicker means a slower rate of diffusion.
Does more channel proteins present increase facilitated diffusion?
Yes
Why is energy needed in active transport?
So molecules and ions can move against the concentration gradient.
What are examples of active transport? (4)
-uptake of glucose and amino acids in small intestine
-root absorption of mineral ions
-exchange of magnesium and sodium ions in neurons and muscle cells
-Excretion of hydrogen ions and urea in kidneys
What factors effect active transport?
-Surface area of membrane
-concentration of carrier proteins
Process of active transport?
-Molecule binds to receptors on carrier protein
-ATP binds to carrier protein on inside and is hydrolysed
-Protein changes shape and molecule is released inside
What is bulk transport used for?
Large substances to moved across cell membranes.
What are the two types of bulk transport?
Endocytosis- transport of material into the cell
exocytosis-transport out of the cell
What is phagocytosis?
Engulfing of solid materials into vesicles and vacuoles.
What is pinocytosis?
The uptake of liquids into pinocytic vesicles for absorbing extracellular liquid
What is the process of Endocytosis?
-The cell surface membrane invaginates when in contact with the material.
-The membrane enfolds the material and membrane fuses to form a vesicle
-The vesicle moves within the membrane to move into the cytoplasm
What is exocytosis used for?
When toxins need to be exerted from the cell.
Definition of osmosis?
A net movement of solvent from a region of high concentration to an region of low concentration across a partially permeable membrane
What is the definition of water potential?
The tendency of water molecules in a system to move from one area to another by osmosis.
What way do water molecules move ?
High water potential to low water potential(more negative)
What is the unit of water potential?
kPa ( kilopascals)
What is the water potential of pure water?
0 kPa
Is solute potential a negative or positive value?
Negative.
Is pressure potential a negative or positive value?
Positive.
What effects water potential?
Pressure potential- the amount of pressure applied
Solute potential-Water molecules attach to the solute where there are less water molecules to diffuse.
What is the equation for water potential?
water potential=solute potential + pressure potential
What is osmotic concentration/potential?
The amount of dissolved solutes in a solution.
What does a high osmotic concentration mean?
A concentrated solution
What does a low osmotic concentration mean?
A dilute solution.
What is an isotonic solution?
Have the same osmotic concentration as cytoplasm of cell
What is a hypotonic solution?
Have a high osmotic concentration outside the cell than the cytoplasm
What is a hypertonic solution?
Have lower osmotic concentration outside than in cytoplasm of the cell.
What effect does a isotonic solution have a on a animal cell?
Cell does not change
What effect does a hypotonic solution have a on a animal cell?
Cell will shrink
What effect does a hypertonic solution have a on a animal cell?
Cell will burst
Why dont carrier proteins need ATP?
The particles have their own kinetic energy.
