7 Membrane Structure and Function Flashcards
What is the key feature of the plasma membrane?
It is selectively permeable.
What is the key feature of the plasma membrane?
It is selectively permeable.
What are the physical properties of a phospholipid
It has a hydrophilic head and hydrophobic tail (it is amphipathic)
What does ‘amphipathic’ mean?
It has a hydrophilic and a hydrophobic region?
A phospholipid has both a hydrophilic and hydrophobic section. What does this mean it is?
Amphipathic.
What model describes how a phospholipid membrane is arranged?
The phospholipids and proteins are arranged according to the ‘fluid mosaic model’
How does the fluid mosaic model describe the phospholipid membrane?
It is bilayer of phospholipids interspersed with proteins. This layer is fluid i.e. dynamic.
Where are the proteins of the phospholipid membrane located?
These proteins are also amphipathic so they go all the way through the membrane.
How is the lipid bilayer held together?
By the hydrophobic tails of the phospholipids as they exert an attractive force ad thus prevent the layers form separating.
In what was is a phospholipid membrane dynamic?
It has fluidity in which adjacent phospholipids with places as do the occasional opposite phospholipids.
What can cause a decrease in membrane fluidity?
A decreased temperature.
How can the components of the phospholipid membrane affect its fluidity?
If the phospholipids have unsaturated hydrocarbon tails they will be kinked which prevents packing and thus makes it more fluid.
Alternately cholesterol can be added to adjust fluidity.
How does integrating cholesterol into a membrane affect membrane fluidity?
At moderate temperatures it reduces fluidity by reducing phospholipid movement.
However at low temperatures it prevents solidification by preventing packing.
Thus it acts as a buffer to cause intermediate fluidity.
Why is membrane fluidity important?
It allows the enzymes and other membrane proteins to more easily collide with their substrates etc.
What are the basic functions of transmembrane proteins?
Transport, Enzymes, Signal Transduction, Cell-Cell recognition, Joining adjacent cells; and attaching to the cytoskeleton and ECM.
What are the basic functions of transmembrane proteins?
Transport, Enzymes, Signal Transduction, Cell-Cell recognition, Joining adjacent cells; and attaching to the cytoskeleton and ECM
What are the physical properties of a phospholipid
It has a hydrophilic head and hydrophobic tail (it is amphipathic)
What does ‘amphipathic’ mean?
It has a hydrophilic and a hydrophobic region?
A phospholipid has both a hydrophilic and hydrophobic section. What does this mean it is?
Amphipathic.
What model describes how a phospholipid membrane is arranged?
The phospholipids and proteins are arranged according to the ‘fluid mosaic model’
How does the fluid mosaic model describe the phospholipid membrane?
It is bilayer of phospholipids interspersed with proteins. This layer is fluid i.e. dynamic.
Where are the proteins of the phospholipid membrane located?
These proteins are also amphipathic so they go all the way through the membrane.
In what way and where a membrane proteins and lipids modified?
The ER adds carbohydrates to some transmembrane proteins to make them glycoproteins.
However only in Golgi are carbohydrates added to lipids to form glycolipids. In the Golgi the carbohydrates of some glycoproteins are also modified.
In what was is a phospholipid membrane dynamic?
It has fluidity in which adjacent phospholipids with places as do the occasional opposite phospholipids.
What can cause a decrease in membrane fluidity?
A decreased temperature.
How can the components of the phospholipid membrane affect its fluidity?
If the phospholipids have unsaturated hydrocarbon tails they will be kinked which prevents packing and thus makes it more fluid.
Alternately cholesterol can be added to adjust fluidity.
How does integrating cholesterol into a membrane affect membrane fluidity?
At moderate temperatures it reduces fluidity by reducing phospholipid movement.
However at low temperatures it prevents solidification by preventing packing.
Thus it acts as a buffer to cause intermediate fluidity.
Why is membrane fluidity important?
It allows the enzymes and other membrane proteins to more easily collide with their substrates etc.
When might organism need special adaptions to maintain membrane fluidity?
If they are extremophiles i.e. living in especially hot or cold climates.
What are the basic functions of transmembrane proteins?
Transport, Enzymes, Signal Transduction, Cell-Cell recognition, Joining adjacent cells; and attaching to the cytoskeleton and ECM
What are the types of membrane protein?
Integral and Peripheral.
What are integral membrane proteins?
Proteins which penetrate into the hydrophobic interior of the phospholipid membrane.
Some are classed as ‘transmembrane proteins’ as they cross all the way through the membrane and out the other side.
What are peripheral membrane proteins?
Proteins which simply bond onto the surface of the membrane, often by attracting to integral proteins/
What is the typical composition of an integral membrane protein?
They have a hydrophobic region consisting of non polar amino acids. coiled into a-helices.
How can cell recognise each other?
Different species have different glycolipids (carbs+lipid) and different glycoproteins (carbs+proteins.)
These ‘membrane carbohydrates’ can be detected by receptors in the membranes of other cells allow them to distinguish each other?
How do red blood cells from different blood groups differ?
The ‘membrane carbohydrate’ glycoproteins in their plasma membranes have different carbohydrate parts and thus are recognised differently.
Where are membrane proteins and lipids manufactured?
In the ER.
In what way and where a membrane proteins and lipids modified?
The ER adds carbohydrates to some transmembrane proteins to make them glycoproteins.
However only in Golgi are carbohydrates added to lipids to form glycolipids. In the Golgi the carbohydrates of some glycoproteins are also modified.
How are transmembrane proteins embedded in the correct place of the phospholipid membrane?
As transmembrane proteins move through the Golgi they are constantly embedded in the membrane. Therefore when the vesicle buds off at the trans face they cross the membrane of the vesicle. Therefore when the vesicle fuses with the plasma membrane the protein is transmembrane.
How are non-transmembrane proteins embedded in the correct place?
When the vesicle buds off from the trans Golgi proteins etc. to go on the outside of the plasma membrane are placed in the centre of the vesicle whereas those to go on the intracellular side go on the outside.
Therefore when the vesicle fuses with the plasma membrane the proteins end up in the correct place.
What type of molecules are able to easily cross the phospholipid membrane? why?
Non-polar molecules such as carbon dioxide and hydrocarbons as they are hydrophobic and thus can easily dissolve in the lipid bilayer and cross the hydrophobic interior.
What type of molecules can’t easily cross the phospholipid membrane?
Polar molecules such as sugars and water as they are hydrophilic and thus can’t easily pass through the hydrophobic interior of the phospholipid membrane.
Also charged molecules i.e. ions.
What are the forms of transport through a phospholipid membrane?
Passive diffusion, facilitated diffusion and active transport.
How can polar and charged molecules pass through a phospholipid membrane?
By undergoing facilitated diffusion using a transport protein such as a channel protein to avoid the hydrophobic interior of the phospholipid membrane.
How is facilitated diffusion performed?
With transport proteins that span the membrane.
What is a subtype of transport protein?
A ‘channel protein’ with is basically acts as a tunnel.
How does water undergo facilitated diffusion through a phospholipid membrane?
Through aquaporins (a form of channel protein)
What provides the energy for molecules to undergo diffusion?
They have heat i.e. kinetic energy.
What factors influence the rate of diffusion?
- temperature
- concentration gradient
In what direction does diffusion occur?
High concentration to low concentration.
Why is diffusion called passive transport?
It does not require the expenditure of energy.
What drives osmosis?
A difference in FREE water molecules.
How does adding a solute affect the concentration of free water molecules?
It decreases the number because:
1) The solute takes up space and thus displaces the water
2) To be soluble the solute must be hydrophilic. This causes a clustering of non-free water molecules around the solute.
What is a solution that has a higher tonicity named?
Hypertonic.
What is a solution that has a lower tonicity named?
Hypotonic.
What is a solution that has the same tonicity named?
Isotonic
If diffusion is based on the difference in concentration, what gradient drive osmosis?
Tonicity
Define osmosis.
The movement of water through a SEMI-PERMEABLE membrane due to a difference in TONICITY.
Why does drinking sea water cause dehydration?
It has a high concentration of solutes (salt) and thus is hypertonic to the cells of the intestine causing them to lose water.
What is the typical tonicity of the environment a typical plant cell is in and why?
Hypotonic so that water enters and makes it turgid.
What is the typical tonicity of the environment a typical animal cell is in and why?
Isotonic so there is no net intake or release of water.
What happens if a plant cell is placed in a Hypotonic solution?
It goes turgid (which is normal)
What happens if a plant cell is placed in a isotonic solution?
It goes FLACCID (wilts)
What happens if a plant cell is placed in a hypertonic solution?
It undergoes plasmolysis and shrivels
What happens if an animal cell is placed in a Hypertonic solution?
It shrivels (not plasmolysis as this is the separation of cell wall and plasma membrane)
What happens if an animal cell is placed in a Hypotonic solution?
It gain water, swell and may undergo lysis (burst)
What is it called when a cell ruptures after begin placed in a hypotonic solution?
Cytolysis.
In what form of passive diffusion are polar etc. molecule able to cross the phospholipid membrane?
Facilitated diffusion
What structure enable facilitated diffusion?
Transport proteins
What are the types of transport proteins?
Channel proteins and carrier proteins
What are transport proteins?
Proteins that perform facilitate diffusion by binding with a solute then changing shape to move it through the plasma membrane.
How does carrier proteins work?
They bind to the solute on the extracellular side. This binding causes them to change shape so that the binding site is now in the cytoplasm where the solute is released.
What are channel proteins?
Proteins which enable facilitated diffusion by providing a hydrophilic channel through the otherwise hydrophobic interior of the plasma membrane.
How do transport proteins aid in the semipermeable nature of a plasma membrane?
Carrier proteins only change shape when they bind with a specific substrate.
Many channel proteins have gates (forming a ‘gate channel’) so that only a specific substrate will open them.
How does active transport differ fundamentally form passive transport?
It require energy and thus can move substrates against their concentration gradients.
How does a pump like the sodium-potassium pump work?
The desired solute binds to it. The terminal phosphate group of an ATP molecule also binds to it (ATP–>ADP+Pi) This added Phosphate group is of a high energy state so provides the energy to move the pump.
What does the active transport of ions across the plasma membrane do?
Creates an electric charge.
What is the general name of a pump which moves ions to create a charge?
An electrogenic pump.
What factors determine the direction of movement of an ion undergoing passive transport?
The ion has two gradients: a normal concentration gradient and a electrical gradient if there is a difference in charge due to electric forces pulling it over etc.
The combined gradient, known as the ELECTROCHEMICAL gradient, determines the direction of diffsion.
What are the forms of active transport?
Using a pump or a co-transporter.
What is co-transport?
A form of active transport (against concentration gradient) in which the passage of one substance down its concentration gradient provides the energy to move a different substance against its concentration gradient.
Does co-transport use energy?
Not necessarily, (even though it is active transport) but it often does because the substance which moves down its concentration gradient is often pumped back out of the cell to maintain such a gradient/
What is an example of co-transport?
Plants use pumps to move H+ ions out of the cell. This provides a gradient that allows a sucrose-H+ co-transporter to move sucrose against its concentration gradient into the cell.
In what forms does bulk transport across the plasma membrane occur? What do they mean?
Endocytosis: bulk movement in
Exocytosis: bulk movement out
Describe exocytosis.
Vesicles filled with substances fuse with the plasma membrane causing their contents to be released into the extracellular environment.
When is exocytosis used?
The removal of wastes and the secretion of substances i.e. from the Golgi or ER
What are the types of endocytosis?
Phagocytosis, Pinocytosis and receptor-mediated endocytosis.
Generally speaking, how is endocytosis performed?
By forming a vesicle around something outside the cell then bringing it in.
What is phagocytosis?
“cell-eating” In which a vesicle is formed to engulf a single large molecule etc.
Where is phagocytosis used?
To engulf food particles and also in the immune cell to capture infected cells.
Where are food particles etc. engulfed through phagocytosis processed?
In lysosomes i.e. starch –> glucose
Using correct terminology, describe phagocytosis.
Pseudopodia wrap around the substrate so that it is engulfed into a food vacuole (not vesicle)
What is pinocytosis?
“cell-drinking” In which a section of plasma membrane pinches in to form a vesicle that captures the fluid and thus solutes outside the cell.
How substrate specific are the various forms of endocytosis?
Pinocytosis is extremely non specific as it involves taking random “gulps”
Phagocytosis is more specific in the regard that it only operators in the presence of a large lump.
Receptor-mediated endocytosis is the most specific as it involves using receptors to target specific molecules.
Describe receptor-mediated endocytosis.
Receptors on the surface of the plasma membrane bind to specific ligands (substrates). This triggers the region to pinch in so that these receptors with bound ligands are now part of a vesicle.
Note: non-bound substrates could potentially be in the vesicle as well as there is no ‘gate’
How does cholesterol travel through the blood?
In particles called low-density lipoproteins (LDLs) which are lipids bound to proteins.
What is a ligand?
A substrate that binds to and triggers a receptor.
What is the name of a substance that binds to and triggers a receptor?
A ligand
What is the square root of 4 x 36?
12 (this is the 99th question)
When did the Vietnam war end?
1975 (this is the 100th question!)
What does ‘plasmolysis’ refer to?
The separation of the cell wall and plasma membrane due to a loss of water.
Note that it does not occur in animal cells as they do not have cell walls.
What does ‘cytolysis’ refer to?
The rupturing of a cell due to it being placed in hypotonic solution and thus water water rushing in.
