Transport across membranes Flashcards
Describe the fluid mosaic model of membranes.
TRIGGER WORDS:
move
describe shape of membrane
size
Fluid = phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape.
Mosaic: extrinsic & intrisic protiens of different sizes and shapes are embedded.
Explain the role cholesterol & glycolipids in membranes
Trigger words:
Cholestrol: -Certain molecule Found in what? Connect? reduces ?
how does this affect the bilayer?
Glycolipids:
- Cholesterol: steroid molecule in some plasma membranes; connects phospholipids & reduce fluidity to make bilayer more stable
- Glycolipids: cell signalling & cell recognition
Explain the function of entrinsic proteins in membranes
Clue:
- sites
- -
- together
- what is it involved in?
- Binding sites/receptiors e.g for hormones
- Antigen (glycoproteins)
- Bind cells together
- Involved in cell signalling
Explain the function of Intrinsic proteins in membranes
Trigger words:
- electron for..
- types of protein for..
-
- Electron carries (respiration/photosynthesis)
- Channel proteins (facilliated diffusion)
- Carrier proteins (facilliated diffusion/ active transport)
Explain the functions of membranes within cells,
TRIGGER
- Internal..
- What type of Permeable & why
- Provide what?
- Isolate from what? For what?
- Provide internal transport system.
- Selectively permeable to regulate passage of molecules into/out of organelles.
- Provide reaction surface.
- Isolate organelles from cytoplasm for specific metablic reactions.
Explain the functions of the cell-surface membrane
- Isolates what from extracelluar ..
- type of membrane to regulate..
- Involved in what?
- Isolates cytoplasm from extracelluar enviroment.
- Selectively permeable to regulate transport of substances.
- Involved in cell signalling/cell recognition
Name and explain 3 factors that affect membrane permeability.
use
- Temperature
- pH
- Use of solvent.
Give a reason why temperature that affect membrane permeability?
What type of energy
High temperature denatures membrane proteins/phospholipid as molecules have more kinetic energy & move further apart.
Give a reason why pH that affect membrane permeability?
Can Change what
Changes tertiary structure of membrane proteins
Give a reason why using a solvent that affect membrane permeability?
May dissolve the membrane.
Define osmosis]
Until what is reached
semi
Water diffuses across semi-permeables membranes from an area of high potential to an area of lower water potential until a dynamic equilibrium is reached
What is waterpotential? (Ψ)
Pressure
Degrees & kPa =
The more solute = the more
- Pressure created by water molecules measure in kPa
- Ψ of pure water is 25 degrees & 100 kPa: 0
- More solute = Ψ more negative
How does osmosis affect plant and animal cells?
Into the cell = ? = making it …
Plant:
Animal =
Out of the cell =
Plant:
Animal =
Osmosis INTO cell:
- Plant: protoplast swells = cell turgid
animal = lysis
Osmosis OUT of cell:
Plant: protplast skrinks = cell flaccid
animal = crenation
Define simple diffusion
What type of process?
Directly through..
Molecules or
Passive process requires no energy from ATP hydrolysis.
Net movement of molecules or ions directly through the bilayer from an area of ↑
concentration to an area of lower concentration (i.e down a concentration gradient)
Define facilitated diffusion
Through what.
How do molecules diffuse.
Net
Passive process.
The net movement of particles down a concentration gradient (i.e. from a region of high concentration to a region of lower concentration). Molecules diffuse through carrier proteins or channel proteins spanning across the membrane.
Explain how channel proteins work.
phobic or phillic channels
Bind to what?
one side
Hydrophillic channels bind to specific ions = one side of the protein closes & the other opens.
Explain how Carrier proteins work.
Bind to what type of molecule
Conformational does releases what?
Binds to complementary molecule = conformational change releases molecule on other side of membrane;
Used in:
Facilitated diffusion
Active transport
Name 5 factors that affect the rate of diffusion
- Temperature
- Diffusion distance
- Surface area
- Size of molecue
- Different in concentration gradient (how steep the concentration gradient is)
State Fick’s law.
Difference
something in X some / ….
Surface area x difference in concentration / diffusion distance
How are cells adapted to maximise the rate of transport across their membranes?
The types of proteins
State of membrane means what
- Many carrier/ channel proteins
- Folded membrane ↑ surface area
Explain the difference between the shape of a graph of concentration (x-axis) agaisnt rate (y-axis) for simple vs facilitated diffusion.
Simple diffusion: What is the line like?
Rate of diffusion?
As what?
Facilitated diffusionL
What is line like and what proteins are…
Simple diffusion: straight diagonal line; rate of diffusion ↑ proportionally as concentration ↑
Facilitated diffusion: straight diagonal line later levels off when all channel/carrier proteins are saturated.
Define active transport.
ATP Releases what PG that does what. Causing what
Active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.
The active movement of substances from a low concentration to a higher concentration (up their concentration gradient) with the use of energy in the form of ATP.
Compare and contrast active transport and facillitated diffusion
Similarity = 1
Differences = 2
- Both involve carrier proteins
- Active transports requries energy from ATP hydrolysis; facillitated diffusion is a passive process.
- Facilitated diffusion may also involve channel proteins.
Define co-transport
Same time.
Substances bind to what type of protein
Symport = Same Antiport = Opposite.
A process in membrane transport where two substances are both transported across a membrane at the same time either in the same direction or opposite directions.
Substances bind to complementary intrisic protien.
Symport: Transports substances in same direction
Antiport: Transport substances in opposite direction e.g. sodium potassium pump.
Explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine.
- Lower
blood - than
- Transport of what? From what to what?
Is coupled to what type of diffusion.
What type of concentration gradient
- Na+ concentration lower in epithelial cells & into bloodstream.
- Na+ concencertation lower in epithelial cells than lumen of gut.
- Transport of glucose/amino acids from lumen to epithetial cells is ‘coupled’ to facililitated diffusion of Na+ down electrochemical gradient.
Function of phospholiids in the membrane:
- Allow what?
- Prevent what?
- Make the membrane what?
- Allow lipid-soluble substances to enter and leave the cell
- Prevent water-soluble substances entering and leaving the cell
- make membrane flexible and self-sealing.
Selectively peremable membrane
A membrane that is permable to water molecule and a few other small molecules but not too large ones.
If ψ of external solution compared to cell solution is higher (less negative) in a plant cell
Net movement of water = enter cell
Protoplast = swells
Condition of cell = turgid
If ψ of external solution compared to cell solution is equal in a plant cell
Net movement of water = neither enters or leaves cell
Protoplast = no change
Condition of cell = incipient plasmolysis
If ψ of external solution compared to cell solution is lower (more negative) in a plant cell
Net movement of water = leaves cell
Protoplast = shrinks
Condition of cell = plasmolysed
The higher the Water potential (ψ)
The less negative
The lower the Water potential (ψ)
The more negative
What happens when a plant cell is placed in a solution with water potential lower than its own?
Water leaves by osmosis and the volume of water decreases
Incipient plasmolysis
Where the protoplast no longer presses on the cellulose cell wall.
Plasmolysed
Further loss of water will cause the cell contents to shrink further and the protoplast pull away from the cell wall
Turgid
Protoplast of the cell is kept pushed against the cell wall
Contrast (difference) Faciltated diffusion and simple diffusion
3.
- No ATP from respiration used in the process only energy used is build in kinestic energy.
- Facilitaed diffusion only occurs at channels on the membrane where there are special protein carrier molecules.
-
Explain why facilitated diffusion is a passive process.
It relies only on the inbuilt motion (kinetic energy) of the diffusing molecules.
- No external input of ATP
Glucose molecules are transported into cells through the pores in the proteins that span the phospholipid bilayer, Explain why they do not pass easily through the phospholipid bilayer.
Only lipid-solube substances diffuse across phospholipid bilayer easiler. Water soluble substances like glucose diffuse very slowlt.
List two changes to the structure of cell-surface membranes that would increase the rate of glucose transported into a cell.
- Large Surface area with microvilli
- it could have more proteins with pores that span the phospholipid bilayer
3 factors that affect the rate of diffusion.
Temperature.
Thickness of exchange surface
Concentration graident.
State which end of the phospjolipid molecule lies towards the inside of the cell-surface membrane
Hydrophobic tails
State through which molecule in the cell-surface membrane each of the following are likely to passs in order to get in or out of a cell.
A. a molecule that is soluble in lipids
B. A mineral ion
A. Phospholipid
B. Protein (Carrier or Channel)
State through which molecule in the cell-surface membrane each of the following are likely to passs in order to get in or out of a cell.
A. a molecule that is soluble in lipids
B. A mineral ion
A. Phospholipid
B. Protein (Carrier or Channel)
From knowledge of cell-surface membrane.Suggest two properties that a drug should possess if it is to a enter a cell rapidly.
- Lipid soluble
- Small in size
- Have no electric charge
From knowledge of cell-surface membrane. Suggest two properties that a drug should possess if it is to a enter a cell rapidly.
- Lipid soluble
- Small in size
- Have no electric charge
If ψ of external solution compared to cell solution is higher (less negative) in an animal cell.
Net movement of water enters cell
State of cell = swells and bursts
If ψ of external solution compared to cell solution is lower (more negative) in an animal cell
Net movement of water = neither enters nor leaves
State of cell = change
State of cell = shrinks.
The presence of many mitochondria is typical of cells that carry out active transport. Expain why this is so.
Active transport requires energy in the form of ATP. Mitochondira supply ATP in cells and therefore they are numerous in cells carrying out active transport.
In the production of urine, glucose is initially lost from the vlood but is then reabsorbed into the blood by cells in the kidneys. Explain why it is important that this reabsorption occurs by active transport rather than by diffusion.
How much glucose can diffusion absorb?
What happens to the other 50% lost from the body with active transport?
Diffusion, at best can only reabsorb 50% of the glucose lost from the blood.
The other 50% will be lost from the body. Active transport can absorb all the glucose leaving none to be lost in the body.
What does increasing the number of channel proteins and carrier proteins do to the transport across membrane
It increases the transports and makes it faster.
Process of Co-transport of a glucoe molecule.
- Actively transport out of .. by what? Where does this take place
- What does this do to concetration of Na+ in what? than the inside of?
- Where does Na+ diffuse into? through what type of protein carrier? in what?
- Where does the glucose/amino acids pass and how?
- Na+ are actively transported out of the epithelial cells, by the Sodium-potassium pump into the blood. This takes place in protein-carrier protein
- This maintains a much higher concentration of sodium ions in the lumen of the intestine than the inside of the epithelial cells.
- Na+ difuses into the epithetial cell down this concentration gradient through a co-transport protein in the cell-surface membrane,
- The glucose/amino acids pass into the blood plasma by facilitated diffusion using another type of carrier
State three ways in which the rate of movement across membranes can be increased.
By increasing the concentration gradient either side of it.
Increasing surface area
By increasing density of protein channels (carrier proteins)
Explain why the term ‘co-transport’ is used to describe the transport of glucose into cells.
because glucose molecules and Na+ ions mve into the cells coupled together
In each of the following events in the glucose co-transport system, state whether the movements are active or passive
a. Na+ ions move out of the epithetial cell
b. Na+ ions move into the epithelial cell
c. Glucose molecules move into epithelial cel
a. active
b. passive
c. passive
