Transport Across Cell Membranes Flashcards
What is cell surface membrane made from?
Phospholipid bilayer
What other attributes are within the cell surface membrane?
Intrinsic proteins Extrinsic proteins Glycoproteins Glycolipid Cholesterol Pore
What is the function of an intrinsic protein?
Helps carry substances across as they lay across the cell surface membrane
E.g glucose or ions
What do extrinsic proteins do?
Add more stability to enzymes
What does cholesterol do?
Increases stability and rigidity by binding to the phospholipid head
Why are the hydrophobic areas of the membrane useful?
Allows selectivity
Stops water loss
Allows movement of soluble or non-polar molecules
Vitamins
Enzymes
What are glycoproteins used for?
Receptor site for hormones
What are glycolipids used for?
Receptor sites for toxins
What does the phospholipid allow?
Small, non-polar or lipid soluble substances pass into or out of the cell
Eg oxygen and water
What term is used to describe the arrangement of the cell membrane?
Fluid-mosaic
Why is the term fluid mosaic used to describe the cell membrane?
Fluid - the individual molecule within the membrane is able to move
Mosaic - proteins ‘float’ in the phospholipid bilayer
What are possible functions of proteins in the cell membrane?
Carriers
Receptors
Enzymes
What is diffusion?
The net movement of molecules or ions from an area of high concentration to an area of lower concentration with no additional energy required
What kind of process is diffusion?
Passive
Once particles have diffused what happens?
They don’t spread out any more but they move around as they are in constant random motion
What are the two types of diffusion?
Simple
Facilitated
What is simple diffusion?
Just molecules spreading out
How does facilitated diffusion take place?
A molecule binds to a carrier protein in the membrane
They form a water filled pore or channel in the membrane
Allowing ions to diffuse across cell membrane
What is required in facilitated diffusion? What is not?
Channel proteins
No energy required
How do carrier proteins work?
They have a binding site for a specific solute and constantly flip between two states so the site is alternately open to opposite sides of the membrane
The substance will bind on the side with a high concentration and be released where it is at a low concentration
What is used to determine factors affecting rate of diffusion?
Fick’s Law
What is Fick’s law?
Large surface area X steep concentration gradient
——————————————
Short diffusion distance
What are protein channels?
Water-filled tubes to allow water soluble ions to diffuse across the membrane
What do carrier proteins do?
Bind to ions/molecules then change shape in order to move them across the membrane
What is osmosis?
The net movement of water molecules
From a higher water potential to a lower water potential
Through a partially permeable membrane
What are the stages of concentrations?
Pure
Diluted
Concentrated
What is the symbol of water potential?
Ψ
A trident
What is water potential?
The potential energy of water to move
What unit is used to show water potential? Why?
kPa (kilo pascals)
Pa - is the unit for pressure
The water particles hitting surface edges causes pressure
What is the water potential of pure water?
O kPa
What happens to water potential as it becomes more diluted and then more concentrated?
The water potential goes down
i.e -200kPa to -500kPa
Why does water potential decrease as a solution becomes diluted/concentrated?
Less water is hitting the sides therefore there is less pressure
Less water hits the sides as water hangs around solute molecules so they aren’t whizzing around - therefore fewer collisions against surfaces
What happens to an animal cell and a palisade cell in pure water?
Too much water moves in
Animal - the cell bursts called lysis
Palisade - fills but doesn’t burst because of the cell wall (turgid)
What happens to an animal cell and a palisade cell in an isotonic solution?
The same water potential inside and out therefore water moves evenly into and out of the cell
Animal and Palisade - stay the same size
What happens to an animal cell and a palisade cell in an concentrated salt solution?
There is a low water potential outside therefore water moves out of the cell
Animal - the cell shrivels called crenation
Palisade - the cell membrane pulls away from the cell wall called plasmolysis
What is active transport?
The net movement of molecules or ions
From an area of lower concentration to an area of higher concentration (against it’s gradient)
Using energy from the hydrolysis of ATP
Using carrier proteins
What factors affect active transport?
High temperature
High concentration of oxygen
A respiratory inhibitor ie cyanide
How does high temperature affect active transport?
It will denature the carrier proteins by changing the tertiary structure as it breaks the hydrogen bonds with high kinetic energy
Therefore less successful collisions
How does concentration of oxygen affect active transport?
More aerobic respiration can take place therefore releases more energy from mitochondria
This energy is used in active transport
How does a respiratory inhibitor affect active transport? Example?
Cyanide
It binds to cytochrome oxidase in the mitochondria with prevents respiration taking place
Therefore less energy produced for active transport
Why is it good for cells to have a large surface area for active transport?
More membrane and therefore more proteins available to bring substances across
What actually happens in active transport?
A molecule/ion binds to the receptor site on the carrier protein
On the inside of the cell ATP binds to the protein causing it to split into ADP + PO4
Therefore the protein changes shape and opens on the other side of the membrane
This carries to molecule/ion to other side
The PO4 is released causing the protein to go back to it’s original shape for the process to be repeated
What is metabolic energy provided from?
ATP
Where does co-transport take place?
Through the microvilli of the ileum
What happens in co-transport?
- Sodium moves out of the cell via active transport and potassium moves in using a protein carrier
- Sodium ion will diffuse into the cell (now low concentration) and sodium activates the carrier protein used for facilitated diffusion bringing in glucose with it
- The glucose will diffuse out of the cell because of the concentration gradient by facilitated diffusion
Why do sodium ions move into the cell after stage 1 of co-transport?
The sodium ion concentration will have decreased inside the cell and the sodium that moved out will have been taken away by the blood stream
Therefore a steep concentration gradient is created
Why is glucose moved by facilitated diffusion?
It moves with the concentration gradient
But glucose is to large to just diffuse through the cell membrane therefore needs a channel protein to aid it’s movement
What is the mechanism called that moves glucose and amino acids out of the ileum?
Sodium-Potassium pump
