Transport across cell membranes Flashcards
What is the cell surface membrane made up from?
Phospholipids
Proteins
Cholesterol
Glycolipids
Glycoproteins
How does a phospholipid bilayer form?
Hydrophilic phosphate heads
point to the outside of the cell surface membrane
Attracted to water either side
Hydrophobic fatty acid tails
point Into the centre of the cell membrane
Repealed by water either side
What is the function of the phospholipid bilayer?
Allow lipid soluble substances to move through the cell membrane
Prevent water soluble substances moving through the cell membrane
Make the membrane flexible and self sealing
What is the function of a protein that DOESN’T extend across the bilayer?
Give mechanical support to the membrane
Act as cell receptors
For cell identification
For hormones
Help cells adhere together
What is the function of a protein that DOES extend across the bilayer?
Act as channels for water soluble substances
Allow active transport across the membrane
Describe the properties of cholesterol
Occur within the phospholipid bilayer
Very hydrophobic
What is the function of cholesterol in the bilayer?
Reduce movement of phospholipids /
Make the membrane less fluid at high temperatures
By pulling the fatty acid tails together
Prevent leakage of water and dissolved ions from the cell
What is a glycolipid?
A carbohydrate covalently bonded to a lipid
Extends from the bilayer
What is the function of glycolipids in the bilayer?
Recognition sites
Maintain membrane stability
Help cells to adhere
To form tissues
What is a glycoprotein?
Carbohydrate chains attached to extrinsic proteins
On the outer cell surface of the membrane
What is the function of glycoproteins in the cell membrane?
Cell recognition sites
Hormone and neurotransmitter receptors
Help cells adhere
To form tissues
What is the function of membranes WITHIN a cell?
Control movement into and out of discrete organelles
Separate organelles from the cytoplasm
So metabolic reactions occur in the organelle
Provide an internal transport system
Isolate enzymes that may damage the cell
Provide surfaces for reactions to occur
What molecules CANNOT diffuse across the cell surface membrane?
Non lipid soluble molecules
Large molecules
Charged ions (same as the protein channel)
Polar molecules
Define the term fluid mosaic
Fluid: individual phospholipid molecules are not bonded and can move relative to one another
Giving the membrane a flexible structure constantly changing shape
Mosaic: proteins embedded in the bilayer vary in shape size and pattern
Like that of mosaic tiles
Define diffusion
The net movement of particles or ions
From a region of high concentration
To a region of lower concentration
Until even distribution is reached
Down a concentration gradient
Define facilitated diffusion
The net movement of particles or ions From a region of high concentration To a region of lower concentration Until even distribution is reached Down a concentration gradient
Using protein channels or carrier proteins
Describe how a protein channel functions
Opens in the presence of a specific ion
Ions bind to the protein
Causing a change in shape of the protein
That causes one side to open and the other side to close
Allowing passage
Describe how a carrier protein functions
Specific (large) molecules bind to the protein
Causing a change in the proteins shape
Realising the molecule into the membrane
Name three factors affecting the rate of diffusion
Concentration gradient
Area over which diffusion is occurring
Thickness of exchange surface
Temperature
Define passive
No ATP from respiration is used
Only the inbuilt kinetic energy of the molecules themselves
Define osmosis
The net movement of water molecules
From a region of high water potential
To a region of lower water potential
Through a partially permeable membrane
What factor lowers water potential?
Addition of solutes
Describe the effects of a higher water potential outside of animal cell
Water enters the cell by osmosis
The cell swells and eventually bursts
Releasing the contents of the cell
By breaking the bilayer
(Haemolysed in rbc only)
Describe the effects of a lower water potential outside of animal cell
Water exits the cell by osmosis
Causing the cell to shrink and shrivel
(Gives rbc a darker appearance
Due to concentrated Hb)
Making the cell plasmolysed
Describe the effects of a lower water potential outside of plant cell
Water exits the cell by osmosis
Causing the protoplast to shrink
And pull away from the cell wall
Making the cell plasmolysed
Describe the effects of a higher water potential outside of animal cell
Water enters the cell by osmosis
Causing the protoplast to swell
And push against the cell wall
Making the cell turgid
Why don’t plant cells burst when surrounded by a higher water potential?
The cell wall keeps the protoplast from bursting
Define active transport
The net movement of molecules or ions
Into or out of a cell
From a region of low concentration
To a region of higher concentration
Using ATP and carrier proteins
How is ATP used in active transport?
Directly moves molecules
Individually moves molecules using a concentration gradient set up by active transport
Co-transport
How does active transport differ from passive forms of transport?
ATP is needed
Substances move against the concentration gradient
Carrier protein molecules act as pumps
It’s a selective process
Describe direct active transport
Molecule or ion binds to the carrier proteins receptor sites
ATP binds to the protein
Causing it to split into ADP and a phosphate
Causing the protein to change shape
Releasing the molecule in the otherwise of the membrane
Releasing the phosphate molecule
-Reverting the protein to its original shape
Describe co-transport of sodium and potassium
Na+ is actively transported out of the epithelial cell into the the blood by the NaK pump
While K+ is actively transported into the epithelial cell from the blood
Maintaining a high concentration of Na+ in the lumen
Na+ ions (facilitated) diffuse from the lumen into the epithelial cell
Carrying amino acids or glucose
Glucose/Amino acids (facilitated) diffuse into the blood
