Plasma membrane Flashcards
What substances can pass through plasma membrane?
- Lipid soluble molecules
- Small uncharged molecules e.g. water
What is the base of the plasma membrane made up of?
Phospholipid bilayer - hydrophilic heads facing out, hydrophobic tails facing in
What substances cannot pass through plasma membrane?
- Large polar molecules
- Charged ions
What is interstitial fluid?
Fluid found between cells
How does water get through plasma membrane?
Osmosis across membrane and aquaporins (channel proteins)
What are integral proteins? + 2 examples
- Sit within the membrane
- Permanently attached to bilayer
- E.g. carrier proteins, Ion channels
Can integral protiens be isolated?
- Cannot be isolated without disrupting the bilayer e.g. via detergents
What are peripheral proteins?
- Temporarily associated with one side of membrane
- Attached either to integral proteins, polar heads or held in place by cytoskeleton
Can peripheral proteins be isolated?
- Can be isolated with polar solvents (without disrupting bilayer)
How does the ratio of saturated to unsaturated lipids in bilayer change fluidity?
More unsaturated lipids (kinked chains) - more fluid because lipids are less densely packed
More saturated lipids (straight chains) - less fluid and more viscous because lipids can be packed closely
Functions of membrane proteins
J - Junctions (connecting two cells together)
E - Enzymes (localise metabolic pathways)
T - Transport (facilitated diffusion and active transport)
R - Recognition (markers for cell identification)
A - Anchorage (Attachment to cell matrix and cytoskeleton)
T - Transduction (receptors for peptide hormones)
What are aquaporins?
Channel proteins which are lined with hydrophilic side chains to allow passage of water but not ions
Osmosis definition
Net movement of water particles from a region of low to high solute concentration across a semi-permeable membrane until equilibrium is reached.
Facilitated diffusion definition
Passive movement of molecules across a cell membrane via the help of membrane proteins
How do channel proteins transport particles?
- Contain tiny pores which only specific ions can pass through
- Can be gated to regulate passage of ions in response to stimuli
What makes channel proteins selective?
- Size of pores acts as a filter
- Binding site of amino acid sinde chains in lining are ion specific - only attract certain ions
What stimulus can cause channel proteins to be gated?
- Mechanical forces e.g. pressure
- Binding of small molecules to protein
- Changes in voltage across membrane
How do carrier proteins transport particles?
- Solute molecule binds to protein (specific)
- Protein undergoes conformational change
- Transfers molecle to other side of membrane
Active transport definition
Using energy to move moluecles against a concentration gradient
How does direct active transport work?
Energy (e.g. ATP) used to cause a conformational change in a protein and release molecule into area with higher concentration (e.g. carrier proteins)
How does indirect active transport work?
Ions are pumped out of cell using direct active transport to make a high concentration outside, then channel proteins use energy stored in gradent to let those ions in and pump other ions in with them.
Components of plasma membrane
- Phospholipid bilayer
- Proteins (peripheral and integral)
- Glycoproteins
- Glycolipids
- Cholesterol (only in animals)
What is the importance of membrane fluidity? (4 points)
- Enables diffusion
- Facilitates interaction between proteins
- Membranes can fuse - vital for vesicle formation
- Ensures even distribution of membrane between daughter cells during division
How does the cell membrane react to high temperatures?
- Fluidity increases, so chains have to become longer and more saturated to coutneract this
What is the basic structure of cholesterol?
- Hydroxyl group pounting outwards from cell membrane
- Hydrocarbon rings in middle
- Hydrocarbon tail at the bottom
Which parts of cholesterol are polar or not?
Hydroxyl group is polar
Hydrocarbon rings and tail are non polar
What is the function of cholesterol in membrane fluidity at different temperatures?
At high temperatures - Restrains movement of phospholipids, providing stability, decreasing fluidity and permeability
At low temperatures - Prevents tight packing of phospholipids, maintaining fluidity and preventing stiffening of membrane
What is an example of direct active transport in humans?
SODIUM-POTASSIUM PUMP - integral carrier protein
- Three sodium ions from inside the cell bind to pump
- Protein is phosphorylated by ATP and a conformational change occurs
- Na+ ions released out of cell
- Two potassium ions bind to pump
- Protein is dephosphorylated and conformational change occurs
- This causes K+ to be released into cell
High K+ concentration inside cell and high Na concentration outside - causes an electrochemical gradient
How are sodium-potassium pumps used in nerve cells?
Three Na+ ions pumped out for every 2 K+ ions pumped in, so inside of cell is negative.
Neuron cells stimulated, causing sodium ion channels to open and Na+ rush into cell down gradient
This causes charge to reverse across membrane which generates an electrical impulse
What is an example of indirect active transport in humans?
Sodium glucose cotransport proteins - found in epithelial cells of microvilli
- Sodium potassium pump actively pumps Na+ out of cell and K+ into cell
- Low concentration of Na+ in the cell so Na+ moves from lumen of small intestine into cell and carries glucose with it
- Higher glucose concentration in cell cause glucose to move into capillaries
Why are sodium glucose cotransport proteins so important in the kidneys?
Glucose temporarily moves into urine in nephron during ultrafiltration and it is moved back into blood by sodium glucose cotransporters to be used in respiration
What are the two types of cell adhesion in tissues?
1) Cell-cell - adhesions between neighboring cells
2) Cell-matrix - anchoring of a cell to EC matrix
What are cell adhesion molecules? (CAMs)
Proteins embedded in membranes which bind to other CAMs or matrix
What is cancer metastisis
The spreading of cancerous cells to tissues beyond primary tumor origins to form new secondary tumors
How do cancer cells affect cell adhesion molecules?
Cause CAMs within that cell to stop functioning so they break free and spread to other tissues in the body
