Transport Across The Cell Membrane Flashcards
How can solutes cross the cell membrane?
By diffusion, active transport, endocytosis and exocytosis
How can solvents cross the cell membrane?
By osmosis and filtration
What is diffusion?
The tendency of molecules or ions to move from an area of high concentration to an area of low concentration
What does the diffusion across the cell membrane depend on?
Molecular size, lipid solubility, charge of the substance
What are the main 2 types of diffusion across the cell membrane?
Simple and facilitated diffusion
Where does simple diffusion occur?
Through the lipid bilayer
Which substances can diffuse through the lipid bilayer of cell membrane?
Lipid-soluble substances, water, small uncharged water-soluble molecules
What are the factors that directly affect diffusion?
Lipid solubility, concentration gradient, surface area, temperature
What are the factors that inversely affect diffusion?
Thickness of the membrane, molecular weight
What is facilitated diffusion?
Passive movement of substances in the direction of their concentration which requires carrier proteins
How does facilitated diffusion work?
Molecules like glucose or amino acids bind to one of the carrier proteins, causing a change in the shape of the protein and this moves bound molecule from one side of the cell to the other
What is facilitated diffusion regulated by?
Hormones
What are types of carrier proteins?
Uniport, symport, antiport
What is uniport?
When the carrier transports only one molecule
What is symport?
When the carrier transports two molecules in the same direction
What is antiport?
When the carrier transports two molecules in opposite direction
What are the characters of facilitated diffusion?
Carrier proteins, specificity, competitive inhibition, saturation
What is meant by specificity in facilitated diffusion?
Each carrier is specific for one or few substances
What is meant by competitive inhibition in facilitated diffusion?
Similar molecules compete for the same carrier
What is meant by saturation in facilitated diffusion?
As the concentration of the substance increases, the rate of facilitated diffusion increases up to a maximum due to saturation of all carriers
What is primary active transport?
The transport of substances against their concentration or electrica gradients, requires specific carrier proteins and energy
What are examples of primary active transport?
Na-K pump, Ca 2+ pump, H+ pump
How does the Na+ - K+ pump work?
3 Na+ ions will bind to the carrier from inside, while 2 k+ ions will bind from outside. This will activate ATPase of carrier leading for hydrolysis of ATP liberating the energy. This energy causes the carriers pushing Na+ to outside and K+ to inside the cell
What can inhibit the activity of Na+ - K+ pump?
Ouabain and related digitalis glycosides, used in treatment of heart failure
What are the functions of Na+ - K+ pump?
Electrogenic pump ( creates more positivity outside the cell)
Controls the cell volume
What is secondary active transport?
It is the contransport of Na+ down its electrochemical gradient( created by the primary active transport) and another substance; glucose or amino acids by a carrier protein
What is osmosis?
Passive movement of water through a semipermeable membrane from an area of low solute area to an area of high solute area
What is osmotic pressure?
The pressure applied on the concentrated solution to prevent water movement from the diluted solution
What is filtration?
The passive movement of water through a porous membrane due to difference in hydrostatic pressure on the two sides of membrane
What are the factors that will affect filtration?
Pressure gradient, surface area of the membrane, membrane permeability
