Chapter 4(Passive transport) Flashcards
What is passive transport? Energy required?
When molecules move across the membrane down their chemical or electrochemical gradients. No energy is required.
Three types of passive transport.
Simple diffusion, facilitated diffusion and diffusion through ion channels.
What is simple diffusion based on?
Random thermal motion
A population of molecules always does what?
Moves down its’ concentration gradient.
Rate of simple diffusion depends on what?
magnitude of the driving force, membrane surface area, permeability of the membrane.
What influences the permeability of a cell? Which is the strongest?
Lipid solubility of the diffusing substance, size and shape of diffusing molecules, temperature, membrane thickness. Lipid solubility.
What are most substances in the body? Name some.
Hydrophillic, do not penetrate lipid layers easily. Fatty acids, steroid hormones, thyroid hormones, oxygen, carbon dioxide, and fat soluble vitamins.
What is facilitated diffusion?
When molecules cross by way of transport proteins in the membrane.
What is a carrier in facilitated diffusion?
A transmembrane protein that binds molecules on one side of a membrane and transports them to the other side.
Net flux of facilitated diffusion depends on what?
The frequency of the solute binding to the carrier molecule on the two sides of the membrane, so net transport occurs from the side with a greater frequency of binding.
Two factors affecting the binding of a solute to a carrier.
- the affinity of the binding site on the carrier. 2. the concentration gradient of the solute across the membrane.
Rate of facilitated diffusion is determined by what?
transport rate of individual carriers, the number of carriers in the membrane, and the magnitude of the concentration.
What is a channel?
A transmembrane protein that transports molecules via a passageway or pore that extends from one side of the membrane to the other.
How does most water cross the membranes? How else can it happen?
Through aquaporins. They only permit water and not solutes. Through ion channels
What are the three principles of diffusion?
Electrochemical gradient, osmosis and diffusion across membrane
What is active transport?
Movement of molecules up their concentration gradient.
What is primary active transport?
Uses ATP or some other chemical energy directly to transport substances.
What is secondary active transport?
Powered by a concentration gradient or an electrochemical gradient that was previously created by primary active transport.
What are pumps?
Transport proteins that carry out active transport. Ability to harness energy to drive transport of molecules in preferred direction.
What is the difference between pumps and carriers?
Pumps have greater affinity for molecules on one side of the membrane.
What results from active transport?
One side of the membrane becoming more concentrated.
What is ATPase
membrane proteins that primarily perform active transport function as transport protein and as an enzyme.
Why is the sodium potassium pump important?
Electrical signalling in neurons and absorption of glucose by intestinal epithelial cells.
For each Na, K pump cyclce, how many molecules move out and in. Can they move in either direction?
Three Na are transported out and two K are transported in. No, they are unidirectional.
Where is the energy stored for secondary transport?
In a Na+ or H+ concentration gradient
How does Secondary use ATP?
Indirectly uses ATP because Na+/K+ pumps are driven by ATP
What affects the rates of active transport?
Rate of transport by individual pump proteins and the number of pumps that are present in the membrane.
Flow of water across a membrane is always what?
Passive, unaffected by membrane potentials and is always driven by its own concentration gradient
What is osmosis?
The flow of water across a membrane down its concentration gradient
