Cell Processes: Transport Across Cell Membranes Flashcards
What is non-mediated transport?
transport that doesn’t directly use a integral membrane transport protein (molecules are permeable across the hydrophobic core of phospholipid bilayer)
What is mediated transport?
transport that moves materials with the help of a transport protein
What is passive transport?
transport that moves substances down their concentration or electrochemical gradient with only their kinetic energy
What is active transport?
transport that uses energy to drive substances against their concentration or electrochemical gradients
What is vesicular transport?
transport that moves materials across membranes in small vesicles either by exocytosis or endocytosis
What is non-mediated transport important for?
absorption of nutrients – excretion of wastes
What type of molecules undergo non-mediated transport?
Nonpolar and hydrophobic molecules
Examples of molecules that undergo non-mediated transport
oxygen, carbon dioxide, nitrogen, fatty acids, steroids, small alcohols, ammonia and fat-soluble vitamins (A, E, D and K)
What is the function of ion channels?
mediate the movement of ions down their electrochemical gradient
What is formed in the centre of an ion channel and what is its functions
a water filled pore that shields the ions from the hydrophobic core of the lipid bilayer
Why is transport through the ion channel rapid?
ions do not bind to the channel pore (passive diffusion)
What determines what ions can pass through an ion channel (ionic selectivity)
certain amino acids lining the pore determine
What is ionic selectivity?
ion channels only allow certain ions to pass through
What is the result of channels being ion selective?
the channel can harness the energy stored in the different ion gradients
Why can ion channels NOT be open all the time?
it would get rid of the ion gradient
What do ion channels contain to control passage of ions
gates
Examples of stimuli that control channel gate opening and closing
voltage, ligand binding, cell volume (stretch), pH, phosphorylation
What is a patch clamp?
A sensitive voltage clamp method that permits the measurement of ionic currents flowing through individual ion channels
Number of ions that are able to diffuse through one ion channel per second
1 million
the current through a single ion channel
10^-12 amps
How does carrier mediated transport work?
The substrate to be transported directly interacts with the transporter protein
Is carrier mediated transport faster or slower than ion channels and why?
Slower because the transporter undergoes a conformational change
What is the general function of carrier mediated transport?
to take one molecule from one side of the membrane to the other
Carrier proteins exhibit these 4 properties
specificity, inhibition, competition, saturation
Is carrier mediated transport active or passive?
it can be both
What does saturation mean for carrier mediated transporters?
They have only a certain number of binding pockets so they cannot intake anymore molecules that their binding pockets allow
Does increasing concentration increase uptake with carrier mediated transporters
To a point, eventually it will reach a point where uptake is saturated
Name of protein that takes up glucose
Glucose transporter protein (GLuT)
Amount of glucose in blood
5
Process of glucose moving into a cell
Glucose BINDS to transport channel protein > changes conformational shape of protein > allowing it to go into cell
Does glucose move down its concentration gradient in facilitated diffusion?
Yes
What is glucose converted into in the cell by a kinase enzyme?
glucose-6-phosphate
Why is glucose converted into glucose-6-phosphate
to maintain glucose concentration gradient
What cells do Facilitated diffusion of glucose
Muscle, nervous, fat cells
what is GluT NOT called
do not call this a glucose channel that is doing passive diffusion (it is a carrier protein, passive facilitated diffusion)
What is active transport?
An energy requiring process that moves molecules and ions against their concentration or electrochemical gradients
What is primary active transport?
A form of active transport in which energy is directly derived from the hydrolysis of ATP to make ion gradients
How much cell energy is used on primary active transport?
30%
What is secondary active transport?
A form of active transport in which energy is stored in an ionic concentration gradient is used to drive the active transport of a molecule against its gradient
Process of Sodium and Potassium ATPase
- Na+ binds
- ATP is split and Na+ is pushed out of the cell
- K+ binds and phosphate is released
- K+ is pushed in
With a Na/KATPase, how many Na+ are removed
3 Na+ ions are removed from the cell
With a Na/KATPase, how many K+ are brought into a cell
2 K+ ions are brought into the cell
What is the result of a Na/KATPase
pump generates a net current and is electrogenic
What does electrogenic mean
producing a change in the electrical potential of a cell.
Other examples of ATPase ion pumps
Ca/K ATPase (Muscle SR), H/K ATPase (stomach)
What does a Na pump do
maintains a low concentration of Na+ and a high concentration of K+ in the cytosol
What type of transport is a Na pump
primary active transport
What is a Na ion concentration gradient important for (6)
Maintain resting membrane potential
Electrical excitability
Contraction of muscle
Maintenance of steady state cell volume
Uptake of nutrients via secondary active transporters
Maintenance of intracellular pH by secondary active transporters
What is the pump-leak hypothesis
Na and K are continually leaking back into the cell down their respective gradients so the pump works continuously to maintain the ion gradient
What type of transport are Na+ antiporter/exchangers
secondary active transport
What do Na+ antiporter/exchangers do?
Allow Na+ ions to rush inwards and Ca2+ or H+ are pushed out
What do Na+ symporter/cotransporters do?
Glucose or amino acids rush inward together with Na+ ions
What are secondary active transporter powdered by?
Na+ gradient initially established by the Na pump
