Flashcards in Lectures 1-4? Deck (65)
What are two forms of carrier mediated transport?
1)Facilitated diffusion( not requiring energy)
2)Active transport ( requiring energy)
What is Km?
Substarte concentration at which half-maximal rate of transport occurs
What is the comparison of caries mediated transport and simple diffusion down a concentration gradient? ( graph)
Facilitated is a hyperbolic relationship and simple diffusion is a linear relationship.
Describe the saturation characteristic of carrier mediated transport?
Unlike simple diffusion, rate of transport is not linearly related to the concentration of substrate. The rate of transport has a maximum (Tm) which is reached when all carriers are occupied by substrate
Describe the selectively characteristic of carrier mediated transport?
Each carrier is specialised to transport or specific substance or a few structurally related compounds
What 3 important characteristics determine the kind and amount of material transferred across the membrane?
The difference in the change of molecules when molecules move to an area of least concentration
What 2 properties influences entry into the selectively permeable membrane?
- Solubility of particle in lipid
-Mass of particle
What occurs when there is no net movement of K+ and what equation can you use?
The equilibrium potential for K+ is reached (Ek) and the Nernst equation
What is secondary active transport?
The transfer of a solute across the membrane is always coupled wit the transfer of the ion that supplies the driving force (typically Na+)
Describe the mechanism of Na+/K+ ATPase?
1)3Na+ bind from ICF
2)Pump is phosphorylated (ATP hydrolysis)
3)3Na+ unbind (dissociate) and are released into ECF
4)2K+ bind from ECF
5)Pump is dephosp
What is the resting membrane potential?
The diffusion of ions down their concentration gradients gradients generates an electrical potential
What is a membrane potential?
Is the separation of opposite charges across the membrane
What is antiport ( exchange)?
Type 2 of secondary active transport. The solute and Na+ move in opposite directions (Na+ into cell, solute out the cell)
What is the difference between primary and secondary active transport?
Primary transport uses energy directly derived from the pump, hydrolysing ATP to ADP + Pi by acting as ATPase. Secondary transport does not use energy directly , it uses second-hand energy stored in the form of an electrochemical gradient (usually Na+)
What are the exofacial state and endofacial state?
Exofacial - carrier protein open, facing the extracellular fluid
Endofacial- carrier protein open, facing the intracellular fluid
What is facilatated diffusion?
Uses a carrier to facilitate (assist) the transfer of a substance across a membrane from high to low concentration (never against the concentration gradient)
What is depolarisation?
When the membrane potential becomes less negative ( sometimes even positive)
How is Na+/K+ ATPase electrogenic?
The net transfer of the equivalent of 1 negative charge into the cell for each cycle of the pump
What is the role of Na+/K+ ATPase?
Maintains the concentration gradients by pumping back K+ that has leaked from the cell and pumping out Na+ that has entered the cell in the ratio 3Na+(out):2K+(in)
How do you calculate the driving force?
Membrane potential (Vm) - equilibrium potential (Elon)
When is there no net movement of K+?
When the energy in the concentration gradient is equal and opposite to that In the electrical gradient
What is hyperpolarization?
When the membrane potential becomes more negative
What is the membrane potential determined by?
-the selective permeability of the membrane to certain ionic species
- the concentration gradients of the permeant ions across the membrane
Describe the competition characteristic of carrier mediated transport?
When a carrier can fit 2 substrates, the presence of both diminishes the rate of the transfer for either since they compete with each other
What are the important roles for the Na+-K+ ATPase?
1)maintains Na+ and K+ concentration gradients across the plasma membrane
2)Helps regulate cell volume b y controlling concentration of solutes to the cell
3)Energy stored in the EC gradient established by the pump can be harasses to drive secondary transport by coupling movement of a solute to Na+
What is the rate of diffusion governed by?
It is governed by the permeability coefficient and concentration gradient
What do occlusion junctions do?
-Appear as a focal region of close opposition between adjacent cell membranes
-Known as tight junctions
What are the 3 types of intercellular junctions?
1)Occluding junctions:link cells to form barrier
2)Anchoring junctions:provide mechanical strength
3)Communicating junctions: allow movement of molecules between cells