Membrane structure and function II Flashcards
what is the major function of the plasma membrane
barrier, transport, signal transduction
what is the major function of the mitochondria membranes
inner - energy transduction
outer- barrier
what is the function of nuclear membranes
attachment of chromatin
what does the ratio protein to lipid depend on in membranes
- type of membrane
- function of the membrane
what is the main componant of myelin and how does it allow myelin to function
myelin main component are lipids which allows it to act as an insulator and form a sheath around neurons.
which molecules can readily cross the membrane
hydrophobic molecules e.g N2 or 02, small uncharged or polar molecules e.g H20, urea, glycerol, C02.
- Lipid soluble molecules can move either way through the membrane. Movement of these molecules is dependent on their concentration. This Is called simple diffusion.
which molecules will not readily cross the membrane.
large uncharged or polar molecules such as glucose, or ions e.g H+, Na+.
In order to cross the membrane, there needs to be a transport mechanism.
describe non-mediated passive transport across the membrane
- Non mediated : simple diffusion A, simple diffusion facilitated by a protein carrier B.
- In simple diffusion, molecules can pass through the membrane but in B the molecules would not be able to readily cross the hydrophobic region and so it requires a channel.
- both mechanisms are driven by concentration.
describe carrier mediated passive transport across the membrane.
- There are proteins within the membrane which act to pass these molecules from one side to the other. It is driven by concentration gradient. Uses a uniport system
what are the two contransporters.
Symporter : molecules are transported in the same direction. This type of transport requires the prescence of both A and B
Antiporter: movement of one molecule in one direction, and the other molecule in the opposite direction. -ie antiparallel. .
compare the kinetics of simple diffusion and carrier mediated transport.
Kinetics of simple diffusion, the rate of uptake is dependent on solute concentration,
Kinetics of carrier mediated transport, at lower concentrations of solute, a small change in solute concentration can lead to a rapid increase in transport. This means that carrier mediated transport is quicker. As the concentration of solute increases, the rate of transport beings to decrease and leads to saturation – difference between simple diffusion and carrier mediated diffusion.
compare carrier mediated and simple diffusion
driven by conc gradient : sd - yes , cm - yes
energy requirement : sd -no, cm - no
specificty : sd - no, cm -yes
speed : sd- slow, cm - fast,
capacity limited : sd- no limit, cm - can be saturated
what is vmax
the max rate at which transport can take place even if solute concentration increases.
what is kt
- the affinity of the transporter for its substrate.
given an exampe of a transport that requires carrier mediated facilitative diffusion
glucose transport
Glucose transporter- has large molecules consisting of 12 transmembrane domains.
describe the family of glucose transporters
GLUT 1 - all mammalian tissue - small Km - basal glucose uptake
GLUT 2 - liver and pancreatic beta cells - high km - in the pancreas it plays a role in the regulation of insulin and in the liver it removes excess glucose from the blood
GLUT3- all mammalian tissues - low km -basal glucose uptake
GLUT 4 - muscles and fat clles - intermediate km - amount in muscle plasma membrane increases with endurance training
GLUT 5 - small intestines - fructose transporter
comment on the Km of GLUT 1 and GLUT 3
Small km - 1 mM
• This means that GLUT1 and GLUT3 are fully active at this concentration, and so all tissues will have a supply of glucose at all concentrations.
which transporters are activated when glucose conc increases after a meal or in diabetes
transporters that will be activated are those expressed in the liver and pancreatic beta cells. = pancreatic beta cells produce insulin in response to the high circulating blood glucose and the liver takes glucose up in order to store it either as glycogen or fatty acids.
How do glucose transporters function
glucose will bind to the transporter and will undergo a series of confromational changes, allowing the glucose to pass across the membrane and into the cell.
After the glucose has been released , the transporter then returns to its original conformation and allows transport to continue until the gradient of glucose is diminished.
- To prevent this from happening, the cell removes the glucose from the inside of the cell by converting it to glucose 6-phosphate.
- Transport of glucose can be increased by increasing the number of transporters on the cell surface. This overcomes saturation
Is the transport of glucose selective or non-selective. give an example
selective e.g d glucose not l
how is the glucose gradient maintained
phosphorylation
active transport is - and requires -
selective and integral membrane protein
describe the gradient of sodium ions in the cell and explain how it is maintained.
conc of Na+ is high outside the cell and low inside the cell.
to maintain this gradient - active transport which requires ATP pumps out excess sodium
-transporter responsible for the transport of Na outside the cell against its electrochemical gradient. It is a co transporter, and the co transport is with potassium ions. The potassium ions are very low on the outside of the cell, and high inside the cell. It is also an antiporter, as it is transporting the Na and k in opposite directions.
describe the interaction between SGLUT1 and sodium potassium atpase
the aim of this transporter is to increase the uptake of glucose from the gut into the blood stream . It does this by transporting both glucose and sodium together. Its called SGLUT-1, and will transport glucose when there is sodium present. The driving force for the movement of glucose is the concentration of the sodium ions.
The cocentration of the sodium ions is 10x less inside the cell than outside, if the transport of glucose is to continue, then the Na must be removed from the cell. This is achieved by the sodium potassium ATPase.
