Membrane Structure & Function II

Question 1

what are the major functions of the plasma membrane?

Answer 1

• transport
• physical barrier
• signal transduction

Question 2

what are the major functions of the inner and outer membranes of the mitochondria?

Answer 2

• inner:energy transduction

- outer: barrier

Question 3

what is the major function of the nuclear membranes?

Answer 3

attachments of chromatin

Question 4

what is the major function of the peroxisomal membrane?

Answer 4

fatty acid oxidation

Question 5

what types of molecules can pass through the membrane by simple diffusion?

Answer 5

lipid soluble, small, uncharged, polar molecules

Question 6

what are the 2 ways can molecules pass through the membrane?

Answer 6

-passive and active
or
-non mediated and carrier mediated

Question 7

what are the two co-transporter systems and their functions?

Answer 7

• co-transport is when two molecules are transported at the same time
• antiporters: transports two molecules but in opposite directions
• symporters: tranports two molecules in the same direction

Question 8

what does it mean if a system is a uni-porter system?

Answer 8

transports one molecule at a time

Question 9

describe the glucose transport system

Answer 9

• it is carrier mediated so requires a carrier protein on the plasma membrane
• there are many glucose transporters and diff types expressed on different cells
• glucose is transported by facilitated diffusion
• it is a bidirectional process
• the [glucose] maintained by phosphorylation

Question 10

why is the transport if glucose carrier-mediated?

Answer 10

• if there was no carrier, glucose transport would be incredibly slow.
• the carrier-mediated facilitated diffusion speeds up the rate of glucose transport greatly.

Question 11

what does Kt tell us about the glucose transporters?

Answer 11

• Kt shows the affinity glucose has to the transporters

- the lower the Kt, the higher the affinity

Question 12

how does the glucose transporter work?

Answer 12

• the transporter binds to glucose and undergoes a conformational change.
• opens the inner portion to the cytoplasm and the glucose diffuses in.
• because the transport of glucose is driven by the concentration gradient of glucose, the cell maintains this gradient by phosphorylating the glucose as it enters the transporter.

Question 13

how can glucose intake be increased in cells using insulin?

Answer 13

• when there is no insulin present, the transporters are brought inside the cell via a vesicle (ie. away from the membrane).
• this stops the transporters from functioning.
• when insulin is present, the vesicle with the transporters fuses with the membrane to express them on the membrane.
• this allows the transporters to function.

Question 14

give an example of active transport

Answer 14

• movement of Na+ out of the nerve cell
• the [Na+] outside the cell is 140mM and 15mM inside the cell
• the Na+ channels are closed so they are unable to move into the cell by facilitated diffusion
• the Na+/K+ pump is an anti port system that pumps 3Na+ out for every 2K+ pumped into the cell
• this requires ATP

Question 15

where is the SGLUT-1 found?

Answer 15

• the SGLUT-1 is a Na+ driven glucose symporter present on the gut lumen side of the enterocyte
• this transports glucose from area of lower concentration to an area of higher concentration using the concentration gradient of Na+.

Question 16

where is the SGLUT-2 found?

Answer 16

• on the other side of the cell (facing the extracellular fluid, the basal domain) is the GLUT -2 which transports glucose down its concentration gradient (from higher in the cell to lower in ECF)
• the Na+/K+ ATPase pump also works down here.

Question 17

what is compartmentalisation for?

Answer 17

• separates creations
• allows localised environment to regular pH
• brings reactants together