Membrane structure and function II

Question 1

what is the major function of the plasma membrane

Answer 1

barrier, transport, signal transduction

Question 2

what is the major function of the mitochondria membranes

Answer 2

inner - energy transduction

outer- barrier

Question 3

what is the function of nuclear membranes

Answer 3

attachment of chromatin

Question 4

what does the ratio protein to lipid depend on in membranes

Answer 4

• type of membrane

- function of the membrane

Question 5

what is the main componant of myelin and how does it allow myelin to function

Answer 5

myelin main component are lipids which allows it to act as an insulator and form a sheath around neurons.

Question 6

which molecules can readily cross the membrane

Answer 6

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.

Question 7

which molecules will not readily cross the membrane.

Answer 7

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.

Question 8

describe non-mediated passive transport across the membrane

Answer 8

• 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.

Question 9

describe carrier mediated passive transport across the membrane.

Answer 9

• 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

Question 10

what are the two contransporters.

Answer 10

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. .

Question 11

compare the kinetics of simple diffusion and carrier mediated transport.

Answer 11

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.

Question 12

compare carrier mediated and simple diffusion

Answer 12

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

Question 13

what is vmax

Answer 13

the max rate at which transport can take place even if solute concentration increases.

Question 14

what is kt

Answer 14

• the affinity of the transporter for its substrate.

Question 15

given an exampe of a transport that requires carrier mediated facilitative diffusion

Answer 15

glucose transport

Glucose transporter- has large molecules consisting of 12 transmembrane domains.

Question 16

describe the family of glucose transporters

Answer 16

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

Question 17

comment on the Km of GLUT 1 and GLUT 3

Answer 17

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.

Question 18

which transporters are activated when glucose conc increases after a meal or in diabetes

Answer 18

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.

Question 19

How do glucose transporters function

Answer 19

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

Question 20

Is the transport of glucose selective or non-selective. give an example

Answer 20

selective e.g d glucose not l

Question 21

how is the glucose gradient maintained

Answer 21

phosphorylation

Question 22

active transport is - and requires -

Answer 22

selective and integral membrane protein

Question 23

describe the gradient of sodium ions in the cell and explain how it is maintained.

Answer 23

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.

Question 24

describe the interaction between SGLUT1 and sodium potassium atpase

Answer 24

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.

Question 25

what is the difference between the sodium glucose cotransporter and the sodium potassium atpase

Answer 25

The sodium glucose cotransporter is passive whereas the sodium potassium transporter is active

Question 26

describe the distribution of the transporters involved in order for glucose transport to take place

Answer 26

assymetrically distributed.

SGLUT1, takes up the glucose and sodium. The sodium will then be exchanged for potassium using the sodium potassium atpase, the location of this transporter is on the basal surface of the cell.

The concentration of glucose as its being transported in increases and will reach a point where its concentration is greater than the concentration of glucose in the extracellular fluid.

Therefore the glucose will be transported across the basal membrane by a mechanism of faciliated diffusion using the transporter GLUT 2. This is done following the concentration gradient.

Question 27

how is the assymtery of glucose transport maintained

Answer 27

plasma membrane of adjacent cells come together tightly forming tight junctions. These tight junctions prevent the redistrubiton of the transport proteins around the cell. This retains the sglut1 in the apical surface and glut2 and sodium potassium ATPase in the basal surface.

Question 28

what is rehydration therapy

Answer 28

• Targets the loss of water, electrolytes or off nutrient during bouts of diahhera.
• Targets the co-transport of glucose and sodium
• 1 litre of water, 1tsp of salt, 8 tsp of sugar,
• The sodium and glucose are absorbed by the gut, and the glucose can then be used as an energy source. The sodium draws in water and rehydrating the individual

Question 29

what are the functions of compartmentilization

Answer 29

• Intracellular membranes create local microenvironments and separate reactions
• Enables electrochemical gradients to be established such as in mitochondria
• Brings enzymes and reactants together and/or keep them apart( ie restrict the activity of enzymes )

Question 30

describe the compartmentalisation of the mitochondria

Answer 30

It has 2 membranes, an inner and outer mitochondrial membrane
The protein content of the inner mitochondrial membrane is greater than the other mitochondrial membrane. this is due to their functions : This is because the outer mitochondrial membrane has a barrier function and the ability of the inner mitochondrial membrane to generate ATP. There are a lot of proteins in the inner mitochondrial membrane that are important in the generation of a hydrogen ion/electrochemical gradient and generation of ATP.
The impermeability of the inner mitochondrial membrane allows the gradient to decrease.

Question 31

what is the function of the lysosomal membrane

Answer 31

• establishes difference in pH

The membranes of the lysosomes have proton pumps within them that pump hydrogen ions into the luminal space of the lysosome. This process requires the hydrolysis of ATP.

Question 32

what is the function of the peroxisomal membrane

Answer 32

breakdown of long chain fatty acids and contains oer 50 enzymes.

Question 33

describe 2 experiments that demonstrate the importance of signal sequences

Answer 33

1. • A cytosolic protein which has been tagged with a fluoresecnt marker.
     
     • If u take the cytosolic protein and add a small nucleur localising sequence, that protein would be seen in the nucleus and not in the cytoplasm
2. • Add a carbohydrate signal to the protein.
     
     • This directs an enzyme to the lysosome.

Question 34

what are the consequences if an individual is deficient in a phosphotransferase enzyme present in the golgi.

Answer 34

can not modify the mannose normally present on enzymes targeted to for the lysosomal enzymes. They appear in the blood and urine.
- The substrate for the particular hydrolases start to accumulate in the lysosome. – category of disorders called lysosome storage diseases. – icell disease. Forms inclusions. – can lead to cellular disfunction.

Question 35

what are membrane glycoproteins involved in?

Answer 35

cell to cell recognition

Question 36

what are blood groups dependent on?

Answer 36

the glycolipids present on the surface of red blood cells. The carbohydrate is almost the same just one modification which is dependent on the expression or not of a specific glycosyltransferases
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