Membrane structure and function II

Question 1

Membrane permeability

Answer 1

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 2

Glucose transport

Answer 2

Carrier mediated

Passive proves à diffusion à rate determined by concentration gradient  

Bi directional 

Conformational change in the carrier protein shape resulting in transportation  

Glucose can now fit in the binding site  

Carrier protein changes shape again and this causes the release of glucose through the other side of the membrane 

Glucose is phosphorylated to maintain the glucose concentration gradient 

This allows the cell to take in glucose continuously

Question 3

Glucose kinetics

Answer 3

Kt = the measure of affinity of the transporter of the substrate

Low Kt = high affinity

Question 4

Glut 4L

Answer 4

Primarily found in Adipocytes and skeletal muscle

Stimulated by insulin 

Cells have a reserve of transporters 

Glucose uptake can be increased by increasing the number of transporters

Question 5

Active transport

Answer 5

Selective

Requires an integral membrane protein  

Na+ gradient maintained by ATP

Question 6

Foxglove

Answer 6

Used to treat dropsy (congested heart disease)

Active ingredient is digitalis (Cardiotonic steroid) 

This inhibits the Na+/K+ ATPase pump 

Intracellular Na+ is required for correct regulation of the contraction of the heart 

Also Ca2+ determine the strength of the contraction of the heart

Question 7

SGLT-1 and 2

Answer 7

Members of the SLC5A gene

Use energy from the NA+ gradient created by the ATPase pump to transport glucose across apical membrane 

Sodium and glucose are moved in the same direction across the membrane, therefore known as symporters 

SGLT2 inhibitors, like glifiozins, used to treat type 2 diabetes

Question 8

Oral rehydration therapy

Answer 8

Used to treat severe dehydration

Oral rehydration contains both sodium and glucose 

SGLT1 transports glucose and sodium across the cell membrane 

Hundreds of water molecules move into epithelial cell for each cycle of transport  

This can achieve rehydration

Question 9

Membranes

Answer 9

Act as partially permeable membranes

Transport across maybe passive or active  

ATP production is dependent on the properties of membranes  

Cystic fibrosis is a disease of transport across membranes

Question 10

Compartmentalization

Answer 10

Separates reactions

Enables the local environment to be regulated for instance, pH 

Bring reactants together 

Proteins have particular signal sequences which target them to specific organelles

Question 11

Lysosomal storage disease

Answer 11

lysosomal hydrolase is synthesized in the ER and transported to Golgi where mannose is added forming mannose 6 phosphate

Mannose directs the protein to the lysosomes 

Mannose 6 phosphate binds to the receptor 

Reaches lysosome where it fuses and hydrolyses

Question 12

I-cell disease

Answer 12

Caused by the deficiency of GIcNAc phosphotransferase which phosphorylates mannose residues

This means proteins cannot be marked and be excreted out of the cell  

Lysosomes unable to function and results in a build up of substances within the lysosome which its unable to degrade