Membrane structure and function II

Question 1

What is special about the inner membrane composition of mitochondria and why

Answer 1

It has a high protein content since its main function is producing ATP

Question 2

What is special about myelin membrane and why

Answer 2

It has a low concentration of protein but a high lipid content since it is used in electrical insulation

Question 3

What is special about erythrocyte membrane and why

Answer 3

It has a high glycoprotein concentration because of its need in cell recognition

Question 4

What can pass though the membrane via simple diffusion and why

Answer 4

N2, O2, H20, Urea, Glycerol and CO2

They are small and hydrophobic

Question 5

What is passive transport

Answer 5

Transport driven by a concentration gradient

Can be non-mediated and carrier mediated

Question 6

What is active transport

Answer 6

Transport driven by ATP

Is carrier mediated

Question 7

What are the two types of co-transport

Answer 7

1. Antiporter - carries molecules different ways

2. Symporter - carries molecules the same way

Question 8

Why carrier mediated diffusion

Answer 8

Improves the efficiency and the rate of transport compared to simple diffusion
The higher the concentration the greater the transport, until a saturation point is reached
Its a physical process that has a maximum

Question 9

where is GLUT 1 found and whats special about it

Answer 9

Found in all mammalian tissues

1mM Kt therefore is saturated at low levels of glucose

Question 10

Where is GLUT 2 found and whats special about it

Answer 10

Found in liver and pancreatic B cells

15-20 mM Kt therefore it has a much higher capacity than GLUT 1 but a lower affinity for glucose

Question 11

Where is GLUT 3 found

Answer 11

Found in all mammalian cells

Question 12

Where is GLUT 4 found

Answer 12

Found in muscle and fat cells

Question 13

Where is GLUT 5 found

Answer 13

Found in the small intestine

Question 14

How does facilitated diffusion work

Answer 14

The transporter has 12 transmembrane domains
Glucose binding will result in conformational changes resulting in transport to the other side of the membrane
Driven by concentration gradient

Question 15

How can the gradient of glucose be maintained

Answer 15

Through phosphorylation
Glucose is trapped in the carrier using kinase to convert it into glucose-6-phosphate
This allows the cell to continue to take up more glucose

Question 16

Transporters are specific for the molecules they transport

Answer 16

D-glucose and L-glucose differ

Question 17

How can glucose uptake be increased

Answer 17

Stimulation by insulin will cause endocytosis of membrane vesicle containing glucose transporters, therefore increases the number of transporters

Question 18

Transport of sodium ions

Answer 18

Na+ / K+ co transport using ATP as an energy source using an integral membrane protein

Question 19

Early medical therapeutics

Answer 19

digitalis is a foxglove flower extract
Its a cardiotonic steroid that inhibits the Na+/K+ pump so the intracellular calcium concentration remains high so the heart beats stronger and for longer

Question 20

Sodium dependant glucose transport SGLUT-1 and 2

Answer 20

Co-transport symporter of glucose and sodium
Glucose is transported against its concentration gradient into the cell as sodium goes down its concentration gradient and is transported into the cell too
Glucose is phosphorylated in the cell so the concentration gradient isn’t too steep
The Na+ gradient is maintained by the sodium potassium pump as sodium is pumped back out the cell

Question 21

Rehydration therapy

Answer 21

Counters water lost through diarrhoea

Targets the co-transport of glucose and sodium

Question 22

Cystic fibrosis

Answer 22

A single mutation changes the activity of the CFTR (membrane protein and chloride channel)
This leads to impaired chloride transport and enhanced sodium transport
Therefore more water is reabsorbed in areas with CFTR such as the lungs
In the lungs, mucus becomes stickier, so it isn’t cleared as effectively and the lungs become prone to bacterial infection

Question 23

why is compartmentalisation useful

Answer 23

separates reactions enabling the local environment to be regulated for instance pH
Also brings reactants together

Question 24

How are proteins compartmentalised

Answer 24

Proteins have signal sequences in their primary structure which target them to specific organelles

Question 25

Lysosomal storage disease

Answer 25

lysosomes have a very low pH for its enzymes
A mannose sugar is added to these enzymes so it reaches the lysosome
In a particular mutation, the enzyme required for the addition of the mannose sugar doesn’t work
Therefore the enzyme is sent to the cytoplasm instead of the lysosome
The lysosome becomes engorged by that particular substrate and so the cell starts to malfunction and die

Question 26

Lymphocyte transmigration

Answer 26

Membrane carbohydrates are involved in cell recognition
Lymphocytes in the blood stream interact with specific molecules on endothelial cells surface which are only expressed at a site of infection
These adhesion molecules interact with the surface of the immune cells
This allows the lymphocyte to transmigrate across the cell and find an area where it can pass into the tissue below