Membrane structure and function II Flashcards
What is special about the inner membrane composition of mitochondria and why
It has a high protein content since its main function is producing ATP
What is special about myelin membrane and why
It has a low concentration of protein but a high lipid content since it is used in electrical insulation
What is special about erythrocyte membrane and why
It has a high glycoprotein concentration because of its need in cell recognition
What can pass though the membrane via simple diffusion and why
N2, O2, H20, Urea, Glycerol and CO2
They are small and hydrophobic
What is passive transport
Transport driven by a concentration gradient
Can be non-mediated and carrier mediated
What is active transport
Transport driven by ATP
Is carrier mediated
What are the two types of co-transport
- Antiporter - carries molecules different ways
2. Symporter - carries molecules the same way
Why carrier mediated diffusion
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
where is GLUT 1 found and whats special about it
Found in all mammalian tissues
1mM Kt therefore is saturated at low levels of glucose
Where is GLUT 2 found and whats special about it
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
Where is GLUT 3 found
Found in all mammalian cells
Where is GLUT 4 found
Found in muscle and fat cells
Where is GLUT 5 found
Found in the small intestine
How does facilitated diffusion work
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
How can the gradient of glucose be maintained
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
Transporters are specific for the molecules they transport
D-glucose and L-glucose differ
How can glucose uptake be increased
Stimulation by insulin will cause endocytosis of membrane vesicle containing glucose transporters, therefore increases the number of transporters
Transport of sodium ions
Na+ / K+ co transport using ATP as an energy source using an integral membrane protein
Early medical therapeutics
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
Sodium dependant glucose transport SGLUT-1 and 2
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
Rehydration therapy
Counters water lost through diarrhoea
Targets the co-transport of glucose and sodium
Cystic fibrosis
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
why is compartmentalisation useful
separates reactions enabling the local environment to be regulated for instance pH
Also brings reactants together
How are proteins compartmentalised
Proteins have signal sequences in their primary structure which target them to specific organelles
Lysosomal storage disease
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
Lymphocyte transmigration
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
