Membrane Structure and Function

Question 1

What are the functions of the plasma membrane?

Answer 1

Barrier and transport signal transduction.

Question 2

What are the functions of the mitochondria membranes?

Answer 2

Energy transduction and synthesis of complex lipids.

Question 3

What are the functions of the golgi membrane?

Answer 3

Post-translational modification and processing of secretion.

Question 4

What are the functions of the nuclear membrane?

Answer 4

Attachment of chromatin.

Question 5

What are the functions of lysosome membrane?

Answer 5

Hydrolytic enzymes.

Question 6

What are the functions of peroxisomes membrane?

Answer 6

Fatty acid oxidation.

Question 7

What is simple diffusion?

Answer 7

The movement of lipid soluble molecules through a membrane, moving either way which is dependant on the concentration- the net movement of lipid soluble of molecules across a partially permeable membrane from an area of high concentration to an area of low concentration.

Question 8

What is passive diffusion?

Answer 8

Simple diffusion or large/charged molecules moving through channel proteins.

Question 9

What is carrier mediated diffusion?

Answer 9

Where the transmembrane channel protein changes shape to release the molecules to the other side- this can be passive or it can also use energy and be a type of active transport.

Question 10

What is co-transportation?

Answer 10

This is when there are two molecules that need to cross the membrane via the same transmembrane protein but in order for either one to pass through the membrane, both molecules need to be present.

Question 11

What is an antiporter?

Answer 11

A transmembrane protein used in co-transport and works by moving each molecule move through the membrane in opposite directions.

Question 12

What is a symporter?

Answer 12

A transmembrane protein used in co-transport and works by moving the two molecules through the membrane in the same direction.

Question 13

Why is glucose transport carrier mediated?

Answer 13

It increases the ability for a molecule to enter- the higher the concentration the higher the diffusion until very high concentration where it becomes saturated.

Question 14

LOOK AT NOTES TO SEE THE DIFFERENT TYPES OF GLUCOSE TRANSPORTERS.

Answer 14

LOOK AT NOTES TO SEE THE DIFFERENT TYPES OF GLUCOSE TRANSPORTERS.

Question 15

How is glucose transported?

Answer 15

The glucose is transported by facilitated diffusion. It is driven by a concentration gradient. The glucose will bind to the transporter and will then undergo conformational change releasing the glucose into the cell. This transport is bidirectional so it can happen both ways. The gradient is maintained by phosphorylation, where glucose is phosphorylated.

Question 16

What are the kinetics of glucose transport?

Answer 16

• the transporter is specific for the molecules they transport i.e. D-glucose not L-glucose; they can identify the subtle difference but some transporters are able to transport more than one kind.
• exhibit saturation type kinetics.
• They can be regulated.

Question 17

How can the uptake of glucose be increased regards to the amount of transporters there are?

Answer 17

If you increase the amount of transporters there are, you can increase the amount of glucose is uptaken.

Question 18

What are some glucose transporters sensitive to?

Answer 18

External factors such as insulin- but not all cells are sensitive.
One example of a transporter that is sensitive is GLUT4, which is expressed on adipocytes and skeletal muscles. This can be stimulated by insulin- it doesn’t stimulate the activity but rather stimulated the number of glucose transporters at the surface of the cell. Cells have a reserve of transporters.

Question 19

What is active transport?

Answer 19

Is a selective transport and requires of integral membrane proteins.
An example of this is a sodium-potassium pump where 3 Na+ are taken in and 2 K2+ are taken out, via a ATP synthases.
NOTE: Digitalis cardiotonic steroid (foxglove) inhibits the pump.

Question 20

What does SGULT-1 and -2 in the Gut do?

Answer 20

They transport both glucose and sodium.

LOOK AT NOTES TO SEE THE DIAGRAM.

Question 21

What does diarrhoea do?

Answer 21

Cause rapid dehydration- rehydration therapy include 8 tsp sugar, 1 tsp salt and 1 litre of water. The mixing of salt and glucose provides a solution that can be readily taken up.

Question 22

What are membranes?

Answer 22

• Membranes act as semi-permeable barriers
• Transport across them may be passive or active
• ATP production is dependent on the properties of membranes
• Cystic fibrosis is a disease of transport across membrane

Question 23

What is compartmentalisation?

Answer 23

• Separates reactions
• Enables the local environment to be regulated for instance pH
• Brings reactants together
• Shown by experiment: labelled a particular protein – primarily a cytosolic protein. They changed the signal sequence from being a cytoplasmic sequence to a nuclear sequence – the same molecule ends up in the nucleus. This shows that within the protein structure that tells the protein where to go.

Question 24

What is lysosomal storage disease?

Answer 24

• The lysosome has a low pH and recycles molecules. In order for it to function the enzymes have to be transported specifically to that organelle. A mannose is added (sugar molecule) which will direct the protein to the lysosomes.
• Lysosomal hydrolase is synthesised in the ER and transported to the Golgi where mannose is added. This forms Mannose 6 – phosphate which binds to its receptor. This is released and reaches the lysosome where it fuses and hydrolyses.
• I-cell disease: when the mannose 6 – phosphate targets enzymes made in the Golgi to the lysosome

Question 25

What are the membrane carbohydrates that are involved in cell recognition?

Answer 25

• Blood antigens

- Lymphocyte trafficking