16. Structure And Function Of Crell Membrane Proteins

Question 1

Membrane proteins
How much is the wet weight of membrane proteins in the cell membrane? Where are membrane proteins synthesised? Where are their molecules competed? What’s happens when after they are packed in the Golgi?

Answer 1

It’s at least 50% of the cells membranes wet weight. They are synthesised in the rER. The molecules of newly synthesised membrane proteins are completed in the cisternae of the Golgi. After that it’s packed in secretory vesicles and transported to the cell membrane where it is used to build at least half of the cell membrane.

Question 2

Transport proteins
Pumps
What kind of binding site does the pump have? What kind of metabolic precursor are they?
Carriers
What is it called when one molecule is transported through a carrier?
What is it called when two or more molecules are transferred through a carrier in the same direction?
What is it called when two or more molecules travel in the opposite direction at same time in a carrier?
Channels
Are channels mostly single pass? Are they opened or closed? What do they transport? Do they form gap junctions? What are they’re different types of modifications?

Answer 2

It has a binding site to bind ions and transport the in and out of the membrane. They are metabolic precursors of macromolecules such as amino acids and sugars.

When one molecule is transported it is then called uniport or facilitated diffusion.
When two or more molecules are transported in the same direction it is then called symport.
When two or more molecules are transported in the opposite direction it is then called antiport or exchange diffusion.

Channels are mostly single pass. They are either opened or closed. They allow passage of small ions, molecules and water. Channels form gap junctions between them and adjacent cells where ions and molecules can pass from one cell to the adjacent cell. It’s modifications is voltage gated, ligand gated or mechanically gated.

Question 3

Structural proteins
What do structural proteins do? Where are they often concentrated? What are they typically? What kind of bindings do they have? What is a homophillic binding? What is a heterophilic binding?

Answer 3

Structural proteins form junctions with neighbouring cells. They are often concentrated with lipids in the membrane. They are typically integral receptors. They have Homophillic bindings and Heterophillic bindings. Homophillic binding is the binding of an receptor molecule to an identical one. Hereroohillic binding is the binding of an adhesion molecule to and non identical adhesion molecule of another cell.

Question 4

Receptor proteins
Membrane receptors
What are the kinds of neurotransmitter receptor? What are the kinds hormone receptors? What do receptor proteins do? What are Ligands? What are some processes that receptor proteins are involved in?

Answer 4

The types of neurotransmitter receptors are iontropic channels that transport ions and metabotropic receptors that bind GTP. The kinds of hormone receptors are peptide and steroid hormones. Receptor proteins allow recognition and localised binding of ligands. Ligands are molecules that bind to the the extracellullar surface of the plasma membrane. Some process that receptor proteins are involved in are hormone stimulation, coated vesicles, endocytosis and antibody reactions.

Question 5

Linker proteins
What do linker proteins anchor? What is an example of a linker protein? What do they link together?

Enzymes
How many different enzymes are there? Can you name some of them?

Answer 5

Linker proteins anchor the intercellular cytoskeleton to the extracellular matrix. Example of an linker protein is the family of integrins. The family of integrins link cytoplasmic actin filaments to an extracellular matrix pertinent called fibronectin.

There’s 30 different enzymes. Some of the are alkaline phosphatase, ATPase and digestive enzymes like disaccharidases and dipeptides.