Components of the cell surface membrane

Question 1

What is a phosphosolid?

Answer 1

• Contains hydrophilic head and hydrophobic tail.

* Creates bilayer and acts as barrier preventing the movement of ions.

Question 2

What is a Glycoprotein?

Answer 2

• Branching carbohydrates of protein which acts as a chemical receptor (e.g for hormones).
• Plays role in cell adhesion (cells forming together).

Question 3

What is a glycolipid?

Answer 3

•Lipids attached to carbohydrate chains, called antigens, which can be recognised by the immune system.

Question 4

What is a channel protein?

Answer 4

• Protein that allows passive movement of polar molecules down a concentration gradient, by providing a hydrophilic channel.
• Held in position by interactions between hydrophobic core of membrane and hydrophobic R-groups on the outside of the proteins.

Question 5

What is a carrier protein?

Answer 5

• Involved in passive transport and active transport (against the gradient) of substances and ions.
• Often involves changing the shape of the protein

Question 6

What is Cholesterol?

Answer 6

• Lipids containing a hydrophilic end and a hydrophobic end, which are positioned in between phospholipids, regulating the fluidity of the membrane.
• It provides stability by giving the membrane a level of rigidity without allowing the structure to become too solid.

Question 7

What are receptor sites?

Answer 7

• Acts as a boundary between internal and external environments.
• Ligands (e.g. drugs, hormones, neurotransmitters) bind onto receptor cells.

Question 8

What are enzymes (in a plasma membrane)?

Answer 8

•Enzymes can be found throughout membranes and can be used in chemical reactions.

• Enzyme ATP synthase is used in the production of ATP during respiration.
• Enzymes for photosynthesis are found on membrane stacks within chloroplast.

Question 9

What are intrinsic proteins?

Answer 9

• Transmembrane proteins that are embedded through both layers of membrane.
• Amino acids with hydrophobic R groups on external surfaces, interacting with hydrophobic core of membrane keeping them in place.

Question 10

What are extrinsic proteins?

Answer 10

• Also called peripheral proteins, are present in one side of the bilayer.
• They normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or intrinsic proteins.
• Can be present in either layer and sometimes move between layers.

Question 11

Describe protein synthesis (including inter ratio ship between organelles.

Answer 11

1. mRNA copies gene in the nucleus.
2. mRNA travels through the nuclear pores in the nuclear envelope to the ribosomes.
3. Ribosome may be attached to rough endoplasmic reticulum. The ribosome then translates the mRNA molecules to create the protein until the stop codon is reached.
4. The protein (e.g. insulin) then (are “pinched off”) travel towards Golgi apparatus in vesicles.
5. These vesicles then fuse with Golgi apparatus.
6. Golgi apparatus then processes and packages molecules ready for release.
7. The packaged protein (e.g. insulin molecules) then travels in vesicles from Golgi apparatus towards cell surface membrane.
8. Vesicles fuses with cell membrane.
9. Cell surface opens to release protein molecule (e.g. insulin) outside.