4.1 Structure of the cell surface membrane

Question 1

What is the function of the phospholipid bilayer?

Answer 1

-allows lipid-soluble substances to enter and exit the cell, and prevents water-soluble substances from doing the same
-makes the cell membrane flexible and self-sealing

Question 2

Name the two types/positions of proteins in the cell membrane.

Answer 2

peripheral/extrinsic and transmembrane/intrinsic

Question 3

What are the functions of proteins in the cell membrane?

Answer 3

-(peripheral proteins) give structural support to the membrane, help cells adhere together or be cell receptors/recognition sites alongside glycolipids
-(transmembrane proteins) protein channels to allow water-soluble ions to diffuse across the membrane, or actively transport ions and molecules across the membrane

Question 4

What is the function of cholesterol in the cell membrane?

Answer 4

-limits (lateral) movement of other molecules in the membrane (incl. lipid via their fatty acid tails)
-reduces fluidity of membrane at higher temp.
-prevents water and dissolved ion leakage from the cell due to hydrophobic nature

Question 5

What are the functions of glycolipids and glycoproteins in the cell membrane?

Answer 5

-gives structural support to the membrane
-helps cells adhere together
-recognition sites alongside peripheral proteins
-(glycoproteins) cell-surface receptors for hormones and neurotransmitters

Question 6

What are the possible characteristics of molecules that can’t freely diffuse across the cell surface membrane?

Answer 6

-not lipid soluble
-too large
-polar
-has the same charge as the channel proteins

Question 7

Why is the fluid-mosaic model called as such?

Answer 7

-fluid due to flexibility of membrane
-mosaic due to embedded proteins variation in size, shape, and patterns (like mosaic tiles)