Plasma membranes

Question 1

What are plasma membranes made up of?

Answer 1

A phospholipid bilayer

Question 2

What make up the phospholipid bilayer?

Answer 2

Two phospholipids arranged tail to tail.
The hydrophillic phosphate heads are present on both surfaces of the membrane, sandwiching the fatty acid tails to form a hydrophobic core

Question 3

What is the fluid mosaic model?

Answer 3

The model of the phospholipid bilayer where proteins occupy various positions in the membrane, and the phospholipids are free to move (within their layers)

Question 4

What are the two types of membrane proteins?

Answer 4

Intrinsic and extrinsic membrane proteins

Question 5

What are intrinsic membrane proteins?

Answer 5

Transmembrane proteins that are embedded through both layers of the membrane

Question 6

How are intrinsic proteins kept in place?

Answer 6

They have amino acids with hydrophobic R-groups which interact with the hydrophobic core of the membrane, holding the proteins in place

Question 7

What are 2 types of intrinsic proteins?

Answer 7

Channel proteins

Carrier proteins

Question 8

What are glycoproteins?

Answer 8

Embedded extrinsic proteins that have an attached carbohydrate chain

Question 9

What are the functions of glycoproteins?

Answer 9

• Role in cell adhesion

- Act as receptors for chemical signals

Question 10

What is chemical signalling?

Answer 10

When a chemical binds to the receptor, it elicits a response from the cell, known as cell communication or chemical signalling

Question 11

What are glycolipids?

Answer 11

Similar structure to glycoproteins, they are lipids with an attached carbohydrate chain

Question 12

What are the function of glycolipids?

Answer 12

They are called cell markers or antigens, and can be recognised by the cells of the immune system as self (of the organism) or non-self (of another organism)

Question 13

What are extrinsic proteins?

Answer 13

Proteins that are present on only one side of the bilayer. They can be present on either layer and some move between layers

Question 14

What is the structure of extrinsic proteins?

Answer 14

They typically have hydrophilic R-groups and interact with the polar heads of the phospholipids or with intrinsic proteins.

Question 15

What is cholesterol?

Answer 15

A lipid with a hydrophilic end and hydrophobic end, much like a phospholipid. Cholesterol molecules are positioned between phospholipids in the membrane.

Question 16

What is the function of cholesterol in plasma membranes?

Answer 16

Cholesterol regulates the fluidity of the membrane.

Question 17

How does cholesterol regulate the fluidity of the plasma membrane?

Answer 17

Cholesterol has a hydrophilic end which interacts with the phosphate heads, and a hydrophobic end which interacts with the tail, and this works to add stability without making the membrane too rigid.
Cholesterol molecules stop the phospholipids from grouping too closely and crystallising

Question 18

What is the impact of alcohol molecules on membranes?

Answer 18

Alcohol molecules disrupt the structure of the phospholipid bilayer, causing it to become more fluid and permeable

Question 19

What molecules are able to pass freely through membranes by diffusion?

Answer 19

O2
CO2
H2O
Ethanol
Non-polar molecules

Question 20

Why is water able to pass freely though the membrane despite being polar?

Answer 20

Due to its small size

Question 21

Why are membranes described as partially permeable?

Answer 21

As some species diffuse freely, whereas others (like ions and larger polar molecules) cannot freely diffuse

Question 22

Why do charged and polar species struggle to diffuse freely through membranes?

Answer 22

As they are repelled by the hydrophobic interior of the membrane

Question 23

What molecules pass through membranes using carrier proteins?

Answer 23

• Sugars: glucose
• Amino acids
• Nucleotides

Question 24

What molecules pass through membranes using channel proteins?

Answer 24

Many ions including:

• K+
• Na+
• Cl-
• Ca2+

Question 25

How do channel proteins allow ions to pass through?

Answer 25

Channel proteins provide a hydrophilic channel that ions are able to transport through down a concentration gradient