Lesson 1 - structure

Question 1

What is the structure of cell membranes?

Answer 1

Mainly composed of phospholipids

Question 2

What is a phospholipid?

Answer 2

A molecule composed of a phosphate group, a glycerol and two fatty acids

Question 3

What bond joins the glycerol and fatty acids together?

Answer 3

An ester bond

Question 4

What bond joins the phosphate head and the glycerol together?

Answer 4

Phosphodiester bond

Question 5

Which part of the phospholipid is hydrophobic?

Answer 5

The glycerol and fatty acid tails

Question 6

Which part of the phospholipid is hydrophilic?

Answer 6

The phosphate group

Question 7

Why do phospholipids form a bilayer in plasma membranes?

Answer 7

The phosphate heads are hydrophilic (love water), therefore they orientate themselves towards the aqueous solution (e.g. cytoplasm and extracellular tissue fluid)
Whereas the fatty acid tails are hydrophobic (water repelling), so they orientate themselves away from the aqueous solution(s).
This forms a bilayer

Question 8

What is the fluid mosaic model?

Answer 8

The name used to refer to the plasma membrane

Question 9

Why is it called the fluid mosaic model?

Answer 9

• Proteins are scattered throughout the bilayer (randomly), which represents a mosaic
• These proteins and phospholipid molecules move freely throughout the membrane, therefore it is fluid.
• It is a model as it is based on chemical and experimental evidence.

Question 10

Why are membranes partially permeable?

Answer 10

• Control what substances are let through
• Substances that are small, or not charged can pass through

Question 11

List 4 functions of a cell membrane

Answer 11

• Allowing selected molecules to move in and out of a cell
• Isolating organelles from the rest of the cell (allow cellular processes to occur separately)
• A site for biochemical reactions
• Allow a cell to change shape

Question 12

How can polar and non polar molecules pass through the membrane?

Answer 12

• Polar molecules, e.g. sodium ions, require a protein to enable them to pass through the membrane
• Non-polar molecules don’t require a protein, and they can diffuse directly through the phospholipid bilayer, e.g. vitamins.

Question 13

What are the 4 types of carrier protein in the membrane?

Answer 13

• Carrier protein (passive) -> no energy required to carry molecules
• Gated-channel protein -> opens and closes
• Channel protein -> like a tunnel
• Carrier protein (active) -> requires energy to transport molecules

Question 14

What does an active carrier protein do in order to meet the demands of the body/cell?

Answer 14

Self replicates

Question 15

Give 3 examples of proteins within a cell membrane?

Answer 15

• Receptors
• ATP synthase (enzymes)
• Electron carriers (e..g electron transport chains)

Question 16

What is the function of cholesterol within a cell membrane?

Answer 16

Cholesterol regulates fluidity of the membrane, maintains mechanical stability and resists the effects of temperature changes on the membranes structure.

Question 17

What is a glycocalyx?

Answer 17

it is outside the membrane, and is composed of carbohydrate chains attached to either lipids (glycolipids) or proteins (glycoproteins) in the membrane.

Question 18

What is the composition of cell membranes in neurones?

Answer 18

Protein channels and carriers in the plasma membrane covering the long axon, allow entry and exit of ions to bring about the conduction of electrical impulses along their length.

Question 19

What is the composition of cell membranes in mitochondria?

Answer 19

Cell membranes of mitochondria are 76% protein and 24% lipid, this is because their inner membranes contain many electron carriers that are made of proteins, and also hydrogen ion channels associated with ATP synthase enzymes