2.5.1- The Structure Of Cell Membranes

Question 1

Define what a glycolipid is.

Answer 1

A lipid molecule with a chain of carbohydrate molecules attached to it, on the outside of a membrane.

Question 2

Define what a glycoprotein is.

Answer 2

A protein molecule with a chain of carbohydrate molecules attached, positioned on the outside of a membrane.

Question 3

The cell surface membrane is called the…

Answer 3

Plasma membrane.

Question 4

What is permeability?

Answer 4

The ability to let substances pass through.

Question 5

Explain how some very small molecules can pass through the plasma membrane.

Answer 5

They can diffuse through the membrane in between its structural molecules.

Question 6

What are the four options for matter that want to pass through a cell membrane?

Answer 6

• diffusing through the bilayer
• protein channels
• protein carriers
• dissolve in the lipid layer and pass through

Question 7

As the phospholipid bilayer does not allow all substances through, it is referred to as what?

Answer 7

A partially permeable/ selectively permeable membrane.

Question 8

What determines the permeability of the cell membrane first and foremost?

Answer 8

The component molecules of the membrane.

Question 9

List seven functions of the plasma membrane at the surface of cells?

Answer 9

• Regulates transport of material in and out of cell
• Can contain enzymes involved in metabolic pathways
• may release chemicals for chemical signalling
• may have receptors for cell signalling
• separates cells components and external environment
• has antigens
• can be the site of chemical reactions

Question 10

Give a simple definition of the fluid mosaic model

Answer 10

The theory of cell membrane structure with proteins embedded in a sea of phospholipids.

Question 11

explain why the membranes at the surface of the celebs have antigens.

Answer 11

So the organisms immune system can recognise the cell as being ‘self’ and not attack it

Question 12

In some organelles, _________ _________ occur on the membranes

Answer 12

Metabolic processes

Question 13

Explain why a lot of the organelles present in eukaryotic cells have membranes.

Answer 13

So the organelle contents is separate from the cytoplasm and that each organelle is a discrete entity and able to perform its function.

Question 14

Discuss two reasons as to why mitochondria have folded inner membranes called cristae.

Answer 14

They give a large surface area for some of the reactions of aerobic respiration.

And localise some of the enzymes needed for respiration to occur.

Question 15

Identify two functions of the inner membrane of chloroplasts (thylakoids).

Answer 15

House chlorophyll

Some of the reactions of photosynthesis occur here

Question 16

Explain the functions of the plasma membrane of epithelial cells that line the small intestine.

Answer 16

There are digestive enzymes that catalyse some of the final stages of the breakdown of certain sugars on the membrane.

Question 17

The fluid mosaic model (proposed 1972 by Singer and Nicholson) is a model that allows…

Answer 17

The passage of molecules through the membrane.

Question 18

The fluid mosaic model explains how cell membranes could me more what?

Answer 18

Dynamic and interact more with the cells environment.

Question 19

Explain how the FM model describes the fluidity of the membrane.

Answer 19

It suggests the lipid molecules can change places with each other and some of the proteins in the model can move.

Question 20

What are the three types of protein that can be found spanning the membrane?

Answer 20

Protein channels

Protein carriers

Other proteins that can be attached to the carrier proteins

Question 21

Describe what three functions the proteins that are attached to the carrier proteins sometimes can have.

Answer 21

Can act as enzymes, antigens or receptor sites for complementary shaped signalling chemicals, e.g. Hormones

Question 22

Eukaryotic cell membranes contain ________

Answer 22

Cholesterol

Question 23

What are the three main functions of cholesterol in membranes?

Answer 23

Control membrane fluidity

Maintain mechanical stability

Resist the effects of temperature changes on membrane structure

Question 24

How thick is the total thickness of the cell membrane?

Answer 24

5-10 nanometers

Question 25

What is the glycocalyx?

Answer 25

A carbohydrate enriched coating that covers the outside of many cells, consisting of glycolipid a and glycoproteins.

Question 26

List four functions of glycolipids.

Answer 26

• Often act as markers for cell recognition
• provide cell stability
• help cells join to other cells to form tissues
• blood type determination stems from different glycolipids present on the surface of red blood cells

Question 27

List four functions of glycoproteins.

Answer 27

• Structural integrity
• cell adhesion
• cell-cell recognition roles
• roles in protection and immune response

Question 28

Explain how protein carriers take matter from one side of the cell to the other.

Answer 28

By changing their shape

Question 29

Explain how protein channels carry molecules to the other side of the membrane.

Answer 29

They have pores and act as channels to allow ions (with an electrical charge and are surrounded by water) to pass through

Question 30

Why do the protein channels and carriers in the plasma membrane of neurones covering the long axon allow the entry and exit of ions?

Answer 30

To bring about conduction of electrical impulses along their length

Question 31

Neurones have a myelin sheath (about 20% protein and 76% lipid) formed by…

Answer 31

Flattened cells wrapped around them several times to give several layers of cell membrane.

Question 32

Explain how the plasma membranes of white blood cells are specialised.

Answer 32

It contains special protein receptors to enable the recognition of the antigens of foreign cells, from invading pathogens, tissue or organ transplants

Question 33

Explain how root hair cells can have specialised membranes.

Answer 33

The membrane can have many carrier proteins to actively transport nitrate ions from the soil into the cells

Question 34

What re the ratios of protein and lipid that the inner membrane of mitochondria is made up of?

Answer 34

76% protein and 24% lipid

Question 35

Explain why the inner membrane of mitochondria has such a high ratio of protein present.

Answer 35

It has many electron carriers made of protein and hydrogen ion channels