5.1. STRUCTURE AND FUNCTION OF MEMBRANES

Question 1

What are the different types of cell membrane?

Answer 1

-Plasma membrane (AKA cell surface membrane)
-Tonoplast membrane
-Outer mitochondrial membrane
-Inner mitochondrial membrane
-Outer chloroplast membrane
-Nuclear envelope

Question 2

What type of membrane is the cell surface membrane?

Answer 2

Partially Permeable

Question 3

What is compartmentalisation?

Answer 3

Formation of separate membrane-bound areas

Question 4

What does compartmentalisation allow?

Answer 4

-metabolic reaction to be separated
-different environmental conditions in different parts of the cell
-chemical concentration gradients to be made
-protection of cellular components

Question 5

What does the plasma membrane surround?

Answer 5

The cytoplasm of living cells, physically separating the intracellular components from the extracellular environment

Question 6

What is the main ability of membranes?

Answer 6

They are flexible (fluid) and able to break and fuse easily

Question 7

What are the roles of the Cell Surface Membrane?

Answer 7

Environment (homeostasis)
Transport
Cell to Cell Signalling (communication)
Detection of changes in the environment
Site of Chemical Reactions
Anchorage for cytoskeleton/extracellular matrix
Cell to Cell Joining

Question 8

What does the Cell surface membrane not do?

Answer 8

Does NOT provide support for the cell shape

Question 9

What are membranes made out of?

Answer 9

Phospholipids

Question 10

What is the structure of a phospholipid?

Answer 10

-consists of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule
-consists of two non-polar tails (hydrophobic) composed of fatty acid chains (hydrocarbon)

Question 11

What is the definition of hydrophilic?

Answer 11

Water-loving

Question 12

What is the definition of hydrophobic?

Answer 12

Water-hating

Question 13

Why are phospholipids classed as amphipathic?

Answer 13

As they contain both hydrophilic and lipophilic regions

Question 14

What is the definition of lipophilic?

Answer 14

Fat- loving

Question 15

How are phospholipids arranged?

Answer 15

-into a bilayer
-hydrophobic tails face inwards and are shielded from the surrounding polar fluids
-hydrophilic heads face outwards into the cytosolic and extracellular fluids

Question 16

What does bilayer mean?

Answer 16

Two layers

Question 17

What does a kink in the tails represent?

Answer 17

A double bond - increases fluidity

Question 18

What are micelles?

Answer 18

Phospholipids form micelles when submerged in water

Question 19

What is the common structure all phospholipids share?

Answer 19

-polar organic molecule
-phosphate group
-glycerol molecule
-two fatty acid tails

Question 20

What was the first model for plasma membranes?

Answer 20

By Davson and Danielli in 1935
-when under a membrane, showed a ‘trilaminar’ appearance
-model was described as a lipo-protein sandwich
-dark segments representing two protein layers were artifacts

Question 21

What is a trilaminar?

Answer 21

3 layers (two dark outer layers and a lighter inner region)

Question 22

What is an artefact?

Answer 22

defraction of electrons through cell membrane
- shows something that isn’t there

Question 23

What is the fluid-mosaic model?

Answer 23

-By singer and nicolson
Proteins were embedded within the lipid bilayer and were constantly moving

Question 24

According to the fluid-mosaic model, how easily can proteins move within the bilayer?

Answer 24

dependent on the number of phospholipids with unsaturated fatty acids

Question 25

What can often be found within the plasma membrane?

Answer 25

-phospholipids
-integral/transmembrane proteins (channel/carrier)
-peripheral proteins
-cholesterol
-glycoproteins

Question 26

What are extrinsic membrane proteins?

Answer 26

-AKA peripheral proteins
-only present on one side of the membrane
-often have amino acids with hydrophilic R groups on the outer surface of the protein that will bind to the phospholipid heads/a transmembrane protein

Question 27

What are glycoproteins?

Answer 27

proteins that contain oligosaccharide chains covalently attached to amino acid R groups (‘glycosylation’)

Question 28

What are the functions of glycoproteins?

Answer 28

-cell adhesion
-cell signalling
-cell surface markers for cell to cell recognition
-immune responses
-ABO blood groups

Question 29

What is the structure of a glycoprotein?

Answer 29

The phosphate groups in a phospholipid is replaced by the sugar residue

Question 30

What is cholesterol?

Answer 30

-a sterol/type of lipid
-modulates membrane fluidity
-maintains membrane integrity
Hydroxyl group of each cholesterol molecule interacts with water molecules (near phospholipid heads)

Question 31

Why do animal cells not need cell walls?

Answer 31

Cholesterol increases membrane packing which allows the membrane to remain stable and durable without being rigid - allows animal cells to change shape and animals to move

Question 32

What is a feature of intrinsic membrane proteins?

Answer 32

Some act as enzymes
-i.e. the enzymes used in aerobic respiration in the inner mitochondrial membrane
e.g. ATP Synthase

Question 33

What is ATP Synthase?

Answer 33

Formation from ATP to ADP and Pi is energetically unfavourable and would normally proceed in the reverse direction - ATP synthase couples with ATP synthesis to overcome this.