Lecture 1 - Membrane Bilayer Structure

Question 1

What are the major functions of biological membranes?

Answer 1

Highly selective permeable barrier
Controls enclosed electrochemical environment
COMMUNICATION
Generating signals in response to stimuli

Question 2

How are membranes involved in communication?

Answer 2

Recognition
Signalling
Adhesion proteins
Immune surveillance

Question 3

How would you describe the structure of a cell membrane generally?

Answer 3

A dynamic fluid phospholipid bilayer with proteins and additional structures

Question 4

What is meant by membranes being heterogenous within and between cells?

Answer 4

The structure and therefore undying function of membranes are different based on the cells/organelles function

Question 5

What types of molecules are cell membranes made up of?

Answer 5

Lipids
Proteins
Carbohydrates

Question 6

What is a major component of the cell membrane?

Answer 6

Water
Membranes are hydrated structures

Question 7

What is the role of water in hydrating membranes?

Answer 7

It interacts with the charged/polar regions
This stabilises the lipid head regions of the bilayer

Question 8

What are the 3 types of lipids that can compromise cell membranes?

Answer 8

Phospholipids
Glycolipids
Cholesterol

Question 9

What is the difference between saturated and unsaturated phospholipids making up the cell membrane?

Answer 9

Saturated have single C-C bonds in the fatty acid chains

Unsaturated have some C=C bonds in the fatty acid chains

Question 10

What are the 2 structural forms of unsaturated phospholipids?

Answer 10

Cis
Trans

Question 11

What is the structure of a Cis phospholipid?

Answer 11

One of the fatty acid chains is kinked at the point of the double bond

Question 12

Which is the structure of a trans phospholipid?

Answer 12

Double C=C bond where the fatty acid chains are straight

Question 13

What is the name of a type of glycolipid?

Answer 13

Ganglioside

Question 14

What does Amphipathic mean?

Answer 14

One part of the molecule is hydrophilic
One part of the molecule is hydrophobic

Question 15

What is amphipathic about the cell membrane?

Answer 15

The polar (hydrophilic) heads
The non polar (hydrophobic) fatty acid chains of the bilayer

Question 16

What is a Micelle?

Answer 16

3D sphere of phospholipids

Question 17

What is the main type of phospholipid that makes up the cell membrane?

Answer 17

Glycerophospholipids

Question 18

What is the structure of a Glycerophospholipid?

Answer 18

Polar phosphate group = hydrophilic head

Glycerol backbone

Fatty acid chains (hydrophobic tail)

Question 19

What property of glycerol in a phospholipid allows the polar phosphate head and hydrophobic fatty acid tails to swivel?

Answer 19

The single bonds in glycerol

Question 20

What is esterification?

Answer 20

An acid group being added to an alcohol group

Question 21

Which group of fatty acid chains can interact with water?

Answer 21

-C=O (acyl group)

Question 22

What are 2 common polar head groups that can be found attached to the phosphate group?

Answer 22

Choline
Inositol

Question 23

What type of molecule is sphingomyelin?

Answer 23

Phospholipid

Question 24

What is different between a sphingomyelin molecule and a glycerophospholipid?

Answer 24

Sphingomyelin does not have a glycerol backbone, it has a Sphingosine molecule instead

Question 25

What process does sphingomyelin have a key role in?

Answer 25

Lipid raft formation

Question 26

What are the 2 types of glycolipids?

Answer 26

Cerebrosides Gangliosides

Question 27

What is special about glycolipids structurally?

Answer 27

No glycerol backbone (sphingosine) No phosphate group

Question 28

Where are cerebrosides and gangliosides mainly found?

Answer 28

CNS/PNS

Question 29

On the membrane, where are sphingomyelin and glycolipids found?

Answer 29

On the outer face of the membrane

Question 30

What is the structure/properties of cholesterol?

Answer 30

Amphipathic Hydrophilic -OH head Hydrophobic 4 planar carbon rings and short fatty acid tail

Question 31

What is the key membrane function of cholesterol?

Answer 31

Regulates membrane fluidity and stability by enhancing/extending temerature range that the membrane is thermodynamically stable Lipid raft formation

Question 31

What is the key membrane function of cholesterol?

Answer 31

Regulates membrane fluidity and stability by enhancing/extending temerature range that the membrane is thermodynamically stable Lipid raft formation

Question 32

What is membrane fluidity?

Answer 32

The property of the cell membrane that allows it to adapt its shape and movement to different conditions

Question 33

What happens when the cell membrane is too fluid?

Answer 33

There is a loss of molecular organisation needed for membrane/protein function

Question 34

What happens when the membrane is not fluid enough and is gel like?

Answer 34

It restricts and constrains the mobility of proteins and restricts the ability for diffusion to take place

Question 35

What is the main Physical factor affecting membrane fluidity, name another factor?

Answer 35

Temperature Molecular mass of phospholipid

Question 36

What are the ways that individual phospholipid molecules move?

Answer 36

Individual chain bond Flexion/vibration (wobbly bob) Fast axial rotation (whole lipid spins on head) Fast lateral diffusion (lipid moves randomly through bilayer Protrusion (Bobbing up and down) Flip-flop

Question 37

How is vibration/movement of phospholipid molecules affected by temperature and molecular mass?

Answer 37

Higher temp = higher vibration Higher molecular mass = less vibration

Question 38

How do cell membrane bilayers behave that have saturated phospholipids at 37ºC?

Answer 38

Fluid behaviour

Question 39

How does adding unsaturated phospholipid to a membrane bilayer affect its fluidity?

Answer 39

Decreases the temperature by which the membrane changes form a gel to fluid state INCREASES FLUIDITY

Question 40

How does adding unsaturated phospholipids to cell membrane increase its fluidity?

Answer 40

Due to the cis C=C bond with kink Less dense packing of fatty acid tails

Question 41

At high temperatures, what type of movement of phospholipids happens too much causing the structural integrity of the membrane to become too disordered?

Answer 41

Increased bond chain Flexion/vibration

Question 42

What does cholesterol due to the range of fluidity?

Answer 42

Increases range by making membrane fluid at lower temperatures

Question 43

How does cholesterol stabilise the membrane at higher temperatures?

Answer 43

-OH polar group of cholesterol binds to acyl group of phospholipid head Rigid carbon rings limits movement of fatty acid tails

Question 44

How does cholesterol increase the fluidity of the membrane at low temperatures?

Answer 44

Interferes with crystalline packing of the fatty acid chainns

Question 45

How is water important in the structure of the membrane?

Answer 45

It dynamically interacts with the membrane

Question 46

What is a lipid raft?

Answer 46

Areas of organised/specialised distribution of lipids in cell membranes

Question 47

What molecules are increased in numbers in lipid rafts?

Answer 47

Cholesterol Sphingomyelin Glycolipids

Question 48

What is the role of lipid rafts?

Answer 48

Role in stabilising and organising proteins Domains for receptors and signalling molecules

Question 49

What is the importance of the membrane fluid and flexible?

Answer 49

Protein function Able to transmit force throughout cell structures

Question 50

Why is it important for forces to be distribute throughout the whole body?

Answer 50

Excessive force that is localised can cause damage