1.3 Membrane Structure

Question 1

What are the two main components of phospholipids?

Answer 1

A hydrophilic polar head and two non polar hydrophobic tails

Question 2

What are the hydrophilic heads composed of?

Answer 2

A glycerol and a phosphate molecule

Question 3

What are the non polar hydrophobic tails composed of?

Answer 3

Fatty acid hydrocarbon chains

Question 4

What are phospholipids classed as?

Answer 4

Amphipathic

Question 5

What does amphipathic mean?

Answer 5

Contains both hydrophobic and hydrophilic regions

Question 6

How do phospholipids arrange themselves?

Answer 6

Spontaneously into a bilayer

Question 7

Which direction do the tails face?

Answer 7

Inwards

Question 8

What are the tails shielded from?

Answer 8

Surrounding polar fluids

Question 9

Which direction does the heads face?

Answer 9

Outwards

Question 10

What fluids do the heads associate with?

Answer 10

Cytosolic and extracellular

Question 11

What holds the phospholipid bilayer together?

Answer 11

Weak hydrophobic interactions between the tails

Question 12

What do the the hydrophobic/hydrophilic layers restrict?

Answer 12

Passages of many substances

Question 13

What can move within the bilayer?

Answer 13

Individual phospholipids

Question 14

What does the fact that individual phospholipids can move within the bilayer allow the membrane to have?

Answer 14

Fluidity and flexibility

Question 15

What does the fluidity of the phospholipid bilayer allow for?

Answer 15

Spontaneous breaking and reforming of membranes

Question 16

What are examples of spontaneous breaking and reforming of membranes?

Answer 16

Endocytosis and exocytosis

Question 17

What are the phospholipid bilayers embedded with?

Answer 17

Proteins

Question 18

How long may proteins be attached to the membrane for?

Answer 18

Permanently or temporary

Question 19

What are the two types of proteins you can get?

Answer 19

Integral and peripheral proteins

Question 20

Are integral proteins permanently or temporarily attached to the membrane?

Answer 20

Permanently

Question 21

Are peripheral proteins permanently or temporarily attached to the membrane?

Answer 21

Peripheral

Question 22

How would you typically find integral proteins?

Answer 22

Transmembrane

Question 23

How are peripheral proteins temporarily attached?

Answer 23

Via non covalent interactions

Question 24

Where would you find a peripheral protein on the membrane?

Answer 24

On one surface of the membrane

Question 25

What are the amino acids of a membrane protein localised in accordance to?

Answer 25

Polarity

Question 26

How do non polar amino acids associate with the lipid bilayer?

Answer 26

Directly

Question 27

Where are polar amino acids located?

Answer 27

Internally

Question 28

What do polar amino acids face?

Answer 28

Aqueous solutions

Question 29

What level of structures do transmembrane proteins typically adopt?

Answer 29

Tertiary

Question 30

What are the two tertiary structures transmembrane proteins can adopt?

Answer 30

Single helices/ helical bundles Beta barrels

Question 31

What are the six functions of membrane proteins? (JET RAT)

Answer 31

Junctions Enzymes Transport Recognition Anchorage Transduction

Question 32

How do membrane proteins function as junctions?

Answer 32

They serve to connect and join two cells together?

Question 33

How do membrane proteins function as enzymes?

Answer 33

They fix to membranes which localises metabolic pathways

Question 34

How do membrane proteins function as transport?

Answer 34

They are responsible for facilitated diffusion and active transport

Question 35

How do membrane proteins function as recognition?

Answer 35

May function as markers for cellular identification

Question 36

How do membrane proteins function as anchorage?

Answer 36

They are attachment points for cytoskeleton and extracellular matrix

Question 37

How do membrane proteins function as transduction?

Answer 37

They function as receptors for peptide hormones

Question 38

What is cholesterol a component of?

Answer 38

Animal cell membranes

Question 39

What is the function of cholesterol?

Answer 39

To maintain integrity and mechanical stability

Question 40

Where is cholesterol absent?

Answer 40

In plant cells

Question 41

Why is cholesterol absent in plant cells?

Answer 41

Their plasma membranes are surrounded and supported by a rigid cell wall made of cellulose

Question 42

What type of molecule is cholesterol?

Answer 42

Amphipathic

Question 43

What part of cholesterol is hydrophilic?

Answer 43

The hydroxyl group

Question 44

Which way does the cholesterol hydroxyl group align?

Answer 44

Towards the phosphate heads of phospholipids

Question 45

What parts of cholesterol is hydrophobic?

Answer 45

The steroid ring and hydrocarbon tail

Question 46

What does the hydrophobic parts of cholesterol associate with?

Answer 46

The phospholipid tails

Question 47

How are phospholipid bilayers fluid?

Answer 47

They are in constant movement relative to one another

Question 48

What does the cholesterol interact with?

Answer 48

The fatty acid tails of the phospholipids

Question 49

How does cholesterol reduce fluidity?

Answer 49

It functions to immobilise the outer surface of the membrane

Question 50

How does cholesterol affect the permeability of the membrane?

Answer 50

It makes it less permeable to small water soluble molecules that otherwise would freely cross

Question 51

How does cholesterol prevent crystallisation of the membrane?

Answer 51

It functions to separate phospholipid tails

Question 52

How does cholesterol help secure peripheral proteins?

Answer 52

By forming high density lipid rafts capable of anchoring the protein

Question 53

What are the four ways cholesterol moderates the properties of the membrane?

Answer 53

- reduces fluidity - makes it less permeable - prevents crystallisation - Helps secure peripheral proteins

Question 54

What type of model are cell membranes represented in accordance to?

Answer 54

A fluid mosaic model

Question 55

When talking about the membrane model what does the term fluid mean?

Answer 55

The phospholipid bilayer is viscous and individual phospholipids can move positions

Question 56

When talking about the membrane model what does the term mosaic mean?

Answer 56

The phospholipid bilayer is embedded with proteins causing a mosaic of components

Question 57

What are the three components of the plasma membrane?

Answer 57

Phospholipids Cholesterol Proteins

Question 58

Who created the first model that attempted to describe the position of proteins in the bilayer?

Answer 58

Davson and Danielli

Question 59

What type of model did Danielli and Davson propose?

Answer 59

A lipo protien sandwich

Question 60

What were the three things that the Danielli and Davson model assumed?

Answer 60

A uniform thickness Constant lipid- protein ration All membranes to be symmetrical

Question 61

What did the Danielli and Davson model not account for?

Answer 61

Permeability of certain substances and temperatures

Question 62

What methods helped show that the Danielli and Davson model was incorrect?

Answer 62

Fluorescent antibody tagging of membrane proteins and freeze fracturing

Question 63

What did the fluorescent antibody tagging of membrane proteins prove?

Answer 63

That membrane proteins could move and did not form a static layer

Question 64

What did freeze facturing prove?

Answer 64

That proteins were not solely localised to the outside of the membrane structure

Question 65

What are the key differences of the two membrane structures?

Answer 65

Davson-Danielli model says that proteins form distinct layers whereas Singer-Nicholson model says that proteins are embedded within bilayer