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IB Biology > 1.3 Membrane Structure > Flashcards

1.3 Membrane Structure Flashcards

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1
Q

What are the two main components of phospholipids?

A

A hydrophilic polar head and two non polar hydrophobic tails

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2
Q

What are the hydrophilic heads composed of?

A

A glycerol and a phosphate molecule

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3
Q

What are the non polar hydrophobic tails composed of?

A

Fatty acid hydrocarbon chains

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4
Q

What are phospholipids classed as?

A

Amphipathic

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5
Q

What does amphipathic mean?

A

Contains both hydrophobic and hydrophilic regions

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6
Q

How do phospholipids arrange themselves?

A

Spontaneously into a bilayer

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7
Q

Which direction do the tails face?

A

Inwards

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8
Q

What are the tails shielded from?

A

Surrounding polar fluids

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9
Q

Which direction does the heads face?

A

Outwards

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10
Q

What fluids do the heads associate with?

A

Cytosolic and extracellular

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11
Q

What holds the phospholipid bilayer together?

A

Weak hydrophobic interactions between the tails

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12
Q

What do the the hydrophobic/hydrophilic layers restrict?

A

Passages of many substances

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13
Q

What can move within the bilayer?

A

Individual phospholipids

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14
Q

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

A

Fluidity and flexibility

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15
Q

What does the fluidity of the phospholipid bilayer allow for?

A

Spontaneous breaking and reforming of membranes

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16
Q

What are examples of spontaneous breaking and reforming of membranes?

A

Endocytosis and exocytosis

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17
Q

What are the phospholipid bilayers embedded with?

A

Proteins

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18
Q

How long may proteins be attached to the membrane for?

A

Permanently or temporary

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19
Q

What are the two types of proteins you can get?

A

Integral and peripheral proteins

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20
Q

Are integral proteins permanently or temporarily attached to the membrane?

A

Permanently

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21
Q

Are peripheral proteins permanently or temporarily attached to the membrane?

A

Peripheral

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22
Q

How would you typically find integral proteins?

A

Transmembrane

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23
Q

How are peripheral proteins temporarily attached?

A

Via non covalent interactions

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24
Q

Where would you find a peripheral protein on the membrane?

A

On one surface of the membrane

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25
Q

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

A

Polarity

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26
Q

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

A

Directly

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27
Q

Where are polar amino acids located?

A

Internally

28
Q

What do polar amino acids face?

A

Aqueous solutions

29
Q

What level of structures do transmembrane proteins typically adopt?

A

Tertiary

30
Q

What are the two tertiary structures transmembrane proteins can adopt?

A

Single helices/ helical bundles
Beta barrels

31
Q

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

A

Junctions
Enzymes
Transport
Recognition
Anchorage
Transduction

32
Q

How do membrane proteins function as junctions?

A

They serve to connect and join two cells together?

33
Q

How do membrane proteins function as enzymes?

A

They fix to membranes which localises metabolic pathways

34
Q

How do membrane proteins function as transport?

A

They are responsible for facilitated diffusion and active transport

35
Q

How do membrane proteins function as recognition?

A

May function as markers for cellular identification

36
Q

How do membrane proteins function as anchorage?

A

They are attachment points for cytoskeleton and extracellular matrix

37
Q

How do membrane proteins function as transduction?

A

They function as receptors for peptide hormones

38
Q

What is cholesterol a component of?

A

Animal cell membranes

39
Q

What is the function of cholesterol?

A

To maintain integrity and mechanical stability

40
Q

Where is cholesterol absent?

A

In plant cells

41
Q

Why is cholesterol absent in plant cells?

A

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

42
Q

What type of molecule is cholesterol?

A

Amphipathic

43
Q

What part of cholesterol is hydrophilic?

A

The hydroxyl group

44
Q

Which way does the cholesterol hydroxyl group align?

A

Towards the phosphate heads of phospholipids

45
Q

What parts of cholesterol is hydrophobic?

A

The steroid ring and hydrocarbon tail

46
Q

What does the hydrophobic parts of cholesterol associate with?

A

The phospholipid tails

47
Q

How are phospholipid bilayers fluid?

A

They are in constant movement relative to one another

48
Q

What does the cholesterol interact with?

A

The fatty acid tails of the phospholipids

49
Q

How does cholesterol reduce fluidity?

A

It functions to immobilise the outer surface of the membrane

50
Q

How does cholesterol affect the permeability of the membrane?

A

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

51
Q

How does cholesterol prevent crystallisation of the membrane?

A

It functions to separate phospholipid tails

52
Q

How does cholesterol help secure peripheral proteins?

A

By forming high density lipid rafts capable of anchoring the protein

53
Q

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

A
  • reduces fluidity
  • makes it less permeable
  • prevents crystallisation
  • Helps secure peripheral proteins
54
Q

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

A

A fluid mosaic model

55
Q

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

A

The phospholipid bilayer is viscous and individual phospholipids can move positions

56
Q

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

A

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

57
Q

What are the three components of the plasma membrane?

A

Phospholipids
Cholesterol
Proteins

58
Q

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

A

Davson and Danielli

59
Q

What type of model did Danielli and Davson propose?

A

A lipo protien sandwich

60
Q

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

A

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

61
Q

What did the Danielli and Davson model not account for?

A

Permeability of certain substances and temperatures

62
Q

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

A

Fluorescent antibody tagging of membrane proteins and freeze fracturing

63
Q

What did the fluorescent antibody tagging of membrane proteins prove?

A

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

64
Q

What did freeze facturing prove?

A

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

65
Q

What are the key differences of the two membrane structures?

A

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

IB Biology (57 decks)

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