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Biology 2 > Lecture 6- Biological membranes > Flashcards

Lecture 6- Biological membranes Flashcards

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1
Q

What is the general design of a biological membrane called?

A

The fluid mosaic model

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2
Q

What are some functions of proteins embedded in the phospholipid bilayer?

A

Moving materials

Receiving chemical signals

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3
Q

What are carbohydrates associated with a membrane attached to?

A

Either lipids or protein molecules

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4
Q

What makes up the bulk of a membrane?

A

Lipids

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5
Q

What are the features of the hydrophilic region?

A

Phosphorus containing head, electrically charged (associates with polar water)

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6
Q

What are the features of the hydrophobic region?

A

Long, non-polar fatty acid tails

Associate with non-polar materials

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7
Q

What happens when a small hole forms on the phospholipid bilayer?

A

It seals spontaneously

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8
Q

What feature of phospholipid bilayers helps membranes fuse during vesicle formation or phagocytosis?

A

The capacity for lipids to associate with one another and maintain bilayer organisation

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9
Q

Given biological membranes have similar structure, what produces different types of bilayers?

A

They have different compositions

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10
Q

How can phospholipid composition change?

A

Fatty acid chain length
Degree of unsaturation
Polar (phosphate containing) groups present

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11
Q

Other than changing the phospholipids, how can the composition of a membrane be changed?

A

Up to 25% can be cholestrol
Cholestrol is important in membrane integrity
Cholestrol is common next to unsaturated fat

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12
Q

What 2 aqueous regions does the membrane separate?

A

The cytosol and the interstital fluid

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13
Q

What does the phospholipid membrane do to the membrane structure?

A

Stabilizes it

But keeps it flexible- it is fluid

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14
Q

What does fluidity of the membrane do?

A

Permits some molecules to move laterally (side to side)

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15
Q

What type of movement of a phospholipid molecule happens rarely?

A

It flips over to the other side, called flip-flop

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16
Q

Why is flip-flopping rare?

A

The polar part of each molecule would have to move through the hydrophobic interior.

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17
Q

What two factors affect membrane fluidity?

A

Lipid composition

Temperature

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18
Q

What type of membrane is more fluid?

A

Shorter chains
Unsaturated fatty acids
Less cholestrol

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19
Q

Why is membrane fluidity important for a membranes function?

A

Molecules move more slowly

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20
Q

What happens to membranes of organisms who cannot keep their bodies warm?

A

Molecules move more slowly, fluidity decreases- may adjust lipid composition

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21
Q

Where is changing lipid composition important?

A

Survival of plants and hibernating animals and bacteria over winter

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22
Q

How are membrane proteins distributed?

A

Asymmetrically

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23
Q

How many proteins molecules are there in a typical membrane?

A

1 per 25 phospholipid molecules

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24
Q

What regions do proteins embedded in phospholipid bilayers have?

A

Hydrophillic and hydrophobic regions

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25
Q

What are the hydrophilic regions of a membrane protein?

A

Stretches of amino acids with hydrophilic side chains

Domains interact with aqueous environment

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26
Q

What are the hydrophobic regions of a membrane protein?

A

Stretches of amino acids with hydrophobic side chains

Domains interact with interior of phospholipid bilayer

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27
Q

How are proteins embedded in the phospholipid bilayer seen?

A

Freeze-fracturing (electron microscopy)

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28
Q

How do proteins and lipids in the interior of membranes interact?

A

Non-covalentley

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29
Q

What are the two types of membrane protein?

A

Integral membrane protein

Peripheral membrane protein

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30
Q

What are integral proteins?

A

Proteins with a hydrophobic domain in the bilayer- long alpha helix regions that span the core
Hydrophilic heads

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31
Q

What are peripheral proteins?

A
  • Do not have hydrophobic domains
  • Not embedded in bilayer
  • Polar/charged regions interact with regions on exposed parts of integral proteins or polar head of phospholipid molecules
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32
Q

How are some membrane proteins attached to the membrane?

A

Covalently to fatty acids or other lipid groups

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33
Q

What are proteins covalently bonded to fatty acids/lipid groups called?

A

A special type of integral protein

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34
Q

How are proteins distributed on inner and outer membrane surfaces?

A

Asymmetrically

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35
Q

What are integral proteins that protrude on both sides of the membrane called?

A

Transmembrane proteins

36
Q

What do transmembrane proteins have?

A

Specific domains on each side of the membrane

37
Q

Where are peripheral membranes localised?

A

One side of the membrane or the other

38
Q

How does asymmetrical distribution affect the membrane?

A

Gives the two surfaces different properties

39
Q

How do membrane proteins move around?

A

Relatively freely across the bilayer

40
Q

What type of experiment demonstrates membrane protein movement?

A

Cell fusion

41
Q

What happens in cell fusion experiments?

A

Two cells are fused
A single, continuous membrane forms
Proteins distribute uniformly around membrane

42
Q

How are some proteins anchored/restricted?

A

Cytoskeleton- components below membrane attach to protein

Lipid rafts-semisolid lipids trap proteins within a region

43
Q

What does it mean that membranes are dynamic?

A

They are constantly forming, transforming, fusing and breaking down

44
Q

How are membranes constantly changing?

A
  • Phospholipids are synthesised in SER
  • Membrane proteins form on ribosomes
  • Functioning membranes (ER buds away as vesicles join cis region, trans region buds join plasma membrane)
  • Removal by phagocytosis
45
Q

What serves as recognition sites?

A

Membrane carbohydrates on the outer surface

46
Q

What may membrane carbohydrates be covalently bonded to?

A

lipids to form glycolipids

Proteins to form glycoproteins

47
Q

What are glycolipids?

A

Carbohydrate covalently bonded to lipid

Carbohydrate extends outside plasma membrane to act as a recognition signal between cells

48
Q

When does the carbohydrate of a glycolipid change?

A

When a cell becomes cancerous- allows white blood cells to target cancer for destruction

49
Q

What is a glycoprotein?

A

Carbohydrate covalently bonded to a protein

50
Q

What type of carbohydrate is bound to a glycoprotein?

A

Oligosaccharides (not usually exceeding 15 monosaccharides)

51
Q

What do glycoproteins do?

A

Enable cells to be recognised by other cells and proteins

52
Q

What two processes allow cells to arrange themselves in groups?

A

Cell recognition

Cell adhesion

53
Q

How does cell recognition contribute to cells arranging themselves into groups?

A

One cell specifically binds to another cell of a certain type

54
Q

How does cell adhesion contribute to cells arranging themselves into groups?

A

The connection between the two cells is strenghtened

55
Q

The study of what organisms has revealed how cells associate?

A

Sponges- multi-cellular marine animal

56
Q

How are the cells of a sponge separated?

A

Mechanically by passing through a fine mesh screen

57
Q

In most cases, what type of binding of cells occurs?

A

Homotypic binding- the same molecules sticks out of both cells and exposed surfaces bind to each other

58
Q

What is the other type of cell binding that can occur?

A

Heterotypic binding in which cells with different proteins bind

59
Q

Give an example of heterotypic binding in mammals

A

Mammalian sperm and egg have different proteins which are complementary

60
Q

Give an example of heterotypic binding in non-mammals.

A

Algae form similar appearing male and female reproductive cells with flagella
Heterotypic proteins on their flagella enable them to recognize each other

61
Q

Where can cell junctions be seen easily?

A

Electron micrographs of epithelial tissues

62
Q

What are the three types of cell junction?

A

Tight junctions, desmosomes and gap junctions

63
Q

What do tight junctions do?

A

Seal tissues

64
Q

What are tight junctions?

A

Specialized structures that link adjacent epithelial cells

65
Q

What are tight junctions the result of?

A

Mutual binding of specific proteins in the plasma membranes of epithelial cells, forming a series of joints encircling each cell

66
Q

What are the two functions of tight junctions?

A
  • Prevent substances moving through spaces between cells

- Define functional regions of the membrane by restricting migration of membrane proteins/phospholipids

67
Q

Why is it important that tight junctions prevent substances moving through spaces between cell?

A

Substances entering the body from the lumen of the intestine must pass through the epithelial cells that form the tight junction

68
Q

Why is it important that tight junctions define functional regions of the membrane by restricting migration of membrane proteins/phospholipids?

A

Membrane proteins/phospholipids in the apical region (tip) facing lumen are different from those on the basolateral regions (facing body cavity)

69
Q

How do the two functions of tight junctions effect movement?

A

They ensure the directional movement of materials into the body

70
Q

What do desmosomes do?

A

Hold cells together by connecting adjacent membranes like spot welds or rivets

71
Q

What does each desmosome have?

A

A dense structure called a plaque on the cytoplasmic side

72
Q

What is attached to the plaque?

A

Cell adhesion molecules (CAMs) that stretch from the plaque through the plasma membrane of one cell, across intercellular space and through the plasma membrane of the adjacent cell

73
Q

What else is the plaque attached to?

A

Fibers in the cytoplasm- the intermediate filaments of the cytoskeleton- made of keratin

74
Q

What do the fibers attached to the plaque do?

A

Stretch across the cell to connect with another plaque on the other side to anchor on both sides

75
Q

How do these fibers that attach plaques in desmosomes effect the properties of the tissue?

A

Provide great mechanical strength and stability to epithelial tissue

76
Q

What are gap junctions?

A

Junctions which facilitate communication between cells

77
Q

What are gap junctions made up of?

A

Specialised channel proteins called connexons

78
Q

What property do plasma membranes of some cell types such as neurons, muscles cells and some eggs have?

A

They respond to electric charges carried on ions

They are electrically excitable

79
Q

What are three other functions of some membranes?

A
  • Help transform energy
  • Organize chemical reactions
  • Process information
80
Q

How do some specialized membranes help to transform energy?

A

Inner mitochondrial membrane helps convert energy from fuel molecules into ATP
Thylakoid membranes help convert light energy into chemical bond energy

81
Q

How do some specialized membranes help to organize chemical reactions?

A
  • Cellular processes depend on a series of enzyme catalyzed reactions
  • Membranes bring these molecules together in a sequential order
  • More rapid and efficient chemical reactions
82
Q

How do some membranes help to process information?

A

Binding of ligands to membrane proteins or carbohydrates initiates, modifies or stops a cell function

83
Q

Give an example of a membrane helping to process information.

A

Insulin, a hormone, acts on specific target cells to elicit a response in that cell

84
Q

How many subunits does the cholera toxin protein have?

A

2 subunits

One binds to cell surface glycolipid

85
Q

What does the cholera toxin protein do once one subunit has bound to a glycolipid?

A

A change in the 3D shape of the toxin protein means the second subunit enters the cell

86
Q

How does the second subunit of the cholera toxin protein effect the cell once inside?

A

It acts on an enzyme to modify a peripheral protein adenylate cyclase on the inner surface of the cells plasma membrane

87
Q

What does modified adenylate cyclase do inside the cell?

A

It opens chloride channels in the membrane which results in Na+ and Cl- accumulating in the intestine and hence osmotic water loss

Biology 2 (14 decks)

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