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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
What are the hydrophilic regions of a membrane protein?
Stretches of amino acids with hydrophilic side chains | Domains interact with aqueous environment
26
What are the hydrophobic regions of a membrane protein?
Stretches of amino acids with hydrophobic side chains | Domains interact with interior of phospholipid bilayer
27
How are proteins embedded in the phospholipid bilayer seen?
Freeze-fracturing (electron microscopy)
28
How do proteins and lipids in the interior of membranes interact?
Non-covalentley
29
What are the two types of membrane protein?
Integral membrane protein | Peripheral membrane protein
30
What are integral proteins?
Proteins with a hydrophobic domain in the bilayer- long alpha helix regions that span the core Hydrophilic heads
31
What are peripheral proteins?
- 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
32
How are some membrane proteins attached to the membrane?
Covalently to fatty acids or other lipid groups
33
What are proteins covalently bonded to fatty acids/lipid groups called?
A special type of integral protein
34
How are proteins distributed on inner and outer membrane surfaces?
Asymmetrically
35
What are integral proteins that protrude on both sides of the membrane called?
Transmembrane proteins
36
What do transmembrane proteins have?
Specific domains on each side of the membrane
37
Where are peripheral membranes localised?
One side of the membrane or the other
38
How does asymmetrical distribution affect the membrane?
Gives the two surfaces different properties
39
How do membrane proteins move around?
Relatively freely across the bilayer
40
What type of experiment demonstrates membrane protein movement?
Cell fusion
41
What happens in cell fusion experiments?
Two cells are fused A single, continuous membrane forms Proteins distribute uniformly around membrane
42
How are some proteins anchored/restricted?
Cytoskeleton- components below membrane attach to protein | Lipid rafts-semisolid lipids trap proteins within a region
43
What does it mean that membranes are dynamic?
They are constantly forming, transforming, fusing and breaking down
44
How are membranes constantly changing?
- 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
What serves as recognition sites?
Membrane carbohydrates on the outer surface
46
What may membrane carbohydrates be covalently bonded to?
lipids to form glycolipids | Proteins to form glycoproteins
47
What are glycolipids?
Carbohydrate covalently bonded to lipid | Carbohydrate extends outside plasma membrane to act as a recognition signal between cells
48
When does the carbohydrate of a glycolipid change?
When a cell becomes cancerous- allows white blood cells to target cancer for destruction
49
What is a glycoprotein?
Carbohydrate covalently bonded to a protein
50
What type of carbohydrate is bound to a glycoprotein?
Oligosaccharides (not usually exceeding 15 monosaccharides)
51
What do glycoproteins do?
Enable cells to be recognised by other cells and proteins
52
What two processes allow cells to arrange themselves in groups?
Cell recognition | Cell adhesion
53
How does cell recognition contribute to cells arranging themselves into groups?
One cell specifically binds to another cell of a certain type
54
How does cell adhesion contribute to cells arranging themselves into groups?
The connection between the two cells is strenghtened
55
The study of what organisms has revealed how cells associate?
Sponges- multi-cellular marine animal
56
How are the cells of a sponge separated?
Mechanically by passing through a fine mesh screen
57
In most cases, what type of binding of cells occurs?
Homotypic binding- the same molecules sticks out of both cells and exposed surfaces bind to each other
58
What is the other type of cell binding that can occur?
Heterotypic binding in which cells with different proteins bind
59
Give an example of heterotypic binding in mammals
Mammalian sperm and egg have different proteins which are complementary
60
Give an example of heterotypic binding in non-mammals.
Algae form similar appearing male and female reproductive cells with flagella Heterotypic proteins on their flagella enable them to recognize each other
61
Where can cell junctions be seen easily?
Electron micrographs of epithelial tissues
62
What are the three types of cell junction?
Tight junctions, desmosomes and gap junctions
63
What do tight junctions do?
Seal tissues
64
What are tight junctions?
Specialized structures that link adjacent epithelial cells
65
What are tight junctions the result of?
Mutual binding of specific proteins in the plasma membranes of epithelial cells, forming a series of joints encircling each cell
66
What are the two functions of tight junctions?
- Prevent substances moving through spaces between cells | - Define functional regions of the membrane by restricting migration of membrane proteins/phospholipids
67
Why is it important that tight junctions prevent substances moving through spaces between cell?
Substances entering the body from the lumen of the intestine must pass through the epithelial cells that form the tight junction
68
Why is it important that tight junctions define functional regions of the membrane by restricting migration of membrane proteins/phospholipids?
Membrane proteins/phospholipids in the apical region (tip) facing lumen are different from those on the basolateral regions (facing body cavity)
69
How do the two functions of tight junctions effect movement?
They ensure the directional movement of materials into the body
70
What do desmosomes do?
Hold cells together by connecting adjacent membranes like spot welds or rivets
71
What does each desmosome have?
A dense structure called a plaque on the cytoplasmic side
72
What is attached to the plaque?
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
What else is the plaque attached to?
Fibers in the cytoplasm- the intermediate filaments of the cytoskeleton- made of keratin
74
What do the fibers attached to the plaque do?
Stretch across the cell to connect with another plaque on the other side to anchor on both sides
75
How do these fibers that attach plaques in desmosomes effect the properties of the tissue?
Provide great mechanical strength and stability to epithelial tissue
76
What are gap junctions?
Junctions which facilitate communication between cells
77
What are gap junctions made up of?
Specialised channel proteins called connexons
78
What property do plasma membranes of some cell types such as neurons, muscles cells and some eggs have?
They respond to electric charges carried on ions | They are electrically excitable
79
What are three other functions of some membranes?
- Help transform energy - Organize chemical reactions - Process information
80
How do some specialized membranes help to transform energy?
Inner mitochondrial membrane helps convert energy from fuel molecules into ATP Thylakoid membranes help convert light energy into chemical bond energy
81
How do some specialized membranes help to organize chemical reactions?
- 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
How do some membranes help to process information?
Binding of ligands to membrane proteins or carbohydrates initiates, modifies or stops a cell function
83
Give an example of a membrane helping to process information.
Insulin, a hormone, acts on specific target cells to elicit a response in that cell
84
How many subunits does the cholera toxin protein have?
2 subunits | One binds to cell surface glycolipid
85
What does the cholera toxin protein do once one subunit has bound to a glycolipid?
A change in the 3D shape of the toxin protein means the second subunit enters the cell
86
How does the second subunit of the cholera toxin protein effect the cell once inside?
It acts on an enzyme to modify a peripheral protein adenylate cyclase on the inner surface of the cells plasma membrane
87
What does modified adenylate cyclase do inside the cell?
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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