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BIOL 2321 - Cell Biology > Plasma Membrane > Flashcards

Plasma Membrane Flashcards

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1
Q

What are the 6 membrane properties?

A

fluid (in 2 dimensions)

asymmetric (two sides of membrane are different)

Specific to the function of the cell/organelle

self-assembled - held together mostly by non-covalent interactions

semi-permeable to control contents

mosaic of lipids and proteins and some carbohydrate chains attached

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2
Q

Approximately how wide is the plasma membrane?

A

5-10 nm wide

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3
Q

What are the four major properties of the membrane? (FASS)

A

Fluid

Asymmetric

Self-assembled

Specific

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4
Q

What are 7 membrane functions

A
  1. compartmentalization
  2. basis for biochemical reactions
  3. selectively permeable membrane controls contents
  4. transport
  5. responds to external stimuli
  6. intracellular interactions
  7. energy transductions
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5
Q

Explain how the structure of the membrane allows it to function in compartmentalization

A

Membranes are continuous lipid sheets which encapsulate the cell or regions of the cell

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6
Q

How does the membrane function in compartmentalization?

A
  • creates discrete compartments that can house different contents
  • allows activities to be chemically isolated (ex. intracellular digestion, photosynthesis)
  • cellular activities can be regulated independent of one another in their compartments
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7
Q

How does the membrane act as a basis for biochemical reactions?

A

Reactants of biochemical reactions can be embedded in membranes

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8
Q

What are the benefits of reactants being embedded in membranes?

A
  • increases likelihood of interactions because they are not just free-floating in the cytosol
  • effectively orders components to increase speed of interactions
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9
Q

How does the membrane act as a semi-permeable barrier between the inside and outside of a cell or organelle?

A

membranes control the exchange of molecules between the inside and the outside of a cell/organelle and prevent unregulated movement

membranes also allow for communication between the compartments they separate by being semi-permeable

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10
Q

How does a membrane facilitate transportation?

A

contains machinery to physically transport substances across the membrane (ex. ions, amino acids, sugars)

from concentration gradients of either high –> low or low –> high

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11
Q

What does functioning in transport allow a cell to do?

A

Accumulate substances it needs to power its metabolism and build the macromolecules it needs

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12
Q

What needs to be established across the membrane and how for the function of nerve and muscle cells?

A

ionic gradients established by transport

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13
Q

What do membranes have that allows them to respond to external stimuli?

A

receptors that interact with ligands or other stimuli (ex. light or mechanical pressure)

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14
Q

T or F: all types of cells have the membranes with the same receptors. why/why not?

A

FALSE because there is more than one kind of external stimuli, different cells will need to have different receptors to respond appropriately

Different types of cells have membranes with different receptors in order to respond to different stimuli

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15
Q

What do membrane receptors allow for?

A

signal transduction

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16
Q

What is signal transduction? Give some examples of responses

A

When an external stimulus triggers an internal reaction

ex. release specific ions, divide, move, synthesize specific compounds, die by apoptosis

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17
Q

How does the membrane function in intracellular interactions?

A

by allowing the communication between cells

ex. contact or adhesion between 2 cells, exchange of materials, interaction between the inner cytoskeleton and the ECM

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18
Q

How does the membrane function in energy transduction?

A

Membranes are crucial for converting energy into different forms

ex. the chlorophyll pigments required to absorb photons and the photosystems are embedded in membranes –> required for photosynthesis
ex. the electron transport chain and ATP synthase are embedded in membranes –> required for cellular respiration

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19
Q

T or F: lipids only have a few functions

A

FALSE. Lipids have SO many functions

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20
Q

List at least 5 functions of lipids

A

energy storage

components of cell membranes

can be enzyme cofactors

help in folding proteins

act as electron carriers

act as light absorbing pigments

hormones

act as membrane anchors for proteins

intracellular messages

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21
Q

Which key lipid is involved in most lipid functions?

A

fatty acids

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22
Q

Describe the structure of a fatty acid

A

a carboxyl group bonded to a long hydrocarbon tail

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23
Q

In what 3 ways can the hydrocarbon tails of fatty acids vary?

A
  1. can be from 4-36 carbons (most common is 12-24)
  2. can include branches
  3. can include double bonds
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24
Q

Define an amphipathic molecule

A

A molecule that has both a polar region and a non polar region

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25
Q

Are fatty acids hydrophobic, hydrophilic, or amphipathic? why?

A

amphipathic

they contain a carboxylic head which is polar AND
a hydrocarbon tail which is non polar

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26
Q

What does a carboxyl group look like?

A

An OH bonded to a C which is double bonded to an O

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27
Q

What two structures could a fatty acid have?

A

Either saturated or unsaturated

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28
Q

Define a saturated fatty acid

A

A fatty acid that does not contain any double bonds

This is because every single carbon is ‘saturated’ with a hydrogen - these have the max number of hydrogens

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29
Q

Define an unsaturated fatty acid

A

A fatty acid that has at least one double bond

The double bond means there are less hydrogens

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30
Q

Define a monounsaturated fatty acid

A

An unsaturated fatty acid that contains only one double bond

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31
Q

Define a polyunsaturated fatty acid

A

An unsaturated fatty acid that contains more than one double bond

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32
Q

Are most fatty acid double bonds cis or trans?

A

cis

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33
Q

Describe the structure of a saturated fatty acid

A

Straight
packed tightly

no double bonds

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34
Q

Describe the structure of an unsaturated fatty acid

A

Kinked

less tightly packed because of kinks

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35
Q

If a fat has more unsaturated fatty acids, will it be liquid or solid at room temperature? why?

A

liquid

it is less tightly packed because of the double bonds that create the kinks in the structure

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36
Q

If a fat has more saturated fatty acids, will it be liquid or solid at room temperature? why?

A

Solid

it is more tightly packed due to the lack of double bonds

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37
Q

Give examples of common food fats with unsaturated fatty acids

A

vegetable oils

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38
Q

Give examples of common food fats with saturated fatty acids

A

butter
dairy products
animal fat

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39
Q

What compound do almost all fats and oils have in their structure? What does this make them?

A

almost all have a fatty acid in their structure

makes them FATTY ACID DERIVATIVES

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40
Q

What will happen to a free carboxyl group of a fatty acid?

A

it will be ionized

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41
Q

What part of a fatty acid will link to other groups? and to form what?

A

a free carboxyl group will often link to other groups to form

ESTERS or AMIDES

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42
Q

Describe the structure of an ester

A

The C in the carbon skeleton is double bonded to an O and single bonded to an O which is bonded to another C

O = C - O - C

43
Q

Describe the structure of an amide

A

The C in the carbon skeleton is double bonded to an O and single bonded to an N-H

         | O = C - N - H
44
Q

What kinds of linkages will a fatty acid form when it links to other groups?

A

Either an ester linkage to form esters

Or an amide linkage to form amides

45
Q

What are fatty acids called when they are attached to another group via an ester or amide linkage?

A

Acyl chains or acyl groups

Fatty acyl group

46
Q

What does TAG stand for?

A

Triacylglycerol

47
Q

Describe the structure of a TAG

A

three fatty acids (tri) attached to a glycerol molecule by an ester linkage (acyl)

48
Q

When most people talk about fats, what are they talking about?

A

TAGs

49
Q

How are TAGs formed?

A

A dehydration reaction combines the glycerol and fatty acid

by removing an OH from the carboxyl group of the fatty acid and an H from the glycerol (to remove H2O) and form an ester linkage

50
Q

T or F: TAGs are in membranes

A

FALSE FALSE FALSE FALSE

51
Q

What is the function of TAGs? Why are they well suited for their function?

A

Energy storage

Well suited because they are so highly reduced, so oxidizing them at a later time will produce a LOT of ATP

52
Q

Where are TAGs found?

A

Packed tightly into adipocytes (fat cells) in huge quantities

53
Q

Are TAGs polar or non-polar?

A

essentially Non-polar even with the ester linkages

54
Q

What 3 lipids are in membranes?

A
  1. glycerophospholipids
  2. sphingolipids
  3. cholesterol
55
Q

What type of backbone do most phospholipids have? And what does this make them?

A

Glycerol backbones

Makes them glycerophospholipids or phosphoglycerides

56
Q

Describe the structure of a glycerophospholipid

A

BACKBONE: glycerol

Attached to the glycerol:

  • 1 fatty acid on C1
  • 2nd fatty acid on C2
  • A phosphate + head group on C3
57
Q

What are common head group chemicals for glycerophospholipids?

A

serine

ethanolamine

choline

58
Q

What type of backbones do sphingolipids have? which functional group does it include?

A

sphingosine

an amine

59
Q

Why is it called sphingosine?

A

named after the Sphinx due to its mysteriousness

60
Q

Describe the structure of sphingolipids

A

A sphingosine backbone which has 3 carbons (like glycerol) but attached to

C1 is a head group
C2 is an amine which will link to a fatty acid with an amine linkage
C3 is a long hydrocarbon chain of sphingosine

61
Q

On a sphingosine backbone, which two places are available for other groups to bond to?

A

The OH and the amine (NH2)

because the third carbon is involved in a very long hydrocarbon chain

62
Q

Where does the fatty acid attach to the sphingosine backbone? How?

A

The fatty acid attaches to the amine on the sphingosine backbone at C2 by an amine linkage

63
Q

What kind of linkage connects the sphingosine backbone to a fatty acid?

A

amine linkage (C-N)

64
Q

What are common head groups for sphingolipids? when attached, what does this make sphingolipids?

A

monosaccharides (simple sugars)

a sugar head group makes a GLYCOLIPID

65
Q

T or F: when sugars are attached to a sphingolipid, the molecule becomes polar. Why/why not?

A

True. Sugars are polar

66
Q

What are the other most common head groups aside from sugars for sphingolipids?

What is this specific lipid called?

A

Phosphate + Choline

Called Sphingomyelin

67
Q

What is the only sphingolipid that is also a phospholipid? Why?

A

sphingomyelin

because it has an phosphate (and choline) head group

68
Q

What are the major differences between glycerophospholipids and sphingolipids?

A

Glycerophospholipids have glycerol backbones

Sphingolipids have sphingosine backbones

All Gs have a phosphate group + a head group that can be a variety of things

Only one (Sphingomyelin) sphingolipid has a phosphate head group

G: have 2 fatty acids and they are attached by an ester linkage

S: have only one and it’s attached to an amine in the backbone by an amine linkage

69
Q

Describe the structure of cholesterol

A

Four fused rings and a hydroxyl (OH) group

70
Q

Is cholesterol hydrophobic, hydrophilic, or amphipathic? why?

A

Amphipathic because the hydroxyl (OH) group is polar and the hydrocarbons are non-polar

71
Q

How does cholesterol align itself in the membrane bilayer?

A

It aligns its polar hydroxyl groups with the polar head groups of phospholipids in the bilayer

72
Q

T or F: fluidity of a membrane is critical to membrane function

A

True

73
Q

What 5 things dictate levels of fluidity in the membrane?

A

Van der Waals forces

Temperature

levels of unsaturated fatty acids

length of hydrocarbon tails
cholesterol

74
Q

How do Van der Waals forces contribute to membrane fluidity?

A

Non-polar molecules or non polar portions of molecules (ex. hydrocarbon tails) interact with each other and attract one another

75
Q

How does temperature contribute to membrane fluidity?

A

A decrease in temperature will cause lipids to pack closely together –> solidifying the membrane

76
Q

Describe transition temperature

A

the temperature at which the lipid bilayer is converted from relatively fluid state (liquid crystalline) to FROZEN crystalline GEL

77
Q

In what ways will membranes counteract solidification/freezing?

A
  1. Having double bonds - intro of unsaturated fatty acids to reduce packability of the membrane
  2. having lots of short hydrocarbon chains
78
Q

How do many organisms (yeast, bacteria) keep their membranes fluid when temperatures change?

A

By adding or removing unsaturated fatty acids

79
Q

How does cholesterol contribute to membrane fluidity?

A

Cholesterol acts as a FLUIDITY BUFFER by preventing any extremes in fluidity

80
Q

How does cholesterol prevent membranes from gelling?

A

Prevents hydrocarbon chains from packing too closely together

81
Q

How does cholesterol prevent membranes from melting?

A

Limits the movement/rotations of the phospholipid tails

82
Q

What is the net result of cholesterol in the membrane?

A

the change between phases in the membrane is more GRADUAL

83
Q

How does cholesterol impact membrane solubility?

A

Adding a rigid, planar cholesterol molecule REDUCES solubility of the membrane and reduces the ability of small molecules to move through it

84
Q

Describe the asymmetry of a membrane

A

OUTER LAYERS:
glycolipids and anything with sugars

INNER LAYERS:
PS and PE on the inside to create a more negative charge

phospholipid head group will differ between the inner and outer layers

85
Q

Why might some lipids be required on one side of the bilayer while others are required on the other side?

A

Certain lipids are involved in signalling and are needed on one side of the bilayer or the other to transfer a signal from the outside to the inside of a cell

86
Q

How important is it that the correct phospholipids are on the correct side of the bilayer?

A

VERY

If they are on the wrong monolayer, it can trigger apoptosis

87
Q

What is the glycocalyx? What is it composed of?

A

a layer of sugars on the outer surface of the membrane bilayer which all face the outside of the cell

Composed of glycolipids and glycoproteins

88
Q

T or F: different membranes in the cell and in different cell types will have different lipid compositions?

A

TRUE

The lipid content of each membrane type is very specific

89
Q

How do membranes self-assemble?

A

Phospholipids can spontaneously cluster to form bilayers because they are amphipathic

Water molecules move freely when hydrophobic portions of molecules cluster –> increasing entropy

90
Q

What two structures can a phospholipid form depending on its shape?

A

Micelle

Bilayer

91
Q

What is the shape of a phospholipid dictated by?

A

its lipid composition

92
Q

Describe the micelle structure

A

A single layer of individual fatty acids that have aggregated with their fatty acyl chains on the inside to form a wheel-like shape

Individual fatty acids are wedge shaped, so when they aggregate with their tails in they form a pie/wheel

Inside is a hydrophobic centre

93
Q

Describe the structure of a bilayer

A

Phospholipids are cylindrical (even head: tail ratio) and form a flat bilayer (TWO LAYERS)

94
Q

Describe the structure of a liposome and how it forms?

A

When a phospholipid bilayer forms, it folds in on itself to protect its edges from water to form a liposome

Have two layers and an inside cavity that is hydrophilic

95
Q

Why are liposomes so useful in scientific research?

A

They can be artificially created and the exact lipids and proteins of interest can be added to be studied

96
Q

Why are liposomes so useful in delivering drugs?

A

They can act as vehicles to deliver drugs to the body

their hydrophilic polymer protects from immune cells

they can be antibodies and be targeted at specific body tissues

97
Q

How do lipids move around within a layer? How do they move around BETWEEN layers?

A

WITHIN:
very quickly - their HC tails move around and they spin on their axis

BETWEEN:
Very rare for lipids to move from one monolayer to another because the polar head section would have to move through a hydrophobic core to get to the other layer –> unlikely

98
Q

Describe flip-flopping

A

When a lipid moves from one monolayer to another

99
Q

In what circumstance would it be required for a lipid to move from one monolayer to another?

A

Ex. when they are first synthesized in the ER

ex. maintains membrane symmetry

100
Q

How is flip flopping facilitated?

A

A group of membrane proteins called PHOSPHOLIPID TRANSLOCATORS or FLIPPASES catalyze the rapid flip flop of the phospholipids from one monolayer to another

101
Q

Describe lipid rafts

A

Occurs when lipids (with the same function) and proteins (with the same signalling pathway) cluster and float around the membrane in a group –> creates a thicker bit of membrane because of the tightly packed and long saturated HC tails

this contributes to asymmetry because it means the lipids and proteins are not evenly distributed throughout the membrane

102
Q

What structures are common in lipid rafts?

A
  1. cholesterol
  2. sphingolipids
  3. GPI anchored proteins
  4. longer hydrocarbons
  5. saturated hydrocarbon tails
103
Q

T or F: Rafts are less ordered than the rest of the membrane

A

FALSE

Rafts tend to be more ordered than the rest of the membrane

104
Q

T or F: rafts are thicker than the rest of the membrane

A

True because they contain long hydrocarbon chains and saturated HC tails so they tightly pack together

BIOL 2321 - Cell Biology (26 decks)

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