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BIOL 2321 - Cell Biology > Plasma Membrane > Flashcards

Plasma Membrane Flashcards

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
Are fatty acids hydrophobic, hydrophilic, or amphipathic? why?
amphipathic they contain a carboxylic head which is polar AND a hydrocarbon tail which is non polar
26
What does a carboxyl group look like?
An OH bonded to a C which is double bonded to an O
27
What two structures could a fatty acid have?
Either saturated or unsaturated
28
Define a saturated fatty acid
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
29
Define an unsaturated fatty acid
A fatty acid that has at least one double bond The double bond means there are less hydrogens
30
Define a monounsaturated fatty acid
An unsaturated fatty acid that contains only one double bond
31
Define a polyunsaturated fatty acid
An unsaturated fatty acid that contains more than one double bond
32
Are most fatty acid double bonds cis or trans?
cis
33
Describe the structure of a saturated fatty acid
Straight packed tightly no double bonds
34
Describe the structure of an unsaturated fatty acid
Kinked | less tightly packed because of kinks
35
If a fat has more unsaturated fatty acids, will it be liquid or solid at room temperature? why?
liquid it is less tightly packed because of the double bonds that create the kinks in the structure
36
If a fat has more saturated fatty acids, will it be liquid or solid at room temperature? why?
Solid it is more tightly packed due to the lack of double bonds
37
Give examples of common food fats with unsaturated fatty acids
vegetable oils
38
Give examples of common food fats with saturated fatty acids
butter dairy products animal fat
39
What compound do almost all fats and oils have in their structure? What does this make them?
almost all have a fatty acid in their structure makes them FATTY ACID DERIVATIVES
40
What will happen to a free carboxyl group of a fatty acid?
it will be ionized
41
What part of a fatty acid will link to other groups? and to form what?
a free carboxyl group will often link to other groups to form ESTERS or AMIDES
42
Describe the structure of an ester
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
Describe the structure of an amide
The C in the carbon skeleton is double bonded to an O and single bonded to an N-H | O = C - N - H
44
What kinds of linkages will a fatty acid form when it links to other groups?
Either an ester linkage to form esters Or an amide linkage to form amides
45
What are fatty acids called when they are attached to another group via an ester or amide linkage?
Acyl chains or acyl groups Fatty acyl group
46
What does TAG stand for?
Triacylglycerol
47
Describe the structure of a TAG
three fatty acids (tri) attached to a glycerol molecule by an ester linkage (acyl)
48
When most people talk about fats, what are they talking about?
TAGs
49
How are TAGs formed?
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
T or F: TAGs are in membranes
FALSE FALSE FALSE FALSE
51
What is the function of TAGs? Why are they well suited for their function?
Energy storage Well suited because they are so highly reduced, so oxidizing them at a later time will produce a LOT of ATP
52
Where are TAGs found?
Packed tightly into adipocytes (fat cells) in huge quantities
53
Are TAGs polar or non-polar?
essentially Non-polar even with the ester linkages
54
What 3 lipids are in membranes?
1. glycerophospholipids 2. sphingolipids 3. cholesterol
55
What type of backbone do most phospholipids have? And what does this make them?
Glycerol backbones Makes them glycerophospholipids or phosphoglycerides
56
Describe the structure of a glycerophospholipid
BACKBONE: glycerol Attached to the glycerol: - 1 fatty acid on C1 - 2nd fatty acid on C2 - A phosphate + head group on C3
57
What are common head group chemicals for glycerophospholipids?
serine ethanolamine choline
58
What type of backbones do sphingolipids have? which functional group does it include?
sphingosine an amine
59
Why is it called sphingosine?
named after the Sphinx due to its mysteriousness
60
Describe the structure of sphingolipids
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
On a sphingosine backbone, which two places are available for other groups to bond to?
The OH and the amine (NH2) because the third carbon is involved in a very long hydrocarbon chain
62
Where does the fatty acid attach to the sphingosine backbone? How?
The fatty acid attaches to the amine on the sphingosine backbone at C2 by an amine linkage
63
What kind of linkage connects the sphingosine backbone to a fatty acid?
amine linkage (C-N)
64
What are common head groups for sphingolipids? when attached, what does this make sphingolipids?
monosaccharides (simple sugars) a sugar head group makes a GLYCOLIPID
65
T or F: when sugars are attached to a sphingolipid, the molecule becomes polar. Why/why not?
True. Sugars are polar
66
What are the other most common head groups aside from sugars for sphingolipids? What is this specific lipid called?
Phosphate + Choline Called Sphingomyelin
67
What is the only sphingolipid that is also a phospholipid? Why?
sphingomyelin because it has an phosphate (and choline) head group
68
What are the major differences between glycerophospholipids and sphingolipids?
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
Describe the structure of cholesterol
Four fused rings and a hydroxyl (OH) group
70
Is cholesterol hydrophobic, hydrophilic, or amphipathic? why?
Amphipathic because the hydroxyl (OH) group is polar and the hydrocarbons are non-polar
71
How does cholesterol align itself in the membrane bilayer?
It aligns its polar hydroxyl groups with the polar head groups of phospholipids in the bilayer
72
T or F: fluidity of a membrane is critical to membrane function
True
73
What 5 things dictate levels of fluidity in the membrane?
Van der Waals forces Temperature levels of unsaturated fatty acids length of hydrocarbon tails cholesterol
74
How do Van der Waals forces contribute to membrane fluidity?
Non-polar molecules or non polar portions of molecules (ex. hydrocarbon tails) interact with each other and attract one another
75
How does temperature contribute to membrane fluidity?
A decrease in temperature will cause lipids to pack closely together --> solidifying the membrane
76
Describe transition temperature
the temperature at which the lipid bilayer is converted from relatively fluid state (liquid crystalline) to FROZEN crystalline GEL
77
In what ways will membranes counteract solidification/freezing?
1. Having double bonds - intro of unsaturated fatty acids to reduce packability of the membrane 2. having lots of short hydrocarbon chains
78
How do many organisms (yeast, bacteria) keep their membranes fluid when temperatures change?
By adding or removing unsaturated fatty acids
79
How does cholesterol contribute to membrane fluidity?
Cholesterol acts as a FLUIDITY BUFFER by preventing any extremes in fluidity
80
How does cholesterol prevent membranes from gelling?
Prevents hydrocarbon chains from packing too closely together
81
How does cholesterol prevent membranes from melting?
Limits the movement/rotations of the phospholipid tails
82
What is the net result of cholesterol in the membrane?
the change between phases in the membrane is more GRADUAL
83
How does cholesterol impact membrane solubility?
Adding a rigid, planar cholesterol molecule REDUCES solubility of the membrane and reduces the ability of small molecules to move through it
84
Describe the asymmetry of a membrane
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
Why might some lipids be required on one side of the bilayer while others are required on the other side?
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
How important is it that the correct phospholipids are on the correct side of the bilayer?
VERY | If they are on the wrong monolayer, it can trigger apoptosis
87
What is the glycocalyx? What is it composed of?
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
T or F: different membranes in the cell and in different cell types will have different lipid compositions?
TRUE The lipid content of each membrane type is very specific
89
How do membranes self-assemble?
Phospholipids can spontaneously cluster to form bilayers because they are amphipathic Water molecules move freely when hydrophobic portions of molecules cluster --> increasing entropy
90
What two structures can a phospholipid form depending on its shape?
Micelle Bilayer
91
What is the shape of a phospholipid dictated by?
its lipid composition
92
Describe the micelle structure
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
Describe the structure of a bilayer
Phospholipids are cylindrical (even head: tail ratio) and form a flat bilayer (TWO LAYERS)
94
Describe the structure of a liposome and how it forms?
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
Why are liposomes so useful in scientific research?
They can be artificially created and the exact lipids and proteins of interest can be added to be studied
96
Why are liposomes so useful in delivering drugs?
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
How do lipids move around within a layer? How do they move around BETWEEN layers?
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
Describe flip-flopping
When a lipid moves from one monolayer to another
99
In what circumstance would it be required for a lipid to move from one monolayer to another?
Ex. when they are first synthesized in the ER ex. maintains membrane symmetry
100
How is flip flopping facilitated?
A group of membrane proteins called PHOSPHOLIPID TRANSLOCATORS or FLIPPASES catalyze the rapid flip flop of the phospholipids from one monolayer to another
101
Describe lipid rafts
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
What structures are common in lipid rafts?
1. cholesterol 2. sphingolipids 3. GPI anchored proteins 4. longer hydrocarbons 5. saturated hydrocarbon tails
103
T or F: Rafts are less ordered than the rest of the membrane
FALSE Rafts tend to be more ordered than the rest of the membrane
104
T or F: rafts are thicker than the rest of the membrane
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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