Lipids Flashcards
1
Q
Are lipids are homogeneous group or heterogeneous?
A
Heterogeneous group
2
Q
What common properties do lipids share?
A
- Insolubility in aqueous or water based solutions
2. Solubility in organic or non-polar solvents
3
Q
What is one of the best organic solvents?
A
Chloroform
4
Q
How does the solubility of short-chained fatty acids compare to long-chained fatty acids? Why?
A
- Solubility decreases as the length of the carbon chain increases
- Charge distribution is relatively stronger
5
Q
Which fatty acids are infinitely soluble in water?
A
Acetic acid (2C) Butanoic acid (4C)
6
Q
Which fatty acids are soluble in chloroform (organic solvent)? How does the solubility chain with increase in size? Why?
A
- 10 C are ++ soluble (normal saturated fatty acids)
- Increase size, decrease solubility
- Long hydroC chain = Van der Waals interaction, will keep molecules together
7
Q
What are normal saturated fatty less soluble in?
A
Acetonitrile
8
Q
Name the 5 biological functions of lipids.
A
1) Storage of energy
2) Membrane structure
3) Signaling molecules
4) Cofactors for enzymes
5) Antioxidants
6) Pigments
9
Q
Why are lipids good molecules for storage of energy?
A
Reduced compounds: lots of available energy
Hydrophobic nature: good packing, Why?
10
Q
How do lipids act as signaling molecules?
A
Hormones (steroids)
Vitamins A and D (hormone precursors)
11
Q
What colour is canthaxanthin? Zeaxanthin?
A
Canthaxanthin = bright red Zeaxanthin = bright yellow
12
Q
What is the major difference between complex lipids and biologically active lipids?
A
Complex lipids: fatty acids
Biologically active lipids: no fatty acid
13
Q
What is special about prostaglandins?
A
Derived from FA, do NOT contain FA
14
Q
What are the two main groups of complex lipids, how do they differ?
A
Storage Lipids: non-polar
Structural Lipids: polar lipids
15
Q
Name 2 storage lipids.
A
Triglycerides and Waxes
16
Q
Name 2 structural lipids.
A
Phospholipids and sphingolipids
17
Q
Name 2 biologically active lipids.
A
Prostaglandins and steroids
18
Q
What kind of molecules are fatty acids? What are their chains composed of?
A
- Amphipathic molecules
- Hydrocarbon chains
- 3 to 35 carbons and a carboxylic acid group
19
Q
Are lipids even or uneven in number? How?
A
- Even in number
- Nb of carbons + carboxylic group = makes it even
20
Q
How can fatty acids be written in terms of structure?
A
CH3-(R)n-COOH , where R= CH2
n = or > 2.
21
Q
What is the most common fatty acid chain length?
A
C14 to C18
22
Q
Which fatty acid is infinitely soluble in water? How does solubility change with increased hydrocarbon chain?
A
- Butanoic acid (4C)
- Solubility decreases
23
Q
Where is butanoic acid found in?
A
High concentration in breast milk -> promotes development of stem cells + metaboism
24
Q
Is Lauric acid soluble in water? What is its main function?
A
- Partially soluble in water to the extent of 0.06 per gram of water
- Antimicrobial (soaps)
25
What kind of fatty acids form waxy solids at room temperature?
Fatty acids with C10 or higher saturated hydrocarbon chains
26
What kind of fatty acids form oily liquids at room temperature?
Fatty acids with C9 or lower saturated or unsaturated hydrocarbon chains
27
What is the difference between the systematic and common names of fatty acids?
- Systematic: chemist
| - Common: based on the source
28
Are most natural fatty acids branched or unbranched? What is the prefix?
- Unbranched
| - Prefix: n indicates normal or unbranched
29
What is the pKa of COOH group? At pH 7, how are the fatty acids?
- Below 5
| - Fully ionized
30
What are saturated double bonds? Unsaturated?
Saturated: no double bonds
Unsaturated: one or more double bonds
31
What do cis-double bonds affect in terms of positioning?
- The positions of fatty acids tails relative to the plan of saturated lipid tails of the same length
- Produce more kinks or bents
32
Which are more packed: saturated fatty acids or unsaturated?
Saturated fatty acids are more packed
33
What does less ordered packing lead to?
- Weaker intermolecular interactions (Van der Waal)
| - Lower melting point for unsaturated fatty acids
34
What does configuration mean? Conformation? What is cis/trans?
Configuration: breaking covalent bonds
Conformation: weak bonds being broken
Cis/Trans is a configuration change
35
How do you name fatty acids? Where do you start counting?
- #C: #DB (△positions of DB)
| - numbered starting with COOH, as carbon #1
36
What are fatty acids physical properties defined by?
Their hydrocarbon length and degree of saturation
37
Naturally occurring double bonds have which configuration?
Naturally: cis-configuration
38
How does the packing of trans unsaturated fatty acids compare to cis unsaturated fatty acids?
Trans looks like saturated in terms of packing, can pack tighter than unsaturated and have higher melting points
39
How are trans fatty acids formed?
by partial hydrogenation of unsaturated fatty acids and cis-double bond Isomerization to Trans-double bonds.
40
Name 2 reasons why saturated (animal fat) and trans fats (animal or plants) are bad for health.
1) Saturated Fatty acids increase blood cholesterol levels by providing proper packing domains for cholesterol.
2) Trans-fats do the same, together with increased rigidity around the double bonds
41
Name 3 reasons why high cholesterol and higher incidence of heart disease are related.
1) Reduced membrane Fluidity
2) Reduced membrane Flexibility
3) Reduced membrane protein Functions
42
How does solubility and melting point change as the chain length increases?
Solubility: decreases
| Melting point: Increases
43
Why do saturated and unsaturated fatty acids pack differently?
Saturated: orderly way
extensive favorable interactions (Van der Waals)
Unsaturated: pack less regular due to the kink
Less extensive favorable interactions
44
Why is partial hydrogenation a problem?
- Trans fats
- Reduces the mobility of the FA
- Cholesterol will stick more easily
45
What kind of lipids are fatty acids found in? What are the responsible for in aqueous solutions?
- Found in complex lipids
| - Responsible for the formation of micelles in aqueous solutions
46
What do acylglycerols result from?
Condensation Reaction between one glycerol sugar with one, two or three fatty acids
47
In acylglycerols: glycerol and fatty acids are linked by what?
Ester linkage
48
Lipids containing fatty acids with unsaturated hydrocrabon chain of 20 carbons and 2 cis-double bonds are likely to be what?
Oil at room temperature
49
Fatty acids with trans-unsaturated hydrocarbon chains of 10 C + 3 double bonds have an approximate melting temperature of?
+ 30oC the double bonds make it have a high melting temperature
50
What is the ester bond that you form in triacylglycerides in terms of polarity?
Apolar - forms an aggregate if dropped into water, no micelles
51
How many ester bonds do triacylglycerols have?
3 ester bonds
52
Compare a simple and a complex/mixed triglyceride.
Simple: if all the fatty acids are the length
Complex: if the fatty acids are different lengths and saturation
53
Does a simple triacylglyceride have a asymmetric centre? Does mixed?
Simple: NO, no chiral carbon
Mixed: Yes at carbon number 2
54
What are the solubility and melting point of triacylglycerides determined by?
determined by the nature of the fatty acids that are attached to the glycerol backbone. Whether it is long, saturated or unsaturated will determine the physical property of the triacylglyceride. In the same way that FA determine their own physical properties
55
Why are triacylglycerides good at storage of lipids?
apolar structure, no water associated with it and a highly reduced structure
56
What kind of lipid is the most abundant form of metabolic storage in animal cells (fat cells) and in plants (seeds)
Triacylglycerols
57
Animal and plant triacylglycerols are present in what form?
Insoluble forms
58
Are triacylglycerols fat or oil?
Both
animal triglycerides are solid, while plant and fish triglycerides are oil at room temp
- Oil is unsaturated,
59
How do triacylglycerols compare to sugar in terms of energy storage?
Triacylglycerol are considered light-source of energy compared to sugar
60
Name the 2 reasons why triacylglycerols are key in mammalian survival.
1) Energy storage
| 2) Hygiene (fat dripping on ash formed bubbles)
61
Name 2 advantages of fats over polysaccharides.
- Acylglycerides carry more energy per carbon because they are more reduced
- Fatty acids carry less water along because they are nonpolar
62
How do glucose, glycogen and acylglycerides compare in terms of energy storage?
- Glucose and glycogen are short-term energy needs, quick delivery
= Acylglycerides are for long term (months) energy needs, good storage, slow delivery
63
Where are triacylglycerols digested? By what?
in the small intestine by the enzyme pancreatic lipase
64
Where are mono-acylglycerols absorbed? Converted to what? Assembled to what?
absorbed by intestinal cells and converted to
| tri-acylglycerols and assembled into lipoproteins
65
The treatment of triacylglycerols with a SB or SA leads to what?
The hydrolysis of the ester bond between glycerol and fatty acids
- Creates soaps, hand soap, shaving cream
66
Name 2 ways to hydrolyze acylglycerols. How do they differ?
1) Physiologically with lipases -> energy production
| 2) Chemical with SA and SB -> fatty acid salts and glycerol used for soaps
67
How are waxes formed?
by a condensation reaction between long fatty acids
| and alcohol hydrocarbon chains
68
Which lipids do not contain a glycerol backbone?
- Waxes
- Sphingolipids
- Biologically active lipids (prostaglandins, steroids)
69
What is the melting temperature of waxes? How does it differ from triacylglycerides?
- 60-100oC
| - Higher than TG due to their very long hydrocarbon chain
70
What do waxes act as? What kind of coating do they have?
- Act as metabolic fuel
| - Water impermeable coating
71
What can waxes be broken down with? What does it produce?
Broken down with SA and SB to fatty acids and alcohol hydrocarbons
- You will get some kind of soap, FA can form micelles
72
What are the 2 main roles of structural lipids.
Forming structures and cell signalling
73
What is the backbone of a phospholipid?
Glycerol + phosphate
74
How are phosphoacylglycerols formed?
- Phosphate is attached through a condensation reaction to the third carbon of the glycerol backbone
- 2 FA are attached to the backbone
75
What is the basic unit of phosphoacylglycerols? What is that called?
When the head group (X) is a hydrogen
| - Phosphatic acid
76
Does phosphoacylglycerol have a chiral center?
Yes, at carbon 2
77
Are phosphatic acids charged? Why?
- Yes, negatively charged at pH 7
| - because pKa of phosphoric group is 2 – always ionized
78
What is phosphatic acid made up of?
1, 2- diacylglycerol (two fatty acids plus glycerol) linked to phosphoric acid
79
What are the linkages in phosphatidic acid?
- Two fatty acids are linked to 1st & 2nd hydroxyl of glycerol by Ester bonds
- Phosphoric acid is linked to 3rd hydroxyl of glycerol by Phospho-ester bond
80
How is the saturation of the fatty acids of phospholipids?
- FA linked to the 1st hydroxyl are generally saturated
| - 2nd hydroxyl is unsaturated
81
What are alcohol based compounds linked to phosphatidic acids known as?
Head groups
82
What does the phospholipids head group determine?
The name, the property and the NET CHARGE
83
What is the net charge of phosphatidylcholine
0
84
The properties of what determine the surface properties of membranes?
Properties of head groups
85
What is the major component of most eukaryotic cell membranes? What is the net charge? What kind of cells do not have phosphatidylcholine?
- Phosphatidylcholine
- Net charge 0
- Procaryotes (E coli) cannot synthesize this lipid
86
What type of lipids are major components of cell membranes?
Glycerophospholipids
87
What lipids are amphipatic?
- Glycerophospholipids (charged head groups)
- Sterols
- Sphingolipids (polar)
88
The head group of a glycerophospholipid is linked to what through what linkage?
- Linked to glycerol backbone through a phosphodiester linkage
89
What gives cell membranes their overall positive or negative surface charges?
The differential distribution of glycerophospholipids
90
What kind of lipid does the immune system love? Why?
- Sphingosine
| - CHO linked to lipids --> really rigid structure, since antibodies can recognize these rigid structures
91
What is the backbone of sphingolipids? How long is it?
- Sphingosine
| - 18 carbons (looks like monoacylglycerol but is NOT glycerol backbone)
92
What is attached to the sphingosine? What is it (chemically)?
It is an alcohol amino hydrocarbon
- Hydroxyl group on the 1st and 3rd carbon
- Amino group on the 2nd carbon
93
In a sphingolipid, if you condense a fatty acid onto the amino group attached to the second carbon, what type of bond do you end up with? Where does the fatty acid attach?
```
Amide linkage (NOT ESTER)
- Attaches on the second carbon
```
94
What is a sphingolipid when X = H?
- Ceramide = messenger of death
- High levels will induce death except in skin, which has plenty of ceramide
- Ceramide is very good for your skin
95
What is a sphingolipid when X = phosphocholine? What type of linkage?
- Sphingomyelin, present in myeline sheets
| - Phosphoester linkage
96
What type of linkage in a sphingolipid when X = glucose?
- Glycosidic bond
97
Is there an asymmetric centre in sphingosine? If so, where?
Yes, in carbon 2 and carbon 3
| There are TWO
98
What is a sphingosine?
Long chain amino alcohol
99
What is the class determined by the addition of phosphoryl choline group to sphingosine as the head group of sphingolipids?
Sphingomyelin
100
What is the class determined by the addition of sugar group as the head group of sphingolipids?
Cerebroside
101
What is the class determined by the addition of combination of sugars (or oligosaccharides) as the head group of sphingolipids?
Ganglioside
102
How is a polar head group connected to Carbon I of sphingosine?
By a glycosidic or phosphodiesther linkage
103
The sugar-containing glycosphingolipids are found where?
Largely in the outer face of plasma (cell) membranes, and consequently detectable by the immune-system
104
What are blood groups determined in part by?
The type of sugars located on the head groups of glycosphingolipids
105
What is the structure of sugar located on the head groups of glycosphingolipids determined by?
By an expression of specific glycosyltransferases
106
What kind of individuals have the O antigen?
inactive glycosyltransferase
107
What kind of individuals will have the A blood group?
glycosyltransferase that transfers an N-acetylgalactosamine group
108
What kind of individuals will have the B blood group?
glycosyltransferase that transfers a galactose group
109
What kind of individuals will have the AB blood group?
glycosyltransferase that transfers an N-acetylgalactosamine group AND galactose group
110
What kind of lipids occur in much smaller (minute) quantities in cells and tissue?
Biologically active lipids
111
What is the major physiological roles of biologically active lipids?
Recruiting the activities of proteins and receptors
112
What are steroids important for?
- Metabolically for digestion (bile salts act as fat solubilizers)
- Hormones (human sex hormones)
113
How are prostaglandins generated?
Through modification of fatty acids
114
How are sterols generated?
From 2 carbon acids (acetate) and through modification of other sterols
115
Where do cells turnover their lipids? With what?
- In lysosomes
| - With four phospholipases (or Esterases)
116
What do phospholipases cleave? What don't they cleave?
- Cleave ester linkages
| - Not ethyl linkages (as in sphingosine)
117
What do these phospholipases cleave:
1) Phospholipase A1
2) Phospholipase A2
3) Phospholipase C
4) Phospholipase D
1) Cleaves C1 ester linked fatty acid
2) Cleaves C2 ester linked fatty acid
3) Cleaves C3 phosphoester linked phosphoric acid
4) Cleaves phosphoesterlinked X or head groups
118
Name the 2 classes of phospholipases.
1. Phospholipid-specific lipases
| 2. Broad substrate
119
???? The head group of a phospholipase is linked to a phospohglycerol by what? The head group is linked by what to a glycerol backbone?
- Phosphoglycerol: phosphoester
| - Glycerol backbone: phosphodiester
120
What lipids are present in small amounts but play vital roles as signaling molecules between nearby cells?
Paracrine lipid hormones
121
What does the enzymatic oxidation of arachidonic acid yield?
Prostaglandins, thromboxanes and leukotrienes
122
What inhibits thromboxane A2?
Omega-3, prevents platelet aggregation, good for heart disease
123
What do accumulations of prostaglandins lead to?
Inflammation and fever, smooth muscle contraction in uterus
124
What is the precursor for cholesterol? What can it also lead to?
Isopentenyl pyrophosphate
| Vitamin K, vitamin E, vitamin A
125
What can cholesterol produce?
Steroid hormones, bile acids, vitamin D
126
What is the chemical composition of a sterol?
- Steroid nucleus: four fused rings
- Hydroxyl group (polar head) on the A-ring
- Various non-polar side chains
127
Which lipid has a nucleus that is almost planar?
The steroid nucleus
128
Why is cholesterol interesting? What does it act as? What does it have that gives itself its polarity? Where does it stick itself?
- Acts as a structural lipid in some ways: very rigid structure (sterol nucleus)
- hydroxyl group that gives it its polarity
- sticks itself in the lipid bilayer
129
How does cholesterol act?
- fully saturated fatty acid in one portion of it, almost equivalent to trans VERY rigid
- alky side chain), it has a branched structure, similar to unsaturated cis, it pushes, prevents the packing
- In a membrane: upper portion of the fatty acid will feel like it is next to a trans fat (tight packing)
other end will make it feel as if its sitting next to several unsaturated of the cis-type
- It will make lipids feel that they can pack tighter, but then another part (lower) will prevent them from packing tight
130
What part of cholesterol prevents packing?
The alkyl side chain
131
We wouldn't be able to tolerate temperature change if it weren't for which lipid?
Cholesterol
132
What is the chemical structure of cholesterol?
“steroid” with hydrophobic tail in two parts, rigid planner rings and flexible and branched hydrocarbon chain
133
What part of cholesterol is hydrophilic?
The part made up of hydroxyl group (head group)
134
What does cholesterol prevent? WHERE? What does that decrease?
prevents the close packing of the LOWER ends of the fatty acids hydrocarbon tails, thus DECREASING the melting point of the lipid bilayer
135
What does cholesterol promote? WHERE? What does that increase?
Cholesterol promotes tight packing of the UPPER ends of the fatty acids hydrocarbon tails, thus INCREASING the melting point of the lipid bilayer.
136
Which lipid is known as fluidity buffer? What does it do?
- Cholesterol
- decreases the sharpness of Gel to Liquid crystalline transition (prevents a sudden change)
- STRETCHES the shift in temperature
137
What does cholesterol's rigid structure favour? What does that do?
- interaction with saturated, or trans-fats unsaturated lipid
- these fats enhance cholesterol accumulation in membrane
138
Define the transition state of a lipid.
```
The temperature required to induce
a change in the lipid physical state
from the ordered gel phase, where
the hydrocarbon chains are fully
extended and closely packed to to the disordered liquid crystalline phase, where the hydrocarbon chains are randomly oriented and fluid
```
139
The condensation reaction between glycerol hydroxyls and carboxylic acids of fatty acids lead to the formation of what?
An ester linkage and the release of water
140
Storage lipids, tricylglycerols and waxes, contain what?
Two hydrocarbon chains (1 ester bond)
141
All phospholipases are able to cleave which bond?
Phosphoester bond
142
In aqueous solutions amphipathic structural lipids aggregate
into three possible structures. What are they?
- Lipid micelles
- Lipid bilayer
- Liposomes
143
How is the size of lipid micelles? What is excluded from the interior? What are the building blocks?
- Small spherical structures
- Water excluded
- Free fatty acids and some detergents
144
Why do lipid micelles assume this conformation?
Because the size of head to tail ratio is MORE than 1 (bigger head than its tail, can wedge into the micelle structure)
145
What is the structure of the lipid bilayer? What is excluded from the interior? What are the building blocks?
- Sheet like structure with 2 monolayer
- Water is excluded from the interior
- Phosphoacylglycerides and sphingolipids
146
Why do lipid bilayers assume this conformation?
Size of head to tail ratio is EQUAL to 1
147
What is the structure of liposomes?
Hollow sphere of lipid bilayer folded back onto itself
148
What do liposomes aggregates enclose? What does that do?
- Enclose water
| - Act as barriers between 2 environments
149
What do storage lipids form in aqueous solutions?
Lipid droplets
150
Can storage lipids form micelles?
No since they aren't amphiphatic, they are non-polar
151
Can detergents form micelles?
Yes, because most detergents have a polar head (charged group) and the rest is hydrophobic (ring like structure or tail)
152
What is the cell membrane permeable to? Impermeable?
Permeable: charged ions and large molecules/proteins
Impermeable: hydrophobic molecules and neutral gases/water
153
How did we discover what the cell membrane was permeable/impermeable to?
Take purified phospholipids and you can have any combination of phospholipids and you put them on both sides in an organic solvent and then you evaporate the organic solvant
You end up with dried phospholipids
Take aqueous solutions and you dump it on both sides
Phospholipids will climb up, try to getaway (at least the tails) from the aqueous solution
They get to this one pinhole (1mm) where the tails will be facing one another from each side
You can put drugs and see if they’ll make it on the other side, you can put charged drugs, ions, TO SEE WHAT PASSES THROUGH THE LIPID BILAYER (things will move down the electrical gradient)
154
Why did we use a black membrane and not a cell membrane?
Because it has proteins embedded in it. So it is difficult to know who is doing the transfer
155
How is the cell membrane in appearance? What is the total thickness? How thick is the middle hydrocarbon layer?
- Tri-laminar
- 5 nm
- 3.5-4 nm
156
How did we discover the thickness and the tri-laminar appearance of the cell membrane?
- Erythrocyte stained with osmium tetroxide and viewed with an electron microscope
- Two dark lines separated by a clear line
157
The cell membrane is a fluid-like structure. How can lipid molecules move?
- CAN: diffuse laterally, spin on axis
| - CAN'T: no uncatalyzed Flip-Flop motion
158
How did we discover that lipids can't undergo a Flip-Flop motion?
- Take the intact cell and label with a fluorescent tag the head of the phospholipids of the OUTER membrane
- Examine the portion of the cell under the microscope, the tags that you added will fluoresce (reddish)
- Bleach with a fine laser beam a portion of that fluorescent probe on the cell membrane
- Wait, 2 options: 1) Everything just bang goes back and turns red after time 2) You see dots of red structures in the area that was initially white (bleached)
- Option #2 is what happens
159
Name the 3 ways to undergo catalyzed transbilayer translocation. Which ones require energy?
- Flippase, Floppase and Scramblase
| - Flippase and Floppase require energy
160
Which catalyzed flip flop is at the level of the blood brain barrier?
Floppase
161
How are membrane lipids distributed between the inner and outer leaflets?
Asymetrically
162
What is Phosphatidylinositol important for? Why is it mostly located on the inner monolayer?
important to have on the inner membrane since it is involved in signaling in terms of activating protein kinase
163
What is Phosphatidylserine important for? Why is it mostly located on the inner monolayer?
one of the first steps of cells that are about to die is to flip/leave the phosphotidylserine on the outside, recognize the process of cell death, needs to be on the inside
164
How do the lipid composition of membranes of different cellular organelles differ?
They have different lipid compositions
165
What type of protein does the cell membrane contain? What do the phospholipids act as?
- Many globular proteins
| - Phospholipids act as solvent
166
How do phospholipids in membranes act as solvents?
keep the membrane proteins soluble (float) to NOT make them aggregate and denature
167
Name the 3 classes of membrane proteins.
1) Integral or intrinsic membrane proteins
2) Anchored membrane proteins
3) Peripheral or associated membrane proteins
168
What are integral/intrinsic membrane proteins?
Proteins that transverse the lipid
| bilayer one or several times.
169
Which membrane proteins are extractable from the cell membrane with detergents?
- Integral/intrinsic membrane proteins
| - Anchored membrane proteins
170
What are anchored membrane proteins?
Proteins that do NOT transverse the lipid
| bilayer entirely, but are linked covalently to fatty acids in the inner or outer leaflet of the cell membrane
171
Name the 2 ways anchored membrane proteins can be extracted from the cell membrane.
- Detergent or with treatment with phospholipases (they are covalently linked to phospholipases in the cell membrane)
172
What are peripheral or associated membrane proteins?
Proteins that do NOT transverse the lipid bilayer but associate with transmembrane proteins or interact with lipid surface charges.
173
Why can't peripheral/associated membrane proteins be extracted with detergents?
They are not covalently linked, but attached through weak forces, which can be broken with high pH buffers (changes ionization, repulsion), denaturing and chelating agnets
174
What are the two types of sphingolipids?
They can be phospholipids or glycolipids
175
_____ moves phospholipids from cytosolic to outer leaflet
Floppase
176
_____ moves PE and PS from outer to cytosolic leaflet
Flippase
177
____ moves lipids in either direction towards equilibrium
Scramblase
178
Which lipids are modified with oligosaccharides?
Phospholipids and sphingolipids
