Lipids Flashcards
(122 cards)
1
Q
energy storage, biological membranes, protein modification, signal transduction, and digestion of food
A
functions of lipids
2
Q
- one polar end (carboxyl group) and a long hydrophobic tail (alkyl chain)
- humans usually have an even number of carbons (16-20)
A
structure of fatty acid
3
Q
- 3 FAs esterfied to a glycerol
- very hydrophobic
A
triacylglyerol (TAG)
4
Q
location of FA synthesis
A
cytoplasm
5
Q
location of FA degradation
A
mitochondria
6
Q
Human FA desaturases can only introduce double bonds where?
A
proximal half (up to carbon 9)
7
Q
Essential FAs
A
Linoleic acid (omega 6)>>arachidonic acid Linolenic acid (omega 3)
8
Q
Can TAG be transported?
A
No, it’s too hydrophobic. It must be broken down to FFAs first
9
Q
What is the regulated step of FA degradation?
A
Carnitine-palmitoyltransferase I (CPT1)
10
Q
Where does FA degradation occur?
A
mitochondria
11
Q
What does FA break down to?
A
acetyl-CoA
12
Q
produces CO2 and shortens FA chain by one carbon
A
alpha-oxidation
13
Q
produces acetyl-CoA (2C’s)
A
beta-oxidation
14
Q
ketone is made from…
A
acetyl-CoA
15
Q
What reducing equivalents are made during FA degradation?
A
FADH2 and NADH
16
Q
How is the degradation of unsaturated FA differ than that of saturated FA?
A
requires isomerases to move the double bonds until it looks like simple FA, then proceeds the same way via beta-oxidation
17
Q
beta-oxidation in peroxisomes
A
occur in liver and kidney
minor fraction of FAs are degraded this way.
- H2O2 instead of FADH2
- degrades long chains down to 8 C’s
18
Q
hypoglycemia with unusually low level of ketones in blood and urine
A
FA degradation disorder because it interferes with production of ketone bodies
19
Q
Acute Fatty Liver of Pregnancy
A
long-chain hydroxyacyl-CoA dehydrogenase deficiency leading to accumulation of long chain FAs in liver. rare condition that can occur in pregnant women in the third trimester.
20
Q
Non-ketotic Hypoglycemia
A
- FA import disorder (carnitine deficiency)
- Acyl-CoA Dehydrogenase Deficiencies (along with accumulation of FAs)
21
Q
problems with alpha-oxidation of phytanic acid (branched-FA). patient presents with accumulation of phytanic acid in blood and tissues, also neurological defects
A
Refsum Disease
22
Q
accumulation of long FAs (24-26Cs), plasmologen deficiency, myelination deficiency
A
Zellweger Syndrome - dysfunctional peroxisomes
23
Q
In what organs does synthesis of ketone bodies occur?
A
liver and kidney
24
Q
What is the regulated step in synthesis of ketone bodies?
A
HMG-CoA lyase
25
What intermediate of ketone body synthesis can also be part of cholesterol synthesis?
acetoacetyl-CoA
26
What enzyme is used by both synthesis of ketone bodies and cholesterol?
HMG-CoA synthase
27
What can't the liver and kidney break down ketone bodies?
missing aceoacetate/succinyl-CoA transferase (catalyzes HMG-CoA>>acetoacetyl-CoA)
28
How many molecules of acetyl-CoA does it take to make a ketone body?
two
29
high ketone concentrations
metabolic acidosis
30
What types of FAs are gluconeogenic?
odd number FAs: break down to 1 acetyl-CoA and 1 propinoyl-CoA (gluconeogenic)
31
How does acetyl-CoA get transported out to mitochondria?
citrate cleavage pathway
32
ATP-citrate lyase
citrate>>acetyl-CoA+OAA using one ATP
33
What does high level of cytoplasmic citrate indicate?
CAC is not able to keep up with all the acetyl-CoA. Glycolysis slows and FA synthesis increases
34
In the reaction catalyzed by malic enzyme (malate>>pyruvate), what else is produced?
NADPH
35
Regulated step of FA synthesis
Acetyl-CoA>> Malonyl-CoA catalyzed by acetyl-CoA carboxylase
36
Where does FA synthesis occur in a cell?
cytosol
37
large multifunctional enzyme that catalyzes the synthesis of 16 carbon FA (palmitic acid) without releasing an intermediate
FA synthase
38
Both synthesis and elongation of FAs occur at which end of the molecule?
carboxyl-end
| not omega end
39
Where in the cell does elongation of FAs occur?
either mitochondria or ER
40
In the ER, what is the carbon donor for elongation of FA?
malonyl-CoA (located outside the mitochondrial)
41
In the mitochondria, what is the carbon donor for elongation of FA?
acetyl-CoA (located inside the mitochondria)
42
Both elongation and desaturation of FA requires what?
NADPH
43
What does desaturation occur in the cell?
ER
44
Desaturation of FA uses what system?
p450 monoxygenase system
45
What does TAG synthesis require from glycolysis during well-fed state?
glycerol donor:
| DHAP>>Glycerol-3-Phosphate catalyzed by glycerol phosphate dehydrogenase
46
What is the committed step of TAG synthesis?
catalyzed by DGAT (acyl-CoA:diacylglycerol acyltransferases)
47
In the reverse of TAG synthesis (hydrolysis of TAG), what is the enzyme that catalyzes the reaction?
lipases
48
What does hydrolysis of TAG yield?
TAG+3H20>>Glycerol+3FA
49
What induces the expression of acetyl-CoA carboxylase, FA synthase, malic enzyme and G6PD?
insulin
50
What do malic enzyme and G6PD have in common?
they both produce NADPH (important for FA synthesis)
51
What allosterically activate acetyl-CoA carboxylase and FA synthase?
citrate
52
The presence of malonyl-CoA inhibits what?
FA degradation
53
protein coat surrounding fat droplets
perilipin
54
hormone-sensitive lipase is active under what hormone?
glucagon
55
What transports FFAs in the circulation?
albumin
56
Why does TAG synthesis also occur during fasting state?
too much FFAs are released so the liver re-esterifies them back to TAG
57
synthesis of membrane lipids begins with the formation of ...
diacylglycerol (DAG) from lgycerol phosphate and acyl-CoA
58
What enzyme catalyzes the rate-limiting step in the synthesis of phosphotidylcholine?
phosphocholine cytidyltransferase
59
What are the general reactions to membrane lipid synthesis (PC & PE)?
X is either choline or ethanolamine
1) activation by phosphorylation
2) transfer to CTP to make CDP-X
3) X transferred from CDP-X to DAG to make phosphotidyl-X
60
What enzyme is involved in the synthesis of phosphotidylserine? What reaction does it catalyze?
phosphotidylserine synthase
| - exchanges ethanolamine from PE with serine
61
What enzyme is involved with the synthesis of phosphotidylinositol? What reaction does it catalyze?
phosphotidylinositol synthase
| - CDP-DAG binds with inositol
62
How does the synthesis of PI differ than the synthesis of PE or PC?
CTP binds with DAG first, not the head group
63
helps with folding of mitochondrial ETS and buffers electrons in membranes
cardiolipin
64
outer leaflet membrane lipids
phosphotidylcholine (PC) and sphingomyelin
65
inner leaflet membrane lipids
phosphotidylethanolamine (PE)
| phosphotidylserine (PS)
66
the transfer of this membrane lipid to the outer leaflet signals apoptosis
PS (phosphotidylserine)
67
functions to exchange FAs on membrane lipids
phospholipases
- phospholipase A1>>C1
- phospholipase A2>>C2
- phospholipase C>>removes phosphate head from C3
68
What important signal transduction reaction does phospholipase C catalyzes?
PIP2>>IP3+DAG
69
Which phospholipase produces the signaling molecules prostaglandin and thromboxane?
phospholipase A2
70
What essential acid is required for the synthesis of arachidonic acid?
Linoleic Acid
71
What are the steps to the synthesis of arachidonic acid?
1) elongation and desaturation of linoleic acid to make arachidonic acid
2) it gets incorporated into the phospholipid membrane until signal
3) upon stimulation, phospholipase A2 cleaves arachidonic acid from C2
72
What is the substrate in the synthesis of prostaglandins?
free arachidonic acid
73
What enzyme is involved with the synthesis of prostaglandins?
COX1/2 and Prostaglandin synthase
74
What enzyme is involved with the synthesis of thromboxanes?
thromboxane synthase
75
What enzyme is involved with the synthesis of leukotrienes?
lipoxygenase reaction
76
What can potentially inhibit the synthesis of leukotrienes?
corticosteroids (inhibits phospholipase A2)
| lipoxygenase inhibitors
77
What can potentially inhibit the synthesis of prostaglandins?
corticosteroids (inhibits phospholipase A2)
| aspirin or NSAIDs (inhibits COX1/2 and prostaglandin synthase)
78
cannot be stored and readily diffuses across membrane
prostaglandins
79
promotes smooth muscle contraction, involved with anahylaxis, asthma can be alleviated with the enzyme inhibitor
leukotrienes, lipoxygenase inhibitors
80
inflammatory processes - causes vasodilation
during delivery- contraction of uterus
blood - inhibits platelet aggregation
prostaglandins
81
condensation of leukotriene A4 with glutathione makes...
leukotriene C4
82
membrane lipid with fatty alcohol in ether-linkage
plasmalogens
83
induction of ether linkage in the synthesis of plasmalogens must occur where?
peroxisomes
84
1 FA, 1 polar head group on sphingosine (no glycerol)
sphingolipid
85
ceramide + phosphocholine
sphingomyelin
86
ceramide + glucose or galactose
cerebrosides
87
cerebrosides + sulfate group
sulfatide
88
ceramide + 2-4 neutral sugars
globosides
89
ceramide + negative charged NANA (N-acetyl neuraminic acid)
gangliosides
90
glycosphingolipids are found...
on the outside of the cell because they are glycosylated
91
genetic defects in any of the enzymes required to break down glycolipids will lead to accumulation of undegraded glycolipids in the lysosomes of phagocytic cells
sphingolipidoses
92
defect in the enzyme beta-glucosidase leading to accumulation of glucocerebroside, symptoms include liver and spleen enlargement, erosion of long bones
Gaucher Disease
93
defect in the enzyme beta-hexosaminidase A leading to accumulation of ganglioside GM2, symptoms include intellectual disability, blindness, cherry red spot on macula, death before age 3
Tay-Sachs Disease
94
Where does the synthesis of cholesterol occur (organs)?
liver, intestines, and reproductive tissues
95
What cell compartment does the synthesis of cholesterol occur?
cytosol
96
What is the rate-limiting step for the synthesis of cholesterol?
HMG-CoA reductase (HMG-CoA>>Mevalonic Acid), takes 2 NADPH
97
- can be converted to dolichol-P
- used in prenylation of proteins
- precursor for synthesis of CoQ
Farnesyl PP
98
Regarding regulation of HMG CoA Reductase, what does the action of phosphorylation by AMP-dependent kinase do?
inactivates cholesterol synthesis
99
Regarding regulation of HMG CoA Reductase, what does insulin-dependent dephosphorylation do?
activates it thus cholesterol synthesis occurs when blood glucose increases
100
Regarding regulation of HMG CoA Reductase, what does the presence of cholesterol do?
end-product inhibition
101
hydrophilic surface and lipophilic core
lipoproteins
102
What enzyme catalyzes the esterification of cholesterol to make cholesteryl ester?
LCAT (lecitin:cholesterol acyltransferase)
103
found in hydrophobic center of lipoproteins or in cytoplasmic fat droplets
cholesteryl esters
104
Regarding the regulation of hormone-sensitive lipase (HSL), what does insulin do?
inhibits HSL - prevents release of FFA during well-fed state
105
Regarding the regulation of hormone-sensitive lipase (HSL), what does cortisol do?
induces HSL - increases release of FFA from adipose tissue
106
Regarding the regulation of hormone-sensitive lipase (HSL), what does glucagon do?
stimulates HSL and it's mediated by cAMP and PKA
107
- acidic and water-soluble
- secreted by the liver through the bile duct into the digestive tract and are very effective in emulsifying fat from the diet
bile acids
108
cannot be degraded by human enzymes, must be excreted in the form of bile acids
cholesterol and its derivatives
109
- regulates entry
- activator of LCAT
- extract lipids from membranes
ApoA
110
structural proteins that give lipoproteins its structures
ApoB
| ApoB100 - VLDL, ApoB48 - chylomicrons
111
- regulates the exit
| - modulates function of lipoprotein lipase (LPL)
ApoC
112
- marks the surface to help mediate interactions with receptors
- removal of remnant particles
ApoE
113
secreted into the lymphatic system and enter blood through thoracic duct
chylomicrons
114
packed with TAGs synthesized by enterocytes from dietary fats
chylomicrons
115
functions to distribute dietary lipids throughout the body
chylomicrons
116
How do chylomicron remnants get removed?
- by the liver
- ApoB48 and ApoE on the remnants bind to LDL receptors on the surface of hepatocytes. This initiates receptor-mediated (clarthrin) endocytosis
117
function in reverse cholesterol transport from the peripheral tissues to the liver
HDL
118
delivers lipids made by the liver to peripheral tissues
VLDL
| - leaves full and drop things off
119
leaves the liver empty and brings back cholesterol picked up from peripheral tissues
HDL (reverse cholesterol transport)
120
enzyme that transports cholesterol actively out of the cell membranes to HDL
ATP-binding Transporter A1 (ABCA-1 aka Cholesterol Efflux Regulatory Protein (CERP))
121
enzyme that esterfies cholesterol once it has been transferred into HDL
LCAT (lecitin:cholesterol acyltransferase)
122
liberates FFAs and glycerol from TAGs within the lipoproteins
lipoprotein lipase (LPL)
