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Lipids 2 Flashcards

1
Q

Hormone sensitive lipase

A

Acts on stored TAG (in adipocytes) and is converted to FA and glycerol.
Located in the adipocytes

Inhibited by insulin (activated during diabetic ketoacidosis).

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2
Q

Ketone body synthesis reactions upto primary ketone body formation

A
  1. Acetoacetyl CoA (from beta oxidation) and Acetyl CoA combine with the help of HMG CoA Synthase (RDS)
  2. The HMG CoA formed is split by HMG CoA Lyase to acetoacetate (and Acetyl CoA)
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3
Q

Ketone body synthesis occurs in

A

Exclusively Liver mitochondria

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4
Q

Secondary ketone body synthesis from primary

A

Acetoacetate is either

a) spontaneously decarboxylated to acetone
b) converted to Beta Hydroxy Butyrate by b-OH Butyrate dehydrogenase utilising NADH

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5
Q

Two organs that cannot utilise ketone bodies are

A

Liver, RBC

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6
Q

Ketone body utilisation from primary ketone body

First step

A

Acetoacetate accepts CoA by Thiophorase (S- CoA Acetoacetate CoA transferase) from succinyl CoA to become acetoacetyl CoA (and succinate but no GTP/ATP is generated)

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7
Q

Ketone body utilisation from primary ketone body

Second step

A

Acetoacetyl CoA is converted to 2 Acetyl CoA as part of beta oxidation by thiolase

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8
Q

Fate of secondary ketone bodies

A
  1. Beta OH butyrate is converted to acetoacetate producing NADH+
  2. Acetone is volatilised and excreted through lungs (fruity smell in ketosis)
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9
Q

Energetics of ketone body utilisation from acetoacetate

A

2 Acetyl CoA are formed
TCA cycle occurs twice but in one cycle thiophorase is used instead of thiokinase
So 20-1= 19 ATP

If it is beta OH butyrate 19+2.5= 21.5 ATP

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10
Q

Most common ketone body in a normal person

A

Beta Hydroxy butyrate = acetoacetate

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11
Q

Most common ketone body during starvation

A

Beta Hydroxy Butyrate: Acetoacetate = 6:1

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12
Q

Neutral ketone body

A

Acetone

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13
Q

Test for ketone body

A
  1. Rothera’s test
    a) Purple ring - acetoacetate and acetone
    b) Beta Hydroxy Butyrate does not answer Rothera’s test
  2. Gerhard’s test answered only by acetoacetate
  3. Ketostix - dipstick test
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14
Q

Organs where FA are synthesised

A

Liver, adipose tissue, brain, kidney, lungs, lactating mammary glands

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15
Q

Steps of FA is elucidated by

A

Feodor lynen

Hence FA synthesis is also called Lynen’s spiral

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16
Q

Steps of FA synthesis

A
  1. Transfer of Acetyl CoA from mitochondria to cytoplasm
  2. Acetyl CoA carboxylase
  3. FA synthase complex reactions requires Mn+2
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17
Q

Transport of Acetyl CoA into cytoplasm for FA synthesis

A
  1. First step of TCA occurs
  2. Citrate exits via Tricarboxylic Acid Transporter
  3. It is split into Acetyl CoA and OAA by ATP Citrate Lyase
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18
Q

Acetyl CoA carboxylase , the second step of FA synthesis

A

Acetyl CoA is carboxylated to Malonyl CoA using:

  1. bicarbonate (HCO3-)
  2. Acetyl CoA carboxylase
  3. ATP
  4. Biotin
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19
Q

FA synthase complex structure

A
  1. Homodimer
  2. Each monomer unit has 6 enzyme activity + 1 Acyl carrier protein (ACP)
  3. ACP has a pantothenic acid as 4 phosphopantotheine.
  4. Multifunction enzyme-single polypeptide has more than 2 enzyme activity.
  5. X shaped (using X-ray crystallography)
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20
Q

Domains of FA synthase

A
  1. Condensing unit
  2. Reduction unit
  3. Releasing unit
  4. Acyl Carrier Protein
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21
Q

Condensing unit- enzymes

A
  1. Acetyl/ Malonyl transacylase
  2. Ketoacyl synthase

ACP

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22
Q

Reduction unit-enzymes

A
  1. Ketoacyl reductase
  2. Dehydratase
  3. Enoyl reductase
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23
Q

Releasing unit-enzyme

A

Thioesterase

This unit takes place only once per FA

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24
Q

Cys-SH group of first monomer unit and Pan-SH group of 2nd monomer unit

A

By Acetyl/Malonyl transacylase
a Acetyl group combines with Cys-SH and
a Malonyl group combines with Pan-SH

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25
Action of ketoacyl synthase, 2nd enzyme of first unit
From Malonyl group, a CO2 is removed and then the Acetyl group condenses with it A keto compound of 4C is formed at pan-SH
26
Reduction unit
Ketoacyl compound is reduced using NADPH to Acyl group (Acetoacetyl initially)
27
Releasing unit
Acyl group combines with CoA and separated from the complex by thioesterase.
28
Different types of regulation of FA synthesis
1. Short term a) allosteric b) covalent c) compartmentalisation 2. Long term Increased Acyl CoA decreases the expression of enzymes that synthesise FA
29
Acetyl CoA carboxylase regulation
Inactive state- dimeric Active- polymeric Activator-citrate (also activates TCA transporter) Inhibitor-LCFA (also inhibits TCA transporter)
30
Compartmentalisation of FA acid synthesis
Beta oxidation occurs in the mitochondria while FA synthesis occurs in the cytoplasm
31
Elongation of FA
1. Major In SER by microsomal FA elongase system 2. Minor By mitochondrial FA elongase For myelination of brain
32
Synthesis of unsaturated FA
Involves the enzyme in ER : 1. Desaturase 2. Elongase Humans cannot insert a double bond between C10 and terminal methyl
33
Cholesterol concepts
``` Regulated by insulin Cannot generate energy Purely animal sterol 27C 50% excreted ```
34
Cholesterol is synthesised in
all nucleated cells especially in liver, adipose tissue, adrenal cortex, gonads,intestine It is synthesised in SER and cytoplasm
35
Stages of synthesis of cholesterol
1. Synthesis of HMG CoA (6C) 2. Synthesis of Mevalonate (6C) 3. Synthesis of isoprenoid unit(5C) 4. Isoprenoid units join to form 30C squalene 5. Trimmed to Cholesterol
36
HMG CoA is involved in
1. Synthesis of Cholesterol (cytoplasmic) 2. Synthesis of Ketone body (mitochondrial) 3. Leucine metabolism
37
Synthesis of Mevalonate
HMG CoA is converted to Mevalonate by HMG CoA reductase (RDS) Statins is a competitive inhibitor of this enzymes Occurs in SER
38
Synthesis of isoprenoid units
Mevalonate is decarboxylated and phosphorylated to isoprenoid unit (5C)
39
Squalene formation
2 Isoprenoid unit = Geranyl PPi 10C Combines with isoprenoid unit (5C) to form Farnesyl PPi 2 Farnesyl PPi combine to form Squalene (30C)
40
Trimming to cholesterol
``` Squalene Lanosterol (first cyclical compound) Zymosterol Desmosterol Cholesterol ``` SLZDC
41
Regulation of cholesterol synthesis
1. Feedback regulation 2. Feedback inhibition 3. Hormonal regulation
42
Long-term feedback regulation of Cholesterol synthesis
Dietary cholesterol decreases binding of SREBP at genes which in turn reduces expression of HMG CoA reductase (RDS)
43
Feedback inhibition of cholesterol synthesis
Mevalonate inhibits HMG CoA reductase
44
Formation of primary bile acids in liver
``` From cholesterol by 7-alpha Hydroxylase (Cytochrome P7A1 or CYP7A1) using 1. NADPH 2. vitamin C 3. O2 To get 7-Hydroxy cholesterol ``` This after multiple steps forms primary bile acids cholic acid and chenodeoxycholic acids requiring NADPH and producing propionyl CoA
45
Formation of secondary bile acids
After deconjugation and dehydroxylation of primary bile acids: 1. cholic acid to deoxycholic acid 2. chenodeoxycholic acid to lithocholic acid 98-99% of secondary bile acids undergo enterohepatic circulation
46
Least enterohepatic circulation is for
Lithicolic acid
47
Regulation of bile acid synthesis
Farnesoid X receptor (FXR) RDE is 7-alpha hydroxylase (CYP7A1) Increased bile acid (Chenodeoxycholic acid) will decrease the binding of this receptor to the gene Thus decreasing expression of this enzyme
48
Layers in lipoprotein
1. Hydrophobic lipids (TAG,cholesterol ester) 2. Amphipathic lipids (cholesterol, phospholipids) 3. Proteins (integral, peripheral)
49
Maximum lipid content (TAG) and least protein content is in
Chylomicron
50
Apolipoproteins in chylomicron and remnant chylomicron
Unique : app B 48 Major : Apo C2 Apo E
51
VLDL is assembles in
Liver | and carries endogenous TAG from liver to peripheral organs
52
VLDL contains the apo lipoproteins
Apo B100 From HDL: Apo C2 Apo E
53
Lipoprotein cascade pathway
VLDL to IDL to LDL
54
Maximum cholesterol and cholesterol ester content is present in
LDL or beta lipoprotein
55
Apolipoprotein present in LDL
Apo B100 only
56
Maximum apoprotein and phospholipid content is in
HDL Formed from liver and intestine Participates in reverse cholesterol transport
57
Repository for apo E and Apo C2
HDL or alpha lipoprotein
58
Lipoprotein of HDL | Enzyme activity of HDL
Apo A1 Enzyme activity: 1. LCAT (Lecithin Cholesterol Acyl Transferase) activated by apo A1 2. Cholesterol ester transfer protein (CETP)
59
LCAT
Lecithin + Cholesterol = cholesterol ester + Lysolecithin
60
CETP
1. Transfers cholesterol ester from HDL to other lipoproteins like LDL,... 2. in turn transfers TAG from other lipoproteins to HDL Inhibited by apo C1
61
LP(a)
Lipoprotein that contains apo(a) and apo B100 linked by a disulphide bond apo(a) is a structural analog of plasminogen and hence inhibits clot lysis
62
Lipoprotein X
Lipoprotein produced during cholestasis from unexcreted cholesterol and phospholipids Indicator of cholestasis
63
Pre beta lipoprotein
VLDL
64
Broad beta lipoprotein
IDL
65
Order of lipoproteins from cathode to anode
``` Chylomicron LDL VLDL IDL/remnant VLDL HDL ``` Protein content~ electrophoretic mobility
66
Nascent chylomicron contains the lipoproteins
B48 | Helps in the assembly of chylomicron in intestine
67
LPL HP(Lipoprotein Lipase)
Anchored to the capillaries surrounding the peripheral organs Hydrolyses the TAG Activated by apo C2 Involved in both chylomicron and VLDL metabolism
68
Function of apo E
Ligand for hepatic receptors for internalisation of remnant chylomicron and IDL Receptor mediated endocytosis
69
Apo proteins of nascent VLDL
B100 Helps in the assembly of CLDL Ligand for LDL
70
Fates of IDL
1. Receptor mediated Endocytosis into the liver via ligand apo E 2. Loses some TAG (via endothelial and hepatic lipase) Apo E and Apo C2 are removed and then converted into cholesterol ester rich LDL (having only Apo B100) Thus is the lipoprotein cascade pathway
71
Fates of LDL
1. 70% of LDL is taken by the liver via LDL receptors 2. 30% LDL is taken by extra-hepatic tissues via LDL receptors Ligand for LDL receptors is Apo B100 (receptor mediated endocytosis) Oxidation may occur which is ingested by macrophages leading to atheroma
72
Transporters present in HDL
ABCA1 ABCG1 SRB1 (Scavenger Receptor B1) ATP Binding Casette Transports cholesterol and its esters from peripheral organs to HDL3 (spherical)
73
Why newly formed HDL is disc shaped
Cholesterol and phospholipid which it contains are both amphipathic compounds (which exists in a structure similar to cell membrane)
74
Change of shape from discoidal to spherical HDL3
Due to the formation of hydrophobic cholesterol ester by LCAT from cholesterol
75
Formation of spherical HDL2 and the conversion back to HDL3
After receiving cholesterol from peripheral cells, spherical HDL3 is converted to spherical HDL2 which later donates the cholesterol to liver to mostly form HDL3 again
76
Pre beta HDL
While HDL2 is donating cholesterol, certain lipase liberate apo A1. Apo A1 accepts cholesterol, phospholipid,... to form poorly lipidated HDL, i.e, pre beta HDL The most potent HDL
77
Function of apo C3 Function of apo A2
Inhibits lipoprotein lipase
78
Function of apo A5
Facilitates the binding of chylomicron and VLDL to lipoprotein lipase
79
Apo D
Associated with human neurodegenerative diseases like Parkinson’s disease
80
Special features of apo E
Arginine rich Apo E4 is associated with late onset of Alzheimer’s disease
81
Classification of hyperlipoproteinemia is done by
Fredrickson and Levy
82
Primary hyperlipoproteinemia are classified into (according to Harrison’s)
1. Primary hyperlipoproteinemia with hypertriglyceridemia 2. with hypercholesterolemia 3. with both hypertriglyceridemia and hypercholesterolemia
83
Primary hyperlipoproteinemia with hypertriglyceridemia (Fredrickson’s classification)
Type 1 : Familial chylomicronemia syndrome Type 4 : Familial hypertriglyceridemia apo A-V defect Type 5 : Familial hypertriglyceridemia apo A-V defect and GPIHBP-1 defect
84
Primary hyperlipoproteinemia with hypercholesterolemia (Fredrickson’s classification)
Type 2
85
Primary hyperlipoproteinemia with both hypertriglyceridemia and hypercholesterolemia
Type 3 or Familial Dysbetalipoproteinemia (FDBL)
86
Type 1 hypercholesterolemia | Familial chylomicronemia syndrome
1. Apo C2 2. Lipoprotein lipase Chylomicron and VLDL increased TAG accumulates
87
Clinical features of type 1 hyperlipoproteinemia
1. Milky white plasma 2. Eruptive xanthoma 3. On fundoscopy, lipemia retinalis 4. TAG>1000gm leads to pancreatitis and then abdominal pain
88
Treatment of familial chylomicronemia syndrome
Gene therapy: A lipogene -Tiparvovec Adeno associated viral vector expressing LpL variant leading to myocyte expression of LpL
89
Type 4 hyperlipoproteinemia
Apo A5 defect which facilitate the association of chylomicron,VLDL with LpL Familial hypertriglyceridemia
90
Type 5
1. Apo A5 defective or 2. Defect in glycosylated phosphatidyl inositol HDL binding protein-1 (GPIHBP-1) which helps in the export of lipoprotein lipase to vascular endothelium Increased TAG
91
Familial hypercholesterolemia/ | ADH type 1
Fredrickson’s type 2a Most common Defective LDL receptor Therefore Cholesterol and cholesterol ester is elevated
92
Clinical features of familial hypercholesterolemia
1. Corneal arcus 2. Tendon xanthoma 3. Clear plasma 4. Increased risk of CAD and PVD No abdominal pain
93
Treating of familial homozygous hypercholesterolemia
1. Lomitapide-inhibits Microsomal Triglyceride Transfer Protein (decreases VLDL leading to decreased LDL) 2. Mipomersin-antisense oligonucleotide to apo B
94
Sitosterolemia biochemical defect
Type 2a Primary hyperlipoproteinemia with hypercholesterolemia Defective ABCG5 and ABCG8 (which usually actively excrete plant sterols from liver and intestinal cells)
95
Clinical features of sitosterolemia
Decreased plant sterols in the cells leads to decreased transcription of LDL receptors This leads to increased LDL in blood which leads to increased cholesterol in blood
96
ADH type 2
Familial defective apo B(FDB) Apo B100 defective Autosomal dominant
97
ADH type 3
PCSK9-secreted protein that accelerate lysosomal degradation of LDL receptors Gain of function mutation occurs in PCSK9 (increased activity) Decreased LDL receptor
98
Autosomal recessive hypercholesterolemia
Defect in LDL receptor adaptor protein (LRAP) | Decreased LDL uptake
99
Type 3 Hyperlipoproteinemia/ Familial dysbetalipoproteinemia (FDBL) Clinical features
1. Tuberoeruptive xanthoma (like a bunch of grapes) 2. Palmar xanthoma /Lipid deposition in palmar creases 3. Slight risk of CAD 4. Plasma is clear
100
Type 3 Hyperlipoproteinemia/ Familial dysbetalipoproteinemia (FDBL) Biochemical defect
Apo E mutation (which acted as a ligand for the uptake of chylomicron remnant and IDL/VLDL remnant) Hence these accumulate leading to accumulation of both TAG and cholesterol So called as Remnant removal disease or broad beta disease
101
Hypolipoproteinemia
1. Abetalipoproteinemia 2. Tangier’s disease 3. LCAT deficiency
102
Abetalipoproteinemia biochemical defect
Defective Microsomal Triglyceride Transfer Protein (transport of lipid to the apo protein) So decreased lipoproteins except HDL
103
Clinical features of abetalipoproteinemia
1. Acanthocytes 2. Pigmentary retinitis 3. Bleeding manifestations due to decreased fat soluble vitamins
104
Tangier’s disease | Biochemical defect
Defective ABCA1 (transport cholesterol from peripheral organs to HDL) Decreased spherical HDL Other lipoproteins are normal
105
Clinical features of Tangier’s disease
1. Orange/yellow tonsils (cholesterol accumulation) 2. Hepatosplenomegaly 3. Mononeuritis multiplex
106
Norum’s disease
Complete LCAT deficiency Increased lecithin and cholesterol Decreased lysolecithin and cholesterol ester Progresses to end stage renal disease (ESRD)
107
Fish eye disease
Partial LCAT deficiency Benign Do not progress to end stage renal disease (ESRD)
108
Steps in the action of hormone sensitive lipase
TAG➡️2,3-diacyl glycerol ➡️ 2-Mono Acyl glycerol Then esterases act on the product to form glycerol and FA
109
Activators of hormone sensitive lipase
Glucagon Catecholamines ACTH,TSH Glucocorticoids, thyroid hormones
110
Inhibitors of hormone sensitive lipase
Insulin Nicotinic acid PG E1
111
Lipoprotein lipase is anchored to the capillaries of the organs:
Heart, adipose tissue,spleen,renal medulla,aorta, diaphragm, lactating mammary glands
112
Heparin and lipoprotein lipase
If we inject heparin the lipoprotein lipase is dislodged and is free to be calculated
113
Hepatic lipase function
Act on chylomicron remnant | Convert HDL2 to HDL3
114
Endothelial lipase action
Acts on HDL3 to convert it into HDL2 and pre-beta HDL (most potent)

Biochemistry MBBS (10 decks)

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