Lipids Flashcards
(161 cards)
1
Q
Group of compounds related by certain physical properties: Insoluble in water, Soluble in nonpolar solvents
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Lipids
2
Q
Function of Lipids
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Major source of energyProvide hydrophobic barrierServe as coenzymes, regulatorsHormonesMediators of inflammation
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Q
Amphipathic; have both hydrophilic and hydrophobic groups; enables formation of bilayers
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Phospholipids
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Q
Long chains of carboxylic acids
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Fatty acids
5
Q
Degree of Saturation: Contain 0 double bond
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Saturated Fatty Acids
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Q
Degree of Saturation: Contain 1 double bond
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Monounsaturated Fatty Acids
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Q
Degree of Saturation: Contain >1 double bond
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Polyunsaturated Fatty Acids
8
Q
Are associated with increased risk of cardiovascular diseases
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Trans- and saturated fatty acids
9
Q
Are thought to be protective
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Mono- and polyunsaturated fatty acids
10
Q
Geometric Isomerism of Unsaturated Fatty Acids
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Cis fatty acidsTrans fatty acids
11
Q
On the opposite side of the double bond
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Cis fatty acids
12
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On the same sides of double bonds
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Trans fatty acids
13
Q
Fluidity decreases with
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Increasing chain length Increasing saturation
14
Q
Essential Fatty Acids
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Linoleic AcidLinolenic AcidArachidonic Acid
15
Q
Precursor of arachidonic acid 20:4 (5,8,11,14) which is essential in prostaglandin synthesis
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Linoleic Acid
16
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18:3 (9,12,15)Deficiency results in decreased vision and altered learning vision
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Linolenic Acid
17
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Becomes essential if Linoleic Acid is deficient
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Arachidonic Acid
18
Q
Numbering starts from the last carbon atom
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Omega Fatty Acids
19
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Are correlated with a decreased risk of cardiovascular disease; Lowers thromboxane production; Reduced tendency of platelets to aggregate
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Omega-3 Fatty AcidOmega-6 Fatty Acid
20
Q
Activation of Fatty Acids
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Must first be activated before being used in metabolismEnzyme: fatty acyl-CoA synthetaseCo-factor: pantothenic acidEnergy used: 2 ATP equivalents
21
Q
Formation of Palmitate (16:0)
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Fatty Acid Synthesis
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Fatty Acid Synthesis: Where does it occur?
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In the cytosolMajor: liver and lactating mammary glandsMinor: adipose tissue
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Fatty Acid Synthesis: Substrates
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1 Acetyl CoA7 Malonyl CoA NADPHATP
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Fatty Acid Synthesis: Product
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Palmitate only
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Fatty Acid Synthesis: Rate limiting step
Reaction: Acetyl CoA + ATP➡️Malonyl CoAEnzyme: Acetyl CoA carboxylase
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Necessary co-factor for fatty acid synthesis
Biotin
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Fatty Acid Synthesis: Step 1
Synthesis of cytoplasmic Acetyl CoA
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Fatty Acid Synthesis: Step 2
Acetyl CoA carboxylated to Malonyl CoARate limiting stepEnzyme: Acetyl CoA carboxylaseCofactor: biotinActivators: insulin and citrate
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Fatty Acid Synthesis: Step 3
Assembly of PalmitateEnzyme: Fatty acid synthase
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Where does the cell primarily get the necessary NADPH?
Hexose monophosphate Pathway orPentose phosphate Pathway andNADPH-dependent malate dehydrogenase (malic enzyme)
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Assembly is a sequence of steps
Condensation➡️Reduction➡️Dehydration➡️Reduction
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Regulation of Lipogenesis
Activated by: Citrate, InsulinInhibited by: Fatty acyl-CoA, Glucagon, Epinephrine
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Fate of Fatty Acids
Further elongation in smooth endoplasmic reticulum and mitochondria;Desaturation in the ER through mixed function oxidases (cytochrome b5)
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Essential in the diet because they have double bonds that exceed the 9th carbon
Linoleic AcidLinolenic Acid
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Esters of the trihydric alcohol Glycerol and fatty acids; Main storage forms of fatty acids; Coalesce within adipocytes to form oily droplets that are the major energy reserve of the body
Triacylglycerols (TAGs)
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Synthesis of TAGs: Where does it occur?
LiverAdipose tissue
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Synthesis of TAGs
Glycerol-3-phosphate + 3 fatty acyl CoA➡️triglyceride
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Sources of glycerol-3-phosphate
DHAP from glycolysisPhosphorylation of free glycerol
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DHAP from glycolysis
Enzyme: glycerol-3-phosphate dehydrogenaseIn liver and adipose tissue
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Phosphorylation of free glycerol
Enzyme: glycerol kinaseIn liver only
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What organs synthesize fatty acids?
LiverAdipose tissue
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Hydrolyzes TAGs to yielding free fatty acids and glycerol; Can only release fatty acids from carbon 1 and carbon 3 of the TAG in stored fat
Hormone-sensitive Lipase
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Bound to Albumin in blood for beta-oxidation
Free fatty acids
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Carbon backbone for gluconeogenesis
Glycerol
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Increase glucagonIncrease cAMP➡️phosphorylation
Active Hormone-sensitive lipase
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Increase InsulinDecrease cAMP➡️dephosphorylation
Inactive Hormone-sensitive lipase
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Removal of Acetyl CoA fragments from ends of Fatty acids; Acetyl CoA can enter the citric acid cycle; generates NADH and FADH2 that can enter the ETC
Beta-oxidation of Fatty Acids
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Beta-oxidation of Fatty Acids: Where does it occur?
In the mitochondria of almost all cells but fatty acid activation occurs in the cytosol;Exceptions are: neurons, RBC, testis, kidney medulla
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Beta-oxidation of Fatty Acids: Substrate
PalmitateNAD+ + FADATP
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Beta-oxidation of Fatty Acids: Products
8 Acetyl CoA7 FADH27 NADH
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Beta-oxidation of Fatty Acids: Rate limiting step
Reaction: fatty acyl CoA + Carnitine➡️fatty acyl carnitine + CoAEnzyme: carnithine acyltransferase
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Beta-oxidation of Fatty Acids reverses the process of fatty acid synthesis by
Oxidizing and releasing units of acetyl-CoA
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Oxidation of a fatty acid with an odd number of carbon atoms will yield
Acetyl CoAPropionyl-CoA
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Propionyl-CoA is converted to a TCA intermediate
Succinyl-CoA
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Propionyl-CoA carboxylase requires
Biotin
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Methylmalonyl-CoA mutase requires
Vit. B12
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Oxidize very long chains of fatty acids (C20, C22)
Peroxisomes
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Oxidation of unsaturated FAs require an additional enzyme
3,2 enoyl-CoA isomerase
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Energy Yield of Beta-oxidation
129 ATP
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Regulation of Beta-oxidation
Activated by: GlucagonInhibited by: Malonyl-CoA, Insulin
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Alcohol leads to fat accumulation in the liver, called steatosis, which ultimately leads to cirrhosis; Alcohol dehydrogenase eats up NAD+ to reduce beta-oxidation in the liver
Fatty liver
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Can occur in newborn and manifest as hypoglycemia from impaired FA oxidation and muscle weakness from lipid accumulation
Carnitine Deficiency
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Affects only the liver resulting in reduced FA oxidation and ketogenesis with hypoglycemia
CPT I Deficiency
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Affects skeletal muscle and when severe the liver
CPT II Deficiency
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Decreased FA oxidation; During fasting, hypoglycemia can become profound due to lack of ATP to support gluconeogenesis; can manifest as Sudden Infant Death Syndrome
Medium-chain Fatty Acyl-CoA Dehydrogenase Deficiency (MCAD)
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Caused by eating unripe fruit of the akee tree , which contains hypoglycin, a toxin that inactivates medium and short-chain Acyl CoA dehydrogenase and leads to hypoglycemia
Jamaican Vomiting Sickness
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Rare neurologic disorder due to a defect that causes accumulation of Phytanic Acid which is found in plant foodstuff and blocks Beta-oxidation; Causes neurologic symptoms due to improper myelinization
Refsum's Disease
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Cerebrohepatorenal syndrome, which occurs in individuals with rare inherited absence of peroxisomes in all tissues; Characterized by liver dysfunction with jaundice, marked mental retardation, weakness, hypotonia, and craniofacial dysmorphism
Zellweger's Syndrome
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Defect in peroxisomal activation of VLCFA leads to accumulation of VLCFA in blood and tissues; Initial abnormalities are apathy and behavioral change; Visual loss, spasticity and ataxia follow
X-linked Adrenoleukodystrophy
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Converts acetyl CoA to ketone bodies
Ketogenesis
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Ketogenesis: Where does it occur?
In liver mitochondria
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Ketogenesis: Substrate
Acetyl CoA
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Ketogenesis: Products
Ketone Bodies
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Ketogenesis: Rate limiting step
Reaction: Acetoacetyl CoA + Acetyl CoA➡️HMG-CoAEnzyme: HMG CoA synthase
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6-Hydroxybutyrate➡️Acetoacetate➡️Acetyl-CoA
Ketogenolysis
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Can serve as fuel for extrahepatic tissues especially during fasting
Ketone Bodies
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In prolonged starvation and diabetic ketoacidosis, oxaloacetate is depleted for gluconeogenesis; In alcoholism, excess NADH shunts oxaloacetate to malate; Rate of Ketone Body Formation > Rate of Ketone Body Use
Ketoacidosis
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A steroid alcohol; Very hydrophobic compound; has a single hydroxyl group
Cholesterol
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Adrenal hormone not derived from cholesterol
Epinephrine
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De novo synthesis of Cholesterol
Cholesterol Synthesis
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Cholesterol Synthesis: Where does it occur?
Virtually all cells, in the cytosol and smooth endoplasmic reticulumMajority: in the liver and intestines
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Cholesterol Synthesis: Substrate
Acetyl CoANADPHATP
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Cholesterol Synthesis: Product
Lanosterol➡️Cholesterol
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Cholesterol Synthesis: Rate limiting step
Reaction: HMG CoA➡️mevalonateEnzyme: HMG CoA reductase
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Drugs used for the treatment of hypercholesterolemia, to reduce the risk for cardiovascular diseases
Statins
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Cholesterol Synthesis: Step 1
Biosynthesis of mevalonateRate limiting step
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Cholesterol Synthesis: Step 2
Formation of isoprenoid units(Isopentenyl diphosphate)
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Cholesterol Synthesis: Step 3
Six isoprenoid units form isoprene
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Cholesterol Synthesis: Step 4
Formation of Lanosterol
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Cholesterol Synthesis: Step 5
Formation of Cholesterol
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An intermediate in the pathway
Farnesyl pyrophosphate
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How does the Acetyl CoA reach the cytosol for cholesterol biosynthesis?
Citrate shuttle
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High cholesterol limits the expression of HMG-CoA reductase gene by transcription factor (SREBP)
Production inhibition
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Insulin dephosphorylates and activates; Glucagon phosphorylates and inactivates
Enzyme phosphorylation
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Elimination through conversion to bile salts then secretion into the bile
Cholesterol degradation
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Synthesized in the liver from cholesterol
Bile Acids
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Rate limiting enzyme of Bile Acids
Cholesterol-7-alpha-hydroxylase
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Regulation of Bile Acids
Activated by: CholesterolInhibited by: Bile Acids
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Bile acid conjugated with either glycine or taurine; Primary means of excreting cholesterol; Emulsify lipids in the intestines
Bile salts
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Excreted bile is reabsorbed in?
Terminal ileum95% reabsorbed5% excreted in feces = amount that liver must make
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Steroid Hormone Synthesis: What is it for?
Precursor of ALL steroid hormonesGlucocorticoids (Cortisol)Mineralocorticoids (Aldosterone)Sex Hormones (Testosterone and Estradiol)
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Steroid Hormone Synthesis: Location
In the smooth endoplasmic reticulum of the adrenal cortex, ovaries, testes, placenta
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Steroid Hormone Synthesis: Substrate
CholesterolPregnenolone - "mother hormone" from which all other hormones are derived
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Steroid Hormone Synthesis: Rate limiting step
Reaction: Cholesterol➡️PregnenoloneEnzyme: DesmolaseBlocker: Aminogluthetimide
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Lipid digestion begins in the
Stomach
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Reach the capillaries of skeletal muscle and adipose tissue; Triglycerides broken to FA and glycerol via lipoprotein lipase
Chylomicrons
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Directly enter adjacent muscle cells or adipocytes, or may be transported in blood bound to albumin
Free fatty acids
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Converted to DHAP then enters glycolysis or gluconeogenesis
Glycerol
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Manifests as steatorrhea (greasy stools); results in deficiency in fat-soluble vitamins and essential fatty acids
Lipid Malabsorption
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Causes of Lipid Malabsorption
Liver DiseasePancreatic DiseaseCholelithiasisShortened bowelIntestinal mucosa defects
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Spherical macromolecule complexes composed of neutral lipid core surrounded by shell of amphipathic apoptoteins, phospholipid and nonesterified cholesterol
Plasma Lipoproteins
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Functions of Lipid Transport
1) Keep their component lipids soluble as they transport them in plasma2) Provides an efficient mechanism for transporting their lipid contents to and from the tissues
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Represent the protein moiety of lipoproteins; Some are integral while others are free to transfer to other lipoproteins
Apolipoproteins or APO Proteins
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Transport dietary triglyceride and cholesterol from intestine to tissues
Chylomicrons
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Apoproteins: Chylomicrons assembly + secretion; Secreted by epithelial cells
Apo B-48
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Apoproteins: Chylomicron, VLDL; Cofactor for lipoprotein lipase; Shuttled by HDLs
Apo C-II
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Apoproteins: Chylomicron, VLDL; Mediates uptake of chylomicron remnant
Apo E
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Transport triglyceride from liver to tissues
VLDL
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Picks up Cholesterol from HDL to become LDL; Picked up by the liver
IDL
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Delivers cholesterol into cells
LDL
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Picks up cholesterol accumulating in blood vessels; Delivers cholesterol to liver and steroidogenic tissues via scavenger receptor; Shuttles apo C-II and apo E in blood
HDL
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Apoproteins: HDL; Activates LCAT
Apo A-I
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Apoproteins: LDL, VLDL; Binds to LDL and VLDL receptors
Apo B-100
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Deposition of Cholesterol and Cholesterol esters in the artery walls especially from oxidized LDL; Oxidized LDLs can cause endothelial damage
Atherosclerosis
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Lipoprotein lipase deficiency; High VLDL and Chylomicron; Low LDL and HDL; Xanthomas and pancreatitis
Type I Familial Lipoprotein Lipase
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LDL receptors deficiency; High LDL; Xanthomas and Xanthelasmas with increased risk of atherosclerosis and coronary heart disease
Type II Familial Hypercholesterolemia
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Apo E deficiency; High remnants of VLDL and chylomicron with increased risk of atherosclerosis and coronary heart disease
Type III Familial Dysbetalipoproteinemia
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Increased VLDL production; Triad of: Coronary Artery Disease, DM type 2, Obesity
Type IV Familial Hypertriglyceridemia
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Apo B-48 and 100 deficiency; No chylomicron, No VLDL/LDL; Intestinal malabsorption with accumulation of lipids in intestine and liver
Abetalipoproteinemia
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Apo A1 deficiency; No HDL; Triglycerides and atherosclerosis
Familial a-lipoprotein Deficiency: Tangier's DiseaseFisheye Disease
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High HDL; Associated with benefits to health and longevity
Familial Hyperalphalipoproteinemia
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High LpA; Early atherosclerosis and Thrombosis
Familial Lipoprotein A Excess
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Predominant lipids of cell membranes; Degraded by phospholipases
Phospholipids
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Most abundant phospholipids; Represent a large proportion of the body's store of choline, important in nervous transmission, as acetylcholine and as a store of labile methyl groups
Phosphatidylcholine
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Also found in cell membranes; plays a role in programmed cell death
Phosphatidylethanolamine (Cephalin) and Phosphatidylserine (for apoptosis)
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Major lipid component of lung surfactant; Inadequate levels lead to Respiratory Distress Syndrome in the newborn
Dipalmitoylphosphatidylcholine (DPPC) or Dipalmitoyllecithin
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Reservoir for arachidonic acid in the membranes; Source of 2nd messengers
Phosphatidylinositol
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2 molecules of phosphatidic acid esterified through their phosphate groups to an additional molecule of glycerol; Found only in mitochondria and is essential for mitochondrial function; Antigenic
Cardiolipin
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Part of the glycocalyx located on the outer layer of the cell membrane and functions in cell recognition and cell adhesion; Found in high concentrations in nervous tissues
Glycolipids
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Sphingosine + Fatty Acid
Ceramide
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Ceramide + Glucose or Galactose
Cerebroside
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Ceramide + N-acetylneuramic acid
Ganglioside
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Ceramide + Oligosaccharide
Globoside
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Ceramide + Sulfated Galactose
Sulfatides
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Only significant sphingophospholipid in humans where it is an important constituent of the myelin sheath of nerves
Sphingomyelin
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Deficiency in phospholipids and sphingolipids from white matter resulting in increase CSF phospholipids
Demyelinating Diseases
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Lipid storage diseases often manifested in childhood lipid synthesis is Normal; Lipid degradation in lysosomes is Abnormal
Sphingolipidoses
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Hexosaminidase A Deficiency; Cherry red macula, MR and Hypotonia
Tay-Sach's Disease
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Alpha-galactosidase Deficiency; X-linked recessive, Rash, Renal failure
Fabry's Disease
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Ceramidase Deficiency; Triad of Skin rash, Hoarseness, Bone malformation
Farber's Disease
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Arylsulfatase A Deficiency; Psychologic disturbance in adults due to demyelination
Metachromic Leukodystrophy
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Beta-Galactosidase Deficiency; Mental Retardation
Krabbe's Disease
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Beta-Glucosidase Deficiency; Hepatosplenomegaly + erosion of long bones
Gaucher's Disease
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Sphingomyelinase Deficiency; Hepatosplenomegaly
Neimann-Pick Disease
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Potent compounds that elicit a wide range of physiologic and pathologic responses
Eicosanoids
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3 main kinds of Eicosanoids
ProstaglandinThromboxaneLeukotrienes
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Eicosanoids: Dietary precursor
Linoleic Acid
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Eicosanoids: Immediate precursor
Arachidonic Acid
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Synthesized in platelets; Cause vasoconstriction and platelet aggregation
Thromboxane (TXA2)
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Produced by blood vessel walls; Inhibitors of platelet aggregation
Prostacyclin (PGI2)
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Mixture of leukotrienes C4, D4, and E4; Potent bronchoconstrictors
Slow-Reacting Substances of Anaphylaxis (SRS-A)
