Lipids Flashcards
What bonds do lipids primarily contain ?
non-polar carbon-hydrogen (C-H) bonds
Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline, what phospholipid is an exception to this rule ?
sphingomyelin, which is derived from sphingosine instead of glycerol
It is a steroid alcohol with 27 carbon atoms that are arranged in a tetracyclical sterane ring system, with a C-H sidechain
Cholesterol
What makes cholesterol amphipathic ?
contains a polar hydroxyl (OH) group on it’s a-ring
How much cholesterol is actually absorbed from what you gain in a day ?
30% - 60%
What is composed of the mixed micelles formed through emulsification ?
monoglycerides fatty acids conjugated bile acids. unesterified cholesterol phospholipids
What is the role of bile acids in the formation of micelles ?
it acts as a detergent
Where does cholesterol absorption occur the most ?
middle jejunum and terminal ileum of the small intestine
What electrolyte protein mediates cholesterol absorption ?
NPC1L1 (Niemann-Pick C1-like 1)
What happens when the cholesterol enters the intestinal mucosal cell ?
it is packaged with triglycerides, phospholipids, and a large protein called apolipoprotein (apo) B-48 into large lipoprotein particles called chylomicrons
What is the purpose of cholesterol esterification ?
helps reduce the cytotoxicity of excess free cholesterol
once cholesterol is esterified, it loses its free hydroxyl group and becomes much more hydrophobic
What mediates intracellular cholesterol esterification ?
acylcholesterol acyltransferase (ACAT)
What mediates intravascular cholesterol esterification ?
lecithin acyltransferase (LCAT)
How much bile acids are reabsorbed in the lower third of ileum and are returned to the liver by the enterohepatic circulation ?
90%
What happens to bile acids that enter the large intestine ?
deconjugated by bacterial enzymes to secondary bile acids
What happens when the amount of cholesterol is bile exceeds the capacity of these solubilizing agents ?
it is possible for cholesterol to precipitate and form gallstones
What is the general chemical formula for fatty acids ?
RCOOH
How many carbons are in a short chain of fatty acid ?
2 - 4
How many carbons are in a medium chain of fatty acid ?
6 - 10
How many carbons are in a long chain of fatty acid ?
12 - 26
Which fatty acid chain length is of most importance to human nutrition and metabolism ?
long chain class
Compare the double bonds of saturated, monosaturated, and polyunsaturated fatty acids
Saturated: have no double bonds
Monounsaturated: one double bond
Polyunsaturated: multiple double bonds
Why are unsaturated fatty acids prone to oxidation ?
the nonenzymatic reaction of oxygen with their double bonds
Why do free fatty acids primarily exist in their ionized forms ?
free fatty acid carboxyl group has pKa of approximately 4.8
What is the normal concentration of free fatty acid in humans ?
0.3 to 1.1 mmol/L (8 to 31 mg/dL)
Where does stage three of cholesterol biosynthesis occur ?
endoplasmic reticulum
Where are fatty acids catabolized ?
mitochondria
What is a common pathway for the final oxidation of nearly all metabolic fuels ?
krebs cycle
Why is energy storage by triglyceride efficient in terms of space ?
it does not require any water for hydration, unlike carbohydrates
What does B-oxidation do in fatty acid catabolism ?
produce energy
this process is repeated to shorten the fatty acid chain by two carbon atoms at a time from the carboxy terminal end of the molecule
How do fatty acids exist in human plasma ?
majority of plasma fatty acids are found as a constituent of triglycerides or phospholipids
only a relatively small amounts of fatty acids exist in the free or unesterified form, most of which is bound to albumin
Differentiate cis and trans form of unsaturated fatty acids
CIS
• both hydrogen atoms on the same side of the C=C
double-bond
• bend in their structure
• bends increase the space that unsaturated fatty acids require when packed in a lipid layer and, as a result, these fatty acids are more fluid because they do not as readily self-associate
TRANS
• both hydrogen atoms on opposite side of the C=C double-bond
• no bend
• physical properties more similar to saturated fatty acids
If trans fatty acids are not commonly found in nature, why are they present in our diet ?
chemical hydrogenation treatment used in food processing for converting polyunsaturated plant oils into solid margarine introduces trans double bonds
This lipid is characterized by the presence of a glycerol moiety and fatty acid chains
acylglycerols
Differentiate monoacylglycerols, diacylglycerols, and triacylglycerols
monoacylglycerols
• one fatty acid molecule attached to a glycerol molecule by an ester bond
• present in trace levels in fresh animal and plant tissues
diacylglycerols
• two fatty acid chains attached to a glycerol molecule by an ester bond
• present in trace levels in fresh animal and
plant tissues
triacylglycerols
• three fatty acid molecules attached to one glycerol molecule by ester bonds
• structure has no charged groups or polar hydrophilic groups, making it hydrophobic and water-insoluble
• neutral lipid because it has no charge
Triglycerides containing saturated fatty acids are at what state of matter at room temperature ?
solid as they don’t have bends in their structure making them pack together more closely
Triglycerides containing cis unsaturated fatty acids are at what state of matter at room temperature ?
typically form oils
Triglycerides from plant sources are at what state of matter at room temperature ?
oils as they are rich in polyunsaturated fatty acids
Triglycerides from animal sources are at what state of matter at room temperature ?
contain mostly saturated fatty acids and are usually solid
How much tissue storage fat is constituted by triglycerides ?
95%
What form of glyceryl esters is predominantly found in plasma ?
Triglycerides
Where are dietary triglycerides digested and absorbed at ?
digested in the duodenum and are absorbed in the proximal ileum
Which lipid is similar to phospholipids in structure ?
triglycerides, except that they only have two esterified fatty acids, the third position on the glycerol backbone instead contains a phospholipids head group
Name a few phospholipid head groups
choline, inositol, serine, and ethanolamine
What phospholipid is most commonly found on lipoproteins and in cell membranes ?
Phosphatidylcholine
How many carbon atoms usually make up phospholipids ?
14 - 24
What makes phospholipids amphipathic ?
phospholipids contain both hydrophobic fatty acid C-H chains, and a hydrophilic head group
What common structure do all steroid molecules have ?
cyclopentanoperhydrophenantrene (steroid nucleus) characterized by four fused rings
Terpenes are polymers of the ___ and include vitamins ___, ___, and ___ and the ___, which play important roles in ___.
five-carbon isoprene
A, E, and K
dolichols
protein glycation.
What lipid controls the body’s internal climate with the goal of maintaining constant temperature ?
triglycerides
What does leptin do ?
a hormone that regulates appetite
What essential fatty acids help regulate cholesterol and blood clotting and control inflammation in the joints, tissues, and bloodstream ?
Omega-3 and omega-6
What lipids are required for proper reproductive health ?
fatty acids
How are lipids focal to brain activity in structure and in function ?
they help form nerve cell membranes, insulate neurons, and facilitate the signaling of electrical impulses throughout the brain
Differentiate visceral and subcutaneous fat
Visceral fat surrounds vital organs such as the heart, kidneys, and liver
Subcutaneous fat, or fat underneath the skin:
• insulates the body from extreme temperatures and helps keep the internal climate under control
• pads out hands and buttocks and prevents friction
•gives the body the extra padding required when engaging in physically demanding activities
What are the fat soluble vitamins ?
A, D, E, and K
Cholesterol is the precursor of ___
bile acids, vitamin D, and steroidal hormones
Cholesterol also occurs in blood in free form as ___
plasma lipoproteins
What essential fatty acids are precursors of many different types of eicosanoids ?
linoleic and linolenic acids
What do eicosanoids play an important role in ?
pain, fever, inflammation and blood clotting
These are diseases associated with abnormal lipid concentrations caused by genetic abnormalities or through environmental/lifestyle imbalances
Dyslipidemias
This occurs when plaques develop in the arteries of the arms and legs
Peripheral Vascular Disease (PVD)
The development of plaques in the coronary artery of the heart
Coronary Artery Disease (CAD)
The development of plaques in the in the vessels of the brain
Cerebrovascular Disease (CVD)
What are irritants of the vascular system in relation to the pathophysiology of atherosclerosis ?
(1) Chronic hypertension
(2) Toxins in blood circulation, such as those derived from cigarette smoking
(3) Elevated concentrations of LDL (Low Density Lipoprotein/LDL-C
What causes the formation of a fatty streak ?
accumulation of LDL in the damaged endothelium of the artery
What lymphocyte migrates to the area of the fatty streak ?
monocytes
How are foam cells formed ?
Accumulated LDL will be phagocytized by macrophages -> eventually these macrophages
fill with cholesterol and die -> converted into foam cells
What happens when there is a production and deposition of more foam cells to the damaged vessel wall ?
formation of a fatty plaque
The formation of atherosclerotic plaque has several effects such as
(1) hardening of the damaged vessel wall from the deposition of calcium
(2) thickening of the damaged vessel wall leading to a smaller diameter of the blood vessel wall restricting blood flow in the affected area
What are thrombogenic chemicals ?
chemicals that stimulate clot formation
What happens if there is complete blockage of artery leading to the brain ?
cerebrovascular accident or stroke
What is the range of borderline high triglyceride levels ?
150-200 mg/dL (1.7-2.3 mmol/L)
What is the range of high triglyceride levels ?
200-500 mg/dL (2.3-5.6 mmol/L)
What is the range of very high triglyceride levels ?
greater than 500 mg/dL (>5.6 mmol/L)
What hormonal abnormalities associated with hypertriglyceridemia ?
pancreas, adrenal glands and pituitary, or of diabetes mellitus or nephrosis
What is the cause of increased shunting of glucose into the pentose pathway, causing increased fatty acid synthesis ?
Diabetes mellitus
What is the general cause of Hypertriglyceridemia ?
an imbalance between synthesis and clearance of VLDL in the circulation
deficiency in LPL or by a deficiency in apolipoprotein C-II, which is a necessary cofactor for LPL activity
How do epinephrine and norepinephrine influence an increase in serum triglyceride levels ?
triggering production of hormone-sensitive lipase, which is located in adipose tissue
What are other body processes that trigger hormone sensitive lipase activity ?
cell growth (growth hormone) adrenal stimulation (ACTH) thyroid stimulation (thyrotropin) fasting (glucagon)
How is hypertriglyceridemia a potentially life threatening abnormality ?
it can cause acute and recurrent pancreatitis
What is lipoprotein lipase role in relation to triglycerides ?
hydrolyzes triglycerides carried in chylomicrons and VLDL to provide cells with free fatty acids for energy from exogenous and endogenous triglyceride sources
What is the treatment for hypertriglyceridemia ?
dietary modifications, fish oil, and or triglyceride- lowering drugs (primarily, fibric acid derivatives)
What is the range of desirable total cholesterol levels ?
<200 mg/dL
What is the range of borderline high total cholesterol levels ?
200-239 mg/dL
What is the range of high total cholesterol levels ?
≥ 240 mg/dL
What is the enzyme deficient of Fabry’s disease ?
Alpha galactosidase
What is the enzyme deficient of GM-1 gangliosidosis ?
Beta galactosidase
What is the enzyme deficient of Gaucher ?
Beta galactosidase
What is the enzyme deficient of Krabbe ?
Cerebroside beta galactosidase
What is the enzyme deficient of Niemann Pick ?
Sphingomyelinase
What is the enzyme deficient of Metachromatic leukodystrophy ?
Arylsulfatase A
What is the enzyme deficient of Sandhoff ?
Total hexosaminidase (hexosaminidase A and B)
What is the enzyme deficient of Tay Sach ?
Hexosaminidase A
What are the Clinical (Non-Laboratory) Risk Factors for CHD ?
- Cigarette smoking (any smoking in the past month)
- Hypertension (blood pressure >140/90 mmHg or on antihypertensive medication
- Family history of premature CHD (CHD in male first degree relative <55 years, or in female first-degree relative <65 years)
- Age (Men: >45 years; Women: >55 years)
- Obesity
- Diabetes mellitus
- Sedentary lifestyle
How are triglycerides made soluble ?
attaching to circulating lipoproteins that transport lipids to various tissues
What is the purpose and reagent for extraction in triglyceride analysis ?
PURPOSE: pre-treatment of sample to remove the lipids from proteins
REAGENT: organic solvent (e.g. choloroform, isopropanol, diethyl ether)
What is the purpose and reagent for adsorption in triglyceride analysis ?
PURPORSE: to remove non-triglyceride glycerols such as phospholipids, monoglycerides, and diglycerides as well as interfering substances such as glucose (carbohydrates) and bilirubin
REAGENT: alumina adsorbent mixture, zeolite, florisil or salisilic acid
What is the purpose and reagent for hydrolysis or saponification in triglyceride analysis ?
PURPOSE: to cleave triglyceride molecules into fatty acids and glycerol
REAGENT: potassium hydroxide in ethanol (alcoholic potassium hydroxide) or sodium methoxide
Chemical equation of hydrolysis in triglyceride analysis
Triglycerides + 3H2O à Glycerol + Fatty acids
What is the purpose and reagent for oxidation or saponification in triglyceride analysis ?
PURPOSE: to convert glycerol to a measurable compound
REAGENT: oxidizing agent such as sodium periodate
Chemical equation of oxidation in triglyceride analysis
Glycerol + Sodium periodate (NaIO4) à Formaldehyde + Formic acid
What is the purpose for colorimetry or saponification in triglyceride analysis ?
aids in the measurement of the compound that forms after oxidation; measured by its absorbance after addition of color reagent
In colorimetry for triglyceride analysis what conditions would be observed for chromotopic acid and H2SO4 ?
pink chromophore measured at 500-600 nm
In colorimetry for triglyceride analysis what conditions would be observed for diphenylhydrazone ?
product measured at 500-600 nm
In colorimetry for triglyceride analysis what conditions would be observed for acetylacetone and ammonia
formation of diacetyldihydrolutidine, a yellow product that can be measured either:
SPECTROPHOTOMETRICALLY at 412nm or FLUOROMETRICALLY (Excitaton light: 400 nm; Emitted light: 485 nm)
What is the CDC recommended method for triglycerides ?
Gas Chromatography Isotope Dilution Mass Spectrometry
What is the original reference method for triglyceride analysis ?
- Extraction with chloroform
- Adsorption with salicylic acid
- Hydrolysis with KOH
- Oxidation with periodate
- Color development using chromotropic acid
- Absorbance is measured at 570 nm
What enzymes are included in the initial enzymatic reaction for the enzymatic method of the analysis of triglycerides ?
Lipase and Glycerokinase
What coupled enzymatic reactions can follow the initial enzymatic reaction for analysis of triglycerides ?
glycerophosphate dehydrogenase and diaphorase
or
glycerophosphate-oxidase and peroxidase
or
pyruvate kinase and lactate dehydrogenase
What are the measurements of absorbance in the glycerophosphate dehydrogenase and diaphorase coupled reaction ?
NADH can be measured at 340 nm, after the glycerophosphate dehydrogenase reaction
Formazan dye can be measured between 500-600 nm
What are the measurements of absorbance in the glycerophosphate-oxidase and peroxidase coupled reaction ?
Red quinoneimine dye can be measured at 500-505 nm
How can bilirubin interference be minimized in the glycerophosphate-oxidase and peroxidase coupled reaction ?
Adding potassium ferrocyanide to the reaction mixture with peroxidase -> Potassium ferrocyanide reduces bilirubin into an inactive compound
What can interfere the peroxidase step in the glycerophosphate-oxidase and peroxidase coupled reaction ?
Hemoglobin and ascorbic acid
What are the measurements of absorbance in the pyruvate kinase and lactate dehydrogenase coupled reaction ?
NAD+ can be measured at 340 nm spectrophotometrically or flouometrically (Excitation light at 355nm, Emitted light at 460 nm)
The enzymatic method is linear in the concentration and can range up to
700 mg/dL
What can cause overestimation of triglyceride concentration ?
Endogenous glycerol
What is the expected result in the Zilversmit-Davis chemical method for assays of phospholipids ?
phosphorous reacts with ammonium molybdate to form a blue colored compound measured at 700 nm
Zilversmit-Davis flow of reactions
Lipid -> oxidized -> phospholipid phosphorous -> inorganic phosphate -> oxidized with perchlorate and nitric acid -> releasing phosphorous -> reacted with ammonium molybdate -> blue colour compound
What is the expected result of Baginski et al method ?
Phosphorous reacts with ascorbic acid to form a colored substance
What enzymes are used in the enzymatic method of assays of phospholipids ?
Phospholipase D
Choline oxidase
Peroxidase
What is the purpose and reagent for extraction in total cholesterol analysis ?
PURPOSE: cholesterol is separated from protein
REAGENT: Bloor’s reagent (composed of ethanol-ether at a 3:1 ratio)/ Chloroform/ Hexane
What is the purpose and reagent for extraction in total cholesterol analysis ?
PURPOSE: extracts all forms of cholesterol, leaving behind most of the sterols
REAGENT: zeolite
What is the purpose and reagent for adsorption in total cholesterol analysis ?
PURPOSE: cholesteryl esters after extraction are hydrolyzed into free cholesterol and fatty acid
REAGENT: alcoholic potassium hydroxide (KOH)
What is the purpose and reagent for saponification/hydrolysis in total cholesterol analysis ?
PURPOSE: to precipitate free cholesterol; removes error of non-specific chromogen interference
REAGENT: digitonin (measure cholesterol before and after digitonin treatment to determine cholesterol fraction)
What is the purpose and reagent for colorimetry in total cholesterol analysis ?
PURPOSE: color development, measured spectrophotometrically
REAGENT: color reagent
What is the reagent, end product, and end colour in the Liebermann-Burchard Reaction for total cholesterol analysis ?
Reagent: Acetic anhydride + Sulfuric acid
End product: Cholestedienyl monosulfonic acid
End colour: Green
What is the reagent, end product, and end colour in the Salkowski Reaction for total cholesterol analysis ?
Reagent: Sulfurin acid + Ferric iron
End product: Cholestedienyl disulfonic acid
End colour: Red
How is the end colour stabilized in the Liebermann-Burchard Reaction ?
adding sodium sulfate
What is the CDC Reference Method for Cholesterol (Abell, et. al.) ?
Hydrolysis with alcoholic KOH Extraction with hexane Extract is dried in vacuo Dried extract is then treated with Liebermann-Burchard reagent Read at 620 nm after 30 minutes
What is one drawback of using oxygen consumption as an enzymatic method for the analysis of total cholesterol ?
Not easily automated and generally require a lot of cholesterol oxidase
What is the procedure for standing plasma test ?
2mL of plasma is placed in 10 X 75 mm test tube and allowed to stand in the refrigerator at 4 degrees Celsius undisturbed overnight
How do chylomicrons appear in the standing plasma test ?
floating cream layer
What does it mean for chylomicrons to appear in fasting plasma ?
abnormal
What does it mean for plasma sample that remains turbid after standing overnight ?
excessive amounts of VLDL
How can the patient be prepared for lipid related tests
Fasting requirement of at least 12 hours
Ethanol consumption must be restricted at least 48 hours prior to the test
When are samples rejected for lipid tests ?
hemolyzed and icteric
