LIPOPROTEIN Flashcards
soluble in organic solvents & insoluble in H2O
LIPIDS
Diverse in terms of structure and function human plasma lipids:
cholesterol, triglycerides, phospholipids and free FA
from digestion of cholesterol esters [with fatty acid chain] and triglycerides
free FA
Three fatty acids attached to a glycerol backbone (trihydric alcohol) with FA attached to it
TRIGLYCERIDE
Secondary energy source
TRIGLYCERIDE
Serves as a thermal insulator Protects tissues from physical trauma
TRIGLYCERIDE
Protects tissues from physical trauma
TRIGLYCERIDE
In depletion of stored glycogen, it can be mobilized to provide energy
Secondary energy source
Every gram of fat produces 9 kilo calories (measure of heat)
Serves as a thermal insulator
Greater heat is generated from the metabolism of fat
Serves as a thermal insulator
Specific vital organs are surround by adipose tissue
Protects tissues from physical trauma
Chole ester with an FA attached to a hydroxyl group (esterification) distinguishes itself from free cholesterol
Precursor of biological hormones
CHOLESTEROL
biological hormones
(steroid – aldosterone, progesterone, testosterone)
Source of bile acids
CHOLESTEROL
Component of the Cell membrane
CHOLESTEROL
Produced in the liver
Source of bile acids
Fat digestion is more effective if + blie (emulsifier of fat) – easier for lipase to digest fat
Source of bile acids
Cholic acid, phenodeoxycholic acid, kenodeoxycholic acid
Source of bile acids
Proportional with the cholesterol in blood
Component of the Cell membrane
Two fatty acids and a phosphoric acid with a NB (X) attached to a glycerol backbone
PHOSPHOLIPID
Cell membrane component
PHOSPHOLIPID
Associated with vital life processes (e.g. CNS)
PHOSPHOLIPID
PHOSPHOLIPID
Components:
2 Fatty acids
Glycerol
H3PO4
Nitrogenous base (choline, cholamine, etc.)
Depend of the phospholipid it represents
Nitrogenous base
Phospholipid Ex.
lecithin, cephalin
– has the affinity for water molecules; found on the outer layer ;water-soluble
Phosphate group
– found on the middle layer water-insoluble
Fatty acids
Part of the cell membrane that contributes to its highly selective nature
PHOSPHOLIPID
Dietary sources – lipids from small intestine w/c undergo digetsion
MICELLE
Consists of bile acids, free fatty acids & monoglycerides, cholesterol & phospholipid
MICELLE
These lipids are products of digestion that combin w/ bile acids to form a micelle
bile acids, free fatty acids & monoglycerides, cholesterol & phospholipid
Essential for intestinal absorption
MICELLE
Diffusion of substances from the small intestine to the circulation
MICELLE
Outer layer (water-soluble)
Protein
Phospholipid
Cholesterol
Middle layer (water-insoluble)
Triglyceride
Cholesterol esters
macromolecule which consists of varying proportions of 1) protein, 2) cholesterol, 3) triglyceride and 4) phospholipid
LIPOPROTEIN
water-soluble
LIPOPROTEIN
blood – aqueous (↑% of water)
water-soluble
facilitates the transport of the lipids in the circulation
water-soluble
transported by LDL to the cells (Chole ester; ¾ of total)
Transport of Cholesterol
transported by HDL out of the cells (Free chole; ¼ of total)
Transport of Cholesterol
bad cholesterol
abundant in cholesterol
Chole ester
good cholesterol
abundant in protein
Free chole
secreted unchanged into bile (free cholesterol) or metabolized to form bile acids
Catabolism (LIVER)
- Synthesized & released from the small intestines (Exogenous pathway)
CHYLOMICRON
- Transport of dietary fat
CHYLOMICRON
- Consists of 80% TG, Apo B-48, AI, AII, AIV, C (1-2%)
CHYLOMICRON
- From lymphatics to systemic circulation: hydrolyzed by lipoprotein lipase (LPL) to monoglycerides, glycerol & FA
CHYLOMICRON
Lipase acts on TG and cause digestion of fats in the CM to release the three
CHYLOMICRON
- Synthesized & released from the liver
VERY LOW DENSITY LIPOPROTEINS (VLDL)
- Rich in TG
VERY LOW DENSITY LIPOPROTEINS (VLDL)
- Transports liver-synthesized TG & Cholesterol (Endogenous pathway)
VERY LOW DENSITY LIPOPROTEINS (VLDL)
- Contains Apo B-100 & Apo CII (cofactor for apo-protein lipase)
VERY LOW DENSITY LIPOPROTEINS (VLDL)
- Produced from VLDL hydrolysis by LPL
INTERMEDIATE DENSITY LIPOPROTEIN (IDL)
- Partly depleted of TG
INTERMEDIATE DENSITY LIPOPROTEIN (IDL)
- Has equal amounts of Cholesterol & TG
INTERMEDIATE DENSITY LIPOPROTEIN (IDL)
- Contains Apo B & E
INTERMEDIATE DENSITY LIPOPROTEIN (IDL)
- Formed from IDL by LPL
- LDL binds to membrane receptors
- Once internalized, undergo lysosomal degradation
– acts on proteins
Proteolytic
– acts on esters
Esterases
: hydrolyzed to amino acids
- Apo B
: hydrolyzed to free cholesterol(scavenger molecule)
- Chole ester
- Produced & catabolized in the liver & intestine
HIGH DENSITY LIPOPROTEINS (HDL)
- Contains Apo AI & Apo AII
HIGH DENSITY LIPOPROTEINS (HDL)
- Components arise from the catabolism of VLDL & Chylomicrons due to transfer of apoproteins
HIGH DENSITY LIPOPROTEINS (HDL)
FUNCTIONS OF HDL
a. Cholesterol efflux (removal) from tissues: reduce stored cholesterol
b. Transport of cholesterol to the live for removal as bile acids (Reverse cholesterol transport)
c. Scavenger of lipids & apo-lipoprotein
d. Reservoir of Apo CII
- similar to LDL; apo (a) linked to apoB-100
Lp(a)
- Increased level = increased risk of Congestive Heart Disease, Cerebrovascular Disease & Stroke
Lp(a)
- Obstructive Biliary Disease & Familial Lecithin Cholesterol Acyl Transferase (Lipids 90% of its weight) deficiency (Lipids 90% of its weight)
LpX
[ – catalyzes the esterification of cholesterol]
LCAT
- Type 3 hyperlipoproteinemia
B-VLDL (“floating B” lipoprotein)
- Richer in cholesterol
B-VLDL (“floating B” lipoprotein)
: major protein of HDL and chylomicron
Apolipoprotein A
– involved in activation of LCAT and removal of free chole from extrahepatic tissues
Apo AI
– structural role in HDL
Apo AII
inhibits LCAT
Apo AII
: major protein of all lipoproteins except HDL
Apolipoprotein B
(found in lipoprotein formed in the liver)
Large B or B100
(found in lipoprotein formed in the S.I.)
Small B or B48
: major protein of VLDL and chylomicrons and a minor protein of HDL and LDL
Apolipoprotein C
– cofactor of lipoprotein lipase
Apo CII
– inhibits lipoprotein lipase
Apo CIII
: function as a transfer protein
Apolipoprotein D
- glycoprotein w/c enters plasma as part of the nascent HDL
Apolipoprotein E
- plays a role in the recognition & catabolism of chylomicron remnant and IDL via specific receptors in hepatic cells
Apolipoprotein E
Fasting - ideal fast is
NCEP guidelines :
12 hours
at least 9 hours
Posture -
NCEP guidelines :
standardize position during venipuncture
seated for 5 mins prior to sampling
Venous vs capillary samples -
capillary levels generally lower than venous
- either can be used when only lipid profile is to be measured
Plasma vs serum
preferred for Lipid Profile measurement by ultracentrifugation /electrophoresis
Plasma
: preferred additive
EDTA
- generally, frozen samples can be satisfactorily analyzed
Storage
A. Colorimetric/Stepwise Methods
- Direct Colorimetric/One-Step
- Two-Step Method
- Three-Step Method
- Four-Step Method
Serum + color reagent = color reaction
- Direct Colorimetric/One-Step
Interferences from protein and other chromogens
- Direct Colorimetric/One-Step
Unequal color reactions for cholesterol & its ester
- Direct Colorimetric/One-Step
Involves ‘extraction step prior to colorimetric reaction
Two-Step Method
Separates lipids from proteins
Two-Step Method
Eliminates protein interference
Two-Step Method
Interference from other chromogen
Two-Step Method
Unequal color reaction due to esterified form
Two-Step Method
Requires 1) extraction, 2) saponification and then 3) colorimetric determination
Three-Step Method
Standard method
Three-Step Method
Eliminates protein interference
Three-Step Method
Chole esters are hydrolyzed: uniform color reaction
Three-Step Method
Interference from other chromogen
Three-Step Method
Greatest specificity; reference method
Four-Step Method
Requires 1) extraction, 2) saponification, 3) purification with digitonin then 4) colorimetric determination
Four-Step Method
Eliminates interference from protein & other chromogens
Four-Step Method
Uniformity in color reaction
Four-Step Method
chole ester + H2O –chole esterase –>
cholesterol + FFA
cholesterol + O2 –chole oxidase –>
cholest-4-ene-3-one + H2O2
Quantitation of H2O2 formed:
Trinder reaction
O2 consumption
Other methods