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Lipid
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Lipid
, Cholesterol, Total Cholesterol, Sphingolipid
See Also
Hyperlipidemia
Hyperlipidemia Management
Hypertriglyceridemia
CAD Risk Management
Hydrocarbon
Arachidonic Acid
Definitions
Lipids
Organic molecules containing
Hydrocarbon
s
Poorly soluble in water, but soluble in organic solvents
Examples include free
Fatty Acid
s,
Triglyceride
s, phospholipids
Cholesterol
Lipid precursor for steroid
Hormone
s, bile acids and
Vitamin D
Triglyceride
Lipid composed of three molecules of
Fatty Acid
esterified to glycerol
Triglyceride
s are a non-polar fat synthesized from
Carbohydrate
s or ingested
Triglyceride
s are
High Energy Molecule
s that are stored for later use in animal adipose cells (fat cells)
Physiology
Lipid Functions
Energy Source
Fatty Acid
s are stored for later energy use, bound to glycerol, as
Triglyceride
s within fat cells
Fatty Acid
s are synthesized by adding, in repeated cycles, 2 carbon atoms (acetyl CoA)
Fatty Acid
synthesis occurs in the cytoplasm of most cells to supply numerous uses including cell wall
Fatty Acid
s are burned as fuel in the
Kreb Cycle
(
TCA Cycle
)
Fatty Acid
s are degraded (oxidized) by removing, in repeated cycles, 2 carbon atoms (acetyl CoA)
Energy from each extracted acetyl coA enters the
Kreb Cycle
Each
Kreb Cycle
generates
NADH
and
FADH2
(total energy 17 ATP)
Fats offer high energy stores (9 KCals/g) compared with
Carbohydrate
s and proteins (4 kcals/g)
Triglyceride
s are non-polar and bind less water (more compact than
Carbohydrate
s, proteins)
Each triglcyeride contains 3
Fatty Acid
s, each with 16 to 18 carbons (fueling 24-27
Kreb Cycle
s)
Cell Membrane Components
Cholesterol, glycolipids and phospholipids are important components of cell membranes
Cholesterol Derivatives
Cholesterol
Cholesterol is a sterol ring structure (four interlinked aromatic rings) critical in physiology
Cholesterol may either be ingested or synthesized
Cholesterol synthesis (primarily in the liver)
Acetyl CoA is converted to isoprene (5 carbon structure)
Isoprene is combined with other isoprene molecules to form 10, 15 and 30 carbon rings
Cholesterol (27 carbons) is among many Isoprenoids (isoprene derived molecules)
Others Isoprenoids include all fat soluble
Vitamin
s (A, D, E and K) and Coenzyme Q
Steroid
Hormone
s are derived from Cholesterol with unique side chains at the C17 carbon
Pregnenolone (21 carbons) is derived from Cholesterol
Sex
Hormone
s, mineralcorticoids and
Glucocorticoid
s are all formed from Pregnenolone
Sex
Hormone
s
Testosterone
(primarily synthesized in the
Testes
)
Estrogen
and
Progesterone
(primarily synthesized in the ovary)
Dehydroepiandrosterone
and
Androstenedione
(androgens synthesized in the
Adrenal Cortex
)
Mineralcorticoids (e.g.
Aldosterone
, synthesized in the
Adrenal Cortex
)
Glucocorticoid
s (e.g.
Cortisol
, synthesized in the
Adrenal Cortex
)
Other Cholesterol derivatives and related Isoprenoids
Bile Acids (derived from Cholesterol)
Fat Soluble
Vitamin
s (
Vitamin A
,
Vitamin D
,
Vitamin E
,
Vitamin K
)
Coenzyme Q
Fatty Acid
Derivatives (esp.
Arachidonic Acid Derivatives
)
Gene
ral
Basic structure is a 5 carbon ring "head" with two 6 to 9 carbon chain "legs"
Functions vary by specific molecule, but function in general is summarized here
Thromboxane
s
Increase
Platelet
aggregation
Leukotriene
s
Leukocyte
chemotaxis
Prostacyclin
Inhibits
Platelet
aggregation
Vasodilates
Prostaglandin
s
Contracts
Smooth Muscle
(e.g.
Vasocon
striction, bronchoconstriction, uterine contraction)
Increases inflammatory response as well as pain and fever
Sphingolipids
Similar to
Triglyceride
s with 2 exceptions
Serine backbone (with a NH2 at the middle carbon) instead of a glycerol backbone
First carbon group is a COOH instead of CH2-OH
Sphingosine
Analogous to a monoglyceride, with the first serine carbon attached to a
Fatty Acid
(palmitoyl CoA)
Ceramide
Analogous to a diglyceride, with the first 2 serine carbon chains attached to
Fatty Acid
s
Ceramide serves as a base for many molecules with different attachments at the third carbon
Sphingomyelin (choline at the third carbon), a key component of the
Myelin Sheath
of nerves
Cerebroside (
Glucose
or Galactose at the third carbon)
Ganglioside (
Oligosaccharide
, multiple linked sugars and sialic acid, at the third carbon)
Other important lipids
Glycolipids
Lipoproteins
Precautions
Total Cholesterol <175 mg/dl in elderly: Increased mortality
Schupf (2005) J Am Geriatr Soc 53:219-26 [PubMed]
Components
LDL Cholesterol
VLDL Cholesterol
HDL Cholesterol
Patient Education
Mnemonic: Lower L-DL, Higher H-DL
References
Goldberg (2001) Clinical Biochemistry, Medmasters, Miami, p. 17-23
Guyton and Hall (2006) Medical Physiology, 7th Ed, Elsevier Saunders, Philadelphia, p. 829-58
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