lipids Flashcards
lipids
composed of mostly of C-H bonds
- provide rich source of energy
- efficient way to store excess calories
integral part of cell membranes
- structural role
precursors for steroid hormones
lipids aren’t water soluble
- must form complexes with proteins to stay/travel in solution (lipoproteins )
- do not contribute to osmolality
clinically important lipids
- Sterol Derivatives
- cholesterol & cholesterol esters
- steroid hormones
- bile acids
- vitamin D
2.Fatty acids
- Glycerol Esters
- Triglycerides
- Phospholipids - Sphingosine Deravatives
- Terpenes ( Vitamin A,E,K)
Sterol Derivatives - Cholesterol
unsaturated steroid alcohol containing four rings
Amphipathic - contains both hydrophilic & hydrophobic parts
-the -OH group in the A-ring is hydrophilic
Found on the surface of lipid layers
- polar -OH group on A-ring faces outward ( away from lipid layer)
- the four rings & side chain tail are buried in the membrane
Cholesterol can be freee or esterified with fatty acid
- 70% exist as cholesteryl esters
ester=alcohol+ acid
cholesterol+fatty acid= cholesteryl ester
no polar groups on cholesteryl esters=hydrphobic
- therefore , not found on the surface of lipid layer
- located on the centre if intracellular lipid droplets
cholesterol synthesis - animals & plants
synthesized almost exclusively by animals
plants contain sterols called phytosterols
- similar structure to cholesterol
- known to lower total cholesterol & LDL-C in plasma
- known to raise HDL-C in plasma
cholesterol synthesis
synthesized in most tissued in the body ( particularly the liver)
synthesized from Acteyl-CoA
- >25enzymes involved
cholesterol synthesized in body= endogenous
cholesterol obtained from diet = exogenous
the body can synthesize all cholesterol it needs
precursor of bile salts, hormones & vitamin D
sterol derivatives- steroid hormones
include: testosterone, estrione, estradiol, estriol, progesterone, cortisol, corticosterone & aldosterone
female steroid hormones are produced in the ovaries & adrenal cortex
- Estrogens ex.estradoil
Male steroid hormones are produced in the testes & adrenal cortex
-Androgens ex.testosterone
Adrenal cortex hormones are used for mineral & water balance, CHO levels, liberation of fat from body storage & in response to inflammation, infection & allergies
sterol derivatives - bile acids & salts
bile contains 4 bile acids
- the most abundant is cholic acid
derived frim cholesterol
- of the cholesterol is catabolized into bile acids each day
bile is produced in the liver & stored in the gallbladder
released to small intestine during digestion
act as detergents to emulsify triglycerides in to the intestine to aid digestion
-eventually bile acids are reabsorbed & go back to the gallbladder
Sterol derivatives- vitamin D
fat soluble vitamin
natural sources include : fish, egg yolk
- milk, juice, cheese, yogurt can be fortified with vitamin D
involved in the absorption of calcium from the intestine
metabolizes calcium from bones
low vitamin D causes rickets
- poorly formed & easily broken bones
fatty acids chain lengths
linear chains C-H bonds ending with carboxyl group (-COOH)
- even #of carbon atoms
only a small amount exists in the free form ( bound to albumin)
most are found as constituent of triglycerides or phospholipids
can be classified by length as : short chain ( 4-6 carbon atoms ) medium chain (8-12) long chain (12-18) - most in our diet very long chain ( >20 carbon atoms )
fatty acids C=C bonds
can be classified by the number of C=C bonds :
saturated ( no double bonds)
monounsaturated (one double bond )
polyunsaturated ( 2 or more double bonds)
unsaturated fatty acids can be classified based on the position of the hydrogen atoms in relation to the C=C
- cis unsaturated fatty acids - both H atoms on the same side of C=C
- trans fatty acids-H atoms on opposite sides of C=C
Trans fatty acids
not commonly found in nature
present in diet die to chemical hydrogenation treatment during food processing
consumption of fatty acids increases the risk of coronary heart disease ( CHD)
- increases LDL ( bad cholesterol ) & decreases HDL ( good cholesterol)
polyunsaturated fatty acids
important in the structure & function of most biological membranes
some are beneficial in lowering the risk of cardiovascular disease (omega -3)
classified as:
omega -3 ( ex. linoleic acid)
omega -6 (ex. linolenic acid)
omega -9
fatty acid synthesis
most are synthesized by the body from carbohydrate precursors
exceptions:
linoleic & linolenic acids- essential fatty acids
- found in plants & must be obtained from the diet
- important for growth , maintenance & functioning of physiological processes
fatty acid catabolism
catabolism in the mitochondria to produced energy by a series of reactions known as ß-oxidation
fatty acids are converted tp Acetyl-CoA
Ketone formation
- when carbohydrate metabolism is impaired (ex. diabetes mellitus) , formation of acetyl-CoA is increased
- this results in the formation of excess ketone bodies
- acetone, acetoacetic acid, ß-hydroxybutyric acid
- the condition of ketosis develops from the excessive production of acetyl-CoA ( & therefore excess ketones) to obtain necessary energy from fats when there is a deficiency of carbohydrates
Glycerol Esters- Triglycerides
3 fatty acid molecules attached to a glycerol molecule by ester bonds
triglycerides containing saturated fatty acids tend to be solid at rook temp ( those from animal source)
Triglycerides continuing cis unsaturated fatty acids tend to form oils at room temp ( plant source )
no polar groups, so very hydrophobic & water insoluble
plays important role of tissue storage of lipids
90% of dietary fat
after absorption in the intestine, triglycerides are combined with cholesterol & apolipoprotein to form chylomicra which enters the blood
increased chylomicra in the blood gives the serum /plasma a milky appearance ( fasting specimen required)
