Theme G: lipid metabolism Triglycerides (TAGs) and glycogen are the two major forms of
stored energy in vertebrates
Lecture G1 – lipids, lipid transport, lipoproteins, TAGs (chapter
16) TAGs are very eAicient energy stores:
Lipid metabolism 1. They are stored in an anhydrous form
2. Fatty acids are more reduced than amino acids or
monosaccharides
Lipids
• Non-polar biomolecules
- high C content (H and O) insoluble in water
• Do not form biopolymers, but rather macrostructures, due
to hydrophobic eAect (e.g. membranes)
• Reserve source of reduced C – “energy store”
• Important membrane components
• Protection
- Reduces water loss from exposed plants (waxes)
- thermal and physical shock
- infection
• Precursors of important metabolites (hormones)
TAGs are a form of lipid. Lipids are also commonly referred to as
fats or oils
Lipid metabolism
Sources of fats in plants
Common examples of lipids: • Lipids are synthesized by plants from the products of
photosynthesis
• Triglycerides (TAGs)
• They are synthesized in the plastids & the endoplasmic
• Cholesterol
reticulum
• Phospholipids
• Waxes Fat absorption and mobilization in plants
, • Fats & oils are stored in most seeds in the cytoplasm of Lipid metabolism
either cotyledon or endosperm cells in organelles known as
Oleosomes (pherosomes or oil bodies)
• Composition of fatty acids in plant lipids varies with the
species
• Storage lipids are converted into mobile carbohydrates in
germinating seeds (plants are not able to transport fats
from the endosperm to the root & shoot tissues of the
germinating seedling)
• Breakdown of triglycerides is similar to the processes in
mammals
• Plant use fats and oils for energy production
Sources of fats in mammals
• In the diet
• Stored in adipocytes (fat cells)
Fat absorption and mobilization
Digestion and absorption of diet fats
• Diet lipids absorbed from the gut, e.g. humans
• Transported in the blood as lipoproteins • Most diet lipids of mammals are TAGs
• Serum albumin serves as carrier of fatty acids • In the small intestine, fat particles are coated with bile salts
• Ruminants (cows, sheep, bovines) produce short chain to allow for emulsification, and digested by pancreatic
fatty acids in the rumen, which are absorbed from the small lipases
intestine • Lipases degrade TAGs to free fatty acids and a 2-mono-
acylglycerol
• Lipase catalyzes hydrolysis at the C-1 and C-3 positions of
a TAG
, Bile acids (bile salts) are polar derivatives of cholesterol, formed in
liver and secreted into the gall bladder.
They pass via the bile duct into the intestine, where they aid
digestion of fats & fat-soluble vitamins.
Bile acids are amphipathic, with detergent-like properties.
Lipases degrade TAGs to free fatty acids
Bile salts assist in absorption form the small intestine
stored energy in vertebrates
Lecture G1 – lipids, lipid transport, lipoproteins, TAGs (chapter
16) TAGs are very eAicient energy stores:
Lipid metabolism 1. They are stored in an anhydrous form
2. Fatty acids are more reduced than amino acids or
monosaccharides
Lipids
• Non-polar biomolecules
- high C content (H and O) insoluble in water
• Do not form biopolymers, but rather macrostructures, due
to hydrophobic eAect (e.g. membranes)
• Reserve source of reduced C – “energy store”
• Important membrane components
• Protection
- Reduces water loss from exposed plants (waxes)
- thermal and physical shock
- infection
• Precursors of important metabolites (hormones)
TAGs are a form of lipid. Lipids are also commonly referred to as
fats or oils
Lipid metabolism
Sources of fats in plants
Common examples of lipids: • Lipids are synthesized by plants from the products of
photosynthesis
• Triglycerides (TAGs)
• They are synthesized in the plastids & the endoplasmic
• Cholesterol
reticulum
• Phospholipids
• Waxes Fat absorption and mobilization in plants
, • Fats & oils are stored in most seeds in the cytoplasm of Lipid metabolism
either cotyledon or endosperm cells in organelles known as
Oleosomes (pherosomes or oil bodies)
• Composition of fatty acids in plant lipids varies with the
species
• Storage lipids are converted into mobile carbohydrates in
germinating seeds (plants are not able to transport fats
from the endosperm to the root & shoot tissues of the
germinating seedling)
• Breakdown of triglycerides is similar to the processes in
mammals
• Plant use fats and oils for energy production
Sources of fats in mammals
• In the diet
• Stored in adipocytes (fat cells)
Fat absorption and mobilization
Digestion and absorption of diet fats
• Diet lipids absorbed from the gut, e.g. humans
• Transported in the blood as lipoproteins • Most diet lipids of mammals are TAGs
• Serum albumin serves as carrier of fatty acids • In the small intestine, fat particles are coated with bile salts
• Ruminants (cows, sheep, bovines) produce short chain to allow for emulsification, and digested by pancreatic
fatty acids in the rumen, which are absorbed from the small lipases
intestine • Lipases degrade TAGs to free fatty acids and a 2-mono-
acylglycerol
• Lipase catalyzes hydrolysis at the C-1 and C-3 positions of
a TAG
, Bile acids (bile salts) are polar derivatives of cholesterol, formed in
liver and secreted into the gall bladder.
They pass via the bile duct into the intestine, where they aid
digestion of fats & fat-soluble vitamins.
Bile acids are amphipathic, with detergent-like properties.
Lipases degrade TAGs to free fatty acids
Bile salts assist in absorption form the small intestine
