Chapter 28 Flashcards
what induces fatty acid synthesis?
insulin
what inhibits fatty acid synthesis?
glucagon and epinephrine
where does fatty acid synthesis occur?
in the cytoplasm
what is the first stage of fatty acid synthesis?
the transfer if acetyl CoA out of the mitochondria into the cytoplasm
what happens when citrate is transported into the cytoplasm?
it is cleaved into oxaloacetate
what is the second stage of fatty acid synthesis?
activation of acetyl CoA to form malonyl CoA
what is the third stage of fatty acid synthesis?
repetitive addition and reduction of two carbons units to synthesize C16 fatty acid
in the third stage of fatty acid, where does synthesize of C16 fatty acid occur?
an acyl carrier protein, a molecular scaffold
which step of fatty acid synthesis is the reverse of β - oxidation?
the third stage (repetitive addition and reduction of two carbons units to synthesize C16 fatty acid)
what does citrate do?
it carries acetyl groups from mitochondria to the cytoplasm
where is citrate synthesized?
in the mitochondria
what happens to citrate when it reaches the cytoplasm?
it is cleaved by ATP-citrate lyase to generate acetyl CoA for fatty acid synthesis
what is generated from the cleavage of citrate in the cytoplasm?
acetyl CoA for fatty acid synthesis
what is needed for fatty acid synthesis?
NADPH
what is the committed step in fatty acid synthesis?
the formation of malonyl CoA
what regulates the synthesis of fatty acids?
synthesis of malonyl CoA
how is malonyl CoA synthesized?
by acetyl CoA carboxylase, an allosteric enzyme
what enzyme catalyzes the formation of fatty acids?
fatty acid synthase
where does fatty acid synthesis occur?
on the acyl carrier protein (ACP)
what is the acyl carrier protein (ACP)?
a polypeptide linked to CoA
what are the 4 steps of fatty acid synthesis?
- condensation
- reduction
- dehydration
- reduction
fatty acid synthesis is always…
reducing
how does fatty acid synthesis store energy?
in the form of electrons
every 2 carbons, electrons are added
what sequence is repeated during fatty acid synthesis?
reduction, dehydration, reduction
what is condensed during fatty acid synthesis?
malonyl CoA with butyryl ACP
what are the limitations of fatty acid synthase?
fatty acid synthase cannot generate fatty acids longer than C16 palmitate
how do enzymes extend palmitate?
by adding two carbon units, using malonyl CoA as a substrate
how are double bonds introduced into saturated fatty acids?
by enzymes bound to the endoplasmic reticulum
what is the structure of arachidonate?
a 20-carbon fatty acid with four double bonds, derived from linoleate
what is arachidonate?
a precursor for a variety of signal molecules 20 carbons long (eicosanoids)
what does arachidonate leads to?
prostaglandins
what are examples of local acting agents?
prostaglandins and other eicosanoids
what do local acting agents do?
they are short-lived agents that alter activities of cells that synthesize them or are close by
they bind membrane receptors
what are the functions of prostaglandins and eicosanoids?
stimulate inflammation
regulate blood flow to organs
control ion transport across membranes
modulate synaptic transmission and induce sleep
in general, how is fatty acid synthesis regulation?
- switched off by phosphorylation switched on by Dephosphorylation
- allosterically stimulated by citrate
- insulin stimulates
- glucagon and epinephrine inhibit
what is the committed/irreversible step of fatty acid synthesis?
conversion of Acetyl CoA to Malonyl CoA by Acetyl CoA Carboxylase 1
what activates AMPK?
AMP
Glucagon
Epinephrine
what inhibits AMPK?
ATP
Insulin
what does citrate do to carboxylase?
it partially activates it
what inhibits carboxylase?
glucagon and epinephrine
how do glucagon and epinephrine inhibit carboxylase?
by enhancing AMPK activity
what stimulates carboxylase?
insulin
how does insulin stimulate carboxyalase?
insulin stimulates the Dephosphorylation and activation of carboxylase
what regulates the enzymes of fatty acid synthesis?
adaptive control
what does the adaptive control of enzymes in fatty acid synthesis mean?
if adequate fats are not present in the diet, the synthesis of enzymes required for fatty acid synthesis is enhanced
excess ethanol consumption
what does the pathway for ethanol processing lead to?
excess production of NADH
what does excess NADH result in?
inhibition of gluconeogenesis and fatty acid degradation
enhancement of lactate production
stimulation of fatty acid synthesis
what does the inhibition of gluconeogenesis and enhancement of lactate production from excess NADH result in?
lactic acidosis
what does the inhibition of Fatty acid degradation and stimulation of fatty acid synthesis result in?
accumulation of fats in the liver
