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Cholesterol - Coggle Diagram
Cholesterol
Biosynthesis
Cholesterol
is formed from
acetyl-CoA
the initial stage
three molecules of acetyl-CoA
are condensed
to form mevalonic acid
converted into
an isoprenoid unit
The isoprenoids
are
a family of compounds
made up
of units of isoprene
a series
of condensations
subsequently take place
give rise
to longer isoprenoid chain
like
geranyl pyrophosphate
farnesyl pyrophosphate
geranylgeranyl pyrophosphate
squalene
is cycling
and forminglanosterol
1 more item...
the metabolic pathway of mevalonic acid is the following
In the first step is
conversion of acetyl-CoA into mevalonic acid
First, two acetyl-CoA molecules condense to form acetoacetyl-CoA
then acetoacetyl-CoA reacts with another acetyl-CoA molecule to form 3-hydroxy-3-methylglutaryl-CoA or HMG-CoA
the latter is reduced to mevalonic acid by the enzyme HMG-CoA reductase , the enzyme that regulates the entire biosynthesis of cholesterol. The first two reactions are reversible, while the third is irreversible and determines the speed of biosynthesis
In the second stage
is the formation of activated isoprene units (rich in phosphate)
First three phosphate groups are added to the mevalonate by transfer from the ATP (which is then hydrolyzed to ADP )
Subsequently, by condensation of two molecules of mevalonate, the first isoprene unit is formed
isopentenyl pyrophosphate
in the third stage
squalene is formed by condensation between
between the activated isoprene units formed in the previous reactions
In the fourth stage
squalene is converted into cholesterol
The linear squalene molecule is cyclized to form lanosterol
Finally, lanosterol is converted into cholesterol by displacing or removing methyl groups
Homeostasis
is coordinated
by
different metabolic pathways
synthesis (HMGCR)
bio-transformation (CYP7A1)
cellular efflux to the bile duct (ABCG5 / G8, MRP-2, Mdr1 / 2 and Bsep)
cell efflux towards HDL (ABCA1 / G1)
uptake (CD36, SR-B1, LDL-R)
transcription factors
census intracellular cholesterol levels
increase in cholesterol
in the
membrane alters its structure
Increased levels of cholesterol in the membrane affect the organization
and its physical properties, decreasing fluidity and increasing stiffness
Consequently, these events negatively affect certain transmembrane proteins, which require conformational freedom to perform their functions properly
Metabolism
cholesterol content
is about 150 gr
brain 30 gr
plasma 8 gr
there are cholesterol
Made in the body
booth pools
are subject
to
regulatory mechanisms
consumed in food
is a
steroid
that modulates
membrane fluidity
of eukaryotic cells
precursor to
progesterone
testosterone
estradiol
cortisol