To back up the glucose level in the blood,
so glycogen, the glucose polymer,
can be degraded into glucose hormonal secrete.
The other one is like lypolysis. This is fat.
Lypo means lipid, fat-lysis degradation.
So fat molecules degraded.
Okay. Those catabolic reactions,
well, in terms of glycogen degradation,
catabolic reactions and gluconeogenesis,
glucose production can be stimulated by glucagon hormone.
Let's talk about glycogenolysis in the very beginning.
As I said, glycogen glucose polymer can be split into
glucose phosphate and one glucose reduced shortened glycogen polymer.
So this degradation of glycogen to produce,
to supply the blood glucose,
that reaction takes place in hepatocyte of liver or myocyte in the skeletal muscle.
And you are looking at the mode of glycogen action on your left.
So, glucagon and or other stress hormone epinephrine and those hormones bind to receptor,
and finally activate the degradation of glycogen.
And the degraded product,
glucose, can be released out of cells,
and then get into the circulatory system to
maintain the given amount of minimal basal glucose level.
So glucagon binds to receptor. Glucagon is the hormone.
So glucagon produced from alpha cells of pancreas,
and glucagon binds to glucagon receptor,
and the very interesting enzyme, adenylate cyclase,
or adenylyl cyclase, activated,
and this enzyme is very unique.
Once it's activated, it can convert ATP into cyclic AMP, the semen's cyclic.
And then this cycle again,
the molecules, levels going up,
and it activate cyclic ATP protein kinase, P protein kinase A.
And then throughout interesting phosphorylation cascade,
finally, phosphorylase can be fully activated.
And this phosphorylase can detach the terminal glucose,
the phosphoryleric form of glucose from the glycogen polymer,
and that glucose can release their way into the bloodstream.
So again, in this glycogen dependent hormone action,
the activation of adenylyl cyclase is the key.
So this is ATP, our energy molecules.
So even though the primary function for ATP is to obviously,
to supply the chemical free energy for many, many,
many biochemical reactions, in this case,
ATP can be used for substrate to generate cyclic AMP.
And this cyclic AMP, as you can see,
there is a cyclic chemical can be found,
and this cyclic AMP is so-called signalling messenger molecules inside the cells.
And this cyclic AMP further trigger protein phosphorylation cascade
throughout the activated protein kinase A.
So, the intracellular increase of this second messenger molecule
cyclic AMP control the whole and different types of downstream biological event.
The first case is the glycogenolysis,
the other one is gluconeogenesis.
Cyclic AMP stimulate gluconeogenesis.
So, by definition, this is the biochemical reaction
essential for degeneration of glucose.
So obviously, this is the one of
the key biochemical mechanisms of how our body blood glucose levels can be maintained.
To avoid the low levels of blood glucose sugar,
that phenomenon is called the hypo,
hypo means below, hypo glucose level, hypoglycemia.
Glycemia is glyce, this is like glucose, the sugar.
To avoid those unwanted situation,
the gluconeogenesis can be activated in mainly in
the liver and some fractions of gluconeogenesis can take place in the kidney.
So you are looking at gluconeogenesis biochemical pathway on your left,
and glucose, phosphorylation degradation into pyruvate acetyl-coa optysis glycolysis.
Those blue lines, glycolysis.
Degradation of glucose.
So gluconeogenesis pathway is the reversal of this glucose breakdown.
This glucose breakdown pathway can be reversed throughout glycogenesis.
And then, the substrate to drive this gluconeogenesis, the ultimate source,
can be amino acid,
or glycerol backbone from the lipid degradation or lactate.
So, those substrate in gluconeogenesis can be supplied from the lipid,
or amino acid, or even the glycolysis reaction can be simply be first.
This is the how hepatocyte in the liver,
or kidney cells can generate glucose molecules,
and those glucose molecules can be released into the bloodstream.
So in this session,
we talked about the main actions of glucagon under the low blood glucose levels.
So pancreas, alpha cells, secrete glucagon,
and those glucagons throughout bloodstreams can be
distributed in particular liver or muscle cells in this diagram.
The liver activate the glycogen breakdown as well as gluconeogenesis,
and that biochemical pathway can be mediated by
the synthesis of cyclic AMP as a second messenger.
And this is like a liver dependent of summary or maybe and definitely,
muscle can be also affected by glycogen or even adipose tissue,
adipose tissue can be affected.
So as you can imagine, adipose tissues,
the lipolysis fat molecules degradation,
that pathway can be triggered by glucagon signaling pathway.
This is how the blood glucose levels under
the fasting condition can be maintained
throughout this one of major hormones from the pancreas, I mean, glucagon.
So we are going to talk about more throughout
those insulin dependent signal activation in the following sessions.