Advanced Nutrient Metabolism: Glycogenesis– Glycogenolysis—Glycolysis—-

13 11 2008

Glycogenesis
The formation of glycogen. After you eat, your body will store glycogen in muscle tissue and in liver cells. Your liver & muscle will use this for when you place a demand on your body such as exercise. Your liver also regulates/maintains blood glucose levels as needed so glycogen storage is also important for liver functioning.

It only uses 1 ATP (energy molecule) to branch 1 glucose onto/to form glycogen..BUT its such a good deal because when we break apart glycogen we ultimately get 36-38 ATP’s worth of energy! Talk about bang for your buck!

The liver also acts as a vacuum ( :-(.. i wish I could afford a i-Roomba!)… it collects all this other “crap” laying around ( i.e lactate) to form glycogen. This is called gluconeogenesis and a significant amount of glycogen formation depends on this process ( about 1/3).

Pathway:
Glucose ( from our food) interacts with either these two enzymes
— hexokinase in the muscle cells and liver
—glucokinase in the liver only

Then glucokinase stimulates glucose to use up 1 ATP and forms glucose-6-phosphate
Glucose-6-phosphate—-> glucose 1-phosphate
glucose-1-phosphate—-helped by Uridine Triphophate UTP—> UDP-glucose
UDP glucose—-helped by glycogenin primer—> Unbranched Glycogen
Unbranched glycogen— helped by Glycogen Synthase ( branching enzyme)–> Branched, Glycogen

Hooray! So Now that we have stored glucose into a better branched form- What happens when we need the energy?

Glycogenolysis!

Liver glycogen gets exported to blood
Muscle Glycogen gets exported to muscle cells

This is stimulated/turned on ( ooh la la) by glucagon and epinephrine ( thus these are called allosteric modifiers because they influence the enymes- glycogen synthase ( forming glycogen) AND glycogen phosphorylase

Glycogen phosphorylase is a big enzyme in glycogenolysis and is also turned on/off + / – (modified) by cyclic AMP

Pathway

Fasting/Starving + -> glucagon in liver + with the help of Protein Complex + Adenylate Cyclase

Flight or fight Ahh!!! + epinephrine + with the help of Protein Complex + Adenylate Cyclase

+ Adenylate Cyclase —- +

is all excited, uses up a molecule of energy ATP…… > forming Cyclic AMP (cAMP)

cAMP is interacts with protein kinases that inhibit the branching enzyme glycogen synthase I mentioned above by turning it into the inactive form (B)
cAMP is thus modified by Protein dependent kinases… first the inactive forms then turn to active… which then turns phosphorylase kinase B inactive to active…

Phosphorylase A — > breaks down Glycogen—> Glucose-1-phosphate —> glucose ! and lactate

So now we have lots of free glucose to use up
Glycolysis!
glucose—> pyruvate

yeilds total of 2 ATP but in the future we will know that we end up with more b/c of krebs cycle

Red Blood Cells depend on glycolysis because they have no mitochondria, as do Eye cells as well as they have limited blood supply.
Our Kidneys, Testis, leukocytes and White Muscle Fibers all have no mitochondria so we need this process as well.

If we have high levels of ATP , high levels of alanine, hexokinase and Citrate- these all inhibit glycolysis

High levels of fructose “turn on” glucokinase which turns on glycolysis
The main control point is PFK .. phophofructokinase which can turn on or off the production of fructose and hence the glycolysis process.

Pathway (this is a doozy)

Glucose— gets into the cell as glucose and is phosphorylated using up 1 ATP to make–>
Glucose-6-Phosphate—isomerase turns this into—> Fructose -6-Phosphate
Fructose -6-Phosphate—uses another ATP—> Fructose 1-6-Phosphate

Fructose 1-6-P is then broken down into Glyceraldehyde 3-P and dihydroxyacetone-3-P (DHAP)

DHAP— runs into NADH– froms NADH2 ( which will give us 3 ATP x 2 for krebbs later) and then can turn into Glyceraldehyde 3-P like the other molecule formed

Glyceraldehyde-3-P makes a 3 Carbon Intermediate #1 (3CI #1)

3C I #1 MAKES 1 ATP (x 2 because 1 glucose moledule yeilds 2 carbons so this process is doubled) — forming 3 C I #2 — which changes to 3C I #3

3cI#3 turns into PEP ( phosphoenolpyruvate)

PEP MAKES 1 ATP (x 2) by changing into Pyruvate !

Pyruvate is then turned into Acetyl CoA ( high oxygen conditions, which also forms NADH2 ( future yeild of 6 ATP) or Pyruvate forms Lactate ( no oxygen, which takes NADH2 and forms NAD + which then acts as a taxi to keep the cycle going).

The pyruvate—> lactate is the process that keeps us alive say when we are drowning and have no Oxygen- ( it only lasts for about 400 kcal worth of energy) .. The taxi NAD+ goes back up to help convert glucose to pyruvate so we can continue to have energy!

And I didn’t even look at my notes for any of this!! Phew!!!

Advertisements

Actions

Information

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s




%d bloggers like this: