Glycogen Synthesis Flashcards
How do we store energy in the body?
- Glycogen
2. Triglycerides
Why do we store energy in the body?
- Maintain normal autonomic functions during sleep
- Endurance exercise
- Low carb diet
Basically, for times of high demand
In low carb diets….
Maintain glucose homeostasis for brain and RBC by ?
Maintain energy homeostasis by ?
Maintain glucose homeostasis for brain and RBC by liver conducting gluconeogenesis
Maintain energy homeostasis by oxidizing fatty acids
Glycolysis and gluconeogenesis cannot happen at same time at same rate.
How is this achieved?
Steps 1, 3, 10 have different enzymes
Glycolysis ________ in liver in fed state. Why?
INCREASES
To provide energy for biosynthesis
Why is glucose stored as glycogen in animals?
Glycogen has a fraction of the osmotic pressure associated with an equivalent number of glucose molecules.
What would happen if glucose was not stored as glycogen?
Osmotic stress would increase and cell would take in water and rupture.
Primary sites of glycogen storage (2)
- Liver
2. Muscle
Liver is involved in _________
Why?
Metabolic regulation
Receives incoming glucose from diet before all other tissues
Muscle is involved in ____________
Contraction
Glycogen % in liver vs. muscle
Liver = glycogen is 10% of mass
Muscle = glycogen is 1-2% of mass
Every single carbon has _________ therefore ________
The equivalent of a water molecule associated with it therefore carbs are water soluble
Also another reason energy is stored as glycogen —> would be storing a lot of water therefore weight
Name carbohydrates by
- What carbons are linked
2. Where OH group is
C-1 is called the
Anomeric carbon
Sugars in solution _______
Cyclize
D- glucose in solution
Aldehyde + alcohol hemiacetal
C-1 and OH of C-5 cyclize to yield:
alpha-D-glucopyranose (1/3)
Beta-D-glucopyranose (2/3)
Alpha = OH ________
Below plane
Beta = OH ________
Above plane
D- Fructose in solution
Ketone + alcohol hemiketal
C-1 and OH of C-5 cyclize to yield
Alpha-D-fructofuranose
Beta-D-fructofuranose
________ link monosaccharides
Glycosidic bond
- covalent
O glycosidic bond
Anomeric carbon reacts with an oxygen on the hydroxyl group
2 major functions of polysaccharides
- Energy storage
2. Structural support
Similarities and differences between cellulose, starch, and glycogen.
All contain glucose as monosaccharide
Differences are due to alpha or beta glycosidic linkages and structure
Cellulose
- In plants
- Have beta-1,4- glycosidic linkages
- Primarily for structural support because very rigid and have extensive H bonding
Humans do not have enzymes that can cut
beta glycosidic linkage
Starch
- In plants
- Amylose & amylopectin
- Primarily for energy storage because of open structure
Amylose
- linear polymer
- alpha-1,4-glycosidic bonds
Amylopectin
- Has both alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds at branch points
- Most similar to glycogen
Glycogen
- Has both alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds at branch points
- Branched structure
Advantage of branched structure of glycogen (and amylopectin)
Allows for rapid synthesis and degradation from multiple end/access points —> rapid release of glucose
Increases solubility
Glycogenin
Makes a primer (oligosaccharide of glucose) to initiate glycogen synthesis
Synthesis of glycogen:
When?
Requirements (2)?
Major enzyme?
When: FED state, high I/G, in response to elevated glucose from a meal
Requirements: UTP in activation step for input of energy and a primer made by glucogenin
Major enzyme: glycogen synthase
Step 1
Phosphorylation
Glucose —> G-6-P
Step 2
Isomerization
G-6-P —> G-1-P
Step 3
ACTIVATION / RATE LIMITING STEP
G-1-P + UTP —> UDP- glucose + PPi
Explain where UDP gets its 2 phosphates from
Has 1 phosphate from G-1-P
Gets 1 phosphate from UTP cleavage
Explain what drives step 3 (activation step)
The high energy phosphate bond from UTP provides the energy for the formation of the high energy bond in UDP-glucose.
The liberation of pyrophosphate (PPi) and its hydrolysis drives the reaction because the energy is equivalent to 2 ATP —> 2 ADP
Step 4
Synthesis of primer
Enzyme: glycogenin
Link together 6-8 glucose molecules by alpha-1,4-glycosidic bonds
Primer remains attached to glycogenin
Step 5
Enzyme?
Extend the primer
UDP-glucose + glycogen —> UDP + glycogen
Enzyme: Glycogen synthase
Each glucose molecule that is added must be __________
Activated with UTP
When is a branch point made?
How?
Once chain grows to about 11-12 residues long
By branching enzyme introducing a alpha-1,6-glycosidic bond at one point
Glycogen synthase is __________ and _________ in the FED state in response to?
Result?
Dephosphorylated and active in the fed state in response to insulin signaling.
Result: Stimulate glycogen synthesis and inhibit glycogen degradation.
Glycogen synthase is __________ and _________ in the FASTED state in response to?
Result?
Phosphorylated and inactivate in fasted state in response to glucagon signaling which activates protein kinase A through cAMP.
In general, an enzyme with a bio synthetic function is __________ in fed state in response to insulin signaling.
Dephosphorylated and more active
In fed state, insulin activates (2)
- Kinases (namely Akt)
2. Protein phosphatase 1 (PP1)
In fed state, kinases (Akt) activated by insulin ____________.
Result:
Inactivate glycogen synthase kinase
Result: Glycogen synthase kinase cannot inactivate glycogen synthase by phosphorylating it
In fed state, what does the activation of PP1 do?
- PP1 dephosphorylates glycogen synthase to activate it and promote glycogen synthesis.
- PP1 dephosphorylates glycogen phosphorylase making it inactive to prevent glycogen degradation when I/G increases (*****)
Glycogen synthesis and degradation are _________
Inversely regulated
In the presence of glucose…..
- Glycogen synthase increases activity to promote glycogen synthesis.
- Glycogen phosphorylase decreases activity to decrease glycogen degradation.
