Glycogen Synthesis

Question 1

How do we store energy in the body?

Answer 1

1. Glycogen

2. Triglycerides

Question 2

Why do we store energy in the body?

Answer 2

1. Maintain normal autonomic functions during sleep
2. Endurance exercise
3. Low carb diet

Basically, for times of high demand

Question 3

In low carb diets….

Maintain glucose homeostasis for brain and RBC by ?

Maintain energy homeostasis by ?

Answer 3

Maintain glucose homeostasis for brain and RBC by liver conducting gluconeogenesis

Maintain energy homeostasis by oxidizing fatty acids

Question 4

Glycolysis and gluconeogenesis cannot happen at same time at same rate.

How is this achieved?

Answer 4

Steps 1, 3, 10 have different enzymes

Question 5

Glycolysis ________ in liver in fed state. Why?

Answer 5

INCREASES

To provide energy for biosynthesis

Question 6

Why is glucose stored as glycogen in animals?

Answer 6

Glycogen has a fraction of the osmotic pressure associated with an equivalent number of glucose molecules.

Question 7

What would happen if glucose was not stored as glycogen?

Answer 7

Osmotic stress would increase and cell would take in water and rupture.

Question 8

Primary sites of glycogen storage (2)

Answer 8

1. Liver

2. Muscle

Question 9

Liver is involved in _________

Why?

Answer 9

Metabolic regulation

Receives incoming glucose from diet before all other tissues

Question 10

Muscle is involved in ____________

Answer 10

Contraction

Question 11

Glycogen % in liver vs. muscle

Answer 11

Liver = glycogen is 10% of mass

Muscle = glycogen is 1-2% of mass

Question 12

Every single carbon has _________ therefore ________

Answer 12

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

Question 13

Name carbohydrates by

Answer 13

1. What carbons are linked

2. Where OH group is

Question 14

C-1 is called the

Answer 14

Anomeric carbon

Question 15

Sugars in solution _______

Answer 15

Cyclize

Question 16

D- glucose in solution

Answer 16

Aldehyde + alcohol hemiacetal

C-1 and OH of C-5 cyclize to yield:

alpha-D-glucopyranose (1/3)
Beta-D-glucopyranose (2/3)

Question 17

Alpha = OH ________

Answer 17

Below plane

Question 18

Beta = OH ________

Answer 18

Above plane

Question 19

D- Fructose in solution

Answer 19

Ketone + alcohol hemiketal

C-1 and OH of C-5 cyclize to yield

Alpha-D-fructofuranose
Beta-D-fructofuranose

Question 20

________ link monosaccharides

Answer 20

Glycosidic bond

• covalent

Question 21

O glycosidic bond

Answer 21

Anomeric carbon reacts with an oxygen on the hydroxyl group

Question 22

2 major functions of polysaccharides

Answer 22

1. Energy storage

2. Structural support

Question 23

Similarities and differences between cellulose, starch, and glycogen.

Answer 23

All contain glucose as monosaccharide

Differences are due to alpha or beta glycosidic linkages and structure

Question 24

Cellulose

Answer 24

• In plants
• Have beta-1,4- glycosidic linkages
• Primarily for structural support because very rigid and have extensive H bonding

Question 25

Humans do not have enzymes that can cut

Answer 25

beta glycosidic linkage

Question 26

Starch

Answer 26

- In plants - Amylose & amylopectin - Primarily for energy storage because of open structure

Question 27

Amylose

Answer 27

- linear polymer | - alpha-1,4-glycosidic bonds

Question 28

Amylopectin

Answer 28

- Has both alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds at branch points - Most similar to glycogen

Question 29

Glycogen

Answer 29

- Has both alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds at branch points - Branched structure

Question 30

Advantage of branched structure of glycogen (and amylopectin)

Answer 30

Allows for rapid synthesis and degradation from multiple end/access points —> rapid release of glucose Increases solubility

Question 31

Glycogenin

Answer 31

Makes a primer (oligosaccharide of glucose) to initiate glycogen synthesis

Question 32

Synthesis of glycogen: When? Requirements (2)? Major enzyme?

Answer 32

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

Question 33

Step 1

Answer 33

Phosphorylation Glucose —> G-6-P

Question 34

Step 2

Answer 34

Isomerization G-6-P —> G-1-P

Question 35

Step 3

Answer 35

ACTIVATION / RATE LIMITING STEP G-1-P + UTP —> UDP- glucose + PPi

Question 36

Explain where UDP gets its 2 phosphates from

Answer 36

Has 1 phosphate from G-1-P Gets 1 phosphate from UTP cleavage

Question 37

Explain what drives step 3 (activation step)

Answer 37

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

Question 38

Step 4

Answer 38

Synthesis of primer Enzyme: glycogenin Link together 6-8 glucose molecules by alpha-1,4-glycosidic bonds *Primer remains attached to glycogenin*

Question 39

Step 5 Enzyme?

Answer 39

Extend the primer UDP-glucose + glycogen —> UDP + glycogen Enzyme: Glycogen synthase

Question 40

Each glucose molecule that is added must be __________

Answer 40

Activated with UTP

Question 41

When is a branch point made? How?

Answer 41

Once chain grows to about 11-12 residues long By branching enzyme introducing a alpha-1,6-glycosidic bond at one point

Question 42

Glycogen synthase is __________ and _________ in the FED state in response to? Result?

Answer 42

Dephosphorylated and active in the fed state in response to insulin signaling. Result: Stimulate glycogen synthesis and inhibit glycogen degradation.

Question 43

Glycogen synthase is __________ and _________ in the FASTED state in response to? Result?

Answer 43

Phosphorylated and inactivate in fasted state in response to glucagon signaling which activates protein kinase A through cAMP.

Question 44

In general, an enzyme with a bio synthetic function is __________ in fed state in response to insulin signaling.

Answer 44

Dephosphorylated and more active

Question 45

In fed state, insulin activates (2)

Answer 45

1. Kinases (namely Akt) | 2. Protein phosphatase 1 (PP1)

Question 46

In fed state, kinases (Akt) activated by insulin ____________. Result:

Answer 46

Inactivate glycogen synthase kinase Result: Glycogen synthase kinase cannot inactivate glycogen synthase by phosphorylating it

Question 47

In fed state, what does the activation of PP1 do?

Answer 47

1. PP1 dephosphorylates glycogen synthase to activate it and promote glycogen synthesis. 2. PP1 dephosphorylates glycogen phosphorylase making it inactive to prevent glycogen degradation when I/G increases (*****)

Question 48

Glycogen synthesis and degradation are _________

Answer 48

Inversely regulated

Question 49

In the presence of glucose.....

Answer 49

1. Glycogen synthase increases activity to promote glycogen synthesis. 2. Glycogen phosphorylase decreases activity to decrease glycogen degradation.