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Flashcards in Glycogen Synthesis Deck (49):
1

How do we store energy in the body?

1. Glycogen

2. Triglycerides

2

Why do we store energy in the body?

1. Maintain normal autonomic functions during sleep

2. Endurance exercise

3. Low carb diet

Basically, for times of high demand

3

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

4

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

How is this achieved?

Steps 1, 3, 10 have different enzymes

5

Glycolysis ________ in liver in fed state. Why?

INCREASES

To provide energy for biosynthesis

6

Why is glucose stored as glycogen in animals?

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

7

What would happen if glucose was not stored as glycogen?

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

8

Primary sites of glycogen storage (2)

1. Liver

2. Muscle

9

Liver is involved in _________

Why?

Metabolic regulation

Receives incoming glucose from diet before all other tissues

10

Muscle is involved in ____________

Contraction

11

Glycogen % in liver vs. muscle

Liver = glycogen is 10% of mass

Muscle = glycogen is 1-2% of mass

12

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

13

Name carbohydrates by

1. What carbons are linked

2. Where OH group is

14

C-1 is called the

Anomeric carbon

15

Sugars in solution _______

Cyclize

16

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)

17

Alpha = OH ________

Below plane

18

Beta = OH ________

Above plane

19

D- Fructose in solution

Ketone + alcohol hemiketal

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

Alpha-D-fructofuranose
Beta-D-fructofuranose

20

________ link monosaccharides

Glycosidic bond

- covalent

21

O glycosidic bond

Anomeric carbon reacts with an oxygen on the hydroxyl group

22

2 major functions of polysaccharides

1. Energy storage

2. Structural support

23

Similarities and differences between cellulose, starch, and glycogen.

All contain glucose as monosaccharide

Differences are due to alpha or beta glycosidic linkages and structure

24

Cellulose

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

25

Humans do not have enzymes that can cut

beta glycosidic linkage

26

Starch

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

27

Amylose

- linear polymer

- alpha-1,4-glycosidic bonds

28

Amylopectin

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

- Most similar to glycogen

29

Glycogen

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

- Branched structure

30

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

31

Glycogenin

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

32

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

33

Step 1

Phosphorylation

Glucose —> G-6-P

34

Step 2

Isomerization

G-6-P —> G-1-P

35

Step 3

ACTIVATION / RATE LIMITING STEP

G-1-P + UTP —> UDP- glucose + PPi

36

Explain where UDP gets its 2 phosphates from

Has 1 phosphate from G-1-P

Gets 1 phosphate from UTP cleavage

37

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

38

Step 4

Synthesis of primer

Enzyme: glycogenin

Link together 6-8 glucose molecules by alpha-1,4-glycosidic bonds

*Primer remains attached to glycogenin*

39

Step 5

Enzyme?

Extend the primer

UDP-glucose + glycogen —> UDP + glycogen

Enzyme: Glycogen synthase

40

Each glucose molecule that is added must be __________

Activated with UTP

41

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

42

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.

43

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.

44

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

Dephosphorylated and more active

45

In fed state, insulin activates (2)

1. Kinases (namely Akt)

2. Protein phosphatase 1 (PP1)

46

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

Result:

Inactivate glycogen synthase kinase

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

47

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

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 (*****)

48

Glycogen synthesis and degradation are _________

Inversely regulated

49

In the presence of glucose.....

1. Glycogen synthase increases activity to promote glycogen synthesis.

2. Glycogen phosphorylase decreases activity to decrease glycogen degradation.