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Biochem > Glycogen Synthesis > Flashcards

Glycogen Synthesis Flashcards

1
Q

How do we store energy in the body?

A
  1. Glycogen

2. Triglycerides

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2
Q

Why do we store energy in the body?

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

Basically, for times of high demand

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3
Q

In low carb diets….

Maintain glucose homeostasis for brain and RBC by ?

Maintain energy homeostasis by ?

A

Maintain glucose homeostasis for brain and RBC by liver conducting gluconeogenesis

Maintain energy homeostasis by oxidizing fatty acids

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4
Q

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

How is this achieved?

A

Steps 1, 3, 10 have different enzymes

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5
Q

Glycolysis ________ in liver in fed state. Why?

A

INCREASES

To provide energy for biosynthesis

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6
Q

Why is glucose stored as glycogen in animals?

A

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

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7
Q

What would happen if glucose was not stored as glycogen?

A

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

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8
Q

Primary sites of glycogen storage (2)

A
  1. Liver

2. Muscle

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9
Q

Liver is involved in _________

Why?

A

Metabolic regulation

Receives incoming glucose from diet before all other tissues

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10
Q

Muscle is involved in ____________

A

Contraction

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11
Q

Glycogen % in liver vs. muscle

A

Liver = glycogen is 10% of mass

Muscle = glycogen is 1-2% of mass

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12
Q

Every single carbon has _________ therefore ________

A

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

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13
Q

Name carbohydrates by

A
  1. What carbons are linked

2. Where OH group is

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14
Q

C-1 is called the

A

Anomeric carbon

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15
Q

Sugars in solution _______

A

Cyclize

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16
Q

D- glucose in solution

A

Aldehyde + alcohol hemiacetal

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

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

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17
Q

Alpha = OH ________

A

Below plane

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18
Q

Beta = OH ________

A

Above plane

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19
Q

D- Fructose in solution

A

Ketone + alcohol hemiketal

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

Alpha-D-fructofuranose
Beta-D-fructofuranose

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20
Q

________ link monosaccharides

A

Glycosidic bond

  • covalent
21
Q

O glycosidic bond

A

Anomeric carbon reacts with an oxygen on the hydroxyl group

22
Q

2 major functions of polysaccharides

A
  1. Energy storage

2. Structural support

23
Q

Similarities and differences between cellulose, starch, and glycogen.

A

All contain glucose as monosaccharide

Differences are due to alpha or beta glycosidic linkages and structure

24
Q

Cellulose

A
  • In plants
  • Have beta-1,4- glycosidic linkages
  • Primarily for structural support because very rigid and have extensive H bonding
25
Q

Humans do not have enzymes that can cut

A

beta glycosidic linkage

26
Q

Starch

A
  • In plants
  • Amylose & amylopectin
  • Primarily for energy storage because of open structure
27
Q

Amylose

A
  • linear polymer

- alpha-1,4-glycosidic bonds

28
Q

Amylopectin

A
  • Has both alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds at branch points
  • Most similar to glycogen
29
Q

Glycogen

A
  • Has both alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds at branch points
  • Branched structure
30
Q

Advantage of branched structure of glycogen (and amylopectin)

A

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

Increases solubility

31
Q

Glycogenin

A

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

32
Q

Synthesis of glycogen:

When?
Requirements (2)?
Major enzyme?

A

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
Q

Step 1

A

Phosphorylation

Glucose —> G-6-P

34
Q

Step 2

A

Isomerization

G-6-P —> G-1-P

35
Q

Step 3

A

ACTIVATION / RATE LIMITING STEP

G-1-P + UTP —> UDP- glucose + PPi

36
Q

Explain where UDP gets its 2 phosphates from

A

Has 1 phosphate from G-1-P

Gets 1 phosphate from UTP cleavage

37
Q

Explain what drives step 3 (activation step)

A

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
Q

Step 4

A

Synthesis of primer

Enzyme: glycogenin

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

Primer remains attached to glycogenin

39
Q

Step 5

Enzyme?

A

Extend the primer

UDP-glucose + glycogen —> UDP + glycogen

Enzyme: Glycogen synthase

40
Q

Each glucose molecule that is added must be __________

A

Activated with UTP

41
Q

When is a branch point made?

How?

A

Once chain grows to about 11-12 residues long

By branching enzyme introducing a alpha-1,6-glycosidic bond at one point

42
Q

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

Result?

A

Dephosphorylated and active in the fed state in response to insulin signaling.

Result: Stimulate glycogen synthesis and inhibit glycogen degradation.

43
Q

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

Result?

A

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

44
Q

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

A

Dephosphorylated and more active

45
Q

In fed state, insulin activates (2)

A
  1. Kinases (namely Akt)

2. Protein phosphatase 1 (PP1)

46
Q

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

Result:

A

Inactivate glycogen synthase kinase

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

47
Q

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

A
  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
Q

Glycogen synthesis and degradation are _________

A

Inversely regulated

49
Q

In the presence of glucose…..

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

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