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Biochemistry-Block 2 CC > Glycogen Metabolism > Flashcards

Glycogen Metabolism Flashcards

1
Q

Glucose is obtained from

A

Dietary Intake, Gluconeogensis, Glycogen

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2
Q

____ is the:

  • required to maintain constant levels in the blood
  • preferred energy source for the brain and required for the RBCs
  • Essential for exercising muscles
  • obtained from Diet, GNG, Glycogen stores
A

Glucose

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3
Q

This source of glucose (and glucose precursors) is often sporadic, dependent on the content of the diet, and not always a reliable source of blood glucose.

A

Diet/Dietary Intake

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4
Q

This is a mechanism for storing glucose in a quick mobilizable form.

A

Glycogen

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5
Q

___ can be slow in responding to a falling blood glucose level, but is used to provide sustained synthesis of glucose.

A

Gluconeogenesis

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6
Q

____ may be contained by virtually any cell in the human body

A

Glycogen

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7
Q

Glycogen stores are typically found in _____.

A

Skeletal muscle and the liver

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8
Q

This tissue typically uses glycogen as a source of energy.

A

Skeletal muscle

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9
Q

This tissue uses its glycogen stores in order to maintain blood glucose levels during early stages of fasting.

A

Liver

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10
Q

This tissue is composed of ~100 grams of glycogen. This makes up about 10% of the tissues weight within an adult.

A

Liver

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11
Q

This tissue is composed of ~400 grams of glycogen. This only makes up ~1-2% of the weight of this tissue.

A

(Skeletal) Muscle

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12
Q

Glycogen storage is associated w/significant amounts of ____ storage. It is about ___x the weight of glycogen.

A

Water; ~5

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13
Q

True/False: Your weight can vary due to the amount of glycogen you have stored.

A

True

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14
Q

Why are the branches important on the molecule?

A
  1. Because they increase the solubility of glycogen molecules.
  2. B/c they increasing the number of nonreducing ends that allow for faster synthesis and degradation.
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15
Q

In the absence of a dietary source of glucose, glycogen is degraded to glucose and rapidly released from _______.

A

liver and kidney glycogen

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16
Q

Muscle glycogen is degraded within exercising muscle in order to

A

provide the muscle with an important energy source

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17
Q

As glycogen stores are depleted, the synthesis of glucose through ____ takes over.

A

Gluconeogensis (GNG)

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18
Q

____ serves as the glucose source in the gap b/w the fall of blood glucose hours after a meal and the onset of gluconeogensis which needs time to kick in a few hours after.

A

Glycogen

19
Q

____ molecule is a branched chain polysaccharide made exclusively of alpha-D-glucose

A

Glycogen

20
Q

The primary glycosidic bond within the glycogen structure is a(n)

A

alpha(1,4) linkage

21
Q

True/False: There are 10-40x10^4 glucose molecules within 1 glycogen granule.

A

False: There are 10-40x10^3 glucose molecules per 1 glycogen granule.

22
Q

After an average of ___ glucosyl residues, there is a branch containing a(n) _____.

A

8-10; alpha(1,6) linkage

23
Q

Large molecules of glycogen exist as ___ that are associated w/enzymes necessary for synthesis and degradation.

A

discrete cytoplasmic granules (beta-particles)

24
Q

Steps for the Synthesis of Glycogen (Glycogenesis):

A
  1. Synthesis of Uridine disphosphate glucose
  2. Synthesis of a primer to initiate glycogen synthesis.
  3. Elongation of glycogen chains
  4. Formation of branches
25
Q

Steps for the Degradation of Glycogen (Glycogenolysis):

A
  1. Shortening of chains
  2. Removal of chains
  3. Conversion of Glucose 1-P to Glucose 6-P
  4. Dephosphorylation of Glucose 6-P to Glucose.
26
Q

What occurs during Step 1 of Glycogenesis?

A

The synthesis of uridine disphosphate glucose via Hexo/Glucokinase, Phosphoglucomutase, and UDP-glucose pyrophosphorylase. This is highly exergonic and ensures UDP-glucose is synthesized.

27
Q

What occurs during Step 2 of Glycogenesis? Why does this happen?

A

The synthesis of a primer to initiate glycogen synthesis.. This occurs because glycogen synthase can NOT add UDP-glucose to a single glucose molecule. It can only ELONGATE existing glycogen molecules (primers).

28
Q

What happens if no glycogen primers are available? (3 things)

A
  • a protein glycogenin serves as a primer
  • specific Tyr residue serves as attachment point for Glycogen synthase
  • Glycogenin itself catalyzes this attachment reaction and the attachment of next few UDP-glucose molecules via alpha(1,4) glycosidic bonds
29
Q

What is the enzyme responsible for the 3rd step of Glycogenesis?

A

Glycogen synthase

30
Q

What does Glycogen synthase do in the 3rd step in Glycogenesis? (3 things)

A
  • Elongates existing glycogen primers
  • Transfers UDP-glucose to non-reducing end of the primer
  • Forms alpha(1,4) glycosidic bond ONLY b/w C-1 of UDP-glucose and C-4 from the primer.
31
Q

Which enzyme is the rate limiting enzyme within Glycogenesis?

A

Glycogen synthase

32
Q

What enzyme removes a chain of 6-8 glucosyl residues from the end of the glycogen chain? What type of bond is it breaking?

A

The branching enzyme; breaks an alpha(1,4) bond

33
Q

This enzyme attaches a chain of 6-8 glucosyl residues to a non-terminal glucosyl residue by an alpha(1,6) bond.

A

The branching enzyme

34
Q

This enzyme functions as a 4:6 trasnferase.

A

The branching enzyme.

35
Q

alpha(1,4) –>

alpha(1,6) –>

A

elongation

branching

36
Q

Glycogenolysis is the

A

degradation of glycogen

37
Q

Name the 4-steps of Glycogenolysis:

A
  1. Shortening of chains
  2. Removal of branches
  3. Conversion of glucose-1-P to glucose-6-P
  4. Conversion of glucose-6-P to glucose
38
Q

True/False: The enzymes for Glycogenesis and Glycogenolysis is the same.

A

False; a separate set of enzymes are used for Glycogenolysis.

39
Q

Where does the 4th step in Glycogenolysis occur?

A

Within the liver ONLY

40
Q

The enzyme responsible for the first step in Glycogenolysis is ___

A

Glycogen phosphorylase

41
Q

Tissue specific isoforms for the first step of Glycogenolysis:

A

liver, muscle, brain

42
Q

What type of bonds does the Glycogen phosphorylase cleave in the 1st step of Glycogenolysis?

A

alpha(1,4) glycosidic bonds

43
Q

What does Glycogen phosphorylase use to cleave an alpha(1,4) glycosidic bond?
What else occurs during this step?

A

An inorganic Pi

The inorganic phosphate simultaneously attaches itself to the glucose to yield glucose 1-phosphate

44
Q

What does Glycogen phosphorylase requires as a coenzyme?

Where is this derived?

A 
pyridoxal phosphate (PLP)
derived from Vitamin B6

Biochemistry-Block 2 CC (13 decks)

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