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SURVEY OF BIOCHEMISTRY

Glycogen

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What is Glycogen?

• Branched polymer of glucose

• Storage form of glucose– Liver

• Maintenance of blood glucose levels, especially during fasting

– Skeletal Muscle• Fuel reserve for synthesis of ATP for muscle

contractionDraw Structure

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Types of Polysaccharide Linkages

• What is an alpha 1->4 linkage?

• What is a beta 1->4 linkage?

• How are monosaccharides branched at C6?

Illustrate

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Branched Structure of Glycogen

What is meant bynon-reducing vs.

reducing end?

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Reducing v. Nonreducing Sugars

• A reducing sugar has an anomeric C that has NOT formed a glycosidic bond, such that it can reduce oxidizing agents.

Recall what ananomeric C is!

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Reducing v. Nonreducing Sugars

Glycogen has one reducing end.

All other ends are non-reducing.

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A Closer Look at Glycogen

• Today: Glycogen Breakdown

• Monday: Glycogen Synthesis

• Wednesday: Control of Glycogen Synthesis

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Three Enzymes Involved in Glycogen Breakdown

• Glycogen Phosphorylase– Produces Glucose 1-Phosphate– Uses Pyridoxal 5’-Phosphate (cofactor)

• Glycogen Debranching Enzyme– 2 Enzymatic functions

• Produces glucose • Transfers branches onto main polymer chain

• Phosphoglucomutase

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Glycogen Phosphorylase

Glycogen phosphorylase uses the cofactor pyridoxal 5’-phosphate to catalyze production of

glucose 1-phosphate from a terminal end of glycogen.

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Glycogen Phosphorylase Mechanism

1. Formation of a ternary complex

Glycogen+Pi +

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Glycogen Phosphorylase Mechanism

2. Formation of an oxonium intermediate

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Glycogen Phosphorylase Mechanism

3. Formation of glucose 1-phosphate

+ Glycogenn-1

Glucose1-Phosphate

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Three Enzymes Involved in Glycogen Breakdown

• Glycogen Phosphorylase– Produces Glucose 1-Phosphate– Uses Pyridoxal 5’-Phosphate (cofactor)

• Glycogen Debranching Enzyme– 2 Enzymatic functions

• Produces glucose • Transfers branches onto main polymer chain

• Phosphoglucomutase

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Glycogen Debranching Enzyme

Transferase activity

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Phosphoglucomutase

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Glycogen Debranching Enzyme

Transferase activity

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How To Study

• Learn all 10 steps of Glycolysis– Substrates– Products– Enzymes– Know general process by which

mechanisms occur

• Learn 3 enzyme activities used to break down glycogen

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PRS

• What is the maximum number of O2 molecules that hemoglobin can bind?

1. One2. Two3. Three4. Four

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PRS

• What is the product formed by the activity of triose phosphate isomerase in glycolysis?

1. Glucose 1-phosphate2. Glucose 6-phosphate3. Glyceraldehyde 3-phosphate4. Pyruvate

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PRS

• How many ATP’s are produced after the first stage (Steps 1-5) of glycolysis?

1. None2. One3. Two4. Four

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PRS

• Which of the following vitamins are fat soluble?

1. Vitamin C2. Vitamin A3. Riboflavin4. Folate

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PRS

• B cells mature in the ________.1. Thymus2. Bone marrow3. Muscle tissue4. Myosin

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PRS

• Oxygen binding to myoglobin results in what shaped curve?

1. Sigmoidal2. Hyperbolic3. Linear4. Sinusoidal

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PRS

• Which of the following amino acids is not in the catalytic triad of serine proteases?

1. Ser2. Thr3. His4. Asp

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PRS

• What is Km?

1. The catalytic efficiency2. The catalytic rate constant3. 1/2 Vmax

4. [S] at 1/2 Vmax