Title: BV2 / BV2 - 2 / Modul 5 / Glycogen metabolism

Q: Why is glycogen important?
A: Glycogen is an essential form of energy storage in our bodies

Q: What is glycogen?
A: It is a multibranched polysaccharide of glucose with single glycogen granules containing up to 30,000 glucose molecules

Q: How many glucoses can a signle glycogen granule contain?
A: 30 000

Q: Where is glycogen mainly found?
A: Glycogen is mainly found in liver and skeletal muscle cells

Q: What does the liver use glycogen for?
A: The liver uses glycogen to regulate blood glucose levels

Q: What does the muscles use glucose for?
A: Skeletal muscle cells use glycogen for energy

Q: How is glycogen synthesized?
A: Synthesis of glycogen (glycogenesis) requires the phosphorylation of glucose to glucose 6-phosphate by glucokinase or hexokinase, followed by the conversion to glucose 1-phosphate by phosphoglucomutase. The next step is the activation of glucose 1-phosphate into UDP-glucose (uridine diphosphate glucose) by glucose 1-phosphate uridylyltransferase. UDP-glucose molecules are then joined at their 1–4 carbon positions, initially by glycogenin (generates glycogen primers), and then by glycogen synthase.

Q: How can glycogen synthesis be divided into steps?
A: 1. Phosphorylation of glucose to glucose 6-phosphate by glucokinase or hexokinase
2. Conversion to glucose 1-phosphate by phosphoglucomutase.
3. The next step is the activation of glucose 1-phosphate into UDP-glucose (uridine diphosphate glucose) by glucose 1-phosphate uridylyltransferase.
4. UDP-glucose molecules are then joined at their 1–4 carbon positions, initially by glycogenin (generates glycogen primers), and then by glycogen synthase.

Q: What is step 1 of glycogen synthesis?
A: Glukokinase or hexokinase phosphorylates glucose into glucose-6-phosphate

Q: What is step 2 of glycogen synthesis?
A: Phosphoglucomutase converts the glucose-6-phosphate into glucose-1-phosphate

Q: What is step 3 of glycogen synthesis?
A: Glucose-1-phosphate uridylyltransferase activates glucose-1-phosphate into UDP-glucose

Q: What does UDP-glucose stand for?
A: Uridine diphosphate glucose

Q: What is step 4 of glycogen synthesis?
A: UDP-glucose molecules are joined at their 1-4 carbon positions, initially by glycogenin, which generates glycogen primers, and then by glycogen synthase

Q: What is the overall reaction of glycogen synthesis?
A: Glucose 1-phosphate + UTP + H2O → UDP-glucose + 1 PPi

Q: How does the branching of glycogen occur?
A: Branching occurs via the glycogen branching enzyme, which breaks the growing polymer every 8 glucose residues to form 1,6 glycosidic bonds.

Q: Which type of bond does glycogen branching enzyme create?
A: 1,6-glycosidic bonds

Q: How often does glycogen branching enzyme break/branch the growing polymer?
A: Every 8 glucose residues

Q: What does glycogenolysis require?
A: Requires an orthophosphate (HPO42-)

Q: Which enzyme performs glycogenolysis?
A: Glycogen phosphorylase

Q: How does glycogenolysis occur?
A: Glycogen phosphorylase releases glucose-1-phosphate molecules, which need to be converted into glucose-6-phosphate

Q: What needs to happen to the glucose-1-phosphates released by glycogenolysis?
A: They need to be converted into glucose-6-phosphate

Q: What can glucose-6-phosphate from glucose-1-phosphate from glycogenolysis then do?
A: Glucose 6-phosphate can either enter glycolysis, be transformed into glucose and released into the blood stream or enter the pentose phosphate pathway.

Q: What happens during debranching of glycogen?
A: During debranching, three glycosyl residues are transferred to a different branch/chain by oligoglucantransferase, leaving one residue in a 1,6 glycosidic bond behind. This final residue is released by amyloglucosidase as a single (unphosphorylated) glucose molecule.

Q: What does oligoglucantransferase do?
A: Transfers 3 glucosyl residues to a differnet brach/chain during debraching of glycogen

Q: What does amyloglucosidase do?
A: Releases the final residue of glycogen as a signle unphosphorylated glucose molecule

Q: What is the overall reaction fo glycogenolysis?
A: glycogen + HPO42- → glucose 1-phosphate +glycogen-1

Q: What is glycogen in relation to glucose?
A: Is the storage form of glucose

Q: What is the structure of glycogen?
A: - Is a long polymer that branches about every 10 glucose residues
- Contains alfa-1,4-glycosidic bonds and alfa-1,6-glycosidic bonds

Q: How do cells use glycogen?
A: Cells such as hepatocytes can use glycogen to regulate the blood glucose levels of the body. This is important because cells such as brain cells depend almost solely on glucose for energy.

Q: Other than for increasing blood glucode levels, what does our body depend glycogen?
A: Our body also depends on glycogen breakdown during periods of rapid activity, such as sprinting. The glucose obtained from glycogen can be used to produce energy under anaerobic activity (no O2).

Q: How is glycogen stored?
A: Stored in small cytoplasmic granules

Q: In which tissues is glycogen stored?
A: - The liver
- Skeletal muscle

Q: How does the liver and skeletal muscle use glycogen, respectively?
A: The liver regulates blood glucose levels while skeletal muscle provides the rapid energy needed for sudden and strenuous activity.

Q: What does the metabolism of glycogen consist of?
A: The metabolism of glycogen consists of breakdown and synthesis

Q: Which steps can the breakdown of glycogen be divided into?
A: - The breakdown process consists of 3 steps:
  1. Release of glucose 1-phosphate from glycogen - releases 1 single glucose
  2. Restructuring of glycogen
    1. Happens when one glucose is removed, needs to be remodelled so more can be released
  3. Conversion of glucose 1-phosphate to glucose-6-phosphate
    1. The glucose-6-phosphate can either enter glycolysis, be transformed into glucose and released into the blood, or enter the pentose phosphate pathway

Q: What must happen to the glucose before glucose monomers can be synthesized into glycogen?
A: In order to synthesize glycogen from glucose monomers, the glucose must first be activated to form UDP-glucose