Question

Match the terms on the left with the descriptions on the right. (a) UDP-glucose _____ (b) UDP-glucose pyrophosphorylase _____ (c) Glycogen synthase _____ (d) Glycogenin _____ (e) Branching enzyme _____ (f) Glucose 6 -phosphate _____ (g) Glycogen synthase kinase _____ (h) Protein phosphatase 1 _____ (i) Insulin _____ (j) Glycogen phosphorylase \(a\) _____ 1\. Glucose 1 -phosphate is one of its substrates. 2\. Potent activator of glycogen synthase \(b\) 3\. Glucose sensor in the liver. 4\. Activated substrate for glycogen synthesis. 5\. Synthesizes \(\alpha-1,4\) linkages between glucose molecules. 6\. Leads to the inactivation of glycogen synthase kinase. 7\. Synthesizes \(\alpha-1,6\) linkages between glucose molecules. 8\. Catalyzes the formation of glycogen synthase \(b\). 9\. Catalyzes the formation of glycogen synthase \(a\). 10\. Synthesizes the primer for glycogen synthesis.

Short answer

(a) 4, (b) 1, (c) 5, (d) 10, (e) 7, (f) 2, (g) 8, (h) 9, (i) 6, (j) – (no direct match).

Step-by-step solution

Identify UDP-glucose

UDP-glucose is the activated form of glucose, used as a substrate for glycogen synthesis. It matches with description 4: 'Activated substrate for glycogen synthesis.' Therefore, UDP-glucose corresponds to option (a) 4.

Connect UDP-glucose pyrophosphorylase

This enzyme catalyzes the conversion of glucose 1-phosphate into UDP-glucose, making it involved in the step where glucose 1-phosphate is a substrate. This matches with description 1: 'Glucose 1-phosphate is one of its substrates.' Therefore, UDP-glucose pyrophosphorylase corresponds to option (b) 1.

Match glycogen synthase

Glycogen synthase is responsible for forming the \( \alpha-1,4 \) linkages in glycogen. This matches with description 5: 'Synthesizes \(\alpha-1,4\) linkages between glucose molecules.' Therefore, glycogen synthase corresponds to option (c) 5.

Associate glycogenin

Glycogenin acts as a primer for glycogen synthesis, providing the initial glucose residues to be extended by glycogen synthase. This matches with description 10: 'Synthesizes the primer for glycogen synthesis.' Therefore, glycogenin corresponds to option (d) 10.

Determine the role of branching enzyme

The branching enzyme introduces \( \alpha-1,6 \) linkages in glycogen, creating branches. This matches with description 7: 'Synthesizes \(\alpha-1,6\) linkages between glucose molecules.' Therefore, the branching enzyme corresponds to option (e) 7.

Link Glucose 6-phosphate

Glucose 6-phosphate acts as a potent activator of glycogen synthase. This matches with description 2: 'Potent activator of glycogen synthase \(b\).' Therefore, glucose 6-phosphate corresponds to option (f) 2.

Identify glycogen synthase kinase

Glycogen synthase kinase is involved in converting the active form of glycogen synthase (\(a\)) to its inactive form (\(b\)). This matches with description 8: 'Catalyzes the formation of glycogen synthase \(b\).' Therefore, glycogen synthase kinase corresponds to option (g) 8.

Connect Protein phosphatase 1

Protein phosphatase 1 reactivates glycogen synthase by converting its inactive form (\(b\)) back to its active form (\(a\)). This matches with description 9: 'Catalyzes the formation of glycogen synthase \(a\).' Therefore, protein phosphatase 1 corresponds to option (h) 9.

Role of Insulin

Insulin acts to inactivate glycogen synthase kinase, promoting glycogen synthesis. This matches with description 6: 'Leads to the inactivation of glycogen synthase kinase.' Therefore, insulin corresponds to option (i) 6.

Function of Glycogen phosphorylase \(a\)

Glycogen phosphorylase \(a\) acts when glucose levels are low to mobilize stored glucose. It's monitored by liver glucose levels, however, it doesn't match any description here as a sensor, and seems misplaced in the options provided.

Key concepts

UDP-glucose

UDP-glucose plays a central role in the process of glycogen synthesis. It is an activated form of glucose, which means it's prepared for subsequent chemical reactions necessary for building glycogen. UDP stands for uridine diphosphate, and it acts as a carrier molecule for glucose, facilitating its addition to a growing glycogen chain.
Understanding UDP-glucose is crucial because it serves as the donor of glucose molecules to the glycogen polymer. The formation of UDP-glucose involves the enzyme UDP-glucose pyrophosphorylase, which catalyzes the reaction between glucose 1-phosphate and UTP (uridine triphosphate) to yield UDP-glucose and pyrophosphate. This reaction is significant as it provides the "activated" glucose necessary for glycogen assembly.

Here's a quick breakdown of why UDP-glucose is important:

• It's the direct glucose donor in glycogen synthesis.
• Activation through glycosyl donor forms is a key step in biosynthetic pathways.
• The reaction forming UDP-glucose is a significant point in regulating glucose metabolism.

Understanding these functions will give you insights into how glycogen is synthesized and how it connects with overall glucose management in the body.

Glycogen Synthase

Glycogen Synthase is a vital enzyme in glycogen synthesis, responsible for catalyzing the formation of α-1,4-glycosidic linkages between glucose units. It essentially builds the linear backbone of the glycogen molecule by attaching UDP-glucose molecules one after another.
This enzyme operates along with glycogenin, which acts as an initial primer. Glycogen synthase binds the glucose portion of UDP-glucose and incorporates it into the existing glycogen chain. This is a key process in energy storage, as glycogen serves as the main form of stored glucose in animals.

The function of Glycogen Synthase includes:

• It extends the glycogen chain by adding glucose units one at a time.
• It ensures that the structure of glycogen remains compact and efficient for storage.
• Its activity is regulated by phosphorylation, with protein phosphatase 1 reversing the inactivation caused by glycogen synthase kinase to promote glycogen synthesis.

Comprehending the role of Glycogen Synthase is critical to understanding how the body manages to store energy for future use and how it regulates blood sugar levels.

Branching Enzyme

The Branching Enzyme is another essential component of the glycogen synthesis process. Once glycogen synthase has built a long chain of glucose molecules, the branching enzyme intervenes to create α-1,6-glycosidic linkages. These linkages introduce branches into the glycogen structure, making it more compact and soluble.
Branching is crucial because it allows for rapid synthesis and degradation of glycogen, enabling faster release of glucose when needed. The branched structure provides multiple ends for enzymes to work on, facilitating a quicker response to the body's energy requirements.

Key aspects of the Branching Enzyme include:

• It enhances the solubility and rapid mobilization of stored glycogen.
• The enzyme works by cleaving a 7-residue segment from the glycogen chain and attaching it as a new branch linked by an α-1,6-bond.
• Branching increases the glycogen granule's size, allowing for efficient storage without cellular stress.

By understanding the action of the Branching Enzyme, you gain insight into how glycogen is structured to meet metabolic demands efficiently, making energy readily available when needed.