Biochemistry of Insulin and Enzymes

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Questions and Answers

Which enzyme is NOT involved in bypassing the irreversible reactions of gluconeogenesis?

Phosphoenolpyruvate Carboxykinase (correct)

Fructose 1,6-Bisphosphatase

Glucokinase

Pyruvate Kinase

During fasting, which hormone's release primarily promotes gluconeogenesis?

Insulin

Epinephrine

Cortisol

Glucagon (correct)

What condition is commonly associated with an accumulation of cytoplasmic NADH in alcoholics?

Metabolic Syndrome

Hypoglycemia (correct)

Hyperglycemia

Diabetes Mellitus

Which pathway initiates the conversion of glucose to sorbitol?

Polyol Pathway Signup and view all the answers

What is the outcome of Fructose Aldolase B deficiency?

Essential Fructosuria Signup and view all the answers

What process is triggered by an increase in insulin in the cell?

Exocytosis Signup and view all the answers

What is the primary function of pancreatic amylase?

Digesting polysaccharides into disaccharides Signup and view all the answers

Which enzyme is associated with high affinity for fructose-6-phosphate (F6-P) in the presence of ATP?

Hexokinase Signup and view all the answers

What is the consequence of pyruvate kinase deficiency in red blood cells (RBC)?

Inability to produce ATP Signup and view all the answers

Which type of digestion is completed via brush border enzymes?

Membrane digestion Signup and view all the answers

What does Hexokinase convert glucose into?

Glucose 6-phosphate Signup and view all the answers

Which enzyme is considered the rate-limiting enzyme of the Krebs cycle?

Isocitrate Dehydrogenase Signup and view all the answers

What are the primary products of the Pyruvate Dehydrogenase (PDH) reaction?

Acetyl CoA, NADH, and CO2 Signup and view all the answers

Which compound does Cyanide bind irreversibly to?

Complex IV Signup and view all the answers

What is the role of uncoupling proteins found in brown adipose tissue?

To facilitate thermogenesis Signup and view all the answers

Which substances are precursors for gluconeogenesis?

Glycerol, lactate, and amino acids Signup and view all the answers

Which of the following increases ADP activation in the Krebs cycle?

Isocitrate Signup and view all the answers

What is the effect of a decreased ATP concentration on PDH activity?

Increased PDH activity Signup and view all the answers

What primary role does glycogen synthase play in glycogenesis?

It catalyzes the formation of glucosyl chains. Signup and view all the answers

Which enzymes are involved in the debranching of glycogen?

Transferase and Glucosidase Signup and view all the answers

What trigger is associated with glucose-6-phosphate dehydrogenase (G6PD) deficiency leading to hemolysis?

Infection and oxidant drugs Signup and view all the answers

How does insulin affect glycogen synthase activity?

It inhibits glycogen synthase. Signup and view all the answers

What is the result of a deficiency in glucose-6-phosphatase?

Increased blood glucose levels Signup and view all the answers

What enzyme catalyzes the synthesis of nitric oxide (NO)?

Nitric oxide synthase Signup and view all the answers

Which compound is primarily used as a substrate in glycogenesis?

UDP-glucose Signup and view all the answers

What process is glucose-6-phosphate involved in when discussing RBC capability?

Production of NADPH Signup and view all the answers

Study Notes

Enzyme Functions in Metabolism

Phosphorylase adds phosphate from ATP; Phosphatase removes phosphate.
GLUT-4 is an insulin-dependent transporter; increased insulin stimulates its exocytosis.
Intraluminal digestion occurs via pancreatic amylase breaking down polysaccharides to disaccharides; final digestion at the brush border.

Key Enzymes in Glycolysis and Their Functions

Glucokinase is present in most tissues; Hexokinase is specific to liver and pancreatic beta cells, with dependent ATP levels.
Pyruvate Kinase deficiency leads to ineffective ATP production, causing hemolytic anemia due to premature RBC destruction.

Irreversible Steps of Glycolysis

Key regulatory enzymes include Hexokinase, PFR (Phosphofructokinase-1), and Pyruvate Kinase.
PFR is the rate-limiting enzyme for glycolysis, facilitating conversion from Fructose 6-phosphate to Fructose 1,6-bisphosphate.

Krebs Cycle Overview

Occurs in mitochondrial matrix; generates 3 NADH, FADH2, GTP, and releases 2 CO2.
Isocitrate Dehydrogenase serves as the primary rate-limiting enzyme.

Metabolic Pathways and Interactions

Lipoic acid is involved in converting alpha-ketoglutarate to succinyl-CoA.
Cyanide poisoning irreversibly inhibits complex IV of the ETC, reducing ATP and oxygen levels.

Uncoupling Proteins

Found in brown adipose tissue, facilitate thermogenesis, influenced by ADP, enhancing both ETC and Krebs cycle activity.

Gluconeogenesis Essentials

Precursors include glycerol, lactate, and amino acids; primarily occurs in the liver and kidneys.
Bypasses irreversible reactions in gluconeogenesis require Pyruvate Kinase, PFR-1, and Glucose-6-Phosphatase.

Hormonal Regulation

Increased ATP favors glycolysis while promoting gluconeogenesis.
Glucagon stimulates gluconeogenesis, while insulin inhibits glycogen synthesis and promotes glucose uptake.

NADH Generation and Importance

Excess NADH can lead to hypoglycemia in alcoholics by promoting an imbalance in cellular redox states.
Glucose-6-Phosphate Dehydrogenase deficiency can lead to hemolysis, especially under stress like infection or exposure to oxidants.

Glycogen Metabolism

Glycogen synthesis is catalyzed by glycogen synthase; glycogen phosphorylase is inhibited by insulin and activated by glucagon and epinephrine.
Lack of glycogen phosphorylase results in McArdle disease; Von Gierke's disease is caused by a deficiency in Glucose-6-Phosphatase.

Additional Metabolic Insights

The Polyol pathway converts glucose to sorbitol via aldose reductase and sorbitol to fructose via sorbitol dehydrogenase, linked to peripheral neuropathy and cataracts.
Classic Galactosemia is associated with a deficiency in uridyltransferase, affecting galactose metabolism.

NADPH Role in Cellular Functions

NADPH is crucial for synthesizing nitric oxide, essential for immune response and vascular regulation.
G6PD deficiency diminishes the RBC's ability to generate NADPH, leading to hemolysis under oxidative stress.

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Description

This quiz covers the roles of phosphorylase and phosphatase in relation to insulin, as well as the process of exocytosis and intraluminal digestion. Test your knowledge on how insulin affects GLUT-4 receptors and the function of pancreatic amylase in polysaccharide digestion.