Gluconeogenesis Flashcards

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Questions and Answers

What are the irreversible steps of glycolysis?

Hexokinase, phosphofructokinase, pyruvate kinase

What is the bypass for hexokinase?

Glucose-6-phosphatase

What is the bypass for phosphofructokinase?

Fructose-1,6-bisphosphatase

Describe the bypass for pyruvate kinase.

Pyruvate is converted to oxaloacetate with acetyl CoA. Oxaloacetate is shuttled out of the mitochondria through a conversion to malate, then converted back into oxaloacetate. Oxaloacetate is then converted into phosphoenolpyruvate. Signup and view all the answers

What enzyme catalyzes the conversion of pyruvate to oxaloacetate?

Pyruvate carboxylase Signup and view all the answers

What serves as a coenzyme for pyruvate carboxylase?

Biotin Signup and view all the answers

What serves as a positive modulator for the enzyme pyruvate carboxylase?

Acetyl CoA Signup and view all the answers

What enzyme catalyzes the interconversion of malate and oxaloacetate?

Malate dehydrogenase Signup and view all the answers

What enzyme catalyzes the conversion of oxaloacetate to phosphoenol pyruvate in the cytoplasm?

Phosphoenolpyruvate carboxykinase Signup and view all the answers

What are the substrates for the enzyme phosphoenolpyruvate carboxykinase?

GTP Signup and view all the answers

What high energy bonds are needed for the bypass of pyruvate kinase?

1 from ATP, 1 from GTP Signup and view all the answers

What electron carrier is also shuttled by the malate/oxaloacetate conversion?

NADH is shuttled outward from the mitochondria Signup and view all the answers

What enzyme in gluconeogenesis is missing in muscle cells?

Glucose-6-phosphatase Signup and view all the answers

What happens to excess lactate in muscle cells?

Gets carried back into blood to the liver for conversion to glucose or glycogen Signup and view all the answers

What type of reactions does biotin act as a coenzyme in?

Carboxylation Signup and view all the answers

Is biotin necessary in a diet?

False Signup and view all the answers

What amino acid residue is biotin usually found bound to in the apoenzyme?

Lysine Signup and view all the answers

What protein is found in egg whites that has a high affinity for biotin?

Avidin Signup and view all the answers

What reactions use biotin as a coenzyme?

Fatty acid synthesis, pyruvate to oxaloacetate, propionyl CoA to succinyl CoA Signup and view all the answers

Which of the following compounds increase gluconeogenesis? What about glycolysis?

Protons Signup and view all the answers

Study Notes

Gluconeogenesis Key Concepts

Irreversible Steps of Glycolysis: Enzymes hexokinase, phosphofructokinase, and pyruvate kinase are crucial for glycolysis but represent irreversible steps in the pathway.
Hexokinase Bypass: The bypass for hexokinase in gluconeogenesis involves glucose-6-phosphatase, facilitating the conversion back to glucose.
Phosphofructokinase Bypass: The enzyme fructose-1,6-bisphosphatase acts as a bypass for phosphofructokinase, playing a pivotal role in gluconeogenesis.
Pyruvate Kinase Bypass: Pyruvate is converted to oxaloacetate by pyruvate carboxylase, with oxaloacetate exiting mitochondria as malate, then reconverted and transformed into phosphoenol pyruvate through PEP carboxykinase.
Pyruvate to Oxaloacetate Conversion: Pyruvate carboxylase is the enzyme responsible for this conversion in gluconeogenesis.
Pyruvate Carboxylase Coenzymes: Biotin serves as the essential coenzyme for pyruvate carboxylase, while acetyl CoA acts as a positive modulator stimulating the enzyme's activity.
Malate Dehydrogenase Role: This enzyme catalyzes the conversion between malate and oxaloacetate, aiding in the mitochondrial shuttle mechanism.
Location of PEP Formation: Phosphoenolpyruvate carboxykinase catalyzes the conversion of oxaloacetate to phosphoenol pyruvate, primarily in the cytoplasm, utilizing GTP as a substrate.
Energy Requirements for Pyruvate Bypass: The bypass of pyruvate kinase requires high energy bonds from one molecule of ATP and one from GTP.
NADH in Mitochondrial Shuttle: NADH is shuttled from the mitochondria during the conversion of malate back to oxaloacetate.
Absence of Glucose-6-Phosphatase in Muscle Cells: Muscle tissue lacks this enzyme, preventing direct conversion of glucose-6-phosphate to glucose.
Fate of Excess Lactate: Lactate produced in muscles is transported to the liver, where it's converted back into glucose or glycogen.
Biotin's Role in Carboxylation: Biotin acts as a coenzyme in carboxylation reactions, crucial for gluconeogenesis.
Dietary Necessity of Biotin: Biotin is not essential in the diet as it is synthesized in adequate amounts by the body.
Binding of Biotin: Biotin is typically bound to the amino acid residue lysine in its apoenzyme form.
Effects of Avidin on Biotin: Avidin, a protein found in egg whites, has a high affinity for biotin, potentially leading to biotin-deficiency when consumed in large amounts.
Reactions Utilizing Biotin: Biotin functions as a coenzyme in several reactions including fatty acid synthesis, pyruvate to oxaloacetate conversion, and the transformation of propionyl CoA to succinyl CoA.
Influence on Gluconeogenesis and Glycolysis: Gluconeogenesis is stimulated by amino acids, oxaloacetate, citrate, ATP, protons, and alanine. In contrast, glycolysis is enhanced by glycogen, fructose 2,6-bisphosphate, and AMP.

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Description

This quiz focuses on the key concepts of gluconeogenesis, including the irreversible steps of glycolysis and the bypass reactions related to key enzymes. Each flashcard provides essential definitions and mechanisms that are crucial for understanding metabolic pathways in biochemistry. Perfect for students studying biochemistry or related fields.