Metabolic Pathways Overview
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Questions and Answers

What role does cortisol play in glucose metabolism?

  • Stimulates glycogen synthesis
  • Inhibits gluconeogenesis
  • Stimulates gluconeogenesis (correct)
  • Enhances insulin sensitivity

What triggers the immediate release of glucose during stress?

  • Somatomedins activity
  • Insulin secretion
  • Epinephrine production (correct)
  • Cortisol release

How does human placental lactogen (hPL) affect blood sugar levels?

  • Promotes insulin secretion
  • Increases insulin sensitivity
  • Has anti-insulin activity (correct)
  • Decreases blood sugar levels

What is the function of somatomedins in glucose metabolism?

<p>Promotes entry of glucose into cells (D)</p> Signup and view all the answers

What effect does adrenocorticotropic hormone (ACTH) have on glucose levels?

<p>Increases glucose production (B)</p> Signup and view all the answers

What is the primary result of glycolysis?

<p>Conversion of pyruvate with ATP production (C)</p> Signup and view all the answers

Which metabolic pathway involves the synthesis of excess glucose into glycogen?

<p>Glycogenesis (C)</p> Signup and view all the answers

What is the main energy-producing pathway in metabolic processes?

<p>Kreb's Cycle (A)</p> Signup and view all the answers

Which process converts non-carbohydrate sources into carbohydrate substrates?

<p>Gluconeogenesis (B)</p> Signup and view all the answers

Which substances can be converted into glucose through interconversion in the liver?

<p>Galactose, fructose, and mannose (A)</p> Signup and view all the answers

What is the role of liver cells in fructose metabolism?

<p>They contain enzymes for interconversion. (A)</p> Signup and view all the answers

What are the end products of galactose and fructose metabolism in the liver?

<p>Glucose-6-Phosphate and glucose (A)</p> Signup and view all the answers

Which process is primarily regulated by glucagon?

<p>Glycogenolysis (A)</p> Signup and view all the answers

What is the primary role of fructokinase in carbohydrate metabolism?

<p>Phosphorylates fructose to fructose-1-P (D)</p> Signup and view all the answers

Why does hexokinase preferentially phosphorylate glucose over fructose?

<p>Hexokinase has a higher affinity for glucose compared to fructose (D)</p> Signup and view all the answers

What symptom is commonly associated with fructosuria?

<p>False positive for glucose in the urine (D)</p> Signup and view all the answers

What condition results from a lack of aldolase in the body?

<p>Fructose intolerance (A)</p> Signup and view all the answers

Which of the following is a characteristic of galactose metabolism disorders?

<p>Defects in either Galactose-1-PO4 Uridyl Transferase or Galactokinase (D)</p> Signup and view all the answers

What is a potential consequence of untreated galactosemia?

<p>Cataracts due to galactitol deposition (D)</p> Signup and view all the answers

What dietary change is essential for managing galactosemia?

<p>Eliminate milk products (B)</p> Signup and view all the answers

What happens to excess glycogen in the body?

<p>It is converted to fat with no storage limit. (C)</p> Signup and view all the answers

What symptom might infants experience following sucrose intake in the case of fructose intolerance?

<p>Hypoglycemia and vomiting (A)</p> Signup and view all the answers

Which enzyme initiates glycogenolysis in the presence of hypoglycemia?

<p>Phosphorylase (A)</p> Signup and view all the answers

Which hormone promotes hepatic glycogenolysis and gluconeogenesis?

<p>Glucagon (A)</p> Signup and view all the answers

What form of glycogen storage can be released slowly, typically found in muscle tissue?

<p>Fixed glycogen (D)</p> Signup and view all the answers

What is a common symptom of glycogen storage diseases?

<p>Muscle cramps and wasting (B)</p> Signup and view all the answers

Which hormone inhibits the secretion of both insulin and glucagon?

<p>Somatostatin (D)</p> Signup and view all the answers

What substance is produced when glycogen is broken down in the liver?

<p>Glucose (D)</p> Signup and view all the answers

Which hormone antagonizes insulin and stimulates gluconeogenesis through lipolysis?

<p>Growth Hormone (C)</p> Signup and view all the answers

Flashcards

Glycogen Storage

The process of storing glucose as glycogen in the liver and muscle cells. All cells can store some glycogen, but the liver and muscle cells are the primary storage sites.

Free Glycogen

Glycogen that is readily released from the liver, making it immediately available for energy production.

Fixed Glycogen

Glycogen stored in the muscle cells that is released slowly, providing a sustained source of energy.

Glycogenolysis

The process of breaking down glycogen into glucose. It happens in the liver and muscles.

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Phosphorylase

An enzyme that activates glycogenolysis, breaking down glycogen into glucose-6-phosphate.

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Glucagon & Epinephrine

Hormones that initiate glycogenolysis by activating phosphorylase.

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Insulin

Hormone that enhances glucose uptake into cells, promoting glucose storage as glycogen and lowering blood sugar.

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Glucagon

Hormone that promotes glycogen breakdown and gluconeogenesis, raising blood sugar.

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Cortisol

A hormone produced by the adrenal cortex, specifically in the zona fasciculata. It stimulates gluconeogenesis, the creation of glucose from non-carbohydrate sources, and has an antagonistic effect to insulin.

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Epinephrine and Norepinephrine

These hormones, also known as catecholamines, are produced by the chromaffin cells of the adrenal medulla. They trigger both liver and skeletal muscle glycogenolysis, breaking down glycogen into glucose, resulting in a rapid increase in blood glucose levels.

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Human Placental Lactogen (hPL)

A hormone produced by the placenta during pregnancy. It has an anti-insulin effect, causing a rise in blood sugar levels in pregnant individuals, which can sometimes lead to gestational diabetes.

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ACTH (Adrenocorticotropic Hormone)

This hormone, secreted by the anterior pituitary, also has an anti-insulin effect. It stimulates the adrenal cortex to produce cortisol, which in turn increases blood glucose levels.

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Somatomedins

These hormones, produced by the liver, have insulin-like activity. They promote the uptake of glucose into cells, helping to lower blood glucose levels.

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Glycolysis

The breakdown of glucose into pyruvate, producing a small amount of ATP. This is the first stage of glucose metabolism.

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Gluconeogenesis

The process where non-carbohydrate sources like amino acids, glycerol, and lactate are converted into glucose. This process helps maintain blood glucose levels.

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Pentose Phosphate Pathway

An alternative glucose metabolism pathway that produces NADPH, a reducing agent, and ribose-5-phosphate, a precursor for nucleotide biosynthesis.

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Kreb's Cycle

The main pathway for ATP production that follows glycolysis. It uses acetyl-CoA, derived from pyruvate, to generate high-energy molecules like NADH and FADH2.

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Fructose Metabolism

The breakdown of fructose in the liver, kidneys, intestine, and adipose tissue into glucose and other intermediates.

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Transdeamination

The removal and transfer of an amino group from an amino acid to another molecule, often involved in gluconeogenesis.

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Fructokinase

Phosphorylates fructose to fructose-1-phosphate.

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Hexokinase

Phosphorylates glucose to glucose-6-phosphate, but can also phosphorylate fructose to fructose-6-phosphate. Has a higher affinity for glucose.

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Aldolase

Utilizes fructose-1,6-bisphosphate as a substrate, cleaving it into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

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Fructosuria

A condition caused by a deficiency in fructokinase, leading to the inability to metabolize fructose, which is then excreted in the urine.

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Fructose Intolerance

A condition caused by a lack of aldolase, leading to an inability to break down fructose-1-phosphate, causing a buildup in the liver.

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Galactokinase

Phosphorylates galactose to galactose-1-phosphate. One of the enzymes involved in galactose metabolism.

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Galactose-1-phosphate uridyl transferase

This enzyme is responsible for transferring a uridyl group from UDP-glucose to galactose-1-phosphate, converting it to UDP-galactose.

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Galactosemia

A genetic disorder caused by a deficiency in either galactokinase or galactose-1-phosphate uridyl transferase, leading to the accumulation of galactose-1-phosphate in the body.

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Study Notes

Metabolic Pathways

  • Glucose is used to create energy (ATP) through various pathways.
  • Glycolysis (Embden-Meyerhof Pathway): Breaks down glucose to form pyruvate, releasing ATP.
  • Glycogenesis: Converts non-glucose hexoses (mannose, fructose, galactose) into glucose.
  • Glycogenesis: Synthesizes excess glucose into glycogen.
  • Glycogenolysis: Breaks down glycogen into glucose.
  • Pentose Phosphate Pathway (Hexose Monophosphate Shunt/ Phosphogluconate Oxidative Pathway): Alternative pathway catabolizing glucose to produce ATP.
  • Krebs Cycle (Citric Acid Cycle/ Tricarboxylic Acid Cycle): Main pathway producing ATP.
  • Gluconeogenesis: Converts non-carbohydrate sources (amino acids, glycerol, lactate) into glucose to produce ATP.
  • Transdeamination: Removes and transfers amino groups. Example: Alanine + a-ketoglutarate → Pyruvate + Glutamate; Pyruvate and Glutamate are Krebs Cycle substrates. Another example: Aspartate + a-ketoglutarate → oxaloacetate + glutamate.

Interconversion Between Monosaccharides in the Liver

  • Most human tissues cannot utilize galactose and fructose directly, requiring glycogenesis.
  • Liver cells contain enzymes for converting galactose, fructose, and mannose into glucose.
  • The end products of galactose and fructose metabolism are glucose-6-phosphate, which converts to glucose.
  • Liver, kidneys, intestines, and adipose tissue can use fructose as an energy source.
  • Fructokinase phosphorylates fructose to fructose-1-phosphate (fructose-1-P).
  • Hexokinase has higher affinity for glucose than fructose.
  • Fructose-1,6-diphosphate produces glyceraldehyde-3-P and dihydroxyacetone phosphate.

Clinical Significance of Fructose

  • Fructosuria: Inability to absorb fructose, causing fructose excretion in urine. Symptoms are benign.
  • Fructose intolerance: Lack of aldolase, inhibiting glycogenolysis and gluconeogenesis. Prolonged fructose intake in infants can cause vomiting, poor feeding, jaundice, hepatic failure, and potentially death.

Galactose Metabolism

  • Galactose is obtained from milk sugar.
  • Liver and red blood cells (RBCs) are crucial in galactose metabolism.
  • Galactosemia: Defect in galactose-1-phosphate uridyl transferase or galactokinase, leading to the trapping of galactose-1-phosphate in liver cells and RBCs.
  • Symptoms of galactosemia can include hepatomegaly, impaired liver function, and mental retardation.

Glycogen Metabolism

  • Glycogenesis: Liver and muscle cells primarily store glucose as glycogen.
  • Glycogenolysis: Breakdown of glycogen into glucose, primarily in the liver and, to a slower extent in muscle.
  • Free glycogen (liver) can readily be released, while fixed glycogen (muscle) is released more slowly.
  • Excess glycogen storage can lead to fat production.
  • Enzymes like phosphorylase and amylo-1,6-glucosidase are involved in glycogenolysis.
  • The process produces glucose-6-phosphate which is turned into glucose from the blood.

Hormonal Regulation of Blood Sugar

  • Glucagon and epinephrine regulate blood glucose levels via glycogenolysis and gluconeogenesis.
  • Insulin promotes glucose uptake in various tissues.
  • Other hormones including somatostatin, growth hormone, cortisol and others influence blood sugar levels. These further include the roles of thyroid hormone (TH) (thyroxine/tetraiodothyronine)), and cortisol and corticosteroid.

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Metabolic Pathways: Glycolysis, Gluconeogenesis, and More PDF

Description

Explore the various metabolic pathways involved in energy production from glucose. This quiz covers glycolysis, glycogenesis, glycogenolysis, the Krebs cycle, and more. Test your knowledge on how our body converts glucose and other substrates into ATP and maintains energy balance.

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