Biochemistry of Ketone Bodies and Cholesterol

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the yield of ATP from the oxidation of β-hydroxybutyrate?

  • 22 ATP
  • 19 ATP
  • 21.5 ATP (correct)
  • 17 ATP

Which factor primarily regulates ketolysis?

  • Availability of fatty acids
  • Availability of oxaloacetate (correct)
  • Insulin levels
  • Glucose concentration

What adaptation occurs in the brain during starvation after 5-6 days?

  • Increased fatty acid oxidation
  • Increased glucose utilization
  • Adaptation to using ketone bodies (correct)
  • Decreased energy requirements

Which condition is NOT a cause of ketosis?

<p>High glucose intake (A)</p> Signup and view all the answers

What is the normal range of ketone bodies in blood?

<p>0.5-3 mg/dL (D)</p> Signup and view all the answers

What is the key enzyme involved in cholesterol synthesis?

<p>HMG-CoA reductase (B)</p> Signup and view all the answers

What happens to HMG-CoA reductase when insulin is present?

<p>It is induced and dephosphorylated. (B)</p> Signup and view all the answers

Which hormone acts as a repressor of HMG-CoA reductase?

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

During periods of low energy availability, cholesterol synthesis is affected how?

<p>Cholesterol synthesis decreases. (C)</p> Signup and view all the answers

What mechanism do statins use to lower plasma cholesterol?

<p>Competing with HMG-CoA for reductase binding. (C)</p> Signup and view all the answers

What is the primary enzyme responsible for synthesizing glycerol-3-phosphate in the liver and kidneys?

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

Which tissue synthesizes glycerol-3-phosphate by reducing dihydroxyacetone phosphate (DHAP)?

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

What is the first product formed when glycerol-3-phosphate condenses with two acyl-CoA molecules?

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

Which enzyme is involved in removing phosphate from phosphatidic acid to form diacylglycerol?

<p>PPH-1 (D)</p> Signup and view all the answers

What final product is produced after the esterification of diacylglycerol with an additional acyl-CoA molecule?

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

What is the active form of Acetyl-CoA Carboxylase (ACC)?

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

Which of the following hormones is responsible for inhibiting lipogenesis?

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

Which carbon source is used by the microsomal system for fatty acid elongation?

<p>Malonyl-CoA (A)</p> Signup and view all the answers

What is the role of cholesterol in the formation of cell membranes?

<p>Cholesterol regulates membrane fluidity. (B)</p> Signup and view all the answers

What distinguishes the microsomal system for fatty acid elongation from de novo synthesis?

<p>It cannot initiate de novo synthesis (B)</p> Signup and view all the answers

How is vitamin D3 synthesized from cholesterol?

<p>By dehydrogenation of cholesterol followed by UV radiation. (C)</p> Signup and view all the answers

Which of the following fatty acids cannot be synthesized by the body?

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

What are the steroid hormones derived from cholesterol?

<p>Androgens, estrogens, progesterone, and corticoids. (B)</p> Signup and view all the answers

What proportion of cholesterol in plasma is present as cholesteryl esters?

<p>2/3 (C)</p> Signup and view all the answers

Which of the following is NOT a function of cholesterol?

<p>Storage of carbohydrates. (A)</p> Signup and view all the answers

What is the primary cause of Refsum's Disease?

<p>Deficiency of α-hydroxylase (D)</p> Signup and view all the answers

In which tissues does phytanic acid accumulate due to a deficiency of α-hydroxylase?

<p>Liver and nervous tissues (C)</p> Signup and view all the answers

Which systems are responsible for fatty acid synthesis?

<p>Cytosolic system and microsomal system (D)</p> Signup and view all the answers

What is the initial substrate used for de novo fatty acid synthesis?

<p>Acetyl-CoA (D)</p> Signup and view all the answers

Where does the cytosolic system for de novo fatty acid synthesis primarily occur?

<p>Liver and lactating mammary gland (D)</p> Signup and view all the answers

What occurs as a result of increased lipolysis during ketogenesis?

<p>Increased Acetyl CoA production (C)</p> Signup and view all the answers

Where does ketolysis primarily occur?

<p>In the mitochondria of extrahepatic tissues (A)</p> Signup and view all the answers

What is the primary consequence of increased ketogenesis in ketosis?

<p>Production of acetoacetate and β-hydroxybutyrate (B)</p> Signup and view all the answers

What is the role of succinyl-CoA in the process of ketolysis?

<p>It is necessary for the thiophorase reaction (D)</p> Signup and view all the answers

Which of the following substances is considered anti-ketogenic?

<p>Glucogenic amino acids (C)</p> Signup and view all the answers

Which molecule is produced from the conversion of β-hydroxybutyrate during ketolysis?

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

What is the maximum level of ketonemia considered physiological during a ketogenic diet?

<p>140 mg/dL (A)</p> Signup and view all the answers

What happens to the Krebs cycle during increased ATP production from ketogenesis?

<p>It becomes less active (D)</p> Signup and view all the answers

What is one of the main objectives of administering IV glucose during the management of ketosis?

<p>To help lower blood sugar levels (C)</p> Signup and view all the answers

What happens to acetyl CoA when oxaloacetate is absent and ATP levels are high?

<p>It is used for ketone body synthesis (B)</p> Signup and view all the answers

What is the initial substrate that combines with oxaloacetate to form citrate in the mitochondria?

<p>Acetyl-CoA (A)</p> Signup and view all the answers

Which enzyme converts citrate back into oxaloacetate and acetyl-CoA in the cytosol?

<p>ATP citrate lyase (A)</p> Signup and view all the answers

How many acetyl-CoA molecules are required for the synthesis of palmitic acid?

<p>8 (D)</p> Signup and view all the answers

Which of the following statements is true about malonyl-CoA?

<p>Malonyl-CoA inhibits carnitine palmitoyltransferase I. (C)</p> Signup and view all the answers

What is one source of NADPH used in fatty acid synthesis in the cytosol?

<p>Pentose Phosphate Pathway (C)</p> Signup and view all the answers

What is the primary source of acetyl CoA for ketogenesis?

<p>Oxidation of fatty acids (A)</p> Signup and view all the answers

What is the first step in the ketogenesis process?

<p>Conversion of Acetyl-CoA to Acetoacetyl-CoA (D)</p> Signup and view all the answers

Where does ketogenesis primarily occur in the body?

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

Which enzyme is responsible for the conversion of HMG-CoA to Acetoacetate?

<p>HMG-CoA Lyase (D)</p> Signup and view all the answers

What is the terminal product of β-hydroxybutyrate oxidation?

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

Which ketone body is produced from the spontaneous conversion of Acetoacetate?

<p>β-hydroxybutyrate (B)</p> Signup and view all the answers

Which substrate is required for the conversion of Acetoacetate to β-hydroxybutyrate?

<p>NADH+H^+ (B)</p> Signup and view all the answers

Which of the following is NOT a ketone body produced during ketogenesis?

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

Flashcards

Cholesterol's role in cell membranes

Cholesterol controls the flexibility of cell membranes.

Forms of cholesterol in lipoproteins

Plasma lipoproteins carry cholesterol in two forms: free cholesterol in the outer layer and cholesterol esters inside the core.

Cholesterol's role in Vitamin D3 synthesis

Vitamin D3 is made from cholesterol through a series of steps involving sunlight exposure.

Cholesterol as a precursor for steroid hormones

All steroid hormones (like testosterone, estrogen, and cortisol) are derived from cholesterol.

Signup and view all the flashcards

Cholesterol's role in bile acid formation

Bile acids, which help digest fat, are produced from cholesterol.

Signup and view all the flashcards

Ketosis

An excess of ketone bodies in the blood, leading to a decrease in pH.

Signup and view all the flashcards

Ketoacidosis

A condition characterized by high levels of ketone bodies in the blood, resulting in metabolic acidosis.

Signup and view all the flashcards

Ketogenesis

The process of producing ketone bodies from fatty acids.

Signup and view all the flashcards

Ketogenic Diet

A diet high in fat and low in carbohydrates, which forces the body to burn fat for fuel, resulting in the production of ketone bodies.

Signup and view all the flashcards

Physiological Ketosis

The physiological state of producing ketone bodies as a result of a ketogenic diet, with a normal pH level.

Signup and view all the flashcards

What is HMG-CoA reductase?

An enzyme that catalyzes the rate-limiting step in cholesterol synthesis.

Signup and view all the flashcards

How does insulin and glucagon regulate HMG-CoA reductase?

The active, dephosphorylated form of HMG-CoA reductase is stimulated by insulin, while the inactive, phosphorylated form is inhibited by glucagon.

Signup and view all the flashcards

How does cholesterol regulate its own synthesis?

Cholesterol acts as an allosteric inhibitor of HMG-CoA reductase, reducing its activity when cholesterol levels are high.

Signup and view all the flashcards

What is the role of AMPK in cholesterol synthesis?

AMP-activated protein kinase (AMPK) is activated during periods of low energy availability, leading to the phosphorylation and inactivation of HMG-CoA reductase.

Signup and view all the flashcards

How do statins work to lower cholesterol?

Statins are drugs that competitively inhibit HMG-CoA reductase, preventing cholesterol synthesis and lowering plasma cholesterol levels.

Signup and view all the flashcards

Acetyl-CoA Carboxylase (ACC)

The enzyme that converts acetyl-CoA to malonyl-CoA, a key step in fatty acid synthesis. It exists in two forms: active (dephosphorylated) and inactive (phosphorylated).

Signup and view all the flashcards

Hormonal Regulation of Fatty Acid Synthesis: Excess Glucose

This pathway converts excess glucose into fatty acids and ultimately triglycerides (TAG) during carbohydrate feeding.

Signup and view all the flashcards

Hormonal Regulation of Fatty Acid Synthesis: Anti-insulin Hormones

Hormones like glucagon and epinephrine inhibit ACC, ultimately reducing fatty acid synthesis.

Signup and view all the flashcards

Microsomal System for Fatty Acid Elongation

A system within the endoplasmic reticulum that elongates fatty acids by adding 2-carbon units from malonyl-CoA. It requires NADPH as a hydrogen donor, similar to de novo synthesis. However, it can only elongate existing fatty acids (C10-24) and cannot initiate de novo synthesis.

Signup and view all the flashcards

Essential Fatty Acids (EFA)

These fatty acids include linoleic acid (omega-6) and linolenic acid (omega-3) and they are essential because our bodies cannot synthesize them. They are required in our diet.

Signup and view all the flashcards

Regulation of Ketolysis

The availability of oxaloacetate, a molecule involved in the TCA cycle, controls the rate of ketolysis.

Signup and view all the flashcards

Importance of Ketone Bodies

Ketone bodies are an important alternate energy source during starvation.

Signup and view all the flashcards

Ketogenesis and Fatty Acid Oxidation

Ketogenesis, the process of making ketone bodies, is a preparatory step for the liver to fully oxidize fatty acids.

Signup and view all the flashcards

Glycerol kinase

An enzyme that catalyzes the conversion of glycerol to glycerol-3-phosphate. This process is crucial for triglyceride synthesis in the liver, kidneys, and intestinal mucosal cells.

Signup and view all the flashcards

Triacylglycerol

A molecule formed from glycerol and three fatty acids. It is the major form of energy storage in the body, found primarily in adipose tissue.

Signup and view all the flashcards

Dihydroxyacetone phosphate (DHAP)

A molecule produced during glycolysis, which serves as a precursor for glycerol-3-phosphate synthesis in adipose tissue. It is converted to glycerol-3-phosphate by a different pathway than in other tissues.

Signup and view all the flashcards

Triacylglycerol synthesis (Esterification)

The process of attaching fatty acids to glycerol-3-phosphate to form triacylglycerol. This process is essential for the storage of excess energy in the form of fat.

Signup and view all the flashcards

Phosphatidic acid (1,2-diacylglycerol-3-phosphate)

An intermediate in triacylglycerol synthesis that is formed by attaching two fatty acids to glycerol-3-phosphate. It is further converted to triacylglycerol by adding another fatty acid.

Signup and view all the flashcards

What is ketogenesis?

Ketogenesis is the body's process of producing ketone bodies (like acetoacetate and β-hydroxybutyrate) from fatty acids. This happens when the body's primary fuel source, glucose, is scarce, such as during starvation or uncontrolled diabetes.

Signup and view all the flashcards

How does ketogenesis occur?

When glucose is scarce, the body switches to utilizing fatty acids as fuel. This leads to increased fatty acid oxidation, generating an abundance of acetyl-CoA. However, without sufficient glucose, the Krebs cycle slows down, causing a buildup of acetyl-CoA. The liver then transforms this excess acetyl-CoA into ketone bodies.

Signup and view all the flashcards

What is ketolysis?

Ketolysis is the metabolic process where the body breaks down ketone bodies into usable energy. This occurs primarily in extrahepatic tissues (tissues other than the liver), as the liver lacks a key enzyme needed for this process.

Signup and view all the flashcards

How does ketolysis depend on the Krebs cycle?

The breakdown of ketone bodies requires the participation of the Krebs cycle (also known as the citric acid cycle). One essential component of this process is the enzyme thiophorase, which relies on succinyl-CoA provided by the Krebs cycle. This makes the functioning of the Krebs cycle crucial for ketolysis.

Signup and view all the flashcards

What is the final product of ketolysis?

β-hydroxybutyrate, a ketone body, is converted into acetoacetate, which then produces two molecules of acetyl-CoA. This acetyl-CoA can then enter the Krebs cycle for final energy generation.

Signup and view all the flashcards

Where does ketogenesis occur?

The liver is the primary site where ketone bodies are produced due to the presence of the enzymes HMG-CoA synthase and HMG-CoA lyase.

Signup and view all the flashcards

What are the main ketone bodies?

Acetoacetyl-CoA, β-hydroxybutyrate, and acetone are the three main ketone bodies.

Signup and view all the flashcards

What is the role of ketone bodies?

Ketone bodies are transported to other tissues, like muscles, and used as an alternative energy source when glucose is not readily available.

Signup and view all the flashcards

Why is fatty acid oxidation the main source of acetyl-CoA for ketogenesis?

Ketogenesis primarily utilizes acetyl-CoA from fatty acid oxidation because carbohydrates produce pyruvate, which generates oxaloacetate.

Signup and view all the flashcards

What enzymes are important in ketogenesis?

HMG-CoA synthase and HMG-CoA lyase are crucial enzymes in the process.

Signup and view all the flashcards

When is ketogenesis important?

In certain situations like prolonged fasting or a low-carbohydrate diet, the body relies on ketone bodies for energy.

Signup and view all the flashcards

β-oxidation

The process of breaking down fatty acids by removing two-carbon units at a time, starting from the carboxyl end.

Signup and view all the flashcards

Refsum's Disease

A rare genetic disorder caused by a deficiency of α-hydroxylase, leading to the accumulation of phytanic acid in the body.

Signup and view all the flashcards

De Novo Fatty Acid Synthesis

The process of synthesizing new fatty acids from acetyl-CoA units, primarily in the liver and lactating mammary gland.

Signup and view all the flashcards

HMG-CoA reductase

A molecule that regulates the rate-limiting step in cholesterol synthesis, which is catalyzed by HMG-CoA reductase.

Signup and view all the flashcards

How does Acetyl-CoA get from the mitochondria to the cytosol?

Acetyl-CoA, produced in the mitochondria, cannot directly cross into the cytosol for fatty acid synthesis. It combines with oxaloacetate to form citrate, which is then transported out. In the cytosol, citrate is broken back down to regenerate acetyl-CoA.

Signup and view all the flashcards

What is Acetyl-CoA Carboxylase (ACC)?

This enzyme catalyzes the first committed step in fatty acid synthesis by converting acetyl-CoA to malonyl-CoA, a vital 2-carbon building block. It is regulated by hormones and cellular energy levels.

Signup and view all the flashcards

What is Fatty Acid Synthase (FAS)?

This large multi-enzyme complex, located in the cytosol, is responsible for synthesizing palmitic acid (a 16-carbon saturated fatty acid) from acetyl-CoA units. It also utilizes NADPH for the process.

Signup and view all the flashcards

Where does the NADPH for fatty acid synthesis come from?

The pentose phosphate pathway (HMP), malic enzyme, and cytosolic isocitrate dehydrogenase (DH) all contribute to the production of NADPH, which is essential for fatty acid synthesis.

Signup and view all the flashcards

How does malonyl-CoA control fatty acid metabolism?

Malonyl-CoA, the product of acetyl-CoA carboxylase (ACC), inhibits carnitine palmitoyltransferase I (CPT I), preventing fatty acids from entering the mitochondria for breakdown. This creates a balance between fatty acid synthesis and breakdown.

Signup and view all the flashcards

Study Notes

Regulation of Cholesterol Synthesis

  • Key enzyme: HMG-CoA reductase is the rate-limiting reaction
  • Enzyme activity is controlled by reversible phosphorylation/dephosphorylation.
    • The active form (a) is dephosphorylated
    • Phosphorylation is catalyzed by AMP-activated protein kinase (AMPK).

1. Hormonal Regulation

  • Feeding and insulin

    • Insulin stimulates cholesterol synthesis
    • Insulin acts as an inducer for HMG-CoA reductase gene
    • Activates protein phosphatase which catalyze dephosphorylation of HMGCoA reductase
  • Fasting and glucagon

    • Glucagon acts as a repressor for HMGCoA reductase.

2. Allosteric Regulation

  • Cholesterol is a group of drugs that act through competitive inhibition of HMG-CoA reductase (structural analogs to HMG-CoA) and help to lower plasma cholesterol.
    • Statins are a group of drugs that act through competitive inhibition of HMG-CoA reductase (structural analogs to HMG-CoA) and help to lower plasma cholesterol

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

More Like This

Ketone Bodies and Ketonuria Quiz
18 questions
Ketone Bodies  lec 3
8 questions

Ketone Bodies lec 3

WellBacklitOgre8953 avatar
WellBacklitOgre8953
Use Quizgecko on...
Browser
Browser