Biochemistry: Role of NADH and ATP Production
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Questions and Answers

What is the role of NADH in biochemical reactions?

  • It solely facilitates the synthesis of RNA.
  • It serves as a hydride donor in oxidation-reduction reactions. (correct)
  • It is a byproduct of aerobic respiration.
  • It acts as a primary substrate for energy production.

Which of the following statements about NADP+/NADPH is correct?

  • NADP+ differs from NAD+ by having an esterified phosphate. (correct)
  • NADPH only exists in the oxidized state.
  • Both NADP+ and NAD+ can donate electrons equally.
  • NADPH is primarily involved in catabolic pathways.

How many electrons and protons are accepted by the nicotinamide ring to form NADH?

  • 1 electron and 1 proton.
  • 2 protons and no electrons.
  • 3 electrons only.
  • 2 electrons and 1 proton. (correct)

What compound does the reduction of NAD+ produce along with the acceptance of electrons?

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

Which of the following accurately describes the electron transfer reaction for NAD+?

<p>NAD+ + 2e− + H+ ↔ NADH. (A)</p> Signup and view all the answers

How many ATP molecules are produced from one glucose molecule during cellular respiration?

<p>38 ATP molecules (C)</p> Signup and view all the answers

What role does NADH play in the regulation of the TCA cycle?

<p>It inhibits the majority of cycling enzymes (A)</p> Signup and view all the answers

Which molecule provides feedback inhibition on phosphofructokinase, affecting glycolysis?

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

Where is the electron transport chain located in the cell?

<p>On the inner mitochondrial membrane (A)</p> Signup and view all the answers

What is the process called when ATP is synthesized from the energy released by the oxidation of hydrogen carriers?

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

What is the primary function of ATP in cells?

<p>To store and transfer energy (C)</p> Signup and view all the answers

What process weakens and breaks the last phosphate bond in ATP?

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

How do cells continuously generate ATP?

<p>By breaking down energy-rich glucose (A)</p> Signup and view all the answers

What is the estimated number of ATP molecules generated and consumed by a single cell per second?

<p>10 million (C)</p> Signup and view all the answers

What type of reaction is the hydrolysis of ATP categorized as?

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

What is the primary function of anabolic pathways in metabolism?

<p>To consume energy and synthesize complex molecules (B)</p> Signup and view all the answers

What is released during the endergonic process of dehydration synthesis involving ADP?

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

Which of the following describes catabolic pathways?

<p>They release energy by decomposing complex molecules. (D)</p> Signup and view all the answers

Which molecule acts as an electron acceptor in catabolic pathways?

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

What type of reaction occurs during photosynthesis?

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

What type of bond in ATP contains the most energy?

<p>Last phosphate bond (C)</p> Signup and view all the answers

What is the role of ATP in cellular metabolism?

<p>It acts as a primary energy carrier in cells. (B)</p> Signup and view all the answers

Which process represents an exergonic reaction?

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

What is the significance of the Citric Acid Cycle in cellular metabolism?

<p>It plays a crucial role in extracting energy from carbohydrates. (D)</p> Signup and view all the answers

What distinguishes endergonic reactions from exergonic reactions?

<p>Endergonic reactions require a net input of energy. (B)</p> Signup and view all the answers

Which of the following describes potential energy in the context of bioenergetics?

<p>Energy stored in chemical bonds of molecules. (D)</p> Signup and view all the answers

What is the primary role of FAD in biochemical reactions?

<p>To serve as an e− acceptor (C)</p> Signup and view all the answers

What distinguishes NAD+ from FAD?

<p>NAD+ reversibly binds to enzymes whereas FAD remains tightly bound (D)</p> Signup and view all the answers

During one turn of the citric acid cycle, how many molecules of NADH are produced?

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

What is the net output of carbon dioxide from one triboxylic cycle?

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

Which statement is true regarding the function of FAD?

<p>FAD undergoes reduction to form FADH2 (A)</p> Signup and view all the answers

Where are the enzymes of the citric acid cycle located?

<p>In the matrix of the mitochondria (C)</p> Signup and view all the answers

How does the dimethylisoalloxazine ring function in FAD?

<p>It undergoes reduction/oxidation (D)</p> Signup and view all the answers

What is the general flow of substrates in the mitochondria during the citric acid cycle?

<p>Substrates flow across both the outer and inner membranes (C)</p> Signup and view all the answers

Flashcards

What is Bioenergetics?

The study of how energy is used and transformed in living organisms.

What is Kinetic Energy?

Energy associated with motion. Examples include heat and light.

What is Potential Energy?

Energy stored in an object's position or state. Examples include chemical bonds.

What are Endergonic Reactions?

Reactions that require energy input to proceed. Building complex molecules.

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What are Exergonic Reactions?

Reactions that release energy as they proceed. Breaking down complex molecules.

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What is Metabolism?

The sum of all chemical reactions occurring within a cell.

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What are Anabolic Pathways?

Metabolic reactions that build complex molecules from simpler ones, requiring energy input.

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What are Catabolic Pathways?

Metabolic reactions that break down complex molecules into simpler ones, releasing energy.

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Ribose

A five-carbon sugar that forms part of the structure of ATP.

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Phosphate Group (ATP)

A chain of three phosphate groups attached to a ribose sugar molecule in ATP. Each phosphate bond stores a significant amount of energy.

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Phosphorylation

The breaking of a chemical bond in ATP to release energy. This process is essential for cellular functions.

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ATP-ase

A type of enzyme that helps break down ATP by removing the last phosphate group, releasing energy.

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Adenosine Triphosphate (ATP)

The high-energy molecule used by cells to power various processes. Consists of adenine, ribose sugar, and three phosphate groups.

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Coupled Reaction

A type of chemical reaction where the energy released from an exergonic reaction is used to drive an endergonic reaction. ATP plays a key role in these reactions .

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Hydrolysis of ATP

The process where a water molecule is added to ATP, breaking the last phosphate bond and releasing energy.

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Dehydration of ATP

The process of removing a water molecule from ADP and a phosphate group, reforming ATP and requiring energy.

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What is NAD+ and its role in metabolism?

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme essential for many metabolic reactions. It carries electrons and hydrogen ions, accepting two electrons and one proton (a hydride) to become its reduced form, NADH. NADH is an important electron carrier in reducing reactions, such as those in the electron transport chain.

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What is NADP+ and how does it differ from NAD+?

Nicotinamide adenine dinucleotide phosphate (NADP+) is a coenzyme similar to NAD+, but with an additional phosphate group. It's involved in biosynthesis pathways, serving as an electron donor in anabolic reactions.

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Summarize the electron transfer between NAD+ and NADH.

The electron transfer reaction involving NAD+ and its reduced form, NADH, can be summarized as a reversible equilibrium reaction. In this reaction, NAD+ gains two electrons (e-) and one proton (H+) to become NADH, while NADH loses two electrons and one proton to become NAD+.

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Why are NAD+ and NADH important in metabolism?

NAD+ and NADH are cofactors in many enzymatic reactions, particularly those involving oxidation-reduction reactions. They are critical for energy production (ATP synthesis) and metabolic processes.

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FADH₂

A molecule of reduced nicotinamide adenine dinucleotide, a coenzyme that carries electrons in cellular respiration, produced during the Krebs cycle.

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GTP

Guanosine-5'-triphosphate, a molecule that carries energy, produced during the Krebs cycle.

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The Krebs cycle

A metabolic pathway that occurs in the mitochondria, breaking down pyruvate into carbon dioxide, generating energy carriers like NADH and FADH₂, and producing ATP.

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Electron Transport Chain (ETC)

This is the final stage of aerobic respiration, where energy carriers NADH & FADH₂ are oxidised to create ATP.

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Oxidative phosphorylation

The process of making ATP using the energy from the oxidation of hydrogen carriers. It occurs during the ETC in mitochondria.

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What is NAD+?

A coenzyme that reversibly binds to enzymes, helping them catalyze reactions. It shuttles electrons and protons during energy production, like in cellular respiration.

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What is FAD?

A prosthetic group tightly bound to enzymes, particularly involved in the citric acid cycle. It accepts electrons and protons, helping transfer energy.

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What is NADH?

The reduced form of NAD+, representing its gain of electrons and a proton, carrying energy.

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What is FADH2?

The reduced form of FAD, indicating its acceptance of electrons and protons. It's the energy-carrying state.

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What is the mitochondria?

The primary location within cells for the Citric Acid Cycle (Krebs Cycle). It's where energy is extracted from food molecules.

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What is the Citric Acid Cycle?

A series of chemical reactions in mitochondria that break down glucose, producing energy in the form of ATP and reducing power (NADH and FADH2).

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What is ATP?

A molecule that carries and stores chemical energy within cells, providing power for various cellular functions.

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What is glycolysis?

The breakdown of glucose to pyruvate, producing a small amount of ATP and reducing power (NADH). It's the first stage of cellular respiration, occurring in the cytoplasm.

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Study Notes

Bioenergetics Overview

  • Bioenergetics is the study of energy in living systems and the role of organisms (plants and animals) that utilize them.
  • Energy is essential for all organisms. This energy can be either kinetic or potential.

Energy Types

  • Kinetic energy is the energy of motion. Examples include heat and light energy.
  • Potential energy is the energy of position. This includes energy stored within chemical bonds.

Types of Energy Reactions

  • Endergonic reactions require a net input of energy. An example of an endergonic reaction is photosynthesis, where light energy is used to convert carbon dioxide and water into glucose and oxygen. The equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
  • Exergonic reactions release energy. An example of an exergonic reaction is cellular respiration, where glucose and oxygen are used to produce carbon dioxide, water, and ATP. The equation is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Metabolism

  • Metabolism is the sum of all chemical activities of all cells.
  • Anabolic pathways consume energy to build complex molecules from simpler molecules. Photosynthesis is an example.
  • Catabolic pathways release energy breaking down complex molecules into simpler molecules. Cellular respiration is an example.

ATP (Adenosine Triphosphate)

  • ATP is the primary energy currency of cells.
  • ATP is composed of adenine, ribose (a five-carbon sugar), and three phosphate groups.
  • The high-energy bonds between the phosphate groups store a large amount of energy.
  • Cells continually break down and rebuild ATP.

ATP Breakdown

  • ATP is broken down by a process called hydrolysis releasing energy and the phosphate group PO₄.
  • The enzyme ATPase weakens and breaks the bond between the last phosphate group (PO₄) and the rest of the ATP molecule.
  • ATP is the form which cells store energy produced from breaking down energy rich glucose.

ATP Usage

  • Approximately 10,000,000 molecules of ATP are generated and then consumed per second by each cell.

Coupled Reaction

  • ATP hydrolysis (exergonic reaction) powers endergonic reactions by transferring a phosphate group to another molecule, providing the energy.

Hydrolysis of ATP

  • ATP + H₂O → ADP + P (exergonic)
  • Hydrolysis releases substantial energy.

ATP - Dehydration

  • ADP + P → ATP + H₂O (endergonic)
  • Dehydration stores energy.

NAD+/NADH

  • NAD+ is an electron carrier in catabolic pathways, accepting two electrons and a proton to form NADH.
  • NADH is important in electron transport and energy release.
  • NADP+/NADPH is similar to NAD+, but differs in one phosphate group. NADPH is an electron donor in synthetic pathways.

FAD/FADH2

  • FAD (Flavin adenine dinucleotide) is another electron carrier, derived from the vitamin riboflavin.
  • FAD accepts two electrons and two protons to form FADH2 for energy release

Coenzyme vs Prosthetic group

  • NAD+ is a coenzyme, it reversibly (temporarily) binds to enzymes.
  • FAD is a prosthetic group, it permanently binds to enzymes and stays attached during reactions.

Cellular Respiration Process

  • Glucose → Pyruvic acid (Glycolysis) → Krebs Cycle → Electron Transport Chain
  • 2 ATP from glycolysis - 36 ATP from ETC

TCA Cycle (Tri carboxylic acid cycle)

  • The citric acid cycle is a metabolic cycle that occurs in the inner matrix of the mitochondria.
  • Each turn of the citric acid cycle produces two molecules of carbon dioxide, three molecules of NADH, one FADH₂, one GTP, and three H+ ions.
    • A single glucose molecule produces double the output of the TCA cycle's net output (because two molecules of pyruvate are produced from a single molecule of glucose and the two molecules of pyruvate make two acetyl coAs and then enter the cycle)
  • The citric acid cycle is regulated by metabolites (products of the cycle) providing negative feedback to enzymes in the cycle.

ETC (Electron Transport Chain)

  • ETC is on the inner mitochondrial membrane (Cristae).
  • High energy electrons are transferred through proteins (complex I-IV) across the membrane.
  • This process creates a proton motive force (PMF), and this force drives the synthesis of ATP. This is Oxidative phosphorylation.
  • Oxygen is the final acceptor of electrons

ATP per glucose molecule

  • One glucose molecule is metabolized to yield 38 ATP molecules during cellular respiration.
  • The electron transport system produces 34 molecules of ATP out of a total of 38 molecules.

Regulation of TCA Cycle

  • The TCA cycle is regulated in several ways, including through negative feedback loops involving pathway products.
  • Citrate, for example, inhibits the enzyme phosphofructokinase, which is involved in glycolysis.
  • Calcium also stimulates the TCA cycle.

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This quiz explores the crucial roles of NADH and NADPH in biochemical reactions, the electron transport chain, and ATP synthesis. Questions cover the processes involved in cellular respiration and how energy is generated in cells. Test your knowledge on these key biochemical concepts!

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