Cellular Respiration Quiz
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Questions and Answers

What is the primary reason tumour cells convert a large amount of glucose to lactate, even with sufficient oxygen?

  • To maximize ATP production through oxidative phosphorylation
  • To enhance fat metabolism
  • To facilitate the citric acid cycle
  • Due to the Warburg effect (correct)

What pharmacological strategy is being considered for obesity treatment concerning brown adipose tissue?

  • Increasing UCP1 expression/activity (correct)
  • Lowering lactate production
  • Enhancing oxidative phosphorylation
  • Decreasing glucose uptake

Which metabolic pathway do tumour cells primarily use to produce energy?

  • Both glycolysis and oxidative phosphorylation with lactate conversion (correct)
  • Oxidative phosphorylation only
  • Glycolysis alone
  • Lactate fermentation exclusively

When comparing glycolysis and oxidative phosphorylation, which statement is true about ATP production?

<p>Oxidative phosphorylation produces more ATP than glycolysis (D)</p> Signup and view all the answers

Which of the following accurately describes the fate of pyruvate in tumour cells under aerobic conditions?

<p>It is transformed into lactate preferentially (B)</p> Signup and view all the answers

What is the primary purpose of cellular respiration?

<p>To release energy from glucose as ATP (D)</p> Signup and view all the answers

Which metabolic pathway is used by cells to directly produce ATP?

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

What strategy might inhibit the growth of tumors in cancer cells?

<p>Shifting from aerobic glycolysis to oxidative phosphorylation (B)</p> Signup and view all the answers

What does ATP primarily provide for cellular processes?

<p>Chemical energy to drive reactions (D)</p> Signup and view all the answers

What is released when ATP is hydrolyzed?

<p>ADP and inorganic phosphate (B)</p> Signup and view all the answers

What role does thermogenesis play in energy metabolism?

<p>It uncouples respiration from ATP synthesis. (D)</p> Signup and view all the answers

What type of bond does ATP utilize to store energy?

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

What is a consequence of shifting cellular metabolism to glycolysis during ischemic injury?

<p>Inhibition of oxidative damage (D)</p> Signup and view all the answers

What does DHAP convert to during glycolysis?

<p>Glyceraldehyde-3-phosphate (D)</p> Signup and view all the answers

What is the end product of glyceraldehyde-3-phosphate in the energy-releasing phase of glycolysis?

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

How many ATP molecules are generated from one molecule of glyceraldehyde-3-phosphate?

<p>4 ATP (D)</p> Signup and view all the answers

During which phase of glycolysis is ADP phosphorylated?

<p>Energy-releasing phase (C)</p> Signup and view all the answers

What is released during the decarboxylation of pyruvate?

<p>CO2 (C)</p> Signup and view all the answers

What happens to NAD+ during the conversion of glyceraldehyde-3-phosphate?

<p>It is reduced (D)</p> Signup and view all the answers

What type of reaction primarily describes the conversion of glyceraldehyde-3-phosphate in glycolysis?

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

What is formed when pyruvate is oxidized after decarboxylation?

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

What is the primary function of energy released in an exergonic reaction?

<p>To add a phosphate group to ADP, regenerating ATP (B)</p> Signup and view all the answers

What is substrate level phosphorylation?

<p>The transfer of a phosphate group directly from a substrate to ADP (D)</p> Signup and view all the answers

Which type of work can ATP power after transferring its phosphate group?

<p>Transport, mechanical, or chemical work depending on the molecule (A)</p> Signup and view all the answers

What is the relationship between oxidation and reduction reactions?

<p>One substance is oxidized while another is reduced in a coupled process (A)</p> Signup and view all the answers

In which forms does NAD exist related to its role in cellular respiration?

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

What happens to energy when NAD+ is reduced to NADH?

<p>Energy is stored for later use (A)</p> Signup and view all the answers

Which of the following statements about oxidative phosphorylation is accurate?

<p>It involves the transfer of electrons through a series of carriers (B)</p> Signup and view all the answers

Why do oxygen and carbon tend to 'hog' electrons in biochemical reactions?

<p>They have high electronegativity (D)</p> Signup and view all the answers

What is the role of NAD+ in metabolic reactions?

<p>Functions as an electron carrier (D)</p> Signup and view all the answers

During the process of glycolysis, what are the end products formed from one glucose molecule?

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

What occurs to the hydrogen ions during the oxidation of a molecule?

<p>One is released and one is captured by NAD+ (B)</p> Signup and view all the answers

What type of phase does glycolysis include?

<p>Energy-requiring and energy-releasing phases (C)</p> Signup and view all the answers

What is the first step of the energy-requiring phase of glycolysis?

<p>Phosphate group transferred from ATP to glucose (B)</p> Signup and view all the answers

What does fructose-1,6-bisphosphate split into during glycolysis?

<p>Two three-carbon sugars: DHAP and glyceraldehyde-3-phosphate (C)</p> Signup and view all the answers

What is generated during the energy-releasing phase of glycolysis?

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

What describes the isomers formed during glycolysis?

<p>They have the same chemical formula but different structures (A)</p> Signup and view all the answers

Which process is significantly faster in generating ATP from glucose?

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

What is the ATP yield from complete oxidative phosphorylation of glucose?

<p>36-38 ATP (B)</p> Signup and view all the answers

Which metabolite produced from glucose is essential for nucleotide and protein biosynthesis?

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

What strategy do tumour cells employ concerning glucose metabolism?

<p>Prioritizing aerobic glycolysis for survival (D)</p> Signup and view all the answers

How does high glucose consumption in tumour cells affect surrounding cells?

<p>Limits availability of glucose to other cells (A)</p> Signup and view all the answers

What is the relationship between glucose metabolism and protein translation in tumour cells?

<p>Glucose metabolism provides substrates for protein translation (D)</p> Signup and view all the answers

Why might tumour cells prefer aerobic glycolysis over complete oxidation of glucose?

<p>It is faster and provides necessary metabolites (D)</p> Signup and view all the answers

What is a potential consequence of the metabolic preferences of tumour cells?

<p>Increased nutrient competition with immune cells (C)</p> Signup and view all the answers

Flashcards

Cellular Respiration

A series of reactions breaking down glucose to produce ATP (energy).

ATP

Adenosine triphosphate; the cell's energy currency.

Glycolysis

A metabolic pathway releasing energy from glucose.

Pyruvate oxidation

Conversion of pyruvate into acetyl-CoA, preparing for the citric acid cycle.

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Citric Acid Cycle

A series of reactions producing NADH and FADH2, essential for ATP production.

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Oxidative Phosphorylation

Process making most ATP from NADH and FADH2 using electron transport chain and chemiosmosis.

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Energy Currency of the cell

ATP, which provides energy for cellular processes in the body.

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Metabolic pathway

Series of chemical reactions leading to a specific product (like cellular respiration).

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Exergonic Reaction

A reaction that releases energy, which can be used to regenerate ATP from ADP by adding a phosphate group.

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Substrate-level Phosphorylation

A method to generate ATP wherein a phosphate group is directly transferred from a substrate to ADP.

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ATP Function

ATP powers cellular work via transfer of a phosphate group to another molecule.

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Oxidation

The loss of electrons (or hydrogen) from a molecule.

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Reduction

The gain of electrons (or hydrogen) by a molecule.

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NAD+/NADH

Coenzyme that carries electrons (hydrogen) in cellular respiration.

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Brown Adipose Tissue

A type of fat tissue that burns energy to produce heat, helping regulate body temperature. It plays a crucial role in thermogenesis, especially in newborns and during cold exposure.

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Warburg Effect

The phenomenon observed in cancer cells where they preferentially use glycolysis to produce ATP even in the presence of oxygen, leading to increased lactate production.

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Tumors and Glucose

Tumors consume enormous amounts of glucose, relying heavily on glycolysis for energy production.

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Glycolysis vs. Oxidative Phosphorylation

Glycolysis is a faster energy pathway producing less ATP compared to oxidative phosphorylation, which is more efficient but slower.

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Hydride ion

A negatively charged hydrogen ion (H-) that carries two electrons. It's transferred during oxidation-reduction reactions.

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Energy-requiring phase of glycolysis

The initial steps of glycolysis where energy is invested in the form of ATP. Glucose is modified and prepared for splitting.

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Energy-releasing phase of glycolysis

The later steps of glycolysis where energy is released in the form of ATP and NADH. Pyruvate is produced as a byproduct.

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Glucose-6-phosphate

A modified form of glucose with a phosphate group attached, created during the first step of glycolysis.

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Fructose-6-phosphate

An isomer of glucose-6-phosphate, formed during the second step of glycolysis.

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Fructose-1,6-bisphosphate

A molecule with two phosphate groups attached, formed during the third step of glycolysis. It's unstable and readily splits.

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DHAP to G3P

Dihydroxyacetone phosphate (DHAP) is easily converted to glyceraldehyde-3-phosphate (G3P), which then enters the energy-releasing phase of glycolysis.

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Energy-Releasing Phase

The second phase of glycolysis where glyceraldehyde-3-phosphate is converted into pyruvate, producing energy in the form of ATP and NADH.

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G3P to Pyruvate

Glyceraldehyde-3-phosphate, generated in the first phase of glycolysis, is converted into pyruvate, resulting in the production of 4 ATP and 2 NADH.

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NAD+ Reduction

During glycolysis, NAD+ is reduced to NADH, accepting electrons (and hydrogen) released from the oxidation of glyceraldehyde-3-phosphate.

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Pyruvate Transport

After glycolysis, pyruvate is transported from the cytoplasm into the mitochondria, where it will undergo further breakdown.

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Pyruvate Decarboxylation

Pyruvate undergoes decarboxylation, removing a carbon dioxide (CO2) molecule, resulting in a two-carbon molecule.

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Acetyl Group Formation

The two-carbon molecule from decarboxylated pyruvate is oxidized to form an acetyl group, while NAD+ is reduced to NADH.

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Pyruvate Oxidation Summary

Pyruvate oxidation is the conversion of pyruvate to acetyl-CoA, releasing CO2 and producing NADH, preparing for the citric acid cycle.

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Aerobic glycolysis

A metabolic process where glucose is partially broken down to lactate in the presence of oxygen, generating ATP quickly.

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Tumor cell energy preference

Tumor cells favor aerobic glycolysis over complete glucose oxidation (oxidative phosphorylation) for ATP production.

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Advantages of aerobic glycolysis for tumors

Aerobic glycolysis provides fast ATP production and additional glucose-derived metabolites needed for cell growth and proliferation.

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Glucose consumption by tumors

Tumors consume large amounts of glucose, limiting its availability for other cells (including immune cells) in the body.

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Why is aerobic glycolysis faster than complete glucose oxidation?

Aerobic glycolysis is faster because it involves fewer steps and doesn't require the complex machinery of oxidative phosphorylation.

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ATP produced by aerobic glycolysis vs. complete glucose oxidation

Aerobic glycolysis produces significantly less ATP (4 molecules) compared to complete glucose oxidation (36-38 molecules).

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Glucose-derived metabolites

Molecules produced during glucose metabolism that can be used for building other essential components (like nucleotides, lipids, and proteins).

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Impact of glucose consumption by tumors on other cells

High glucose consumption by tumors can negatively impact other cells by limiting their access to this vital energy source.

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Study Notes

Cellular Respiration

  • Cellular respiration is a metabolic pathway where cells release energy from glucose, producing ATP.
  • Cells can switch between glycolysis and oxidative phosphorylation, depending on energy needs.
  • This flexibility in metabolism is crucial for cells and impacts therapeutic strategies.

ATP: The Energy Currency of the Cell

  • ATP (adenosine triphosphate) is a nucleotide with a nitrogenous base (nucleobase), a five-carbon sugar (pentose), and one to three phosphates.
  • ATP stores energy in high-energy phosphoanhydride bonds.
  • Hydrolysis of ATP (breaking a bond) releases energy, converting ATP to ADP and a phosphate group (Pi).
  • Cells constantly use ATP, so it must be replenished. This uses energy from exergonic reactions to rebuild the ATP from ADP.

Mechanisms for Generating ATP

  • Substrate-level phosphorylation: Phosphate is directly transferred from a substrate to ADP, forming ATP.

    • This occurs in glycolysis and the citric acid cycle.

  • Oxidative phosphorylation: This process produces a significant amount of ATP.

    • Electrons are transferred through a series of protein complexes in the inner mitochondrial membrane (electron transport chain). This movement releases energy.
    • This energy is used to pump H+ ions (protons) across the inner membrane, creating a concentration gradient
    • The flow of hydrogen ions back through a protein called ATP synthase, provides the energy to add a phosphate group to ADP, and create ATP

Oxidation and Reduction

  • Oxidation and reduction reactions are always coupled.
    • Oxidation is the removal of electrons (and sometimes hydrogen ions).
    • Reduction is the gain of electrons (and sometimes hydrogen ions).
  • The transfer of electrons between molecules is a vital part of energy production.

NAD+/NADH

  • NAD+ (nicotinamide adenine dinucleotide) is a coenzyme crucial for cellular respiration.
  • NAD+ can exist in oxidized (NAD+) and reduced (NADH) forms.
  • Energy is stored when NAD+ is reduced to NADH.
  • Energy is released when NADH is re-oxidized to NAD+.

Glycolysis

  • Occurs in the cytosol.
  • Begins with glucose and produces two molecules of pyruvate.
  • Consists of both energy-requiring and energy-releasing phases.
  • Net gain of 2 ATP and 2 NADH molecules.

Pyruvate Oxidation

  • Pyruvate is transported into the mitochondria.
  • A carboxyl group is removed from pyruvate, releasing carbon dioxide (CO2).
  • The remaining two-carbon molecule is oxidized to form an acetyl group.
  • NAD+ is reduced to NADH, and the acetyl group is attached to coenzyme A (CoA), forming acetyl CoA.
  • This prepares the acetyl CoA for entry into the citric acid cycle.

Citric Acid Cycle

  • Also known as the Krebs cycle.
  • Occurs in the mitochondrial matrix.
  • A series of oxidation-reduction and decarboxylation reactions. A product of the cycle is CO2.
  • NAD+ and FAD are reduced to NADH and FADH2, respectively
  • 1 ATP is produced per cycle.
  • An important role for this process is that it provides starting materials for later reactions in cellular respiration

Oxidative Phosphorylation

  • Occurs in the inner mitochondrial membrane.
  • Uses an electron transport chain to generate ATP.
  • Electron carriers (like NADH and FADH2) release energy as they transfer electrons.
  • This energy is used to pump protons (H+) across the inner mitochondrial membrane, generating a proton gradient.
  • ATP synthase uses the flow of protons back across the membrane to generate ATP.

What if Oxygen is Limited?

  • In the absence of oxygen, cells can use fermentation to produce ATP.
  • Lactic acid fermentation is one example in humans. In this case, pyruvate is reduced to lactate.

Glucose metabolism in Tumor Cells

  • Cancer cells often utilize a higher rate of glycolysis (the Warburg effect).
  • This is fast enough to produce ATP, even in the presence of adequate oxygen, compared to using the more complete oxidative phosphorylation pathway.
  • Increased glycolysis creates a rapid supply of glucose-derived molecules, needed building blocks for proteins, lipids and nucleic acids.
  • This increased glucose uptake allows for increased growth and proliferation of tumor cells.

Other Relevant Points

  • Brown adipocytes use uncoupling protein 1 (UCP1).
    • Instead of going through the ATP synthase process to produce ATP, these cells use UCP1 to dissipate the proton gradient by a different mechanism. This releases energy as heat.
  • This is important for maintaining body temperature.
  • Pharmacological activation of thermogenesis in brown adipose tissue using UCP1 might be useful in therapeutic strategies for obesity.

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PL1003 Cellular Respiration PDF

Description

Test your understanding of cellular respiration, focusing on ATP generation, metabolic pathways, and mechanisms like substrate-level phosphorylation. Explore how cells utilize glucose to produce energy efficiently and the significance of ATP as the energy currency in various cellular processes.

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