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Questions and Answers

What is the net gain of ATP during glycolysis?

  • 0 ATP
  • 2 ATP (correct)
  • 4 ATP
  • 6 ATP

    • Which enzyme catalyzes the first regulatory step of glycolysis?

  • Fructose kinase
  • Hexokinase (correct)
  • Pyruvate kinase
  • Phosphofructokinase

    • What inhibits the enzyme phosphofructokinase in glycolysis?

  • High levels of ADP
  • Low levels of glucose-6-phosphate
  • High levels of AMP
  • High levels of ATP (correct)

    • In which cells is fructose converted to fructose-6-phosphate?

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

    What is the role of 1,3-bisphosphoglycerate in glycolysis?

    <p>It provides phosphate groups for ATP production. (C)</p> Signup and view all the answers

    What is a key feature of the regulatory steps in glycolysis?

    <p>They have large negative ΔG values and are essentially irreversible. (B)</p> Signup and view all the answers

    Which compound provides the phosphate group in the formation of ATP during the second half of glycolysis?

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

    Which statement about glycolysis and insulin regulation is true?

    <p>Insulin has no effect on fructose metabolism. (A)</p> Signup and view all the answers

    What is formed when acetoacetate undergoes oxidation?

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

    Which enzyme activates protein digestion in the stomach?

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

    Which of the following is NOT an end product of protein digestion?

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

    What is the primary function of proteins in the body?

    <p>Provide amino acids for protein synthesis (C)</p> Signup and view all the answers

    What happens during the process of transamination?

    <p>An amino group is transferred from an amino acid to an α-keto acid (D)</p> Signup and view all the answers

    Which product is formed when acetoacetate goes through decarboxylation?

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

    During digestion, trypsin is primarily responsible for hydrolyzing which type of molecule?

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

    Which of the following compounds are products of fatty acid digestion?

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

    What is the primary purpose of catabolic reactions in metabolism?

    <p>To break down large molecules for energy. (C)</p> Signup and view all the answers

    What characterizes a cyclic metabolic pathway?

    <p>It regenerates the first reactant after a series of reactions. (A)</p> Signup and view all the answers

    Which stage of metabolism primarily involves breaking down large molecules to smaller ones?

    <p>Stage 1: Digestion and hydrolysis. (D)</p> Signup and view all the answers

    Where does the oxidation of small molecules occur in the process of energy production?

    <p>In the citric acid cycle and electron transport chain. (C)</p> Signup and view all the answers

    How is energy stored in the cells after metabolizing food?

    <p>As adenosine triphosphate (ATP). (A)</p> Signup and view all the answers

    What role do NADH and FADH2 play in metabolism?

    <p>They carry electrons for ATP synthesis. (A)</p> Signup and view all the answers

    What is the composition of the outer membrane of mitochondria?

    <p>50% lipid and 50% protein. (C)</p> Signup and view all the answers

    What is the role of organelles within the cell?

    <p>To carry out specific cellular functions. (A)</p> Signup and view all the answers

    What happens to fructose and galactose in the liver?

    <p>They are converted to glucose. (C)</p> Signup and view all the answers

    What is the primary purpose of glycolysis?

    <p>To degrade glucose to pyruvate. (A)</p> Signup and view all the answers

    Where does glycolysis take place within the cell?

    <p>In the cytoplasm. (D)</p> Signup and view all the answers

    What is the nature of glycolysis in terms of oxygen requirement?

    <p>It is anaerobic and does not require oxygen. (B)</p> Signup and view all the answers

    What characterizes the energy-investment phase of glycolysis?

    <p>Phosphate groups are added to glucose. (D)</p> Signup and view all the answers

    How many ATP molecules are produced during the energy-production phase of glycolysis?

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

    What is the process of substrate-level phosphorylation?

    <p>It involves the direct transfer of a phosphate group to ADP. (A)</p> Signup and view all the answers

    Which of the following molecules are produced from glucose in the glycolysis pathway?

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

    What is the product formed when the carbamoyl group is transferred to ornithine?

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

    In which part of the cell does citrulline combine with aspartate during the urea cycle?

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

    What energy source is utilized during the condensation of citrulline and aspartate?

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

    Which intermediate is cleaved from argininosuccinate in the urea cycle?

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

    What is the final product of arginine hydrolysis in the urea cycle?

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

    What component is returned to the mitochondrion to pick up another carbamoyl group?

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

    What overall transformation does the urea cycle facilitate?

    <p>Aspartate to Fumarate (D)</p> Signup and view all the answers

    In the urea cycle, which of the following represents the stoichiometry of the overall reaction?

    <p>1 NH4+ + CO2 + 3 ATP = 1 Urea + 2 ADP + AMP + 4 Pi + Fumarate (B)</p> Signup and view all the answers

    What occurs during the hydrolysis of succinyl CoA?

    <p>It breaks the thioester bond to generate GTP. (D)</p> Signup and view all the answers

    During the dehydrogenation of succinate, what is produced?

    <p>FADH2 and fumarate (B)</p> Signup and view all the answers

    What is the purpose of hydration in the conversion of fumarate?

    <p>It converts fumarate to malate by adding water. (C)</p> Signup and view all the answers

    What does malate convert to during its dehydrogenation?

    <p>Oxaloacetate with a C=O double bond (B)</p> Signup and view all the answers

    What is the result of the oxidation of succinate during dehydrogenation?

    <p>It creates a double bond in fumarate. (A)</p> Signup and view all the answers

    Which molecule is directly involved in the reduction of FAD to FADH2?

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

    What initiates the conversion of succinyl CoA to GTP?

    <p>The breaking of the thioester bond (C)</p> Signup and view all the answers

    Which of the following statements about the reactions is correct?

    <p>Malate is formed after hydration of fumarate. (D)</p> Signup and view all the answers

    Flashcards

    Metabolic Pathway

    A series of reactions, each catalyzed by an enzyme, to produce energy and molecules.

    Catabolism

    The breakdown of large molecules into smaller ones, releasing energy.

    Metabolism

    All chemical reactions in cells, breaking down (catabolism) or building (anabolism) molecules.

    Anabolism

    The building of large molecules from smaller ones, using energy.

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    ATP

    Adenosine triphosphate; high-energy molecule storing energy for cellular work.

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    Digestion and Hydrolysis

    Breaking down large food molecules into smaller, absorbable units.

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    Mitochondria

    Organelles where ATP is produced through cellular respiration.

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    Cellular Respiration Stages

    Stages involving digestion, degradation, and oxidation to produce ATP.

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    Glycolysis

    A metabolic pathway that breaks down glucose into pyruvate.

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    Glucose

    A 6-carbon sugar, a digestion product, crucial for energy.

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    Pyruvate

    A 3-carbon molecule produced from glucose breakdown in glycolysis.

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    Anaerobic Process

    A metabolic process that does not require oxygen.

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    Cytoplasm

    The region of a cell outside the nucleus where glycolysis takes place.

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    Phosphorylation

    Adding a phosphate group to a molecule to make it more reactive and store energy.

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    Substrate-level phosphorylation

    The direct formation of ATP by transferring a phosphate group from a high-energy compound to ADP.

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    Energy-Investment Phase

    The initial stage of glycolysis where energy is used to modify glucose.

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    Succinyl CoA hydrolysis

    Succinyl CoA breaks its thioester bond, releasing energy to create GTP from GDP and phosphate.

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    GTP formation

    Hydrolysis of succinyl CoA provides energy to convert GDP to GTP

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    Succinate dehydrogenation

    Succinate loses two hydrogen atoms and forms a double bond, reducing FAD to FADH2.

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    FAD reduction

    Succinate dehydrogenation provides electrons to reduce FAD, forming FADH2

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    Fumarate hydration

    Fumarate adds water to its double bond, forming malate.

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    Malate dehydrogenation

    Malate loses two hydrogen atoms, forms oxaloacetate, and reduces NAD+ to NADH+H+.

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    Oxaloacetate formation

    Malate loses two hydrogen atoms to form oxaloacetate.

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    Important concept 1

    This reaction series is part of the citric acid cycle, releasing energy for cellular processes.

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    Ketogenesis reaction types

    Acetoacetate producing acetone is a decarboxylation reaction, while acetoacetate producing beta-hydroxybutyrate is a reduction reaction.

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    Protein digestion in stomach

    Stomach acid (HCl) activates pepsin, which breaks peptide bonds in proteins.

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    Protein digestion in small intestine

    Trypsin and chymotrypsin break down peptides into amino acids in the small intestine.

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    Protein digestion end products

    Proteins are broken down into amino acids, fats into fatty acids and glycerol, and carbohydrates into glucose.

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    Protein functions in body

    Proteins supply amino acids for building new proteins, nitrogen for other molecules, and energy when other fuels are unavailable.

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    Transamination definition

    An amino group is transferred from an amino acid to an alpha-keto acid (often alpha-ketoglutarate), forming a new amino acid (often glutamate) and a new alpha-keto acid in the liver.

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    Transamination catalyst

    Transaminase or aminotransferase catalyzes the transfer of an amino group.

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    Protein degradation location

    Amino acids are degraded in the liver during transamination.

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    Glycolysis ATP Production

    In glycolysis, two ATP are initially used to phosphorylate glucose and fructose-6-phosphate. Later, four ATP are produced by direct phosphate transfers to ADP.

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    Key Glycolysis Regulatory Steps

    Glycolysis is controlled at three main steps (1, 3, and 10) by enzymes hexokinase, phosphofructokinase, and pyruvate kinase. These steps are essentially irreversible.

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    Hexokinase Inhibition

    High levels of glucose-6-phosphate inhibit hexokinase, preventing further glucose phosphorylation.

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    Phosphofructokinase Regulation

    Phosphofructokinase (in glycolysis reaction 3) is regulated allosterically. High ATP inhibits; high ADP/AMP activates.

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    Pyruvate Kinase Inhibition

    Pyruvate kinase (in glycolysis reaction 10) is inhibited by high levels of ATP or acetyl CoA.

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    Fructose Entry into Glycolysis (Muscle)

    In muscle cells, fructose converts to fructose-6-phosphate, directly entering glycolysis at step 3.

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    Fructose Entry into Glycolysis (Liver)

    In liver cells, fructose converts to trioses, entering glycolysis at step 5.

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    Fructose Uptake Regulation

    Fructose uptake into cells is not regulated by insulin. All blood fructose is processed (catabolized).

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    Carbamoyl Phosphate Synthetase I

    An enzyme that catalyzes the synthesis of carbamoyl phosphate from ammonia, carbon dioxide, and ATP in the first step of the urea cycle.

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    Urea Cycle: Reaction 1

    The carbamoyl group from carbamoyl phosphate is transferred to ornithine, forming citrulline. This reaction occurs in the mitochondrial matrix.

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    Urea Cycle: Reaction 2

    Citrulline reacts with aspartate in the cytosol, forming argininosuccinate. This step requires ATP hydrolysis to AMP and inorganic phosphate.

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    Urea Cycle: Reaction 3

    Argininosuccinate is cleaved to form fumarate and arginine. Fumarate enters the citric acid cycle.

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    Urea Cycle: Reaction 4

    Arginine is hydrolyzed to form ornithine and urea. Ornithine returns to the mitochondrial matrix to start the cycle again.

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    Urea Cycle: Overall Function

    The urea cycle converts ammonia to urea, a less toxic form that can be excreted by the kidneys. This process also utilizes aspartate and generates fumarate.

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    Urea Cycle: Energy Requirements

    The urea cycle requires a significant amount of energy, consuming 3 ATP molecules per urea molecule produced.

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    Where does urea formation occur?

    Urea formation occurs in the cytosol.

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    Study Notes

    Metabolic Pathways and Energy Production

    • Metabolism encompasses all chemical reactions within cells, breaking down (catabolism) or building (anabolism) molecules.
    • A metabolic pathway is a sequence of linked reactions, each catalyzed by a specific enzyme.
    • Pathways can be linear, where a final product is generated, or cyclic, where the first reactant is regenerated.
    • Food (polysaccharides, lipids, proteins) is digested into smaller molecules (glucose, fatty acids, amino acids) releasing energy.
    • Cells store energy as ATP (adenosine triphosphate); this is then broken down to do work.
    • Catabolic reactions involve breaking down large, complex molecules into smaller ones, releasing energy.
    • Anabolic reactions use ATP energy to build larger molecules.
    • Metabolism's stages are organized into:
      • Stage 1: Digestion and hydrolysis break down large molecules to small ones.
      • Stage 2: Degradation breaks down molecules into two- and three-carbon compounds.
      • Stage 3: Oxidation of small molecules in the citric acid cycle and electron transport provide ATP energy (electrons are carried by NADH and FADH2).

    Metabolism and Cell Structure

    • Metabolic reactions occur within specific sites in cells, namely organelles.
    • Organelles are minute structures in cytoplasm that perform specific cellular functions.
    • Organelles are surrounded by cytosol, the fluid part of the cytoplasm.
    • The main organelles involved in metabolism are:
      • Nucleus
      • Rough endoplasmic reticulum
      • Smooth endoplasmic reticulum
      • Ribosomes
      • Mitochondria
      • Golgi complex
      • Lysosomes
      • Plasma membrane

    Important Nucleotide-Containing Compounds in Metabolic Pathways

    • ATP (adenosine triphosphate) is the main energy currency in cells, formed by the oxidation of food.
    • ATP consists of adenine, ribose sugar, and three phosphate groups.
    • Hydrolysis of ATP to ADP releases energy (7.3 kcal/mol or 31 kJ/mol).
    • Hydrolysis of ADP to AMP also releases energy.

    Coenzymes in Metabolic Pathways

    • Many metabolic reactions, involved in energy extraction, entail oxidation and reduction.
    • Oxidation involves the loss of Hydrogen atoms.
    • Reduction involves the gain of Hydrogen atoms.
    • Coenzymes are necessary to transport hydrogen and electrons.

    Oxidation and Reduction

    • Oxidation is the loss of electrons or hydrogen or the gain of oxygen.
    • Reduction is the gain of electrons or hydrogen or the loss of oxygen.

    Coenzyme NAD+

    • NAD+ is a coenzyme involved in redox reactions.
    • It accepts hydrogen and electrons when an oxidation reaction occurs in metabolic pathways.

    Coenzyme FAD

    • FAD is a coenzyme involved in redox reactions.
    • It accepts hydrogen and electrons during redox reactions by forming a double bond in the substance.

    Coenzyme A

    • Coenzyme A (CoA) activates acyl groups, especially in the transfer of acetyl groups.
    • It has a reactive thiol group (-SH) that forms a high-energy thioester with acyl groups.

    High-Energy Phosphate Compounds

    • High-energy compounds contain one or more very reactive bonds, often called "strained bonds."
    • The energy balance in chemical reactions between breaking and reforming bonds determines whether there's a net gain or loss of energy.

    Digestion of Carbohydrates (Glycolysis)

    • Stage 1 of carbohydrate digestion: Polysaccharides are broken down into monosaccharides.
    • Stage 2: Degradation of monosaccharides (glucose)into smaller molecules.
    • Glycolysis involves a series of reactions that degrades glucose (6 carbon atoms) to pyruvate (3 carbon atoms).
    • Glycolysis is an anaerobic process that does not require oxygen.

    Pathways for Pyruvate

    • Depending on oxygen availability, pyruvate has different fates:
      • Aerobic conditions: Pyruvate is decarboxylated to Acetyl CoA, a crucial molecule for the citric acid cycle.
      • Anaerobic conditions (humans, animals, and some microorganisms): Pyruvate is reduced to lactate, an important molecule to regenerate NAD+ and sustain glycolysis.
      • Anaerobic conditions (some microorganisms): Pyruvate is converted to ethanol through decarboxylation and reduction.

    The Citric Acid Cycle

    • The citric acid cycle, also known as the Krebs cycle, is a crucial aerobic pathway for energy production in mitochondria.
    • It involves the oxidation of acetyl CoA into CO2, generating energy-carrying molecules (NADH and FADH2) and ATP.
    • This stage of metabolism occurs under aerobic conditions and proceeds in a cycle.

    Electron Transport Chain

    • The electron transport chain involves a series of protein complexes embedded in the inner mitochondrial membrane.
    • Electrons from NADH and FADH2 are passed along the chain to oxygen, generating ATP.
    • The flow of protons through ATP synthase, a protein complex also in the membrane, drives ATP synthesis.

    Oxidative Phosphorylation and ATP

    • Oxidative phosphorylation involves ATP synthase utilizing the proton gradient across the inner mitochondrial membrane to produce ATP.

    Fatty Acid Oxidation

    • Fatty acids are activated in the cytosol by combining them with coenzyme A (CoA) to form fatty acyl-CoA.
    • Fatty acyl-CoA is transported into mitochondria.
    • Fatty acyl-CoA undergoes a cycle known as beta-oxidation to produce acetyl-CoA, NADH, and FADH2, while shortening the fatty acid molecule.
    • The acetyl-CoA molecules enter the citric acid cycle for further energy production.

    Ketogenesis and Ketone Bodies

    • Ketogenesis is a process that produces ketone bodies (acetoacetate, 𝛽-hydroxybutyrate, and acetone) from acetyl CoA when carbohydrates aren't available as an energy source.
    • Ketone bodies are utilized as alternative energy sources by the brain and other tissues.
    • Ketosis, an elevated level of ketone bodies, can result from conditions like uncontrolled diabetes and starvation.

    Protein Metabolism

    • Protein digestion involves breaking down proteins to individual amino acids.
    • In the stomach, HCl activates pepsin to break peptide bonds.
    • Trypsin and chymotrypsin, in the small intestine, further break down polypeptides to individual amino acids.
    • The amino acids are absorbed into the bloodstream to be used by cells.

    Transamination

    • Transamination is the process of transferring an amino group from one amino acid to a keto acid, producing a new amino acid and a new keto acid.
    • Glutamate is the primary amino acid in transamination reactions.
    • Transamination reactions are commonly catalyzed by enzymes called transaminases or aminotransferases.

    Oxidative Deamination

    • Oxidative deamination is a process where the amino group is removed from glutamate, generating ammonium ion (NH4+).
    • This process provides a-ketoglutarate, necessary for transamination reactions and other metabolic processes.

    Urea Cycle

    • The urea cycle converts harmful ammonium ions (NH4+) into urea in the liver.
    • Urea is an excretable waste product that's non-toxic and transported to kidneys for excretion.
    • The urea cycle consists of several reactions that convert ammonium with CO2 and aspartate to urea.

    Fate of Carbon Atoms from Amino Acids

    • Carbon skeletons of different amino acid families (e.g., C-3 family, C-4 family, C-5 family) enter different intermediates via pyruvate, oxaloacetate, or a-ketoglutarate. These intermediates are then used in the citric acid cycle for further energy production.

    Glucogenic and Ketogenic Amino Acids

    • Glucogenic amino acids can be converted to glucose or intermediates used for glucose synthesis.
    • Ketogenic amino acids cannot be converted to glucose, instead they provide carbon skeletons for ketone body synthesis and fatty acid production.

    Additional Information (General Overview)

    • Anabolic pathways build molecules, requiring ATP.
    • Catabolic pathways break down molecules, releasing ATP.

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