Biology Chapter: Metabolism and Energy
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Questions and Answers

What is the sum total of an organism's chemical reactions called?

  • Metabolism (correct)
  • Cellular respiration
  • Metabolic pathway
  • Bioenergetics

    • Which of the following accurately describes catabolic pathways?

  • They release energy by breaking down complex molecules. (correct)
  • They primarily generate oxygen during respiration.
  • They store energy for future use in reactions.
  • They build complex molecules from simpler ones.

    • In what way do anabolic pathways specifically function?

  • They are less efficient than catabolic pathways.
  • They consume energy to build complex molecules. (correct)
  • They primarily occur in the absence of oxygen.
  • They release energy during breakdown of molecules.

    • What is defined as the study of how energy flows through living organisms?

    <p>Bioenergetics</p> Signup and view all the answers

    What role do enzymes play in metabolic pathways?

    <p>They catalyze specific steps of the pathway.</p> Signup and view all the answers

    Which statement about energy in metabolic processes is correct?

    <p>Energy released from catabolic reactions drives anabolic reactions.</p> Signup and view all the answers

    What is a characteristic of metabolic pathways?

    <p>They are organized into sequential steps.</p> Signup and view all the answers

    Which statement correctly describes energy in the context of cellular metabolism?

    <p>Energy capacity enables cells to perform work.</p> Signup and view all the answers

    Which type of energy is associated with the relative motion of objects?

    <p>Kinetic energy</p> Signup and view all the answers

    What form of potential energy is exemplified by water stored behind a dam?

    <p>Gravitational potential energy</p> Signup and view all the answers

    During which type of reaction is potential energy released as usable energy?

    <p>Catabolic reaction</p> Signup and view all the answers

    How does heat transfer primarily occur between systems?

    <p>From warmer to cooler bodies</p> Signup and view all the answers

    What does the first law of thermodynamics state?

    <p>Energy can be transformed but not created or destroyed</p> Signup and view all the answers

    What is entropy a measure of?

    <p>Disorder or randomness in a system</p> Signup and view all the answers

    What is a characteristic of an isolated system?

    <p>Cannot exchange energy or matter</p> Signup and view all the answers

    What process requires an input of energy to occur?

    <p>Nonspontaneous processes</p> Signup and view all the answers

    What happens to ordered forms of energy during most energy transformations?

    <p>They are converted to heat</p> Signup and view all the answers

    In biological systems, what must occur for spontaneous processes to take place?

    <p>They must increase the total entropy of the universe</p> Signup and view all the answers

    Which type of energy transformation occurs when a person dives into water?

    <p>Potential to kinetic energy</p> Signup and view all the answers

    How does an organism create ordered structures from less ordered inputs?

    <p>By transforming energy and matter from surroundings</p> Signup and view all the answers

    What primarily limits the usefulness of heat as an energy source within living cells?

    <p>Constant temperature throughout cell structures</p> Signup and view all the answers

    How does water naturally flow in terms of energy?

    <p>Downhill with no energy input</p> Signup and view all the answers

    What is indicated by a negative value of ΔG in a reaction?

    <p>The reaction occurs without an input of energy.</p> Signup and view all the answers

    Which of the following statements about exergonic and endergonic reactions is true?

    <p>Endergonic reactions require energy to proceed.</p> Signup and view all the answers

    In which condition does a cell reach metabolic equilibrium?

    <p>When the rates of forward and backward reactions are equal.</p> Signup and view all the answers

    What does a positive ΔG indicate about a reaction?

    <p>It is nonspontaneous and requires energy input.</p> Signup and view all the answers

    During cellular respiration, the breakdown of glucose generates how much energy available for work?

    <p>686 kcal/mol</p> Signup and view all the answers

    Which of the following correctly defines a spontaneous process?

    <p>A process that occurs without external energy input.</p> Signup and view all the answers

    What is the effect of decreasing enthalpy on the spontaneity of a reaction?

    <p>It increases the spontaneity of the reaction.</p> Signup and view all the answers

    Which of the following accurately describes metabolic disequilibrium?

    <p>It is critical for ongoing cellular work.</p> Signup and view all the answers

    Which variable in the equation ΔG = ΔH - TΔS represents absolute temperature?

    <p>T</p> Signup and view all the answers

    What is the relationship between free energy and stability in a system?

    <p>Systems with less free energy are more stable.</p> Signup and view all the answers

    What is the ultimate fate of a cell that reaches metabolic equilibrium?

    <p>It is considered dead and cannot do work.</p> Signup and view all the answers

    How does the process of photosynthesis relate to cellular respiration?

    <p>Photosynthesis stores energy, while respiration releases it.</p> Signup and view all the answers

    What role do substrates play in cellular work?

    <p>They are essential for sustaining metabolic disequilibrium.</p> Signup and view all the answers

    What is primarily responsible for energy coupling in cells?

    <p>ATP</p> Signup and view all the answers

    What is the consequence of breaking the terminal phosphate bond of ATP?

    <p>Release of energy</p> Signup and view all the answers

    Which statement about the bonds in ATP is correct?

    <p>They are considered fairly weak covalent bonds.</p> Signup and view all the answers

    What role does a phosphorylated intermediate play in cellular processes?

    <p>It increases the reactivity of the molecule it is attached to.</p> Signup and view all the answers

    During the hydrolysis of ATP, what happens to the free energy?

    <p>It decreases as ATP is converted to ADP.</p> Signup and view all the answers

    What provides the energy for the regeneration of ATP from ADP within the cell?

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

    What is the initial investment of energy needed to start a chemical reaction called?

    <p>Activation energy</p> Signup and view all the answers

    How do enzymes speed up metabolic reactions?

    <p>By lowering activation energy.</p> Signup and view all the answers

    Why is ATP referred to as a renewable resource?

    <p>It can be continuously regenerated from ADP.</p> Signup and view all the answers

    What significant feature of ATP contributes to its instability?

    <p>The crowding of negatively charged phosphate groups.</p> Signup and view all the answers

    What occurs to ATP during mechanical work involving motor proteins?

    <p>ATP is hydrolyzed leading to shape changes in the protein.</p> Signup and view all the answers

    What do plants use to produce ATP apart from catabolic reactions?

    <p>Light energy via photosynthesis</p> Signup and view all the answers

    What key role does thermal energy play in reactant molecules?

    <p>It helps break bonds so that reactions can occur.</p> Signup and view all the answers

    What characterizes the process of ATP hydrolysis within the cell?

    <p>It releases free energy resulting from bond breaking.</p> Signup and view all the answers

    What is the primary factor determining the rate of an enzyme-catalyzed reaction when the enzyme is saturated?

    <p>Speed of the active site conversion</p> Signup and view all the answers

    What happens to an enzyme at temperatures above its optimal range?

    <p>The enzyme undergoes denaturation</p> Signup and view all the answers

    How does competitive inhibition affect enzyme activity?

    <p>It can be reversed by increasing substrate concentration</p> Signup and view all the answers

    Which of the following enzymes works best at a pH of 8?

    <p>Trypsin</p> Signup and view all the answers

    What role do cofactors play in enzyme activity?

    <p>They assist in catalytic activity</p> Signup and view all the answers

    What characterizes irreversible enzyme inhibitors?

    <p>They bind covalently, altering the enzyme permanently</p> Signup and view all the answers

    What is the significance of a mutation in an enzyme's active site?

    <p>It might allow the enzyme to bind to a different substrate</p> Signup and view all the answers

    What effect does allosteric regulation have on an enzyme?

    <p>It affects enzyme activity at a site distinct from the active site</p> Signup and view all the answers

    What compound is known for binding to the active site of bacterial enzymes to inhibit cell wall synthesis?

    <p>Penicillin</p> Signup and view all the answers

    What occurs during the transition state of a reaction?

    <p>The reactants have absorbed enough energy for bonds to break.</p> Signup and view all the answers

    What feature distinguishes thermophilic enzymes from human enzymes?

    <p>Thermophilic enzymes function best at much higher temperatures</p> Signup and view all the answers

    How does an enzyme affect the activation energy of a reaction?

    <p>It lowers the activation energy needed to reach the transition state.</p> Signup and view all the answers

    Which of the following is a common characteristic of metabolic control through enzyme inhibitors?

    <p>Inhibitors can be either natural or synthetic</p> Signup and view all the answers

    What is the primary reason enzymes can be highly specific to certain substrates?

    <p>Their three-dimensional shape allows specific interactions with substrates.</p> Signup and view all the answers

    What happens to enzyme activity in the presence of a noncompetitive inhibitor?

    <p>The enzyme conformation is altered, reducing activity</p> Signup and view all the answers

    What occurs when substrate concentration is low?

    <p>An increase in substrate concentration enhances the reaction rate.</p> Signup and view all the answers

    What is a primary method researchers have used to understand enzyme evolution?

    <p>Introducing random mutations and selecting favorable traits</p> Signup and view all the answers

    What characterizes the active site of an enzyme?

    <p>It is typically formed by a few specific amino acids that catalyze reactions.</p> Signup and view all the answers

    Which statement about enzymes and vitamins is true?

    <p>Many vitamins function as coenzymes</p> Signup and view all the answers

    What does the term induced fit refer to in enzyme activity?

    <p>The change in shape of the enzyme upon substrate binding to facilitate the reaction.</p> Signup and view all the answers

    What results from a decrease in pH for most enzymes?

    <p>Denaturation and loss of function at extreme pH</p> Signup and view all the answers

    Enzymes are typically not affected by the reaction they catalyze. Which statement best explains this?

    <p>Enzymes remain chemically unchanged and are reusable even after extensive catalysis.</p> Signup and view all the answers

    What might prevent a reaction from proceeding even if reactants have sufficient energy?

    <p>The reactants being at low temperature without sufficient thermal energy.</p> Signup and view all the answers

    What process is indicated when a spark plug releases energy to initiate combustion?

    <p>Activation energy provision through heat.</p> Signup and view all the answers

    Which of the following best describes the role of R groups in an enzyme's active site?

    <p>They may participate in the catalysis by forming covalent bonds with the substrate.</p> Signup and view all the answers

    How do enzymes speed up reactions involving more than one reactant?

    <p>By bringing reactants together in the correct orientation at the active site.</p> Signup and view all the answers

    What happens during the bond-forming phase of a reaction, according to free energy changes?

    <p>Energy is released as reactants are converted into products.</p> Signup and view all the answers

    Which statement regarding metabolic enzymes is correct?

    <p>They can catalyze both forward and reverse reactions depending on reactant and product concentrations.</p> Signup and view all the answers

    What limitation occurs when active sites on all enzymes are engaged?

    <p>The reaction rate cannot increase any further regardless of substrate availability.</p> Signup and view all the answers

    What is a primary function of aerobic respiration in organisms?

    <p>To produce energy in the form of ATP using oxygen</p> Signup and view all the answers

    What type of reaction occurs when glucose is oxidized in cellular respiration?

    <p>Redox reaction</p> Signup and view all the answers

    Which statement accurately describes the process of electron transport in cellular respiration?

    <p>Electrons are passed to NAD+ before reaching oxygen</p> Signup and view all the answers

    In the context of aerobic respiration, what role do coenzymes like NAD+ play?

    <p>They accept electrons from glucose during oxidation</p> Signup and view all the answers

    What is the significance of the activation energy barrier in cellular respiration?

    <p>It ensures that reactions occur in a stepwise manner, controlled by enzymes.</p> Signup and view all the answers

    Which product results from the complete oxidation of one mole of glucose in cellular respiration?

    <p>Six moles of CO2, six moles of H2O, and energy</p> Signup and view all the answers

    What happens to the potential energy of electrons during cellular respiration?

    <p>Electrons lose potential energy as they are transferred to more electronegative partners.</p> Signup and view all the answers

    Which of the following substances can be utilized as fuel for aerobic respiration?

    <p>Carbohydrates, fats, and proteins</p> Signup and view all the answers

    When methane reacts with oxygen, what type of reaction is it an example of?

    <p>Combustion</p> Signup and view all the answers

    What characterizes the process of anaerobic respiration in prokaryotes?

    <p>It uses alternatives to oxygen for the reaction.</p> Signup and view all the answers

    How does sodium behave in the formation of table salt from sodium and chloride?

    <p>It donates electrons and is oxidized.</p> Signup and view all the answers

    What is a major source of energy released during the oxidation of organic fuel molecules?

    <p>The movement of electrons releases energy.</p> Signup and view all the answers

    What is the result of an exergonic reaction like glucose catabolism?

    <p>Energy is released and used to generate ATP.</p> Signup and view all the answers

    What is the primary function of NAD + during cellular respiration?

    <p>To trap the released electrons</p> Signup and view all the answers

    What defines redox reactions in the context of cellular respiration?

    <p>They involve the transfer of electrons between reactants.</p> Signup and view all the answers

    How many NADH molecules are yielded from one glucose molecule during glycolysis?

    <p>2</p> Signup and view all the answers

    Which of the following stages generates ATP via oxidative phosphorylation?

    <p>Electron transport chain</p> Signup and view all the answers

    What is the initial substrate for glycolysis?

    <p>Glucose</p> Signup and view all the answers

    What happens to each NAD + molecule during the oxidation of glucose?

    <p>It is reduced to NADH</p> Signup and view all the answers

    In which cellular location does glycolysis take place?

    <p>Cytosol</p> Signup and view all the answers

    What is the role of the electron transport chain in cellular respiration?

    <p>To transfer electrons from NADH to oxygen</p> Signup and view all the answers

    What role does an activator play in allosteric regulation of enzymes?

    <p>It increases the enzyme’s catalytic activity by stabilizing the active conformation.</p> Signup and view all the answers

    What is the primary function of cooperativity in allosteric enzymes?

    <p>To amplify the response of the enzyme to substrates.</p> Signup and view all the answers

    What characterizes the energy investment phase of glycolysis?

    <p>The cell consumes ATP</p> Signup and view all the answers

    How does feedback inhibition benefit a metabolic pathway?

    <p>It prevents overproduction of the end product by inhibiting early enzymes.</p> Signup and view all the answers

    How does oxidative phosphorylation differ from substrate-level phosphorylation?

    <p>Substrate-level phosphorylation directly forms ATP from ADP</p> Signup and view all the answers

    What is the consequence of NADH carrying electrons down an energy gradient to oxygen?

    <p>Water is produced as a byproduct</p> Signup and view all the answers

    What is the significance of allosteric regulation in pharmaceutical applications?

    <p>They can regulate enzyme activity without competing with substrates.</p> Signup and view all the answers

    What is the primary outcome of ATP hydrolysis in terms of metabolic pathways?

    <p>It inhibits catabolic enzymes by reducing substrate affinity.</p> Signup and view all the answers

    Which statement accurately describes pyruvate in cellular respiration?

    <p>It is used for the citric acid cycle after glycolysis</p> Signup and view all the answers

    What is the electronegative receptor at the bottom of the electron transport chain?

    <p>Oxygen</p> Signup and view all the answers

    Which factor most significantly contributes to the regulation of metabolic pathways?

    <p>Cellular compartmentalization and enzyme localization.</p> Signup and view all the answers

    Which statement accurately describes the role of hemoglobin in cooperativity?

    <p>The binding of oxygen at multiple sites enhances the overall affinity for oxygen.</p> Signup and view all the answers

    How are the protons released during the oxidation of glucose by dehydrogenase enzymes?

    <p>They are released into the surrounding solution as H +</p> Signup and view all the answers

    What is the role of enzymes in catabolic pathways?

    <p>They catalyze the degradation of organic molecules into simpler forms.</p> Signup and view all the answers

    What is the typical energy yield of ATP from one molecule of glucose during respiration?

    <p>32 ATP</p> Signup and view all the answers

    What characterizes the metabolic process of fermentation compared to aerobic respiration?

    <p>Fermentation leads to partial degradation of sugars without oxygen.</p> Signup and view all the answers

    How do metabolic enzymes function as part of a multienzyme complex?

    <p>They coordinate reactions where products sequentially become substrates for adjacent enzymes.</p> Signup and view all the answers

    What is the implication of allosteric sites being distinct among enzymes?

    <p>It provides a target for highly specific drug design.</p> Signup and view all the answers

    What is the result of changes in cellular conditions on allosteric regulation?

    <p>They can lead to the stabilization of either active or inactive enzyme forms.</p> Signup and view all the answers

    What effect does ADP have on catabolic enzymes as opposed to ATP?

    <p>ADP functions as an activator enhancing enzyme activity.</p> Signup and view all the answers

    What is the maximum ATP yield from one glucose molecule during cellular respiration if the less efficient shuttle is functioning?

    <p>30 ATP</p> Signup and view all the answers

    How many ATP are theoretically generated from each NADH that donates its electrons to mitochondrial NAD+ in liver cells?

    <p>3 ATP</p> Signup and view all the answers

    What adaptation allows hibernating mammals to generate heat without producing ATP?

    <p>Uncoupling protein activation</p> Signup and view all the answers

    What by-product is produced during anaerobic respiration in sulfate-reducing bacteria?

    <p>Hydrogen sulfide</p> Signup and view all the answers

    What is the efficiency of respiration based on the complete oxidation of glucose?

    <p>34%</p> Signup and view all the answers

    What must occur to maintain glycolysis during fermentation?

    <p>Recycling of NAD+</p> Signup and view all the answers

    Which of the following statements about fermentation is true?

    <p>Fermentation occurs when NADH donates electrons to pyruvate.</p> Signup and view all the answers

    During alcoholic fermentation, what is the first conversion step of pyruvate?

    <p>Conversion to acetaldehyde</p> Signup and view all the answers

    What drives the uptake of pyruvate into the mitochondrion?

    <p>Proton-motive force</p> Signup and view all the answers

    Which type of enzyme is crucial for the conversion of pyruvate to lactate during lactic acid fermentation?

    <p>Lactate dehydrogenase</p> Signup and view all the answers

    What is the role of FAD when receiving electrons in the context of cellular respiration?

    <p>Generating more ATP than NADH</p> Signup and view all the answers

    What is produced as a by-product during lactic acid fermentation?

    <p>Lactate</p> Signup and view all the answers

    How do fermentation and anaerobic respiration differ?

    <p>Anaerobic respiration involves electron transport chains.</p> Signup and view all the answers

    Which effect does the presence of an uncoupling protein have on the overall ATP production?

    <p>Causes heat generation without ATP production</p> Signup and view all the answers

    What is the primary outcome of the conversion of pyruvate to acetyl CoA?

    <p>Formation of high-energy acetyl CoA</p> Signup and view all the answers

    How many molecules of NADH are produced per acetyl group that enters the citric acid cycle?

    <p>3</p> Signup and view all the answers

    What is the role of FAD in the citric acid cycle?

    <p>It accepts electrons in a specific step</p> Signup and view all the answers

    During oxidative phosphorylation, what is the main function of the electron transport chain?

    <p>It synthesizes ATP from ADP and inorganic phosphate</p> Signup and view all the answers

    What is the significance of the regeneration of oxaloacetate in the citric acid cycle?

    <p>It allows the cycle to continue repeatedly</p> Signup and view all the answers

    Which of the following statements about ATP production is true?

    <p>Most ATP is produced through oxidative phosphorylation</p> Signup and view all the answers

    Where does the citric acid cycle occur in prokaryotic cells?

    <p>In the cytoplasm</p> Signup and view all the answers

    What is the primary purpose of acetyl CoA in cellular respiration?

    <p>To enter the citric acid cycle for further oxidation</p> Signup and view all the answers

    What is released during the carboxyl group removal in pyruvate conversion?

    <p>Carbon dioxide</p> Signup and view all the answers

    How many ATP equivalents are produced from one turn of the citric acid cycle?

    <p>1</p> Signup and view all the answers

    Which of these is NOT a component of the electron transport chain?

    <p>Glucose</p> Signup and view all the answers

    What does the reduction of NAD+ during cellular respiration result in?

    <p>The formation of NADH</p> Signup and view all the answers

    Which term is synonymous with the citric acid cycle?

    <p>Krebs cycle</p> Signup and view all the answers

    Why is the interior mitochondrial membrane highly folded?

    <p>To increase the surface area for the electron transport chain</p> Signup and view all the answers

    What is the primary consequence of anaerobic conditions in human muscle cells during exercise?

    <p>Switch from aerobic respiration to lactic acid fermentation</p> Signup and view all the answers

    Which molecule acts as the final electron acceptor in fermentation processes?

    <p>Pyruvate or acetaldehyde</p> Signup and view all the answers

    How do facultative anaerobes differ from obligate anaerobes in their metabolic processes?

    <p>Facultative anaerobes can switch between fermentation and respiration.</p> Signup and view all the answers

    What is the net ATP yield from glycolysis in all three pathways of ATP production?

    <p>2 ATP</p> Signup and view all the answers

    Why is the transfer of electrons from NADH to the electron transport chain significant in cellular respiration?

    <p>It regenerates NAD+ and releases energy for ATP synthesis.</p> Signup and view all the answers

    What impact does oxygen have on the process of cellular respiration compared to fermentation?

    <p>Oxygen facilitates a higher ATP yield due to oxidative phosphorylation.</p> Signup and view all the answers

    What occurs to lactate once it is produced during anaerobic respiration in human muscle cells?

    <p>It is transported to the liver for conversion back to pyruvate.</p> Signup and view all the answers

    What must occur to proteins before they can enter the cellular respiration pathways?

    <p>Their amino groups must be removed through deamination.</p> Signup and view all the answers

    Which statement accurately describes the metabolic pathways available in organisms?

    <p>Facultative anaerobes can adapt their metabolic pathways based on oxygen presence.</p> Signup and view all the answers

    What distinguishes aerobic from anaerobic respiration in terms of final electron acceptors?

    <p>Aerobic respiration uses oxygen; anaerobic uses a less electronegative molecule.</p> Signup and view all the answers

    What is a potential energy yield difference between aerobic respiration and fermentation?

    <p>Aerobic respiration can yield up to 32 ATP per glucose molecule.</p> Signup and view all the answers

    What metabolic pathway is considered to have evolved very early in the history of life on Earth?

    <p>Glycolysis</p> Signup and view all the answers

    What is the main reason facultative anaerobes must consume glucose at a faster rate when relying on fermentation?

    <p>Fermentation generates less ATP than aerobic respiration.</p> Signup and view all the answers

    How does the carbon skeleton of amino acids enter the metabolic pathways for ATP production?

    <p>By being transformed into intermediates of glycolysis or the citric acid cycle.</p> Signup and view all the answers

    What is the primary function of the electron transport chain in cellular respiration?

    <p>To generate a proton gradient for ATP synthesis</p> Signup and view all the answers

    Which component of the electron transport chain directly delivers electrons to oxygen?

    <p>Cytochrome a3</p> Signup and view all the answers

    How does ATP synthase generate ATP?

    <p>By utilizing the energy from an existing ion gradient</p> Signup and view all the answers

    Why do FADH2 electrons contribute to less ATP production compared to NADH?

    <p>The electrons from FADH2 are at a lower energy level.</p> Signup and view all the answers

    What is chemiosmosis primarily responsible for in cellular respiration?

    <p>Synthesis of ATP from ADP and phosphate</p> Signup and view all the answers

    What role does the heme group play in cytochromes?

    <p>It acts as an electron acceptor and donor.</p> Signup and view all the answers

    How does the proton-motive force contribute to ATP production?

    <p>It drives protons back across the membrane through ATP synthase.</p> Signup and view all the answers

    What is the significance of the spatial arrangement of electron carriers in the membrane?

    <p>It minimizes energy losses during electron transfer.</p> Signup and view all the answers

    What is the relationship between redox reactions and ATP synthesis?

    <p>Redox reactions progressively release energy that aids in ATP synthesis.</p> Signup and view all the answers

    How does the electron transport chain maintain the H+ gradient?

    <p>By using the exergonic flow of electrons to pump protons across the membrane.</p> Signup and view all the answers

    What is the role of substrate-level phosphorylation in ATP production?

    <p>It produces a limited amount of ATP during glycolysis and the citric acid cycle.</p> Signup and view all the answers

    What drives the flow of protons through ATP synthase?

    <p>A difference in H+ concentrations across the membrane.</p> Signup and view all the answers

    What is a key distinction between chemiosmosis in mitochondria and chloroplasts?

    <p>Light energy drives proton gradient formation only in chloroplasts.</p> Signup and view all the answers

    Which factor affects the ratio of NADH to ATP production during cellular respiration?

    <p>The direct coupling of phosphorylation and redox reactions.</p> Signup and view all the answers

    Study Notes

    Metabolism Overview

    • Thousands of reactions occur within cells, including assembling polymers from small molecules, hydrolyzing polymers, and exporting chemical products.
    • Cellular respiration extracts energy from fuels to power various cellular processes.
    • Metabolism is complex, efficient, coordinated, and responds quickly to changes.

    Metabolic Pathways

    • Metabolism is the sum of all chemical reactions in an organism, emerging from molecular interactions within the cell.
    • Metabolic pathways consist of a chain of reactions, each catalyzed by a specific enzyme.
    • Catabolic pathways break down complex molecules, releasing energy (e.g., cellular respiration).
    • Anabolic pathways build complex molecules from simpler ones, consuming energy (e.g., protein synthesis).

    Energy Transformations

    • Energy is the capacity to cause change.
    • Kinetic energy is energy of motion (e.g., thermal energy, light).
    • Potential energy is stored energy (e.g., chemical energy).
    • Chemical energy is released in chemical reactions (e.g., catabolism).
    • Energy transformations follow the laws of thermodynamics.

    Thermodynamics

    • An isolated system cannot exchange energy or matter with its surroundings (e.g., liquid in a thermos).
    • An open system can exchange energy and matter (e.g., organisms).
    • The first law of thermodynamics states that energy is conserved.
    • The second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe.
    • Entropy is a measure of disorder.
    • Spontaneous processes increase the entropy of the universe.

    Free Energy and Chemical Reactions

    • Free energy (G) is the portion of a system's energy that can perform work.

    • ∆G is the change in free energy, calculated as ∆G = ∆H - T∆S.

    • ∆G must be negative (∆G < 0) for a spontaneous process.

    • Exergonic reactions release free energy (∆G < 0).

    • Endergonic reactions absorb free energy (∆G > 0).

    • Reactions at equilibrium have a ∆G = 0.

    • Cells maintain metabolic disequilibrium to avoid equilibrium and continue working.

    ATP and Cellular Work

    • ATP (adenosine triphosphate)mediates most energy coupling in cells.

    • ATP hydrolysis releases energy (∆G = -7.3 kcal/mol).

    • Hydrolysis of ATP results in a phosphorylated intermediate, making the recipient molecule more reactive.

    • The hydrolysis of ATP is coupled to endergonic processes.

    • ATP is a renewable resource, regenerated by ATP synthase. Catabolism (respiration) supplies the energy to regenerate ATP.

    Enzymes and Catalysis

    • Enzymes act as catalysts, speeding up reactions without being consumed.

    • Enzymes lower the activation energy (EA), allowing reactions to occur at normal temperatures.

    • Enzymes are substrate-specific, due to the active site's three-dimensional shape.

    • Induced fit describes the enzyme's shape change to accommodate the substrate.

    • Cofactors (inorganic & nonprotein) and coenzymes (organic & protein) aid enzyme activity.

    • The rate of enzyme action depends on substrate concentration and the temperature & pH optima of the enzyme.

    • Inhibitors can bind to enzymes reversibly or irreversibly, altering their function (competitive or noncompetitive).

    Metabolic Regulation

    • Allosteric regulation describes an enzyme's activity alteration by a molecule binding to a non-active site.
    • Feedback inhibition regulates a metabolic pathway by the pathway's final product inhibiting an earlier step.
    • Enzyme localization within the cell helps organize metabolic pathways.

    Cellular Respiration

    • Cellular respiration is a catabolic metabolic pathway. It harvests energy from organic molecules, using oxygen.
    • Cellular respiration has three main stages: glycolysis, citric acid cycle, and oxidative phosphorylation.
    • Redox reactions transfer electrons and release energy used in ATP synthesis.

    Glycolysis

    • Glycolysis breaks down glucose, a six-carbon molecule, into two three-carbon molecules of pyruvate, producing 2 ATP and 2 NADH.
    • Glycolysis occurs in the cytosol and is an anaerobic process.

    Pyruvate Oxidation

    • Pyruvate is oxidized to acetyl CoA, releasing CO2 and transferring electrons to NAD+, producing NADH.

    Citric Acid Cycle

    • The citric acid cycle further oxidizes acetyl CoA, releasing CO2, producing 1 ATP per turn, NADH, and FADH2 by substrate-level phosphorylation.

    Oxidative Phosphorylation

    • Electron transport chain transfers electrons from NADH and FADH2 to oxygen, creating a proton gradient.
    • Chemiosmosis uses the proton gradient to drive ATP synthesis.
    • ATP synthase is a protein that synthesizes ATP using the H+ gradient (proton-motive force).
    • Oxidative phosphorylation produces most of the ATP in cellular respiration.

    Fermentation

    • Fermentation is an anaerobic alternative to respiration, regenerating NAD+ (by reducing pyruvate) for glycolysis, producing a small amount of ATP.
    • Examples are alcohol fermentation (ethanol) and lactic acid fermentation (lactate).

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    Test your knowledge on the fundamental concepts of metabolism and energy transfer within living organisms. This quiz covers key terms, pathways, and the laws of thermodynamics that govern biological energy systems. Challenge yourself to understand how energy flows and the role of enzymes in metabolic reactions.

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