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Questions and Answers
What is the primary end product of glycolysis?
Which enzyme plays a significant role in the glycolysis process by phosphorylating substrates?
What distinguishes catabolic reactions from anabolic reactions in glycolysis?
Which of the following best represents the First Law of Thermodynamics?
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During glycolysis, how do you track the formation of side products?
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What happens to ATP during the initial stages of glycolysis?
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What does the Second Law of Thermodynamics state about entropy?
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What unit measures heat energy in biological contexts?
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What type of reaction occurs when energy is required and DG is positive?
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If a reaction produces 58KJ of energy, what is the classification of this reaction?
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What is the main function of ATP in cells?
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Which statement accurately describes the conversion of ATP to ADP?
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Which part of ATP is primarily responsible for storing energy?
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What happens when a phosphate group is removed from ATP?
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When ADP is phosphorylated to ATP, what type of reaction is occurring?
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How do exergonic and endergonic reactions relate through ATP?
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What type of reaction is associated with the synthesis of ATP from ADP?
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What is the role of a catalyst in a chemical reaction?
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Which of the following statements accurately describes enzymes?
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What happens when an enzyme binds to its substrate?
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What is activation energy?
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Which of the following describes ribozymes?
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Which statement correctly describes the relationship between exergonic and endergonic reactions?
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What is a substrate in the context of enzyme activity?
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Where are electrons stored during the process of respiration?
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What is the final electron acceptor in aerobic respiration?
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What is the net production of ATP at the end of glycolysis?
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What happens to pyruvate in the absence of oxygen?
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What is the initial stage of glycolysis that involves the investment of ATP?
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Which of the following processes occurs last during the complete oxidation of glucose?
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What byproduct is formed at the end of aerobic respiration?
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During which process does fermentation occur when oxygen is not available?
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What is the role of competitive inhibitors in enzyme reactions?
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Which condition would NOT likely affect the rate of an enzyme-catalyzed reaction?
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What is the function of allosteric inhibitors?
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How do cofactors contribute to enzyme function?
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What is the primary effect of feedback inhibition in metabolic pathways?
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Strychnine is an example of which type of inhibition?
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What role do coenzymes typically play in enzymatic reactions?
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Under what condition would an enzyme most likely become inactive?
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Study Notes
Glycolysis
- Glucose is converted into two pyruvate molecules through a series of metabolic reactions
- This process is called glycolysis
- Each initial glucose molecule is converted into two three-carbon molecules of pyruvate
- The end product is 2 sets of 3 carbons for each 6 carbon glucose molecule
- Every step of glycolysis is controlled by a specific enzyme
- Phosphofructokinase phosphorylates a molecule
- ATP is used initially and produced at the end of glycolysis
- ATP phosphorylates glucose, multiple times
- This process is catabolic at the start, and anabolic at the end
- Side products of glycolysis are identified by tracking changes in energy carriers
- ATP, ADP, NADH, protons, and Pi
- The net production of ATP at the end of glycolysis is 2
- 4 ATP are produced, but 2 are used initially
Laws of Thermodynamics
- First Law of thermodynamics: energy cannot be created or destroyed, it can only be converted from one form to another
- For example: sunlight energy is converted into chemical energy
- Second Law of thermodynamics: disorder is more likely than order
- Entropy is disorder, and it always increases in the universe
- The second law states that entropy is always increasing
Biological Energy Sources
- Biological energy comes from chemical reactions which can be described through the transfer of energy
- Endergonic reactions require an input of energy, and their DG value is positive
- This type of reaction stores energy
- Exergonic reactions release free energy, and their DG value is negative
- This type of reaction releases energy
Energy Currency of Cells
- ATP is the energy currency of cells
- Structure: ribose (a 5-carbon sugar), adenine, and three phosphates
- Each phosphate removal converts ATP to ADP, and further to AMP
- The bond between the last two phosphate groups is where the most energy is stored
- ADP is adenosine diphosphate
- Pi is inorganic phosphate
- The reaction of ATP to ADP and Pi is reversible
Coupling Endergonic and Exergonic Reactions
- Exergonic reactions release energy that can be used to phosphorylate ADP to ATP
- This is an endergonic reaction
- Endergonic reactions require energy, which can be added by phosphorylation
- This is achieved by ATP obtained from the release of energy by exergonic reactions
Activation Energy
- Most reactions require some activation energy to start, even exergonic reactions
- Activation energy destabilizes existing chemical bonds
- Catalysts lower the activation energy required by reducing the amount of energy needed to begin the reaction
Enzymes - Biological Catalysts
- Enzymes are catalysts that speed up reactions by lowering activation energy
- Most enzymes are proteins
- The active site is the region of an enzyme where the substrate binds
- Each enzyme has a specific active site that fits only its corresponding substrate
- RNA enzymes, called ribozymes, are made of RNA
Enzyme Function
- The rate of an enzyme-catalyzed reaction depends on the concentrations of substrate and enzyme
- Any condition affecting the enzyme's three-dimensional shape can change the reaction rate
- Optimal temperature
- Optimal pH
Enzyme Inhibition
- Inhibitors are molecules that bind to an enzyme to decrease its activity
- Competitive inhibitors directly compete with the substrate for binding to the active site
- This prevents the substrate from binding to the enzyme
- Noncompetitive inhibitors bind to a site other than the active site, causing a shape change that prevents the substrate from binding
- Allosteric enzymes exist in either an active or inactive state
- They possess an allosteric site where molecules other than the substrate bind
- Allosteric inhibitors bind to the allosteric site to inactivate the enzyme
- Allosteric activators bind to the allosteric site to activate the enzyme
Cofactors and Coenzymes
- Some enzymes require additional molecules for proper activity
- Cofactors are usually metal ions found in the active site, used in catalysis
- Example: minerals
- Coenzymes are nonprotein organic molecules used as electron donors or acceptors in redox reactions
- Example: vitamins
Feedback Inhibition
- The final product of a metabolic pathway can act as an allosteric inhibitor of an earlier enzyme in the pathway
- This process is called feedback inhibition
- Example: strychnine, an inhibitor of the glycine receptor, causes convulsions
Respiration
- Respiration is the process through which electrons are shuttled through electron carriers to a final electron acceptor
- Aerobic respiration uses oxygen (O2) as the final electron acceptor
- Anaerobic respiration uses an inorganic molecule other than O2 as the final electron acceptor
- Fermentation uses an organic molecule as the final electron acceptor
Aerobic Respiration
- Occurs in the presence of oxygen
- Complete oxidation of glucose: C6H12O6 + 6O2 > 6CO2 + 6H2O
- DG is negative, indicating energy release
- Energy is released in small steps by the oxidation of glucose
- The complete oxidation of glucose occurs in four stages:
- Glycolysis
- Pyruvate oxidation
- Krebs cycle
- Electron transport chain and chemiosmosis
Glycolysis
- Glucose is converted to pyruvate in a ten-step biochemical pathway
- Occurs in the cytoplasm
- Two pyruvate molecules are formed for each glucose molecule
- This step requires a net production of 2 ATP molecules by substrate-level phosphorylation
- 2 NADH molecules are produced by the reduction of NAD+
- The fate of pyruvate depends on oxygen availability.
- If full respiration occurs, pyruvate is oxidized to acetyl-CoA and enters the Krebs cycle.
- If oxygen is not present, pyruvate is reduced to oxidize NADH back to NAD+.
The Stages of Glycolysis
- Stage 1 - energy investment
- Energy is used to phosphorylate glucose
- This process uses 2 ATP molecules
- Stage 2 - cleavage
- The six carbon glucose molecules are cleaved into two three carbon molecules
- Stage 3 - payoff
- The two three-carbon molecules are rearranged, producing ATP and reducing NAD+ to NADH
- This step produces 4 ATP and 2 NADH, but because 2 ATP were used initially, the net gain is 2 ATP.
Pyruvate Oxidation
- If oxygen is present, pyruvate is oxidized to acetyl-CoA in the mitochondrial matrix
- This step requires the enzyme pyruvate dehydrogenase
- Acetyl-CoA then enters the Krebs cycle
- The molecule of carbon dioxide is released as pyruvate is oxidized
Krebs Cycle
- Also known as the citric acid cycle
- A series of eight biochemical reactions that occur in the mitochondrial matrix
- The Krebs cycle is a cyclical pathway meaning that the end product of the last reaction is the starting reactant of the first reaction
- Acetyl-CoA and water are used as reactants
- For every molecule of glucose, the Krebs cycle runs twice
- The products of one turn of the Krebs cycle include:
- 3 molecules of NADH
- 1 molecule of FADH2
- 1 molecule of ATP
- 2 molecules of Carbon dioxide
Electron Transport Chain & Chemiosmosis
- Occurs in the inner mitochondrial membrane
- The electron transport chain is a series of protein complexes that pass electrons from one complex to the next
- Each complex has a higher affinity for electrons than the last
- The final electron acceptor is oxygen, which is reduced to water
- The electrons flow from NADH and FADH2 to the electron transport chain
- Chemiosmosis uses the proton gradient (H+) generated by the electron transport chain to produce ATP
- The proton gradient moves protons across the inner mitochondrial membrane and the energy released generates ATP from ADP and Pi
The Electron Transport Chain
- The electron transport chain is made up of four protein complexes:
- Complex I
- Complex II
- Complex III
- Complex IV
- The movement of electrons across the membrane pumps protons from the mitochondrial matrix into the intermembrane space
- This creates a proton gradient across the inner mitochondrial membrane that is used by ATP synthase to generate ATP
ATP Synthase
- ATP synthase is a molecular machine that uses the proton gradient created by the electron transport chain to produce ATP
- It does this by using the energy of the proton gradient to drive the rotation of a rotor component of the enzyme
- The rotation of the rotor component is then coupled to the synthesis of ATP from ADP and Pi
- ATP is then transported out by a transporter protein, and ADP is transported into the matrix
Bioenergetics Summary
- ATP is the energy currency of the cell
- NADH and FADH2 are electron carriers
- ATP is generated by oxidative phosphorylation during cellular respiration
- This process requires the use of oxygen as the final electron acceptor
- The electron transport chain pumps protons across the inner mitochondrial membrane to create a proton gradient which drives ATP synthase to make ATP
- The oxidation of glucose releases energy that can be used to make ATP
- ATP can then be used to power processes such as muscle contraction, active transport, and biosynthesis
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Description
Explore the fundamental processes of glycolysis and the laws of thermodynamics in this quiz. Understand how glucose is converted into pyruvate and the significance of energy transformations. Each question will test your knowledge of enzymatic control and energy production in biological systems.
