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What is the primary function of ATP in microbial metabolism?
What is the primary function of ATP in microbial metabolism?
Which process involves the use of energy to build complex molecules from simpler ones?
Which process involves the use of energy to build complex molecules from simpler ones?
What type of reaction is characterized by the loss of electrons?
What type of reaction is characterized by the loss of electrons?
Which type of enzyme inhibition involves a substance binding to the active site?
Which type of enzyme inhibition involves a substance binding to the active site?
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What is the role of cofactors in enzyme activity?
What is the role of cofactors in enzyme activity?
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What determines the optimum temperature for enzyme activity?
What determines the optimum temperature for enzyme activity?
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What defines an autotroph in microbial classification?
What defines an autotroph in microbial classification?
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Which statement about enzymes is NOT true?
Which statement about enzymes is NOT true?
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What occurs during the dephosphorylation of ATP?
What occurs during the dephosphorylation of ATP?
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Which of the following is a characteristic of feedback inhibition?
Which of the following is a characteristic of feedback inhibition?
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Which molecule serves as an electron carrier in the cell?
Which molecule serves as an electron carrier in the cell?
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What is the impact of competitive inhibitors on enzyme activity?
What is the impact of competitive inhibitors on enzyme activity?
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What happens to enzyme activity when the substrate concentration is increased to saturation?
What happens to enzyme activity when the substrate concentration is increased to saturation?
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Which describes a characteristic of lithotrophs?
Which describes a characteristic of lithotrophs?
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What is the primary function of glycolysis in glucose catabolism?
What is the primary function of glycolysis in glucose catabolism?
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Which phase of glycolysis requires the investment of ATP?
Which phase of glycolysis requires the investment of ATP?
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In the transition reaction, what is pyruvate converted into?
In the transition reaction, what is pyruvate converted into?
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What are the primary products of the Krebs cycle for every molecule of acetyl CoA processed?
What are the primary products of the Krebs cycle for every molecule of acetyl CoA processed?
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What is the final electron acceptor in aerobic respiration?
What is the final electron acceptor in aerobic respiration?
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During the electron transport chain, what directly generates ATP?
During the electron transport chain, what directly generates ATP?
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What is the total net ATP yield from glycolysis?
What is the total net ATP yield from glycolysis?
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Which of the following pathways is NOT a type of glycolytic pathway?
Which of the following pathways is NOT a type of glycolytic pathway?
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What role does chemiosmosis play in cellular respiration?
What role does chemiosmosis play in cellular respiration?
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In anaerobic respiration, which of the following can serve as a final electron acceptor?
In anaerobic respiration, which of the following can serve as a final electron acceptor?
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What is the primary purpose of ATP synthase in cellular respiration?
What is the primary purpose of ATP synthase in cellular respiration?
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Which type of respiration yields less energy than aerobic respiration?
Which type of respiration yields less energy than aerobic respiration?
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What happens to the NAD+ during the transition reaction?
What happens to the NAD+ during the transition reaction?
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Study Notes
Microbial Metabolism
- Metabolism: The sum of all chemical reactions within a cell. It encompasses processes that provide energy and create substances essential for life.
- Catabolism: The breakdown of complex molecules into simpler ones. These reactions release energy (exergonic). An example is the breakdown of glucose into CO2 and H2O.
- Anabolism: The synthesis of complex molecules from simpler ones. These reactions require energy (endergonic). An example is the building of proteins from amino acids.
- ATP (Adenosine Triphosphate): A molecule that serves as the primary energy currency of cells. It links catabolic and anabolic reactions. It stores energy released from catabolism and releases energy to drive anabolic reactions.
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Classifying by carbon and energy source:
Carbon Source
- Autotrophs: Convert inorganic CO2 into organic compounds.
- Heterotrophs: Utilize organic compounds as nutrients.
Energy (Electron) Source
- Phototrophs: Obtain electrons from light.
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Chemotrophs: Obtain electrons from chemicals.
- Organotrophs: Obtain electrons from organic compounds.
- Lithotrophs: Obtain electrons from inorganic compounds. (Unique to microbes)
- Chemoheterotrophs: Utilize organic molecules as both their energy and carbon sources. (Most organisms belong to this category)
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Redox Reactions: Transfer of electrons between molecules. These reactions are critical because most cellular energy is stored in high-energy electrons. Every oxidation reaction is paired with a reduction reaction.
- Oxidation (OIL): Loss of electrons.
- Reduction (RIG): Gain of electrons.
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Energy Carriers: Energy released during catabolism can be stored in the following ways:
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Reduction of electron carriers: Electron carriers bind and transport high-energy electrons. These carriers are readily reduced or oxidized. They often derive from B vitamins and are nucleotide derivatives.
- Examples of electron carriers: NAD (NAD+/NADH), FAD (FAD/FADH2), NADP (NADP+/NADPH)
- Left side: oxidized form
- Right side: reduced form
- Electron carriers are continuously recycled.
- Examples of electron carriers: NAD (NAD+/NADH), FAD (FAD/FADH2), NADP (NADP+/NADPH)
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In bonds of ATP: ATP is the primary energy currency of cells allowing it to store and release energy safely as needed. It consists of an adenine molecule bonded to a ribose molecule and three phosphate groups.
- AMP (one phosphate group): A precursor to ADP and ATP
- ADP (two phosphate groups): A precursor to ATP
- Phosphorylation: The addition of an inorganic phosphate group (Pi) to ADP with the input of energy. High-energy phosphate bonds are formed between the phosphate groups.
- Dephosphorylation: The breakage of high-energy bonds. This releases energy, often as one phosphate (inorganic phosphate Pi) and sometimes, two phosphates (pyrophosphate PPi).
- Energy released from dephosphorylation of ATP is used to drive cellular work.
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Reduction of electron carriers: Electron carriers bind and transport high-energy electrons. These carriers are readily reduced or oxidized. They often derive from B vitamins and are nucleotide derivatives.
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Enzymes: Biological catalysts that speed up chemical reactions without being altered.
- Activation energy: The energy required to initiate the formation or breakage of chemical bonds and convert reactants into products. Enzymes lower the activation energy by binding to reactant molecules, hastening the reaction.
- Substrates: The reactant molecule to which an enzyme binds. The substrate fits into the 3D shape of specific amino acids within the enzyme's active site.
- Active site: The location on an enzyme where the substrate binds.
- Specificity: Enzymes are typically specific for particular substrates although the same compound can be a substrate for multiple different enzymes.
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Components of Enzymes:
- Apoenzyme: The protein component of an enzyme. The apoenzyme is inactive on its own.
- Cofactor: Inorganic ions (e.g., Fe2+, Mg2+) that assist enzyme function.
- Coenzyme: Organic molecules that help enzymes transfer electrons. Coenzymes are often derived from vitamins (e.g., CoA, NAD+, FMN).
- Holoenzyme: The complete active enzyme, consisting of the apoenzyme and its cofactor.
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Enzyme Activity:
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Temperature: As temperature increases, the rate of enzymatic reactions generally increases.
- Low temperatures: Molecular movement is slow.
- High temperatures: Molecules move quickly, increasing collisions.
- Optimal temperature: The maximum rate of reaction. Beyond this point, the rate decreases again.
- Denaturation: Loss of the enzyme's tertiary structure (3D shape). This can occur due to extreme changes in pH, breakage of hydrogen bonds, or alterations in the arrangement of amino acids in the active site. Denaturation results in loss of the enzyme's catalytic ability.
- pH: Each enzyme has an optimal pH where it is most active. Activity decreases above or below this optimal pH.
- Substrate Concentration: At high substrate concentration, the enzyme becomes saturated. This occurs when the active site is constantly occupied by substrate molecules. The enzyme is then catalyzing at its maximum rate. Further increases in substrate concentration do not affect the rate. Under normal conditions, enzymes are typically not saturated.
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Inhibitors: Substances that can slow or stop enzyme activity.
- Competitive inhibitors: Bind to the active site of an enzyme, competing with the substrate. They usually have a similar shape and structure to the substrate. When bound, these inhibitors prevent the formation of products. The concentration of the inhibitor must be equal to or greater than the concentration of the substrate for competitive inhibition to occur.
- Noncompetitive inhibitors: Bind to an allosteric site (a different location) on the enzyme, rather than the active site. This binding causes a change in the shape of the active site, thus hindering the enzyme's function. The concentration of the inhibitor is typically much lower than that of the substrate.
- Allosteric activators: Bind to a site on the enzyme that increases the affinity of the enzyme for its substrate.
- Feedback inhibition: The end product of a metabolic pathway allosterically (noncompetitively) inhibits an enzyme earlier in the pathway. This is a mechanism of biochemical control that prevents cells from making more of a substance than they need.
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Temperature: As temperature increases, the rate of enzymatic reactions generally increases.
Carbohydrate Catabolism
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Carbohydrate catabolism: The breakdown of carbohydrates to release energy. This process involves the enzymatic hydrolysis of glycosidic bonds in polysaccharides to form monomers. Hydrolysis is the splitting of a molecule with the addition of water (the reverse of dehydration).
- Amylase: An enzyme that hydrolyzes glycogen or starch into glucose monomers.
- Cellulase: An enzyme that hydrolyzes cellulose into glucose monomers.
- Glucose: The most common carbohydrate used by cells. Glucose is a highly reduced compound, meaning it contains a lot of energy stored in its reduced bonds.
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Processes of glucose catabolism: Both processes initially involve glycolysis.
- Cellular respiration: A process that produces ATP by oxidizing glucose with the help of an electron transport chain.
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Fermentation: A process that produces ATP by oxidizing glucose.
- Fermentation does not utilize an electron transport chain.
- It relies on organic molecules as its final electron acceptor.
- The process yields much less ATP than cellular respiration.
Glycolysis (Sugar Lysis):
- A central metabolic pathway in most prokaryotes and eukaryotes for the breakdown of glucose.
- Occurs in the cytoplasm: This 10-step process does not require oxygen (anaerobic).
- Splitting of Glucose: A single 6-carbon glucose molecule is split into two molecules of pyruvate (a 3-carbon sugar).
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Glycolytic Pathways: The EMP, ED, and PPP pathways are all glycolytic pathways.
- Embden-Meyerhof-Parnas (EMP) pathway: The most common pathway in microbes and also found in animals.
- Entner-Doudoroff (ED) pathway: Found in some bacteria.
- Pentose phosphate pathway (PPP): Used for biosynthesis of certain amino acids and nucleotides.
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EMP pathway:
- Energy investment phase (2 ATP used): A 6-carbon sugar (glucose) is split into two phosphorylated 3-carbon molecules (G3P).
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Energy payoff phase (4 ATP formed by SLP): The two G3P molecules are oxidized to 2 pyruvate molecules. Four ATP are generated by substrate-level phosphorylation (SLP).
- Net yield of ATP = 4 - 2 = 2 ATP
- SLP: A phosphate group is removed from an organic molecule and directly transferred to an available ADP molecule, producing ATP.
- Two NADH are produced in this phase.
Transition (Bridge) Reaction
- Pyruvate to Acetyl CoA: Pyruvate produced in glycolysis can be further oxidized in the Krebs cycle for additional energy production.
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Decarboxylation: Occurs first in the transition reaction:
- Pyruvate (3 carbons) is oxidized to an acetyl group (2 carbons).
- NAD+ is reduced to NADH.
- Acetyl CoA: The acetyl group attaches to coenzyme A (CoA) forming acetyl CoA.
- Location: Occurs in the cytoplasm (prokaryotes) and the mitochondrial matrix (eukaryotes).
- Yields for every glucose molecule: Two acetyl CoA and two NADH are formed. The acetyl CoA then proceeds to the Krebs cycle.
The Krebs Cycle (Citric Acid Cycle)
- Electron Transfer and Oxidation: The remaining electrons present in the acetyl group are further transferred and oxidized.
- Location: Occurs in the cytoplasm (prokaryotes) and the mitochondrial matrix (eukaryotes).
- Cycle Process: A closed-loop cycle involving 8 steps.
- Acetyl CoA Entry: Acetyl CoA loses the CoA, and the acetyl group combines with oxaloacetate to form citrate (citric acid).
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Product Production: The oxidation of each acetyl group yields:
- 3 NADH
- 1 FADH2
- 1 GTP, equivalent to 1 ATP by substrate-level phosphorylation
- 2 CO2 are liberated.
- Importance of NADH and FADH2: These molecules carry most of the energy originally present in glucose.
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Intermediates: The products of the Krebs cycle are used in numerous biosynthetic pathways.
- Examples: synthesis of amino acids, fatty acids, nucleotides, etc.
Cellular Respiration
- Electron Transport Chain: Begins with the transfer of electrons from NADH and FADH2. These electrons were produced in glycolysis, the transition reaction, and the Krebs cycle.
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Final Electron Acceptor: Involves the transfer of electrons to a final inorganic electron acceptor.
- Oxygen: Aerobic respiration (most efficient form of respiration).
- Non-oxygen inorganic molecules: Anaerobic respiration. These include nitrate, sulfate, carbonate, etc.
- Location: Occurs in the inner part of the cytoplasmic membrane (prokaryotes) and the inner mitochondrial membrane (eukaryotes).
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Electrochemical Gradient: The energy of electrons is used to pump protons (H+) across the membrane, creating an electrochemical gradient.
- Prokaryotes: Protons are pumped from the cytoplasm to the outside of the cytoplasmic membrane.
- Eukaryotes: Protons are pumped from the mitochondrial matrix to the intermembrane space.
- Proton Motive Force: The buildup of protons on one side of the membrane creates potential energy, known as the proton motive force (PMF).
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ATP Production: The proton motive force can be used to drive the synthesis of ATP via oxidative phosphorylation.
- Oxidative phosphorylation: ATP is produced as protons move back across the membrane through protein channels containing ATP synthase.
Electron Transport Chain (ETC)
- Components: Membrane-associated complexes of proteins and mobile electron carriers (e.g., NADH, FADH2).
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Major Carriers:
- Cytochromes: Contain heme (iron-containing porphyrin ring) as a prosthetic group.
- Flavoproteins: Contain a flavin nucleotide (FAD or FMN) as a prosthetic group.
- Iron-Sulfur Proteins: Contain iron-sulfur clusters as prosthetic groups.
- Quinones: Lipid-soluble electron carriers that can move within the membrane.
Chemiosmosis
- ATP Synthase: A membrane-bound protein that catalyzes the conversion of PMF into ATP.
- Phosphorylation: Protons move through ATP synthase, releasing energy that is used to phosphorylate ADP, producing ATP (oxidative phosphorylation).
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Total ATP Yield:
- SLP: 4 ATP are generated through substrate-level phosphorylation.
- Oxidative phosphorylation: 34 ATP are typically generated through oxidative phosphorylation.
Aerobic Respiration
- Oxygen as Final Electron Acceptor: The final electron acceptor in aerobic respiration is oxygen.
- Water Formation: Oxygen is reduced into water by the final ETC carrier, cytochrome oxidase.
- Limitations: Aerobic respiration may not be possible if cytochrome oxidase or other enzymes involved in the process are missing or if oxygen availability is low.
Anaerobic Respiration
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Non-oxygen Electron Acceptor: The final electron acceptor in anaerobic respiration is a substance other than oxygen.
- Examples: nitrate, sulfate, carbonate.
- Electron Transfer: Electrons from NADH and FADH2 are transferred to a non-oxygen, inorganic electron acceptor. This is coupled with the release of energy.
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Examples of Products:
- Nitrate: Reduced to nitrite or nitrogen gas.
- Sulfate: Reduced to hydrogen sulfide.
- Carbonate: Reduced to methane.
- Role in Biogeochemical Cycles: Anaerobic respiration is essential for the nitrogen and sulfur cycles.
- ATP Yield: Yields less ATP than aerobic respiration.
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Description
This quiz focuses on microbial metabolism, highlighting the critical processes of catabolism and anabolism. It explores how cells generate energy through ATP and the classification of organisms based on their carbon and energy sources. Test your understanding of these fundamental biological concepts!
