Chapter 6: Metabolism Flashcards
Define metabolism.
The totality of an organism’s chemical reactions, divided into catabolism (breaking down molecules to release energy) and anabolism (building molecules using energy).
Differentiate catabolic and anabolic pathways with examples.
Catabolic: Breaks glucose → CO₂ + H₂O (cellular respiration). Releases energy (exergonic).
Anabolic: Builds amino acids → proteins. Consumes energy (endergonic).
What is a metabolic pathway? Give an example.
A series of enzyme-catalyzed reactions where the product of one reaction becomes the substrate for the next. Example: Glycolysis (glucose → pyruvate).
How do cells couple exergonic and endergonic reactions?
Energy from exergonic reactions (e.g., ATP hydrolysis) drives endergonic reactions (e.g., synthesizing DNA).
Define potential energy. Give a biological example.
Stored energy based on position/structure. Example: Energy in glucose’s chemical bonds or a proton gradient.
Define kinetic energy. Give a biological example.
Energy of motion. Example: Heat released during cellular respiration or movement of flagella.
What is free energy (ΔG)? How does it determine reaction spontaneity?
ΔG = Energy available to do work.
Exergonic: ΔG < 0 (spontaneous, e.g., ATP → ADP).
Endergonic: ΔG > 0 (requires energy input, e.g., photosynthesis).
What is activation energy (Eₐ)? Why is it important?
The energy required to start a reaction (e.g., breaking bonds in reactants). Without enzymes, Eₐ would make most reactions too slow for life.
How do enzymes lower activation energy?
Enzymes stabilize the transition state, orient substrates correctly, and provide a microenvironment (e.g., acidic residues).
State the First Law of Thermodynamics.
Energy cannot be created or destroyed—only transformed (e.g., sunlight → chemical energy in plants).
State the Second Law of Thermodynamics.
Every energy transfer increases entropy (disorder) in the universe. Example: Heat lost during metabolism increases environmental entropy.
How do living organisms maintain order without violating the Second Law?
Cells create internal order by releasing heat/disordered waste, increasing external entropy.
What is entropy? How does it relate to glucose breakdown?
Entropy = disorder. Glucose (ordered) → CO₂ + H₂O (dispersed molecules) increases entropy.
Describe ATP’s structure.
Adenine (nitrogenous base) + ribose (sugar) + 3 phosphate groups. High-energy bonds between phosphates.
How does ATP store energy?
Energy is stored in the bonds between the second and third phosphate groups.
What happens during ATP hydrolysis?
ATP + H₂O → ADP + Pi (inorganic phosphate) + energy (ΔG ≈ -7.3 kcal/mol).
How is ATP regenerated?
ADP + Pi → ATP via phosphorylation using energy from catabolic reactions (e.g., oxidative phosphorylation).
Why is ATP called the ‘energy currency’ of the cell?
It transfers energy between reactions (e.g., ATP powers muscle contraction, active transport, and biosynthesis).
What are enzymes? How do they work?
Proteins that speed up reactions by lowering Eₐ. They bind substrates at the active site, forming an enzyme-substrate complex.
Explain the induced-fit model.
The enzyme’s active site adjusts shape to snugly fit the substrate, enhancing catalysis (e.g., hexokinase binding glucose).
Define substrate and active site.
Substrate: The molecule the enzyme acts on (e.g., lactase acts on lactose). Active site: Enzyme region where the substrate binds.
How does temperature affect enzyme activity?
Activity increases with temperature until denaturation occurs (e.g., human enzymes peak at ~37°C).
How does pH affect enzyme function?
Enzymes have optimal pH ranges (e.g., pepsin = pH 2 in the stomach; trypsin = pH 8 in the small intestine).
Differentiate competitive vs. non-competitive inhibition.
Competitive: Inhibitor mimics substrate (e.g., statins blocking HMG-CoA reductase).
Non-competitive: Inhibitor binds elsewhere, altering enzyme shape (e.g., cyanide binding cytochrome c oxidase).
What are cofactors and coenzymes?
Cofactors: Inorganic ions (e.g., Fe²⁺ in hemoglobin).
Coenzymes: Organic molecules (e.g., NAD⁺, FAD, vitamins).
What is feedback inhibition?
A product of a pathway inhibits an earlier enzyme (e.g., ATP inhibiting phosphofructokinase in glycolysis).
How do allosteric regulators work?
They bind to enzymes at sites other than the active site, inducing conformational changes (e.g., AMP activating glycogen phosphorylase).
What is enzyme denaturation?
Loss of 3D structure/function due to extreme conditions (e.g., cooking an egg denatures albumin).
How does ATP drive active transport?
ATP hydrolysis provides energy to pump ions against gradients (e.g., Na⁺/K⁺ ATPase moving 3 Na⁺ out and 2 K⁺ in).
Explain ATP’s role in coupled reactions.
ATP hydrolysis (exergonic) is linked to endergonic reactions (e.g., glutamine synthesis: ATP → ADP + Pi provides energy).
What is the role of NAD⁺ in metabolism?
NAD⁺ accepts electrons (becomes NADH) during glycolysis and the citric acid cycle, carrying energy to the electron transport chain.
Why is the first enzyme in a pathway often the target of regulation?
To prevent unnecessary use of resources (e.g., isoleucine inhibits threonine deaminase in its own synthesis pathway).
How do irreversible inhibitors work?
They form covalent bonds with enzymes, permanently disabling them (e.g., penicillin binding transpeptidase in bacteria).
What is a zymogen?
An inactive enzyme precursor activated by cleavage (e.g., pepsinogen → pepsin in the stomach).
How do metabolic pathways intersect?
Intermediates can enter multiple pathways (e.g., acetyl-CoA links glycolysis, fatty acid synthesis, and the citric acid cycle).
