Chapter 6: Energy, Enzymes, and Metabolism

Flashcards based on lecture notes about Energy, Enzymes, and Metabolism.

What does the Zeroth Law of Thermodynamics state?

Two systems in equilibrium with a third system are in thermal equilibrium with each other.

What does the First Law of Thermodynamics (Conservation of Energy) state?

Energy can change forms, but is neither created nor destroyed.

What does the Second Law of Thermodynamics state?

Entropy of an isolated system always increases.

What does the Third Law of Thermodynamics state?

Entropy of a system approaches a constant as temperature approaches absolute zero.

What is usable energy?

Ability to promote change or do work

What is Kinetic Energy?

Energy of motion

What is Potential Energy (including Chemical Energy)?

Energy of location or structure stored in molecular bonds.

What is the equation for total energy (H) in relation to usable energy (G) and unusable energy (S)?

H = G + TS (H = enthalpy, G = free energy, T = absolute temperature, S = entropy)

How is the change in free energy calculated?

ΔG = ΔH – TΔS

What are exergonic reactions?

Spontaneous reactions with ΔG < 0, where products have less free energy than reactants, releasing energy.

What are endergonic reactions?

Non-spontaneous reactions with ΔG > 0, where products have more free energy than reactants, requiring the addition of energy.

How is ATP used to drive reactions in the cell?

ATP hydrolysis releases energy (ΔG = -7.3 kcal/mole) that can be used to drive cellular work.

What is the role of catalysts, enzymes, and ribozymes in chemical reactions?

Catalysts speed up reactions without being consumed. Enzymes are protein catalysts, and ribozymes are RNA catalysts.

What is Activation Energy?

Initial energy input to start a reaction, overcome by heat or enzymes.

How do enzymes lower activation energy?

Enzymes strain bonds, position reactants, change the local environment via temporary bonding to lower activation energy.

What is the Active Site (in enzyme terminology)?

Location where the reaction takes place.

What are Substrates (in enzyme terminology)?

Reactants that bind to the active site.

What is the Enzyme-Substrate Complex (in enzyme terminology)?

Formed when an enzyme and substrate bind.

What is substrate specificity and induced fit?

High specificity; the induced fit, is where conformational changes cause tighter substrate binding, this lowers the activation energy. Affinity is the degree of attraction between an enzyme and its substrate.

What is Saturation, Vmax and KM in enzyme catalyzed reactions?

Plateau where all active sites are occupied; Vmax is the velocity at maximal rate. KM is the substrate concentration where velocity is half maximal.

What are the two types of enzyme inhibition?

Competitive inhibitors bind to the active site (increasing KM), while noncompetitive inhibitors bind to an allosteric site (lowering Vmax).

What are Reversible Inhibitors?

Bind noncovalently to either active site (competitive inhibitors) or to the allosteric site (noncompetitive inhibitors).

What are Irreversible Inhibitors?

Bind covalently to enzyme, preventing the enzyme from catalyzing reaction

What are Prosthetic Groups (enzyme modifications)?

Small molecules permanently attached to the enzyme.

What are Cofactors (enzyme modifications)?

Inorganic ions that temporarily bind to the enzyme.

What are Coenzymes (enzyme modifications)?

Organic molecules (like vitamins) that participate in the reaction.

What are Catabolic Pathways?

Breakdown cellular components; exergonic.

What are Anabolic Pathways?

Synthesis cellular components; endergonic, must be coupled to exergonic reaction.

What is Substrate-level Phosphorylation?

Enzyme directly transfers phosphate from one molecule to another molecule.

What is Chemiosmosis?

Energy stored in an electrochemical gradient is used to make ATP from ADP and Pi.

What is a Redox Reaction?

LEO goes GER (Lose electrons = oxidized; Gain electrons = Reduced); Oxidation removes electrons, and Reduction adds electrons.

What is the role of NAD+/NADH?

Electrons removed by oxidation of organic molecules and NAD+ is reduced to NADH.

How are metabolic pathways regulated?

Turn genes on or off (that encode enzymes), regulate enzymes through cell-signaling pathways (phosphorylation); feedback inhibition (non-competitive), and target rate-limiting steps.

What is Half-life of an organic molecule?

Time for 50% of a molecule to be broken down and recycled.

How are proteins recycled?

Proteases cleave bonds between amino acids and Ubiquitin targets proteins to the proteasome for degradation.

What are the function of Lysosomes?

Contains acid hydrolases to break down proteins, carbohydrates, nucleic acids, and lipids; autophagy recycles worn-out organelles.