Lecture 10 – Bioenergetics and Enzymes

These flashcards cover the fundamental concepts from Lecture 10 on bioenergetics and enzymes, including energy types, thermodynamic laws, Gibbs free energy, exergonic versus endergonic reactions, enzyme structure and function, regulation mechanisms, metabolic pathways, and feedback control.

What is the definition of energy in biological systems?

The capacity to do work or supply heat.

What is potential energy?

Stored energy, often found in position, chemical bonds, gradients, or charge imbalances.

What is kinetic energy?

Energy of movement that does work and causes change, such as heat or motion.

State the 1st Law of Thermodynamics.

Energy cannot be created or destroyed, only transformed.

State the 2nd Law of Thermodynamics.

Energy transformations increase disorder (entropy) and/or release heat to the universe.

What is thermodynamics?

The study of energy transformations.

Define Gibbs free energy (G).

The amount of potential energy in a system that can do work.

What does a negative ΔG indicate about a reaction?

The reaction is exergonic, releases energy, and is spontaneous (favored).

What does a positive ΔG indicate about a reaction?

The reaction is endergonic, absorbs energy, and is non-spontaneous (requires input).

What is activation energy (EA)?

The energy reactants must absorb to reach the transition state and start a reaction.

How do enzymes affect activation energy?

They lower the activation energy barrier, accelerating the reaction without changing ΔG.

What are enzymes?

Biological catalysts (mostly proteins, some RNA) that speed up chemical reactions.

What is a substrate in enzyme terminology?

The reactant molecule(s) that bind to an enzyme's active site.

What is the active site of an enzyme?

The groove or pocket where specific substrates bind and the reaction occurs.

What is meant by induced fit?

The enzyme changes shape slightly to mold around the substrate, facilitating catalysis.

List two ways enzymes lower activation energy.

1) Hold substrates in the correct orientation; 2) Bend/strain bonds to weaken them.

Outline the three basic steps of enzyme catalysis.

1) Substrate binds to enzyme; 2) Reaction occurs (bonds formed/broken); 3) Products released and enzyme is free again.

How can temperature affect enzyme activity?

Increasing temperature generally speeds reactions up to an optimal point; above that, enzymes denature and activity drops.

How can pH affect enzyme activity?

Each enzyme has an optimal pH; deviations alter charge and shape, reducing activity.

Define competitive inhibition.

An inhibitor resembling the substrate binds to the active site, blocking substrate access.

Define noncompetitive inhibition (allosteric regulation).

An inhibitor binds to a separate (allosteric) site, changing enzyme shape and preventing substrate binding.

What is phosphorylation in enzyme regulation?

Addition of a phosphate group (often from ATP) that changes enzyme shape, activating or inactivating it.

What is enzyme saturation?

A point where all enzyme active sites are occupied; reaction rate cannot increase without adding more enzyme.

Define metabolic pathway.

A series of enzyme-catalyzed reactions converting a starting molecule to an end product.

Differentiate anabolic and catabolic pathways.

Anabolic pathways consume energy to build large molecules; catabolic pathways release energy by breaking molecules down.

Are anabolic reactions typically endergonic or exergonic?

Endergonic.

Are catabolic reactions typically endergonic or exergonic?

Exergonic.

What is feedback inhibition?

A regulatory mechanism in which the end product of a pathway inhibits an early enzyme, shutting the pathway down.

Give an example of an enzyme and its function.

Kinase – adds phosphate groups to substrates.

What term describes the unstable configuration reactants must reach during a reaction?

Transition state.

Why can’t organisms simply use high heat to speed up reactions?

Excessive heat denatures proteins and damages cells, so enzymes provide a safe alternative for increasing reaction rates.

What type of inhibition occurs when both inhibitor and substrate can bind to the same active site?

Competitive inhibition.