chapter 6. Energy and Metabolism

Flashcards covering energy, thermodynamics, metabolism, enzyme kinetics, inhibition, and ATP based on the Bio103 lecture by Dr. Hannah Chu.

How is energy defined in the lecture?

The ability to do work.

What is the focus of bioenergetics?

The study of how an organism manages energy resources.

What are the three types of energy identified in the notes?

Kinetic energy (energy of motion), potential energy (stored energy), and chemical energy (energy in chemical bonds).

What is the definition of a calorie?

The heat required to raise $1\,g$ $H_2O$ by $1^{\circ}C$.

What is metabolism?

The sum of an organism's chemical reactions.

Contrast anabolism and catabolism.

Anabolism consumes energy to build large molecules from smaller ones (e.g., making macromolecules), while catabolism releases energy by breaking down large molecules into smaller ones (e.g., breaking down glucose).

What is energy coupling?

A relationship in which energy released from catabolic pathways is used to drive anabolic pathways, often involving ATP.

What happens in a redox reaction?

One substance undergoes oxidation (loss of electron) and another undergoes reduction (gain of electron).

What is the first law of thermodynamics?

Energy in the universe is conserved; it is never created or destroyed, only changed from one form to another.

What is the second law of thermodynamics regarding entropy?

The entropy of the universe is increasing and favored; disorder is favored and releases energy, so energy is required to work against this.

What is the formula for Gibbs free energy ($G$)?

$G = H - TS$, where $H$ is enthalpy (energy stored in chemical bonds), $T$ is absolute temperature ($K$), and $S$ is entropy (unavailable energy).

What does a negative Gibbs free energy change ($\Delta G < 0$) signify?

The reaction is exergonic and spontaneous (favorable), meaning free energy is released and no energy is required to start the reaction.

What does a positive Gibbs free energy change ($\Delta G > 0$) signify?

The reaction is endergonic and non-spontaneous (unfavorable), meaning free energy is absorbed and energy must be supplied.

How is the change in free energy ($\Delta G$) calculated relative to the state of products and reactants?

$\Delta G = G_{final} - G_{initial}$.

What is activation energy ($E_a$)?

The energy barrier forming a \"hill\" that must be overcome for any reaction to proceed.

What is the transition state (TS) of a reaction?

A highly unstable state at the peak of the activation energy hill where bonds are simultaneously breaking and forming.

How do catalysts like enzymes affect the activation energy and rate of a reaction?

They increase the rate of a reaction by stabilizing the transition state and lowering the $E_a$, without affecting the $\Delta G$.

Define substrate and active site.

The substrate is the reactant that is acted upon by an enzyme, and the active site is the precise region of the enzyme that binds to the substrate.

What is the difference between co-factors and co-enzymes?

Co-factors are non-protein based (such as $Zn^{2+}$ or $Mg^{2+}$), whereas co-enzymes are organic based (such as vitamins).

How do competitive inhibitors function?

They bind to the enzyme at the active site, mimicking the substrate and directly interfering with the enzyme-substrate interaction.

How do non-competitive (allosteric) inhibitors function?

They bind to the enzyme at regulatory (allosteric) sites and inhibit activity by inducing a change in the shape of the active site.

What is feedback inhibition?

A regulatory mechanism where a high concentration of the final product inhibits the enzyme pathway to shut it down so energy and materials are not wasted.

What is the energy change ($\Delta G$) for ATP hydrolysis?

$\Delta G = -7.3\,kcal/mol$, which defines it as a very exergonic reaction.

Describe the ATP cycle in terms of energy coupling.

Energy from exergonic catabolic reactions generates ATP from $ADP + P_i$, and energy released from ATP hydrolysis provides power for endergonic anabolic processes.