Chapter 6

What is thermodynamics concerned with?

Thermodynamics is the branch of chemistry that deals with energy changes.

What does energy mean in a biological context?

Energy is the capacity to do work.

What are the two states of energy?

The two states of energy are kinetic energy (energy of motion) and potential energy (stored energy).

Name some forms of energy found in living systems.

Energy exists in forms such as mechanical energy, heat, sound, electric current, light, and radioactive radiation.

What is the significance of kilocalories in metabolism?

Kilocalories (kcal/Cal) are the most common unit of measurement for energy, equal to 1000 calories.

What is the basic equation that describes free energy in a system?

G = H - TS, where G is free energy, H is enthalpy, T is temperature, and S is entropy.

What does a positive ΔG indicate about a reaction?

A positive ΔG indicates that the reaction is endergonic and requires an input of energy.

What characterizes an exergonic reaction?

An exergonic reaction has a negative ΔG and releases excess free energy as heat.

What is ATP and why is it important?

ATP (adenosine triphosphate) powers almost every energy-requiring process in cells.

Describe the structure of ATP.

ATP consists of ribose, adenine, and a chain of three phosphates.

What happens during the hydrolysis of ATP?

Hydrolysis of ATP breaks the outermost phosphate bond, converting ATP to ADP and releasing energy.

What role do enzymes play in biological reactions?

Enzymes lower the activation energy needed for reactions to occur, increasing the rate of the reaction.

What are active sites in enzymes?

Active sites are clefts on enzymes where substrates bind to form enzyme-substrate complexes.

What is feedback inhibition in metabolic pathways?

Feedback inhibition occurs when the end products of a pathway bind to an allosteric site on the enzyme, preventing further reactions.

What factors affect enzyme function?

Factors include temperature, pH, salinity, and the presence of inhibitors or activators.

Define catalysis.

Catalysis is the process of lowering the activation energy needed for a reaction, often facilitated by enzymes.

What distinguishes competitive from noncompetitive inhibitors?

Competitive inhibitors bind to the active site of an enzyme, while noncompetitive inhibitors bind to a different site, altering the enzyme's shape.

What is the difference between anabolic and catabolic pathways?

Anabolic pathways are metabolic processes that construct larger molecules from smaller units, requiring an input of energy, often in the form of ATP. In contrast, catabolic pathways involve the breakdown of complex molecules into simpler ones, releasing energy in the process, which can then be used for various cellular activities.

What is an allosteric inhibitor?

An allosteric inhibitor is a molecule that binds to an enzyme at a site other than the active site, changing the enzyme's shape and decreasing its activity.

What is an irreversible inhibitor?

An irreversible inhibitor is a substance that binds permanently to an enzyme, blocking its activity permanently.

What are coenzymes?

Coenzymes are organic molecules that assist enzymes in catalyzing reactions, often by acting as carriers for chemical groups or electrons.

What are enzyme cofactors?

Enzyme cofactors are non-protein molecules that assist enzyme activity, which can be metal ions or organic molecules, enhancing the enzyme's function.

What are nonprotein enzymes?

Nonprotein enzymes, or ribozymes, are RNA molecules that catalyze chemical reactions, demonstrating that not all catalysts are proteins.

What are multienzyme complexes?

Multienzyme complexes are groups of multiple enzymes that work together, often linked by non-covalent interactions to increase the efficiency of metabolic pathways.

What is the ATP cycle?

The ATP cycle involves the continual conversion of ATP to ADP and the rephosphorylation back to ATP, facilitating energy transfer in cellular processes.