Chapter 6 Metabolism, Energy, and Enzymes

Flashcards for studying cellular metabolism, thermodynamics, ATP functions, enzyme regulation, and redox reactions based on Chapter 6 notes.

What is the biological definition of energy?

Energy is defined as the ability to do work or bring about change.

How do producers and consumers differ in how they obtain energy?

Producers use solar energy to make organic nutrients via photosynthesis, whereas consumers obtain energy by eating other organisms.

What is the fundamental difference in how energy and matter move through an ecosystem?

Energy flows through an ecosystem and ultimately dissipates as heat, whereas matter cycles.

What does the First Law of Thermodynamics state?

Energy cannot be created or destroyed, but it can only be changed from one form to another.

What does the Second Law of Thermodynamics state?

Energy cannot change forms without a loss of usable energy, which dissipates as heat into the environment.

What is the approximate efficiency of energy utilization in cells compared to a gasoline car engine?

Cells operate at approximately $40\%$ efficiency, whereas a car engine operates at approximately $20\text{--}30\%$ efficiency.

What is entropy and how is it affected by cellular processes?

Entropy is the measure of disorder or disorganization, and every cellular process increases the total entropy of the universe.

How do glucose and a mixture of carbon dioxide and water compare in terms of organization and potential energy?

Glucose is more organized, contains more potential energy, and is less stable, whereas carbon dioxide and water are less organized, contain less potential energy, and are more stable.

How is free energy ($\Delta G$) calculated for a chemical reaction?

$$\Delta G = \text{free energy of products} - \text{free energy of reactants}$$

What characterizes an exergonic reaction in terms of energy release, $\Delta G$, and spontaneity?

Exergonic reactions release energy, have a negative $\Delta G$ ($-\Delta G$), and occur spontaneously.

What characterizes an endergonic reaction in terms of energy requirement, $\Delta G$, and spontaneity?

Endergonic reactions require an input of energy, have a positive $\Delta G$ ($+\Delta G$), and are non-spontaneous.

What three structural components make up a molecule of ATP?

Adenine (a nitrogenous base), ribose (a 5-carbon sugar), and three negatively charged phosphate groups.

What term refers to the combination of adenine and ribose without phosphate groups?

Adenosine.

How much energy is released per mole during the hydrolysis of ATP into ADP and inorganic phosphate ($\text{P}_i$)?

Hydrolysis of ATP releases approximately $7.3\,kcal$ per mole.

What percentage of the free energy in glucose is captured as ATP during cellular respiration?

Approximately $39\%$ of the free energy in glucose is captured in ATP.

What are the three main types of cellular work powered by ATP?

Chemical work (building macromolecules), transport work (pumping substances across membranes), and mechanical work (muscle contraction and organelle movement).

What is a coupled reaction in cellular metabolism?

A process in which an energy-releasing (exergonic) reaction occurs in the same place and at the same time to drive an energy-requiring (endergonic) reaction.

What occurs when a reactant molecule is phosphorylated by ATP?

A phosphate group is transferred to the reactant molecule, which alters its shape or adds energy to drive an otherwise unfavorable reaction.

In muscle contraction, what event directly causes the myosin head to pull on actin?

The release of ADP and inorganic phosphate ($\text{P}_i$) causes myosin to change shape and pull on actin.

What is an enzyme?

A biological catalyst (usually a protein) that speeds up a chemical reaction without being consumed or permanently changed by it.

What are ribozymes?

Ribozymes are RNA-based enzymes that assist in synthesizing RNA and proteins at ribosomes.

What is a metabolic pathway?

A series of linked chemical reactions starting with a specific reactant and ending with a final product, with each step catalyzed by a specific enzyme.

What is the induced fit model of enzymatic activity?

The model stating that an enzyme's active site undergoes a slight change in shape to fit the substrate optimally upon binding.

How do three amino acids in the active site of trypsin digest proteins?

They interact directly with the peptide bond of a protein to break it and then add the components of water.

What is energy of activation ($E_a$)?

The minimum energy that must be added to enable molecules to react with one another.

How do enzymes affect the activation energy ($E_a$) and rate of a reaction?

Enzymes lower the activation energy ($E_a$), thereby increasing the rate of the reaction.

By how much can enzymes increase the rate of a chemical reaction?

Enzymes can increase reaction rates by more than $10\text{ million}$ times.

Do enzymes change the overall free energy content of the products of a reaction?

No, enzymes only affect the reaction rate by lowering activation energy and do not alter the energy content of reactants or products.

What is denaturation in reference to enzymes?

A change in the three-dimensional shape of an enzyme's active site that prevents substrate binding and inactivates the enzyme.

What happens to the rate of an enzyme-catalyzed reaction as substrate concentration increases continuously?

The reaction rate increases initially due to more frequent collisions, but eventually levels off at a maximum rate once active sites are saturated.

What are the optimal pH values for the digestive enzymes pepsin and trypsin?

Pepsin has an optimal pH of approximately $2$, while trypsin has an optimal pH of approximately $8$.

How does temperature affect enzyme activity up to approximately $40\,^\circ C$?

The rate of enzyme activity roughly doubles for every $10\,^\circ C$ increase in temperature up to about $40\,^\circ C$.

Why do Siamese cats have darker fur on their ears, face, legs, and tail?

They inherit a mutation that renders a pigment-producing enzyme active only at the cooler temperatures of their body extremities.

What is the difference between an inorganic cofactor and a coenzyme?

A cofactor is an inorganic ion (such as copper, zinc, or iron), whereas a coenzyme is a nonprotein organic molecule (such as NAD, NADP, or FAD).

Which deficiency disorder results from a dietary lack of niacin, a building block of NAD?

Pellagra, which is a skin disease.

What symptom is caused by a dietary deficiency in riboflavin (Vitamin $B_2$)?

Cracks at the corners of the mouth.

What are the specific functions of kinase and phosphatase enzymes?

A kinase adds phosphate groups to proteins, whereas a phosphatase removes phosphate groups.

What is negative feedback in a metabolic pathway?

A regulatory mechanism where the end product of a pathway inhibits an enzyme operating early in that pathway to prevent overproduction.

How does competitive enzyme inhibition differ from noncompetitive enzyme inhibition?

In competitive inhibition, the inhibitor binds directly to the active site; in noncompetitive inhibition, the inhibitor binds to an allosteric site.

What is an allosteric site on an enzyme?

A specific binding location on an enzyme other than the active site.

How does carbon monoxide (CO) disrupt cellular function at the enzymatic level?

Carbon monoxide inhibits cytochrome c oxidase in the mitochondrial electron transport chain, preventing cells from producing sufficient ATP.

What does the mnemonic OIL RIG stand for in oxidation-reduction reactions?

Oxidation Is Loss (of electrons/hydrogen), Reduction Is Gain (of electrons/hydrogen).

How are oxidation and reduction tracked in covalent biological reactions?

They are tracked by following the movement of hydrogen atoms ($e^- + H^+$), where loss of hydrogen is oxidation and gain of hydrogen is reduction.

What is the balanced chemical equation for photosynthesis?

$$\text{Light energy} + 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2$$

During photosynthesis, which molecule is oxidized and which is reduced?

Water ($\text{H}_2\text{O}$) is oxidized to oxygen, and carbon dioxide ($\text{CO}_2$) is reduced to glucose.

How much chemical energy is stored in one mole of glucose produced during photosynthesis?

Approximately $686\,kcal$ of energy is stored per mole of glucose.

What is the balanced chemical equation for cellular respiration?

$$\text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2 \rightarrow 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + \text{energy}$$

During cellular respiration, which molecule is oxidized and which is reduced?

Glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) is oxidized to carbon dioxide, and oxygen ($\text{O}_2$) is reduced to water.

How do chloroplasts and mitochondria function together as a redox cycle?

Chloroplasts convert solar energy, $\text{CO}_2$, and $\text{H}_2\text{O}$ into glucose and $\text{O}_2$; mitochondria break down glucose and $\text{O}_2$ back into $\text{CO}_2$ and $\text{H}_2\text{O}$ to produce ATP.

Why must cells oxidize glucose gradually in multiple steps during cellular respiration?

Gradual oxidation allows the cell to capture energy incrementally to build ATP rather than losing most of the energy as heat all at once.