Metabolism and Cellular Respiration: Energy, Reactions, and Pathways

What do all living organisms require energy for?

To power muscle, pump blood, absorb nutrients, exchange respiratory gases, synthesize new molecules, and establish cellular ion concentrations.

What is ATP?

ATP, or adenosine triphosphate, is the 'energy currency' of cells formed by the breakdown of glucose through metabolic pathways.

Define energy.

Energy is the capacity to do work.

What are the two classes of energy?

Potential energy and kinetic energy.

What is potential energy?

Potential energy is the energy of position or stored energy.

What is kinetic energy?

Kinetic energy is the energy of motion.

How can potential energy be converted?

Potential energy can be converted to kinetic energy before it can do work.

What is chemical energy?

Chemical energy is a form of potential energy stored in a molecule's chemical bonds, released when covalent bonds are broken.

Name three molecules that function in chemical energy storage.

Triglycerides, glucose, and ATP.

What is electrical energy?

Electrical energy is the movement of charged particles, such as ions across the plasma membrane of a neuron.

What is mechanical energy?

Mechanical energy is exhibited by objects in motion due to applied force, such as muscle contraction for walking.

What is sound energy?

Sound energy is caused by the compression of molecules due to a vibrating object, like sound waves causing vibration of the eardrum.

What is radiant energy?

Radiant energy is the energy of electromagnetic waves, such as visible light striking the retina.

What is heat in terms of energy?

Heat is kinetic energy from the movement of atoms, ions, or molecules, usually not available to do work.

What does the first law of thermodynamics state?

Energy can neither be created nor destroyed; it can only change in form.

What does the second law of thermodynamics state?

When energy is transformed, some energy is lost to heat, decreasing the amount of usable energy.

What is metabolism?

Metabolism refers to all biochemical reactions in living organisms.

What are reactants in a chemical equation?

Reactants are substances present prior to the start of a chemical reaction, written on the left side of the equation.

What are products in a chemical equation?

Products are substances formed by the reaction, written on the right side of the equation.

What does a balanced chemical equation indicate?

In a balanced equation, the number of elements is equal on both sides of the reaction.

What are the three criteria for classifying chemical reactions?

Changes in chemical structure, changes in chemical energy, and changes in the number of molecules.

What is a decomposition reaction?

A reaction where a large molecule is broken down into smaller structures (e.g., AB → A + B).

What is an example of a decomposition reaction?

The hydrolysis reaction of sucrose into glucose and fructose.

What term refers to all decomposition reactions in the body?

Catabolism or catabolic reactions.

What is a synthesis reaction?

A reaction where two or more structures combine to form a larger structure (e.g., A + B → AB).

What is the collective term for all synthesis reactions in the body?

Anabolism or anabolic reactions.

What is an exchange reaction?

A reaction where groups are exchanged between two chemical structures, containing both decomposition and synthesis components (e.g., AB + C → A + BC).

What is a redox reaction?

An exchange reaction where electrons are moved from one chemical structure to another, involving oxidation and reduction.

What happens to a structure that loses an electron during a redox reaction?

It is oxidized.

What happens to a structure that gains an electron during a redox reaction?

It is reduced.

What are exergonic reactions?

Reactions where reactants have more energy than products, resulting in energy release (e.g., decomposition reactions).

What are endergonic reactions?

Reactions where reactants have less energy than products, requiring energy input (e.g., synthesis reactions).

What is ATP cycling?

The continuous formation and breakdown of ATP, providing energy for cellular processes.

What defines an irreversible reaction?

A reaction that results in a net loss of reactants and a net gain in products (e.g., A + B → AB).

What defines a reversible reaction?

A reaction that can proceed in both directions, reaching equilibrium with no net change in concentration of reactants or products.

What is an example of a reversible reaction?

The carbonic acid reaction where carbon dioxide and water form carbonic acid, which can dissociate back into its components.

What is reaction rate?

A measure of how quickly a chemical reaction takes place.

What is activation energy (Ea)?

The energy required to break existing chemical bonds, a primary factor determining reaction rate.

How do enzymes affect activation energy?

Enzymes decrease the activation energy of cellular reactions, speeding up the reaction rate.

What is the role of enzymes in chemical reactions?

Enzymes are biologically active catalysts that facilitate reactions by lowering activation energy.

What is the active site of an enzyme?

The unique 3-dimensional structure on an enzyme that allows only a single substrate to bind.

What is the induced fit model in enzyme action?

The model where the enzyme changes shape slightly to fit the substrate more closely, facilitating the reaction.

Where can enzymes be located?

Enzymes can remain within cells, be embedded in plasma membranes, or be secreted from the cell.

What is an example of an enzyme that remains within a cell?

DNA polymerase, which helps form new DNA.

What is an example of an enzyme that is secreted from the cell?

Pancreatic amylase, which participates in starch digestion.

What are cofactors in enzyme action?

Molecules or 'helper' ions required to ensure that a reaction occurs, which can be inorganic or organic.

What is the role of inorganic cofactors?

They attach to enzymes to assist in their function, such as zinc ions for carbonic anhydrase.

What are coenzymes?

Organic cofactors, such as vitamins or modified nucleotides, that assist enzymes.

Name the six major functional classes of enzymes.

1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Isomerases 5. Ligases 6. Lyases

What do oxidoreductases do?

They catalyze redox reactions, with dehydrogenases involved in electron transfer.

What is the function of transferases?

They transfer atoms or molecules between chemical structures, such as kinases transferring phosphate groups.

What is the role of hydrolases?

They split chemical bonds using water.

What do isomerases do?

They convert one isomer to another.

What is the function of ligases?

They bond two molecules together.

What do lyases do?

They split bonds without using water.

How does enzyme concentration affect reaction rates?

Increasing enzyme concentration can accelerate the reaction rate until saturation is reached.

What is enzyme saturation?

A point where all enzyme molecules are engaged in the reaction due to high substrate concentration.

At what temperature do human enzymes function best?

Around 40ºC (104ºF).

What happens to enzymes at high temperatures?

Severe increases in temperature can cause protein denaturation and loss of function.

What pH range do most enzymes function best at?

Between pH 6 and 8.

What is the effect of pH changes on enzymes?

Changes in H+ disrupt electrostatic interactions, leading to enzyme denaturation.

What are competitive inhibitors?

Inhibitors that resemble the substrate and bind to the active site, competing with the substrate.

What are noncompetitive inhibitors?

Inhibitors that bind to a site other than the active site, inducing a conformational change in the enzyme.

What is a metabolic pathway?

A series of enzymes where the product of one enzyme becomes the substrate of the next.

What is a multienzyme complex?

A group of attached enzymes that work in a sequence of reactions.

How is enzyme activity regulated through negative feedback?

The product from a metabolic pathway acts as an allosteric inhibitor, turning off an enzyme early in the pathway.

What is phosphorylation?

The addition of a phosphate group to an enzyme, which can turn it on or off.

What is dephosphorylation?

The removal of a phosphate group from an enzyme, which can also turn it on or off.

What is cellular respiration?

An exergonic multistep metabolic pathway where organic molecules are oxidized and disassembled to release energy.

What is the net chemical reaction for glucose oxidation?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O.

What are the two pathways for ATP production?

1. Substrate-level phosphorylation 2. Oxidative phosphorylation.

Where do the enzymes for glucose oxidation reside?

In the cytosol and mitochondria.

What are the four stages of glucose oxidation?

1. Glycolysis 2. Intermediate stage/pyruvate oxidation 3. Citric acid (Kreb's) cycle 4. Oxidative phosphorylation.

Where does the electron transport system occur?

In the inner membrane of the mitochondria.

Does the electron transport system require oxygen?

Yes, it directly requires oxygen.

What is the net production of ATP and NADH from glycolysis?

2 ATP and 2 NADH.

What happens to pyruvate when sufficient oxygen is available?

It enters the mitochondria and is converted to Acetyl-CoA.

What is the fate of pyruvate when oxygen is insufficient?

It is converted to lactate.

What is the role of pyruvate dehydrogenase?

It combines pyruvate with coenzyme A to form Acetyl-CoA.

What is produced during the intermediate stage of cellular respiration?

Acetyl CoA and NADH, with CO2 released.

What are the products of one turn of the citric acid cycle?

1 ATP, 3 NADH, and 1 FADH2.

How many times must the citric acid cycle occur for each glucose molecule?

Twice.

What is oxidative phosphorylation?

The process of ATP production using energy from the electron transport system.

What is the function of H+ pumps in the electron transport system?

They transport H+ from the matrix to the outer membrane compartment, creating a H+ gradient.

What is the final electron acceptor in the electron transport chain?

Oxygen, which forms water (H2O).

What is the role of ATP synthase in cellular respiration?

It forms ATP by creating a bond between ADP and inorganic phosphate (Pi).

What is the total ATP yield from glycolysis, the intermediate stage, and the citric acid cycle?

30 ATP net after accounting for some ATP used during cellular respiration.

What happens to NADH and FADH2 during cellular respiration?

They enter the electron transport chain to help produce ATP.

What is beta oxidation?

The process of converting fatty acids into Acetyl-CoA for entry into the citric acid cycle.

What happens to the amine group when amino acids are used for fuel?

It is converted to urea and excreted by the kidneys.

What must occur for glycolysis to continue if NAD+ levels are low?

NAD+ must be regenerated, often by converting pyruvate to lactate.