Lecture Set 15 - Intro to Cellular Respiration and Redox Reaction

What is a redox reaction?

A chemical reaction involving the transfer of electrons between molecules; one molecule is oxidized and another is reduced.

What is oxidation?

The loss of electrons; often involves losing hydrogen.

What is reduction?

The gain of electrons; often involves gaining hydrogen.

What does OIL RIG stand for?

Oxidation Is Loss; Reduction Is Gain of electrons.

Why must oxidation and reduction happen together?

Electrons lost by one molecule must be gained by another molecule.

What is an electron donor?

A molecule that gives away electrons and becomes oxidized.

What is an electron acceptor?

A molecule that gains electrons and becomes reduced.

What is a reducing agent?

A molecule that donates electrons to another molecule and is itself oxidized.

What is an oxidizing agent?

A molecule that accepts electrons from another molecule and is itself reduced.

How can hydrogen transfer indicate oxidation or reduction?

Gaining hydrogen usually means reduction; losing hydrogen usually means oxidation.

What is a coenzyme?

A small, non-protein molecule that helps enzymes perform reactions, often by carrying electrons or atoms.

What is NAD⁺?

A coenzyme that accepts electrons during reactions and becomes NADH when reduced.

What happens when NAD⁺ gains electrons?

It is reduced to NADH.

What is NADH?

The reduced form of NAD⁺ that carries high-energy electrons to other molecules, including the electron transport chain.

What is FAD?

A coenzyme that accepts electrons and hydrogen during redox reactions.

What is FADH₂?

The reduced form of FAD that carries high-energy electrons to the electron transport chain.

How are NADH and FADH₂ similar?

Both carry high-energy electrons that help power ATP production during cellular respiration.

What is an exergonic reaction?

A chemical reaction that releases free energy.

What is chemical energy?

Energy stored in the bonds of molecules that can be released during chemical reactions.

What is energy capture?

Transferring energy released by chemical reactions into usable forms, such as ATP.

What is hydrogen transfer?

The movement of hydrogen atoms, including their electrons, from one molecule to another.

What is the terminal electron acceptor in aerobic cellular respiration?

Oxygen.

What happens when oxygen accepts electrons at the end of the electron transport chain?

Oxygen combines with electrons and hydrogen ions to form water.

Why is oxygen important for aerobic cellular respiration?

Oxygen accepts electrons at the end of the electron transport chain, allowing electron transport to continue.

What happens to the electron transport chain when oxygen is unavailable?

The chain cannot pass electrons to oxygen, so electron transport and oxidative phosphorylation stop.

Does the absence of oxygen mean all ATP production immediately stops?

No. Oxidative phosphorylation stops, but glycolysis may continue if NAD⁺ is regenerated through fermentation or another pathway.

How does NADH help cells produce ATP?

NADH donates high-energy electrons to the electron transport chain; the energy released helps establish a proton gradient that powers ATP synthesis.

How does energy released by redox reactions help produce ATP?

Electron transfers release energy that can be used to establish a proton gradient, which powers ATP synthase to make ATP.

What kinds of cellular work require energy from ATP?

Muscle contraction, active transport, and biosynthesis.

What is an anabolic pathway?

A pathway that builds larger molecules from smaller ones and requires an input of energy.

What is a catabolic pathway?

A pathway that breaks down molecules and releases energy.

What is the difference between anabolic and catabolic pathways?

Anabolic pathways build molecules and require energy; catabolic pathways break molecules down and release energy.

What is the difference between an electron donor and an electron acceptor?

The donor loses electrons and is oxidized; the acceptor gains electrons and is reduced.

What happens to a molecule that loses hydrogen?

It is typically oxidized.

What happens to a molecule that gains hydrogen?

It is typically reduced.

What happens to NADH when it donates electrons?

NADH is oxidized back to NAD⁺.

What happens to FADH₂ when it donates electrons?

FADH₂ is oxidized back to FAD.

Why are NAD⁺ and FAD important in cellular respiration?

They accept electrons during the breakdown of fuel molecules and carry them to reactions that help produce ATP.

What does it mean when a molecule is oxidized or reduced?

Oxidation means losing electrons; reduction means gaining electrons.

Why must oxidation and reduction always happen together?

An electron lost by one molecule must be accepted by another molecule.

How can gaining or losing hydrogen show whether a molecule is oxidized or reduced?

Gaining hydrogen generally indicates reduction; losing hydrogen generally indicates oxidation.

How do redox reactions help release energy in cells?

Electrons transfer between molecules, releasing free energy that cells can harness to perform work and produce ATP.

What role does NAD⁺ play in cellular respiration?

NAD⁺ accepts electrons during fuel breakdown and becomes NADH, which carries electrons to the electron transport chain.

What happens when NADH gives up its electrons?

NADH becomes NAD⁺, and its electrons enter the electron transport chain, helping power the proton gradient used for ATP production.

Why does cellular respiration need oxygen to keep going efficiently?

Oxygen is the final electron acceptor in aerobic respiration. Without it, the electron transport chain backs up and oxidative phosphorylation stops.

How does energy from redox reactions help make ATP?

The energy released during electron transport is used to pump protons across the inner mitochondrial membrane. Their flow through ATP synthase powers ATP production.

APPLICATION: Molecule A loses electrons to molecule B. Which molecule is oxidized?

Molecule A, because oxidation is the loss of electrons.

APPLICATION: Molecule A gains electrons from molecule B. Which molecule is reduced?

Molecule A, because reduction is the gain of electrons.

APPLICATION: NAD⁺ accepts electrons during glucose breakdown. Is NAD⁺ oxidized or reduced?

Reduced, because it gains electrons and becomes NADH.

APPLICATION: NADH donates electrons to another molecule. What happens to NADH?

It is oxidized back to NAD⁺.

APPLICATION: A molecule gains hydrogen atoms. What usually happens to its oxidation state?

It is reduced.

APPLICATION: A molecule loses hydrogen atoms. What usually happens to it?

It is oxidized.

APPLICATION: A cell has plenty of glucose but no oxygen. Why does its electron transport chain stop?

Oxygen is unavailable to accept electrons at the end of the chain, so electron transport cannot continue normally.

APPLICATION: A student says oxygen directly provides the energy for ATP synthase. What is the better explanation?

Oxygen accepts electrons at the end of the electron transport chain. Electron transfers release energy that builds the proton gradient, which powers ATP synthase.

APPLICATION: Why can NADH help produce ATP even though it is not ATP itself?

NADH carries high-energy electrons whose transfer releases energy used to establish the proton gradient that powers ATP synthesis.

APPLICATION: A cell cannot regenerate NAD⁺. What problem would this cause for glucose breakdown?

Reactions requiring NAD⁺ would slow or stop because there would be insufficient NAD⁺ to accept electrons.

APPLICATION: A molecule donates electrons and is itself oxidized. Is it the reducing agent or oxidizing agent?

The reducing agent, because it donates electrons to another molecule.

APPLICATION: A molecule accepts electrons and is itself reduced. Is it the reducing agent or oxidizing agent?

The oxidizing agent, because it accepts electrons from another molecule.

APPLICATION: A cell is building proteins from amino acids. Is this anabolic or catabolic?

Anabolic, because the cell is building larger molecules and needs energy.

APPLICATION: A cell breaks down glucose to release usable energy. Is this anabolic or catabolic?

Catabolic, because the cell breaks down a molecule and releases energy.

APPLICATION: Why can a redox reaction help power muscle contraction?

The reaction can release free energy that is captured in ATP, which powers muscle contraction.

APPLICATION: NADH and FADH₂ both deliver electrons to the electron transport chain. What do they have in common?

Both are reduced coenzymes that carry high-energy electrons used to help generate ATP.

APPLICATION: Oxygen accepts electrons and forms water. Is oxygen oxidized or reduced?

Reduced, because it gains electrons.

APPLICATION: Why does electron transfer have to involve both a donor and an acceptor?

Electrons cannot be transferred unless one molecule gives them up and another molecule receives them.

APPLICATION: A reaction releases free energy. What type of reaction is it?

Exergonic.

APPLICATION: A cell uses energy to build a complex molecule from smaller molecules. What type of pathway is involved?

An anabolic pathway.

APPLICATION: A cell breaks down stored fuel molecules. What type of pathway is involved?

A catabolic pathway.