Life Science 7A - Cellular Respiration (Week 3b)

What is the overall purpose of cellular respiration?

Transfer energy in food into ATP for cellular work.

What is the overall cellular respiration equation?

Glucose + 6 O2 → 6 CO2 + 6 H2O + energy.

What happens to matter during cellular respiration?

Atoms are rearranged; glucose carbon becomes CO2 and oxygen helps form water.

What happens to energy during cellular respiration?

Free energy from food is transferred to NADH/FADH2 and ATP; some is released as heat.

Why does highly reduced carbon store high free energy?

Its electrons can be transferred to lower-energy states, releasing usable free energy.

What is oxidation?

Loss of electrons; often loss of hydrogen.

What is reduction?

Gain of electrons; often gain of hydrogen.

What does OIL RIG mean?

Oxidation Is Loss; Reduction Is Gain (of electrons).

What is a reducing agent?

An electron donor; it is oxidized as it reduces another molecule.

What is an oxidizing agent?

An electron acceptor; it is reduced as it oxidizes another molecule.

When NAD+ becomes NADH, what happens?

NAD+ gains electrons and is reduced, storing transferable energy.

When NADH becomes NAD+, what happens?

NADH loses electrons and is oxidized.

How are FAD and FADH2 related?

FAD gains electrons/hydrogen to become reduced FADH2.

What does redox potential indicate in the ETC?

A carrier’s tendency to accept electrons; more positive potential favors electron acceptance.

Which way do electrons generally flow through the ETC?

Toward carriers with increasingly positive redox potentials.

How does ETC electron flow release usable energy?

Electrons move to higher redox potential/lower free energy, and released energy powers H+ pumping.

What redox-potential trend is shown in the lecture ETC model?

It rises overall from about −320 mV for NADH toward +850 mV for O2.

What may happen if an ETC carrier’s redox potential is changed greatly?

Electron transfer may become unfavorable or slowed, disrupting downstream flow.

Where does glycolysis occur in a eukaryotic cell?

Cytosol.

What goes into glycolysis?

Glucose, NAD+, ADP, and inorganic phosphate; 2 ATP are invested initially.

What are the net products of glycolysis per glucose?

2 pyruvate, net 2 ATP, and 2 NADH.

Does glycolysis directly require oxygen?

No; it can occur without oxygen if NAD+ is regenerated.

What is the net ATP yield of glycolysis?

2 ATP per glucose.

Where does pyruvate oxidation occur in eukaryotes?

Mitochondrial matrix.

What are the products of pyruvate oxidation per glucose?

2 acetyl-CoA, 2 CO2, and 2 NADH.

Why is pyruvate oxidation important?

It links glycolysis to the citric acid cycle by making acetyl-CoA.

Where does the citric acid cycle occur?

Mitochondrial matrix.

How many times does the citric acid cycle turn per glucose?

Twice, because one glucose yields two acetyl-CoA.

What are the citric acid cycle products per glucose?

4 CO2, 6 NADH, 2 FADH2, and 2 ATP (or equivalent GTP).

What happens to carbon in the citric acid cycle?

The remaining acetyl-CoA carbon is oxidized and released as CO2.

Before the ETC, where is most captured energy from glucose?

In NADH (and some in FADH2), not in CO2 or ATP.

Where does the ETC occur?

Inner mitochondrial membrane, including the cristae.

What donates electrons to the ETC?

NADH and FADH2.

What is oxygen’s role in the ETC?

It is the final electron acceptor and combines with electrons and H+ to form water.

Which ETC complexes pump protons in the lecture model?

Complexes I, III, and IV.

Where do ETC-pumped protons accumulate?

Intermembrane space, creating a high H+ concentration there.

Where is H+ concentration relatively low during oxidative phosphorylation?

Mitochondrial matrix.

What is chemiosmosis?

Movement of H+ down its electrochemical gradient through ATP synthase to drive ATP synthesis.

What is ATP synthase’s function?

Uses energy from H+ flow to synthesize ATP from ADP and Pi.

How does ATP synthase use the proton gradient?

H+ flow through its membrane channel drives conformational/rotational changes that make ATP.

What powers most ATP production in aerobic respiration?

Oxidative phosphorylation driven by the proton gradient.

How much ATP does the reading guide attribute to ETC/oxidative phosphorylation?

About 26–28 ATP per glucose.

How does aerobic respiration differ from fermentation in ATP yield?

Aerobic respiration makes much more ATP; fermentation supports only 2 ATP per glucose from glycolysis.

Why does the ETC stop when oxygen is absent?

Without its final electron acceptor, electrons cannot pass through the chain to oxygen.

Why is NAD+ regeneration important for glycolysis?

Glycolysis requires NAD+; without it, its ATP-producing payoff steps stop.

How does lactic acid fermentation regenerate NAD+?

NADH transfers electrons to pyruvate, producing lactate and NAD+.

How does ethanol fermentation regenerate NAD+?

Pyruvate releases CO2 to form acetaldehyde; NADH reduces acetaldehyde to ethanol and regenerates NAD+.

Why is fermentation useful when oxygen is absent?

It regenerates NAD+ so glycolysis can keep making 2 ATP per glucose.

What happens to NADH/NAD+ if mitochondrial ETC function is lost?

NADH tends to accumulate and NAD+ availability falls.

What happens to ETC carriers before a block such as cyanide inhibition?

They tend to accumulate in reduced form because electrons arrive but cannot pass the block.

What happens to carriers after a block in the ETC?

They tend to remain oxidized because electrons cannot reach them.

What happens if ATP accumulates and cellular demand is low?

ATP synthase activity tends to decrease as ADP availability/demand falls.

Why does proton leakage across the inner membrane reduce ATP production?

It dissipates the H+ gradient that powers ATP synthase.

In the clicker question, what is the effect of DNP proton leakage?

It dissipates the gradient and does not increase ATP production; ATP yield falls.

Why can raising matrix pH support ATP synthesis?

It lowers matrix H+ relative to the intermembrane space, strengthening the proton gradient.

How are sugars connected to cellular respiration?

Glucose enters glycolysis, then its carbon proceeds through pyruvate oxidation and the citric acid cycle.

How are fats connected to cellular respiration?

Glycerol can enter carbohydrate metabolism; fatty acids are broken down to acetyl-CoA and reduced carriers.

How can acetyl-CoA be used besides oxidation?

When energy is abundant, it can supply carbon for fatty-acid synthesis.

What inputs support fatty-acid synthesis in the lecture model?

Abundant ATP, acetyl-CoA/carbon, and reducing power such as NADH/NADPH.

What happens to fatty-acid synthesis when ATP is depleted?

It decreases because synthesis requires energy input.

In the lecture model, what does isocitrate accumulation do to fatty-acid synthesis?

It increases fatty-acid synthesis.

How does a block in a metabolic pathway usually affect nearby molecules?

Substrates before the block accumulate; products after the block decline.

How can changing one pathway affect another pathway?

Shared intermediates, ATP, and reducing carriers change availability and alter other pathway rates.

What is the difference between catabolic and anabolic pathways?

Catabolic pathways break molecules down and release energy; anabolic pathways build molecules and require energy.

Why is ATP synthesis endergonic on its own?

Making ATP from ADP + Pi requires an energy input.

What exergonic process directly powers ATP synthase?

H+ moving down its electrochemical gradient through ATP synthase.

What happens to NAD+ when it oxidizes a fuel-derived molecule?

NAD+ accepts electrons and is reduced to NADH.

During pyruvate oxidation, why is NAD+ an oxidizing agent?

It accepts electrons removed from pyruvate-derived carbon as pyruvate is oxidized.

What is the difference between electron flow and proton flow in oxidative phosphorylation?

Electrons move along ETC carriers; the released energy pumps H+, which later flows through ATP synthase.

What is the role of the inner mitochondrial membrane?

Holds ETC complexes and ATP synthase and maintains the proton gradient.

What is the role of the intermembrane space?

It accumulates pumped H+ during oxidative phosphorylation.

What is the role of the mitochondrial matrix in respiration?

It hosts pyruvate oxidation and the citric acid cycle and receives H+ flowing through ATP synthase.

Why does the citric acid cycle turn twice per glucose?

One glucose produces two pyruvate and therefore two acetyl-CoA molecules.

What is the key energy carrier produced during glycolysis and the citric acid cycle?

NADH; the citric acid cycle also produces FADH2.

What is the key link between redox reactions and ATP production?

Redox transfers electrons; ETC energy from electron transfer pumps H+, and the gradient drives ATP synthesis.