Chapter 7: How to Harvest Energy

Describe autotrophs

Organisms that make their own food

Describe photoautotrophs.

photosynthetic; produce organic molecules using CO2 that can be used by themselves and by heterotrophs

Describe chemotrophs

organisms that break down chemical compounds for energy

Describe heterotrophs

organisms who get energy by eating other organisms; require an external source of organic carbon (e.g., sugars, lipids, proteins)

Once food is make or eaten, how does glucose enter the cells?

1. Secondary Active Transport (SLGT)

2. Glucose transporer (GLUT)

General equation of cellular respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.

What are the reactants of cellular respiration?

glucose and oxygen

What are the products of cellular respiration?

carbon dioxide, water, and ATP

What is substrate level phosphorylation?

is the direct transfer of a phosphate group from an organic substrate to ADP by an enzyme (usually a kinase). This process occurs during glycolysis and the citric acid cycle.

Substrate level phosphorylation generates much less ATP during cellular respiration than oxidative phosphorylation.

What is oxidative phosphorylation?

The process of using energy from electrons carried by NADH and FADH₂ through the electron transport chain to create a proton gradient that powers ATP synthase to produce ATP. Oxygen is the final electron acceptor.

What is the difference between substrate-level phosphorylation and oxidative phosphorylation?

Substrate-level phosphorylation transfers a phosphate directly from a molecule to ADP or GDP, while oxidative phosphorylation uses a proton gradient and ATP synthase.

Where does Glycolysis occur?

cytoplasm

What are the reactants of Glycolysis?

Glucose and 2 ATP

What are the products of Glycolysis?

net 2 ATP, 2 NADH, 2 pyruvate

What are the two major phases of glycolysis?

1. energy investment phase

2. energy payoff phase

What is the first reaction of glycolysis?

Phosphorylation: 2 ATP are used to add phosphate groups to glucose (PRIMING).

What is the second reaction of glycolysis?

Cleavage: The 6-carbon glucose splits into two 3-carbon molecules, forming 2 G3P.

What is the third reaction of glycolysis?

Oxidation: Both G3P molecules are oxidized, reducing 2 NAD⁺ to 2 NADH.

What is the fourth reaction of glycolysis?

ATP production: Phosphate groups are transferred from intermediates to ADP, producing 4 ATP total.

What is the fifth reaction of glycolysis?

Pyruvate formation: The two 3-carbon molecules are converted into 2 pyruvate.

What is the net reaction of glycolysis?

Glucose + 2Pi + 2ADP + 2NAD+ --> 2 pyruvate + 2ATP + 2 NADH + 2H+ + 2 H2O

What happens to the pyruvate molecules NOT in the present of Oxygen?

1. Fermenation

2. Anaerobic condition

What is aerobic respiration?

Respiration with oxygen

What happens to the pyruvate molecules in the present of Oxygen?

enters the mitochondria and is converted into acetyl-CoA, releasing CO₂ and producing NADH. Acetyl-CoA then enters the Krebs cycle to help produce ATP.

Where does pyruvate oxidation occur?

mitochondrial matrix

Describe pyruvate oxidation

3-carbon pyruvate is concerted to a 2-carbon acetyl group, with the third carbon lost as carbon dioxide. The step is explicitly an oxidation reaction as two hydrogen atoms are stripped from pyruvate by NAD+.

What are the reactants of pyruvate oxidation per 1 glucose molecule?

2 pyruvate, 2 NAD+, 2 CoA

What are the products of pyruvate oxidation per 1 glucose molecule?

2 acetyl CoA, 2 CO2, 2 NADH

What attaches to the acetyl group in pyruvate oxidation?

Coenzyme A

How does the acetyl group get incorporated into the Citric Acid Cycle

The acetyl group of acetyl CoA then enters the Krebs cycle by reacting with oxaloacetate (four carbons) to generate citric acid (six carbons).

Where does the citric acid cycle occur?

mitochondrial matrix

Describe the citric acid cycle

Starts with acetyl CoA and ends with CO2. The potential energy that is released is used to produce NADH, FADH2, and ATP.

What are the reactants of the citric acid cycle per 1 glucose molecule?

2 acetyl-CoA

6 NAD⁺

2 FAD

2 ADP (or GDP, depending on the organism)

4 H₂O (often included in the overall equation)

What are the products of the citric acid cycle per 1 glucose molecule?

4 CO₂

6 NADH

2 FADH₂

2 ATP

How are glycolysis and the citric acid cycle connected?

Glycolysis produces pyruvate, which is converted to acetyl-CoA during pyruvate oxidation, and acetyl-CoA enters the citric acid cycle.

Where does oxidative phosphorylation occur in eukaryotic cells?

At the inner mitochondrial membrane.

What is the role of the electron transport chain?

It transfers electrons from NADH and FADH₂ and uses the released energy to pump protons across the inner mitochondrial membrane.

How does the proton gradient drive ATP synthesis?

Protons flow back through ATP synthase, providing energy for ATP production from ADP and inorganic phosphate.

Which stages produce NADH before oxidative phosphorylation?

Glycolysis, pyruvate oxidation, and the citric acid cycle.

Which stage produces the largest share of ATP in aerobic cellular respiration?

Oxidative phosphorylation.

Why is oxygen crucial in the electron transport chain?

Oxygen accepts electrons at the end of the chain and combines with electrons and protons to form water.

What does OIL RIG stand for in redox reactions?

Oxidation Is Loss, Reduction Is Gain (referring to electrons).

What is a reducing agent?

A compound that reduces another by donating electrons.

What is an oxidizing agent?

A compound that oxidizes another by accepting electrons.

What process breaks apart complex molecules by adding water?

Hydrolysis.

What is the general chemical structure of NAD+?

It is a dinucleotide consisting of two nucleotides joined through their phosphate groups: one containing an adenine base and the other containing nicotinamide.

Which part of the NAD+ molecule is directly involved in accepting electrons during reduction?

The nicotinamide ring, which accepts two electrons and one hydrogen ion (H+) to form NADH.

What is the function of the Electron Transport Chain (ETC)?

Electrons pass between inner mitochondrial membrane proteins through redox reactions, pumping protons to create a gradient.

What is Chemiosmosis?

It uses the H⁺ (proton) gradient to drive ATP production through ATP synthase.

What role does Complex I play in the ETC?

It receives 2 electrons from NADH and pumps H⁺ ions across the membrane from the matrix into the intermembrane space.

What role does Complex II play in the ETC?

It receives 2 electrons from FADH₂, passing them along with electrons from Complex I to the Q molecule.

What is the role of the Q molecule in the ETC?

It shuttles electrons to Complex III and Complex IV.

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

Oxygen, which accepts electrons and forms water.

How many ATP are produced per glucose in aerobic respiration in eukaryotes?

30 ATP / glucose.

What happens during anaerobic respiration?

An organic molecule is used instead of oxygen as the final electron acceptor when oxygen is absent.

What are the two types of fermentation?

Lactic acid fermentation and alcohol fermentation.

Where does lactic acid fermentation occur and what causes muscle soreness?

It occurs in muscles when there isn't enough oxygen, and lactic acid build-up causes soreness.

What is produced during alcohol fermentation?

Pyruvate forms acetaldehyde which is then reduced to ethanol by yeast.

What is the chemical reaction for the hydrolysis of ATP?

ATP + H₂O → ADP + Pi + free energy.

Is the hydrolysis of ATP endergonic or exergonic?

Exergonic.

What is energy coupling?

An exergonic process (releases free energy) drives an endergonic process (requires free energy).