Cellular respiration (stages and explanation)

Cellular Respiration Overview

Cellular respiration is the process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water. It consists of three main stages:

1. Glycolysis

   • Location: Cytoplasm

   • Process: Glucose (6 carbons) is broken down into two molecules of pyruvate (3 carbons).

   • ATP Yield: 2 ATP (net gain) and 2 NADH.

2. Krebs Cycle (Citric Acid Cycle)

   • Location: Mitochondrial matrix

   • Process: Pyruvate is converted into Acetyl-CoA, which enters the cycle. It produces CO2, ATP, NADH, and FADH2.

   • ATP Yield: 2 ATP per glucose molecule.

3. Electron Transport Chain (ETC)

   • Location: Inner mitochondrial membrane

   • Process: NADH and FADH2 donate electrons, creating a proton gradient that drives ATP synthesis via ATP synthase.

   • ATP Yield: Approximately 28-34 ATP.

Total ATP Production

• Total ATP from one glucose molecule: 30-38 ATP (depending on the efficiency of the ETC).

Glycolysis Overview

Glycolysis is the first stage of cellular respiration, occurring in the cytoplasm. It converts one molecule of glucose into two molecules of pyruvate, producing energy in the form of ATP and NADH.

Steps of Glycolysis:

1. Glucose Activation

   • Glucose is phosphorylated, consuming 2 ATP.

2. Cleavage

   • The 6-carbon sugar splits into two 3-carbon molecules (G3P).

3. Energy Harvesting

   • Each G3P is converted to pyruvate, producing 4 ATP (net gain of 2 ATP) and 2 NADH.

Summary

• Net ATP Yield: 2 ATP

• NADH Produced: 2 NADH

• End Product: 2 Pyruvate molecules

Glycolysis Map

• Input: Glucose + 2 ATP

• Output: 2 Pyruvate + 2 NADH + 2 ATP (net)

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Prep Step in Cellular Respiration

The prep step, or pyruvate oxidation, occurs after glycolysis and before the citric acid cycle. Key points include:

• Location: Mitochondrial matrix.

• Process:

  • Pyruvate is converted to acetyl-CoA.

  • One carbon is released as CO₂.

  • NAD⁺ is reduced to NADH.

• Outcome: Produces acetyl-CoA for the citric acid cycle.

The prep step, or pyruvate oxidation, in cellular respiration involves the following steps:

1. Pyruvate Transport: Pyruvate, produced from glycolysis, is transported into the mitochondria.

2. Decarboxylation: Each pyruvate (3 carbons) loses a carbon atom, releasing it as CO₂.

3. NAD⁺ Reduction: The remaining 2-carbon molecule is oxidized, reducing NAD⁺ to NADH.

4. Coenzyme A Attachment: The 2-carbon molecule combines with Coenzyme A, forming Acetyl-CoA.

This process prepares Acetyl-CoA for entry into the Krebs cycle.

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a key metabolic pathway that occurs in the mitochondria. It plays a crucial role in cellular respiration, converting carbohydrates, fats, and proteins into carbon dioxide, water, and energy (ATP).

Steps of the Citric Acid Cycle:

1. Acetyl-CoA Formation: Acetyl-CoA combines with oxaloacetate to form citrate.

2. Citrate to Isocitrate: Citrate is rearranged to form isocitrate.

3. Isocitrate to α-Ketoglutarate: Isocitrate is oxidized, reducing NAD+ to NADH and releasing CO2.

4. α-Ketoglutarate to Succinyl-CoA: Another oxidation occurs, producing NADH and releasing CO2.

5. Succinyl-CoA to Succinate: Succinyl-CoA is converted to succinate, generating ATP (or GTP).

6. Succinate to Fumarate: Succinate is oxidized to fumarate, producing FADH2.

7. Fumarate to Malate: Fumarate is hydrated to form malate.

8. Malate to Oxaloacetate: Malate is oxidized to regenerate oxaloacetate, producing NADH.

The cycle is crucial for energy production and provides intermediates for various biosynthetic pathways.

Sure! Cellular respiration consists of three main stages: Glycolysis, the Krebs Cycle (Citric Acid Cycle), and the Electron Transport Chain. Here’s a mnemonic to help you remember the order of these steps:

Mnemonic: "Good Kids Create Energy"

• Good - Glycolysis

• Kids - Krebs Cycle

• Create - Citric Acid Cycle (same as Krebs Cycle)

• Energy - Electron Transport Chain

Breakdown of Each Step:

1. Glycolysis:

   • Occurs in the cytoplasm.

   • Breaks down glucose into pyruvate.

   • Produces a small amount of ATP and NADH.

2. Krebs Cycle (Citric Acid Cycle):

   • Takes place in the mitochondria.

   • Processes pyruvate into carbon dioxide.

   • Produces ATP, NADH, and FADH2.

3. Electron Transport Chain:

   • Located in the inner mitochondrial membrane.

   • Uses NADH and FADH2 to create a proton gradient.

   • Produces the majority of ATP through oxidative phosphorylation.

Summary:

• Good (Glycolysis) → Kids (Krebs Cycle) → Create (Citric Acid Cycle) → Energy (Electron Transport Chain)

This mnemonic should help you remember the order and names of the steps in cellular respiration!