chapter 9 prt 2

스터디 가이드 - 스마트 노트

자료에 맞춘 맞춤형 노트, 핵심 정의, 예시, 맥락을 확장해 제공합니다.

Cellular Respiration Overview

Main Steps of Cellular Respiration

Cellular respiration is a multi-step metabolic pathway that converts organic molecules into usable energy (ATP) for the cell. It consists of four major steps:

Glycolysis: Occurs in the cytosol, breaks down glucose into pyruvate, producing 2 ATP.
Pyruvate Oxidation & Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix, converts pyruvate to Acetyl CoA, then oxidizes it, producing 2 ATP and electron carriers (NADH, FADH2).
Electron Transport Chain (ETC): Located in the inner mitochondrial membrane, uses electrons from NADH and FADH2 to create a proton gradient.
Chemiosmosis: Utilizes the proton gradient to drive ATP synthesis via ATP synthase.

Total ATP Yield: While glycolysis and the citric acid cycle produce 4 ATP directly, the majority of ATP (~28) is generated through oxidative phosphorylation (ETC and chemiosmosis), totaling about 30-32 ATP per glucose molecule. Diagram of cellular respiration steps and ATP yield

Key Molecules and Locations

Pyruvate: End product of glycolysis, enters mitochondria for further oxidation.
Acetyl CoA: Formed from pyruvate, enters the citric acid cycle.
Electron Carriers: NADH and FADH2 shuttle electrons to the ETC.
ATP: Main energy currency produced.
CO2: Waste product released during citric acid cycle.
O2: Final electron acceptor in the ETC.

Structure of the mitochondrion showing membranes and matrix

Oxidative Phosphorylation: Electron Transport Chain and Chemiosmosis

Electron Transport Chain (ETC)

The ETC is a series of protein complexes embedded in the inner mitochondrial membrane.

NADH and FADH2 donate electrons to the chain.
Electrons move through complexes I-IV, dropping in free energy and powering proton pumps.
O2 is the final electron acceptor, forming H2O.
No ATP is generated directly by the ETC; instead, energy is used to create a proton gradient.

Role of Electron Carriers: NADH and FADH2 provide electrons, enabling controlled energy release for ATP synthesis. Diagram of electron transport chain complexes Electron transport chain with free energy drop and O2 as final acceptor

Chemiosmosis and ATP Synthase

Chemiosmosis is the process by which the energy stored in a proton gradient is used to drive ATP synthesis.

Protons (H+) are pumped into the intermembrane space by ETC complexes.
ATP synthase, a membrane protein, allows protons to flow back into the matrix, using their kinetic energy to phosphorylate ADP to ATP.
This process is the main source of ATP in cellular respiration.

Equation for ATP synthesis: Structure of ATP synthase and H+ gradient Top view of ATP synthase Side view of ATP synthase

ATP Yield and Energy Accounting

ATP Production per Glucose

Glycolysis: 2 ATP
Citric Acid Cycle: 2 ATP
Oxidative Phosphorylation: ~26-28 ATP
Total: ~30-32 ATP per glucose

Energy Conversion Efficiency:

Energy in glucose: 686 kcal/mol
Energy in 32 ATP: 233.6 kcal/mol
Efficiency:

Cellular respiration overview and ATP accounting Electron shuttles and ATP yield per glucose

Cellular Respiration Without Oxygen

Fermentation and Anaerobic Respiration

When O2 is unavailable, cells use fermentation or anaerobic respiration.
Both processes rely on glycolysis, yielding only 2 ATP per glucose.
NAD+ is regenerated to sustain glycolysis.
Aerobic respiration yields ~32 ATP, fermentation yields 2 ATP.

Pathways of glycolysis, fermentation, and aerobic respiration

Metabolic Pathways and Catabolic Versatility

Connections to Other Metabolic Pathways

Glycolysis and the citric acid cycle are central hubs for catabolism and anabolism.
Carbohydrates, proteins, and fats can all enter cellular respiration at various points.
Proteins are broken down to amino acids, which feed into glycolysis or the citric acid cycle.
Fats are digested to glycerol (glycolysis) and fatty acids (acetyl CoA).

Metabolic pathways connecting fats, carbohydrates, and proteins to cellular respiration Diagram of metabolic pathway versatility

Regulation of Cellular Respiration

Feedback Mechanisms

Cellular respiration is tightly regulated to meet the cell's energy needs.

Feedback inhibition is the primary control mechanism.
If ATP levels drop, respiration speeds up; if ATP is abundant, respiration slows down.
Enzyme activity is regulated at key points, especially by allosteric inhibitors and stimulators.
Phosphofructokinase is a major regulatory enzyme in glycolysis, inhibited by ATP and citrate, stimulated by AMP.

Regulation of glycolysis and cellular respiration by phosphofructokinase

Summary Table: Steps and ATP Yield in Cellular Respiration

Step	Location	Main Products	ATP Yield
Glycolysis	Cytosol	Pyruvate, NADH	2
Pyruvate Oxidation	Mitochondrial Matrix	Acetyl CoA, NADH, CO2	0
Citric Acid Cycle	Mitochondrial Matrix	NADH, FADH2, CO2	2
Electron Transport Chain & Chemiosmosis	Inner Mitochondrial Membrane	ATP, H2O	~26-28

Important Concepts to Know

Names and locations of the four steps in cellular respiration
Tracking of major molecules: pyruvate, Acetyl CoA, NADH, FADH2, ATP, CO2, O2
ATP accounting: where and how much is produced
Regulation of the pathway via feedback mechanisms