Chapter 7: How Cells Release Stored Energy - Study Guide

Required Reading: Introduction, 7.1, 7.2, 7.3, 7.4, 7.5

Learning Objectives for Chapter 7:

• Know the difference between aerobic and anaerobic cellular respiration.
• Know the reactants and products of glycolysis, as well as where glycolysis occurs.
• Understand the basic structure of the mitochondria.
• Understand the basic process by which ATP bonds are made in the mitochondria.
• Know that not all organisms carry out aerobic respiration, but multicelled animals use it as their primary energy source (unless they are oxygen deprived).

Hints for this chapter: Focus on the diagrams more than on the text. Do not worry about molecules not named in the study guide below (example, don't worry about NADPH or oxaloacetate, etc.). Don't worry about the Krebs cycle. Also, keep in mind that the mitochondria works very similarly to the chloroplast’s thylakoid in terms of how is forms ATP bonds.

I. Introduction

Key Concepts: Organisms with active lifestyles have an increased need for energy-releasing components of the cell. For eukaryotes (including plants and animals), the major power-producer in the cell are the mitochondria (singlur=mitochondrion), which are ubiquitous, but are found in particularly high numbers in muscle and other high-energy-use tissues, including the tissues of organisms with high metabolisms. This chapter focuses on the energy-releasing reactions and components of the cell.

II. Section 7.1

Definitions: Aerobic respiration, Anaerobic respiration, Glycolysis,

Key Concepts: In the process of photosynthesis, carbon dioxide and light energy are used to make glucose. In the process of aerobic cellular respiration, glucose is broken back down in the presence of oxygen, forming carbon dioxide and energy (in the form of ATP bonds). Not all organisms can carry our aerobic cellular respiration - some organisms break down sugar in the absence of oxygen (called anaerobic cellular respiration), although this process is not as effective in producing ATP energy as aerobic cellular respiration. Prokaryotic organisms (which don't have mitochondria) are usually dependent on anaerobic respiration, which produces a net 2 ATP per glucose molecule. (As an aside, some bacteria use a form of aerobic respiration that doesn’t use the mitochondria, although we won't concern ourselves with this). Eukaryotes - due to their large size and correspondingly high-energy requirements – typically carry out aerobic cellular respiration, as this process produces 36 ATP molecules per glucose molecule. No matter which type of respiration is used by a cell, the end product is ATP, the short-term, high-energy storage molecule used to fuel countless cellular activities.

III. Section 7.2

Definitions: Glycolysis, Glucose (6-carbon molecule), Pyruvate (3-carbon molecule)

Key concepts: Glycolysis is the first step in glucose break-down, and is used in both anaerobic and aerobic cellular respiration. This step occurs in the cytoplasm of a cell, and causes the breakdown of glucose (a 6-carbon molecule) into two 3-carbon molecules (2 pyruvates). Although 2 ATP molecules must be used to carry out glycolysis, 4 ATP molecules are made, resulting in a net 2 ATP gain for the cell. The ATP bonds that are made via glycolysis are formed using the energy in the glucose bonds that were broken.

IV. Section 7.3

Definitions: Mitochondria, Outer mitochondrial membrane, Inner mitochondrial membrane, Outer compartment of the mitochondria, ATP synthase

Key concepts: The two 3-carbon molecules (pyruvate) made in the cytoplasm during glycolysis next move into the mitochondria for breakdown via aerobic cellular respiration. The bond energy in these 3-carbon molecules acts as the energy source to "zap" electrons in the inner mitochondrial membrane into a high-energy state. As the electrons "roll down the hill" or "fall down the waterfall" to a lower energy state, they pull H⁺ ions into the outer compartment of the mitochondria, where they collect. The H⁺ ions repel one another, and also want to leave the compartment via diffusion from the high-concentration outer compartment to the low-concentration inner compartment. They are able to "escape" into the inner compartment by passing through ATP synthase. As they escape, the electrons give their energy to ATP synthase, which then uses the energy to create ATP bonds.

V. Section 7.4

Key concepts: For each glucose molecule that enters the aerobic cellular respiration pathway, a total of 36 ATP are formed. For anaerobic respiration, only 2 ATP are formed. Aerobic cellular respiration is therefore much more efficient, although it requires additional organelles in the cell (mitochondria).

VI. Section 7.5

Definitions: Fermentation

Key concepts: Fermentation is a type of anaerobic respiration that uses glycolysis as its first step, and is used by many organisms. Many single-celled organisms rely completely on fermentation, although multi-celled animals can use fermentation for brief periods of time if oxygen-deprived (which is the reason our muscles get sore after intense exercise). In general, during fermentation pyruvate gets converted into other end products, like lactate and ethanol (alcohol). This additional conversion of pyruvate is used to release a little extra chemical energy to the cell in addition to the ATP made during glycolysis.

Suggested Additional Study Resources:

From Textbook:

Review Questions: 1, 3, 5, 7

Self quiz: 1, 3, 5

From Interactive concepts in Biology CD-ROM:

Chapter 7 Quiz Questions (Under "Learning Tools"): 14

Unit 1 (From Main Menu), Chapter 7:

Aerobic and Anaerobc Respiration: Reading, Picture 1, Movie 2

Glycolysis: Activity 2, Movie 3 (Don’t worry about the details, just watch this to see how the process results in ATP formation)

The Krebs Cycle: Activity 1, Movie 5 (Only watch if you also watch Movie 3 in the next section. Also don’t worry about the details, just watch this to see how pyruvate enters the mitochondrion)

Third Stage Reactions: Reading, Activity 2, Movie 3 & Movie 4

Fermentation: Reading, Activity 1