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Table of Contents

Section 1 Glycolysis and Fermentation

Section 2 Aerobic Respiration

Objectives

� Identify the two major steps of cellular respiration.

� Describe the major events in glycolysis.

� Compare lactic acid fermentation with alcoholic fermentation.

� Calculate the efficiency of glycolysis.

Harvesting Chemical Energy� Cellular respiration is the

process by which cells break down organic compounds to produce ATP.

� Both autotrophs and heterotrophs use cellular respiration to make CO2 and water from organic compounds and O2.

Harvesting Chemical Energy

The products of cellular respiration are the reactants in photosynthesis; conversely, the products of photosynthesis are reactants in cellular respiration.

Harvesting Chemical Energy� Cellular respiration

can be divided into three stages: glycolysis, Krebs cycle (citric acid cycle) and electron transport chain.

Glycolysis� Cellular respiration begins with glycolysis, which

takes place in the cytosol of cells.

Glycolysis� During glycolysis, one

six-carbon glucose molecule is oxidized to form two three-carbon pyruvic acid molecules.

� A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis.

Fermentation� If oxygen is not present, some cells can

convert pyruvic acid into other compounds through additional biochemical pathways that occur in the cytosol. The combination of glycolysisand these additional pathways is fermentation.

Fermentation� Fermentation does not produce ATP, but it does regenerate

NAD+, which allows for the continued production of ATP through glycolysis.

Fermentation� Lactic Acid Fermentation

� In lactic acid fermentation, an enzyme converts pyruvic acid into another three-carbon compound, called lactic acid.

Lactic Acid Fermentation Pathway

Fermentation� Alcoholic Fermentation

� Some plants and unicellular organisms, such as yeast, use a process called alcoholic fermentationto convert pyruvic acid into ethyl alcohol and CO2.

Alcoholic Fermentation Pathway

Efficiency of Glycolysis� Through glycolysis, only about 2 percent of

the energy available from the oxidation of glucose is captured as ATP.

� Much of the energy originally contained in glucose is still held in pyruvic acid.

� Glycolysis alone or as part of fermentation is not very efficient at transferring energy from glucose to ATP.

Objectives• Relate aerobic respiration to the structure of a mitochondrion.

• Summarize the events of the Krebs cycle.

• Summarize the events of the electron transport chain and chemiosmosis.

• Calculate the efficiency of aerobic respiration.

• Contrast the roles of glycolysis and aerobic respiration in cellular respiration.


Copyright © by Holt, Rinehart and Winston. All rights reserved.

ResourcesChapter menu

Overview of Aerobic Respiration� In eukaryotic cells, the processes of aerobic

respiration occur in the mitochondria. Aerobic respiration only occurs if oxygen is present in the cell.

The Krebs cycle occurs in the mitochondrial matrix. The electron transport chain (which is associated with chemiosmosis) is located in the inner membrane.

Overview of Aerobic Respiration

Pre-Krebs Cycle � In the mitochondrial matrix, pyruvic acid produced in

glycolysis reacts with coenzyme A to form acetyl CoA.Then, acetyl CoA enters the Krebs cycle.

• One carbon is removed from pyruvate.

• Coenzyme A is attached to the resulting 2-carbon sugar.

• This makes acetyl-CoA.• Acetyl-CoA enters the Krebs Cycle

(Citric Acid Cycle).

The Krebs Cycle

� One glucose molecule is completely broken down in two turns of the Krebs cycle. These two turns produce four CO2 molecules, two ATP molecules, and hydrogen atoms that are used to make six NADH and two FADH2molecules.

The Krebs Cycle The bulk of the energy released by the oxidation of glucose still has not been transferred to ATP.

Bottom Lineo Reactants

o Acetyl-CoAo Citrate (Citric Acid)o 6 NADo 2 FAD

o Productso Oxaloacetateo 6 NADHo 2 FADH2

o CO2

Running Tally!o Glycolysis

o 2 ATPo 2 NADH

o Krebs Cycleo 2 ATPo 6 NADHo 2 FADH2

**So far aerobic respiration has only made 2 more ATP than an anaerobic organism can make.

Electron Transport Chain and Chemiosmosis� Step #1 - High-energy electrons in hydrogen atoms

from NADH and FADH2 are passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane.

� Step #1 - Protons (hydrogen ions, H+) are also given up by NADH and FADH2.

Electron Transport Chain and Chemiosmosis

Electron Transport Chain and ChemiosmosisStep #2 - As the electrons move through the electron transport chain, they lose energy.

Step # 3 - This energy is used to pump protons from the matrix into the space between the inner and outer mitochondrial membranes.

Electron Transport Chain and ChemiosmosisThe resulting high concentration of protons creates a concentration gradient of protons and a charge gradient across the inner membrane.

Step #4 - As protons move through ATP synthase and down their concentration and electrical gradients, ATP is produced.


Step #5 - Oxygen combines with the electrons and protons to form water.


� ATP can be synthesized by chemiosmosis only if electrons continue to move along the electron transport chain.

� By accepting electrons from the last molecule in the electron transport chain, oxygen allows additional electrons to pass along the chain.

� As a result, ATP can continue to be made through chemiosmosis.

The Importance of Oxygen

Efficiency of Cellular Respiration • Cellular respiration can

produce up to 38 ATP molecules from the oxidation of a single molecule of glucose. Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose.

Thus, cellular respiration is nearly 20 times more efficient than glycolysisalone.

How many ATP are made?

o Each NAD = 3 ATPo Each FAD = 2 ATP

o It delivers at a lower step in the transport chain and so it produces fewer ATP.

o Grand Total for ETC (alone) = 32 ATPo Glycolysis + Krebs + ETC = 36 ATP

A Summary of Cellular Respiration

• Another Role of Cellular Respiration– Providing cells with ATP is not the only important

function of cellular respiration.

– Molecules formed at different steps in glycolysisand the Krebs cycle are often used by cells to make compounds that are missing in food.



Chapter 7

Summary of Cellular Respiration


The Fate of Glucoseo Recall how glucose passes through the cell

membrane? (Facilitated Diffusion) Cells absorb glucose only because insulin triggers the cell membrane (via carrier protein) to begin allowing it into the cell.

The Fate of Glucose

o If you have extra glucose it is turned into glycogen and stored in liver and muscles

o To little glucose? Pancreas (via glucagon) signals release of stored glycogen

o People with diabetes have difficulty with this process

Question:o You, however, can only last on stored

glycogen for 12 Hours…Then what?

o How can a person live for 2 weeks without food if they can only last for 12 hours on stored glycogen?

ANSWER:

o Because the body also stores protein and fat. o78% of total energy reserves is body fat (lipid)

o21% of total energy reserves is in proteins.

•When blood glucose levels declineand glycogen stores are low, triglycerides are tapped as an alternative energy source.•Enzymes in fat cells cleave the bonds between the glycerol and

fatty acids, which enter the blood.•Enzymes in the liver convert glycerol into PGAL (an intermediate of glycolysis)

Energy from Fats

•Enzymes cleave the backbone of the fatty acids. The fragments

are converted to Aceytl CoA.

Energy from Fats

Fats have many more bonds than glucose.

Glucose

Palmitic acid, saturated fatty acid

Glycerol

FAT

• Enzymes split amino groups from amino acids and ammonia is produced. Then it is excreted from the body in the form of urea.

•The carbon backbones can be converted to pyruvate, acetyl CoA, or they enter the Krebs

cycle.

Energy from proteins.

Multiple Choice

1. Which of the following must pyruvic acid be converted into before the Krebs cycle can proceed?A. NADHB. glucoseC. citric acidD. acetyl CoA

Standardized Test Prep



Multiple Choice, continued

1. Which of the following must pyruvic acid be converted into before the Krebs cycle can proceed?A. NADHB. glucoseC. citric acidD. acetyl CoA

Standardized Test PrepChapter 7




2. Which of the following is not a product of the Krebs cycle?A. CO2

B. ATPC. FADH2

D. ethyl alcohol





3. In which way is cellular respiration similar to photosynthesis?F. They both make G3P.G. They both involve ATP.H. They both involve chemiosmosis.J. all of the above





4. ATP is synthesized in chemiosmosiswhen which of the following moves across the inner mitochondrial membrane?A. NADHB. oxygenC. protonsD. citric acid


Summary

o Know the formula (overall)o Know aerobic steps of respirationo Know the ATP and NAD outputs of each

pathwayo Know controls of Glycolysiso Know anaerobic methods of respiration, and

useso Know alternate entries of lipids and proteins

into respiration




6. This reaction occurs during which of the following processes?F. Krebs cycleG. acetyl CoA formationH. alcoholic fermentationJ. lactic acid fermentation

Chapter 7

The illustration showspart of a biochemical pathway. Use the illustration toanswer the question that follows.





7. glycolysis : pyruvic acid :: Krebs cycle :A. O2

B. OxaloacetateC. lactic acidD. acetyl CoA

Chapter 7 Standardized Test Prep




8. At which of the points is ATP, the main energy currency of the cell, produced?F. 1 onlyG. 2 onlyH. 1 and 3J. 1, 2, and 3

Chapter 7

The illustration belowshows some stages and reactants of cellular respiration. Use the illustration to answer the question that follows.




Short Response

The inner membrane of a mitochondrion is folded; these folds are called cristae.How might cellular respiration be different if the innermitochondrial membrane were not folded??




Short Response, continued

The inner membrane of a mitochondrion is folded; these folds are called cristae.How might cellular respiration be different if the innermitochondrial membrane were not folded?

Answer: The cristae increase the surface area of the inner wall of the mitochondria, which allows more electron transport chain pathways and ATP synthase. Thus, the rate of cellular respiration is increased.




Extended Response

Oxygen is produced during the reactions of photosynthesis, and it is used in the reactions of cellular respiration.Part A How does oxygen get into or out of

chloroplasts and mitochondria?Part B What are the roles of oxygen in the processes

of photosynthesis and cellular respiration, and how are the roles similar?




Extended Response, continued

Answer:Part A Oxygen builds up inside chloroplasts as they produce

oxygen, forming a concentration gradient—high oxygen concentration inside and low concentration outside. This causes O2 to diffuse out of the chloroplast. In mitochondria, as O2 is used up, a favorable gradient for the inward diffusion of oxygen occurs.

Part B In photosynthesis, oxygen is formed when water is split during the light reactions. This byproduct of photosynthesis is released by cells and becomes available for aerobic respiration. In aerobic respiration, oxygen is the final electron acceptor at the end of electron transport. When oxygen accepts these electrons (and protons), water is formed. Hence, water supplies oxygen for photosynthesis, and oxygen is used to form water in aerobic respiration.




Section 2 Aerobic RespirationChapter 7


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