7 Notes - Respiration October 25, 2011 7 Cellular...7 Notes - Respiration October 25, 2011 Efficiency of Cellular Respiration Cellular respiration can produce up to 38 ATP molecules

7 Notes - Respiration October 25, 2011

Chapter 7: Respiration

7-1 Glycolysis and Fermentation

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.

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

Cellular respiration can be divided into two stages: glycolysis and aerobic respiration.


Glycolysis

Cellular respiration begins with glycolysis, which takes place in the cytosol of cells.

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.

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 glycolysis and these additional pathways is fermentation.

Fermentation does not produce ATP, but it does regenerate NAD+, which allows for the continued production of ATP through glycolysis.

Cellular Respiration vs. Fermentation

Fermentation, continued

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



Alcoholic Fermentation - Some plants and unicellular organisms, such as yeast, use a process called alcoholic fermentation to convert pyruvic acid into ethyl alcohol and CO2.

A Summary of Fermentation


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.


Any Questions on your 7-1 Study Guide?


7-2 Aerobic RespirationObjectives

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.

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.


The Krebs Cycle (AKA The Citric Acid 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 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 FADH2 molecules.

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

The Electron Transport Chain and ChemiosmosisHigh-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.


Protons (hydrogen ions, H+) are also given up by NADH and FADH2.

As the electrons move through the electron transport chain, they lose energy. This energy is used to pump protons from the matrix into the space between the inner and outer mitochondrial membranes.

The Electron Transport Chain and Chemiosmosis, continued

The resulting high concentration of protons creates a concentration gradient of protons and a charge gradient across the inner membrane.

As protons move through ATP synthase and down their concentration and electrical gradients, ATP is produced. Oxygen combines with the electrons and protons to form water.


The Importance of Oxygen

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.


Electron Acceptor

O2


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 glycolysis alone.

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 glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.

A Summary of Cellular Respiration

Food + O2 Energy + CO2 + H2O


Any questions on your 6-2 study guide?

Food + O2 Energy + CO2 + H2O


Instructor Notes from Previous Explanations


7-2 Aerobic Respiration

Glucose

Pyruvic Acid

Mitochondria

Glycolysis-CytosolKrebs Cycle-matrixElectron Transport Chain-Inner Membrane


Pyruvic Acid-from GlycolysisCoenzyme A

NAD+ - Nicatinamide adenine

dinucleotide

-Goes tonext pathway

* The "Prelude"to the Kreb s

Cycle.

Krebs Cycle. 5 steps

FAD - Flavin Adenine Dinucleotide

each turn of Kreb's produces:2 CO21 ATP3 NADH1 FADH2

Remember, 2 turns because glucose was split into 2 pyruvic acid molecules during glycolysis

onto the ETC...


Electron Transport chainLines inner membrane of mitochondria

Prokaryotes - lines cell mambrane

To produce ATP, NADH and FADH 2 release H atoms resulting in concentration gradient and NAD

+ and FAD are regenerated

NADH and FADH 2: e- @ high energy levels, pass from molecule to

molecule losing energy,

Energy is used to "pump" H+ to space between inner membrane and

outer membrane.

Concentration gradient is created [H+]

[H+] drives ATP synthesis by chemiosmosis (w/ATP synthase)

Oxygen's Job:

Electrons need to keep moving. "Last" molecule in ETC must get rid of e-'s.

Oxygen is the final acceptor of e- and H+ (one part of H atoms supplied by NADH and FADH2

O2 + 4e- + 4H+ yeilds 2H2O


Efficiency?

Summary of Aerobic Respiration:


22.Food (glucose) + 02 → Energy (ATP)+ CO 2 + H20

Glycolysis-cytoplasmMitochondria-the rest

a.


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7 Notes - Respiration October 25, 2011 7 Cellular...7 Notes - Respiration October 25, 2011 Efficiency of Cellular Respiration Cellular respiration can produce up to 38 ATP molecules