Chapter 7 Cellular Respiration Mighty Mitochondria http://www.ageofautism.com/2008/04/dr-blaylock-on.html

Vocabulary Pretest Section 1 Cellular Respiration Pyruvic Acid NADH Anaerobic Aerobic Respiration Glycolysis NAD+ Fermentation Lactic Acid Fermentation Alcoholic Fermentation Kilocalorie Does not require oxygen Anaerobic breakdown of glucose into pyruvic acid Breakdown of carbohydrates in the absence of oxygen Occurs in muscle cells during periods of strenuous exercise A unit of energy equal to 1000 calories Occurs when yeast breakdown sugar Results in large amounts of ATP (uses oxygen) An electron carrier The reduced form of NAD+ Three carbon compound produced by glycolysis The process by which cells obtain energy from carbohydrates

Answer Key Cellular Respiration K Pyruvic Acid J NADH I Anaerobic A Aerobic Respiration G Glycolysis B NAD+ H Fermentation C Lactic Acid Fermentation D Alcoholic Fermentation F Kilocalorie E

Cellular Respiration Cellular Respiration —the process by which cells get energy from carbohydrates; oxygen combines with glucose to form water and carbon dioxide C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)

The equation is a simple summary of a very complex process. The overall purpose is to convert food into energy by breaking down organic fuel molecules. When oxygen is present during this process it is called aerobic respiration ( which is the most efficient). If no oxygen is present it is called anaerobic respiration (which is much less efficient). Both types (aerobic and anaerobic) start with a process called glycolysis.

Glycolysis Glycolysis —first stage of cellular respiration. Glycolysis means “glucose splitting” Occurs in the cytosol No oxygen is needed Glucose molecules are broken down into two 3-carbon molecules of pyruvic acid Pyruvic acid is then used in the Krebs Cycle (which is the second stage of aerobic respiration) Specific enzymes are needed 2 molecules of ATP are produced 2 molecules of NADH (an electron carrier molecule) are produced

4 stages of Glycolysis 1. 2 phosphates are added to glucose. They are released from 2 molecules of ATP (changing it to ADP).

2. The glucose molecule (with its 2 phosphates) is then split into 2 molecules of G3P (glyceraldehyde 3-phosphate) 2 G3P molecules G3P G3P

3. Each G3P gets oxidized by adding another phosphate group 3. Each G3P gets oxidized by adding another phosphate group. Also, electrons and hydrogen atoms are removed from the 3C molecule. They are added to 2 molecules of NAD+ (nicotinamide adenine dinucleotide) to create 2 NADH and 2 H+. These will go to the electron transport chain later on.

4. The phosphate groups are now removed from each molecule creating 2 molecules of pyruvic acid (3C). The phosphates are added to 4 molecules of ADP producing 4 ATP molecules.

G3P G3P http://science.halleyhosting.com/sci/ibbio/cellenergy/resp/respirnotes/glycolysis2.htm

Summary of Glycolysis Basically: One glucose (6C) is broken into two molecules of pyruvic acid (3C) If oxygen is available, the pyruvic acid will move into the mitochondria and aerobic respiration will begin. 4 ATP molecules are produced. Two are used to break apart the next glucose molecule and keep glycolysis going. This leaves a net yield of 2 ATP molecules for use by the cell. Two NAD+ are converted into 2 NADH and 2H+. These go to Electron Transport.

Efficiency of Glycolysis Measured in kilocalories (kcal) One kilocalorie equals 1,000 calories (cal) Complete oxidation of glucose releases 686 kcal Production of ATP absorbs 7 kcal 2ATP are produced from every glucose molecule broken down by glycolysis The efficiency is therefore calculated by the following formula: Efficiency of Energy required to make ATP glycolysis = Energy released by oxidation of glucose = 2 x 7 kcal x 100% = 2% 686 kcal

Section 2 Vocabulary Pretest Mitochondrial matrix Acetyl CoA Krebs Cycle Oxaloacetic Acid Citric Acid FAD Biochemical pathway that generates ATP 6 carbon compound used in the Krebs cycle Electron acceptor: Flavin adenine dinucleotide The space inside the inner membrane of a mitochondrion 2 carbon compound made from pyruvic acid 4 carbon compound used in the Krebs cycle

Answer Key Mitochondrial matrix D Acetyl CoA E Krebs Cycle A Oxaloacetic Acid F Citric Acid B FAD C

Aerobic Respiration In most cells, the pyruvic acid produced in glycolysis enters the pathway of aerobic respiration. This pathway produces nearly 20 times as much ATP as is produced by glycolysis alone and is therefore the most efficient. Oxygen must be available for this to happen. There are two major stages: The Krebs Cycle and the Electron Transport Chain

Intermediate Step Aerobic Respiration takes place in the mitochondria of the cell. Before the Krebs Cycle can begin, each of the two pyruvic acid molecules must be converted. The pyruvic acid enters the mitochondrial matrix (space inside the inner membrane of the mitochondria) It reacts with a molecule called coenzyme A to form Acetyl Coenzyme A (acetyl CoA) http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

Notice that acetyl CoA only has 2 carbon atoms. The lost carbon atom is released in a molecule of CO2 Also, this reaction reduces a molecule of NAD+ to NADH + H+ This happens to both molecules of pyruvic acid Therefore, the end result is: 2 molecules of Acetyl CoA for the Krebs cycle 2 molecules of CO2 to be released 2 molecules of NADH for electron transport. http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

The Krebs Cycle The Krebs Cycle (named for Hans Krebs) is a biochemical pathway that breaks down acetyl CoA. Two turns of the Krebs Cycle produce: 2 ATP molecules 4 CO2 molecules 6 NADH molecule 2 FADH2 molecules

5 Steps of the Krebs Cycle 1. Acetyl CoA (2 carbon compound) combines with Oxaloacetic acid (4 carbon compound) to produce Citric Acid (6 carbon compound). This regenerates and releases CoA.

2. Citric acid releases a CO2 molecule and is oxidized by losing a hydrogen atom. This forms a new 5 carbon compound. The hydrogen atom is transferred to NAD+, reducing it to NADH.

3. The 5 carbon compound now releases a CO2 molecule and a hydrogen atom. This creates a 4 carbon compound and the hydrogen atom is again added to NAD+, reducing it to NADH. A molecule of ATP is also synthesized from ADP.

4. The 4 carbon compound releases a hydrogen atom which is used to reduce FAD (Flavin Adenine Dinucleotide) to FADH2. (FAD, like NAD+ also accepts electrons during redox reactions.

5. The 4 carbon compound now releases a hydrogen atom to regenerate oxaloacetic acid, which can be used to start the Krebs cycle over again. The hydrogen atom released again reduces NAD+ to NADH.

http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

Review of the Gylcolysis and the Krebs Cycle In Glycolysis, one glucose molecule produces two pyruvic acid molecules, which can then form two molecules of Acetyl CoA. Both of the Acetyl CoA molecules enter the Krebs Cycle creating two turns of the cycle. This produces 6 NADH, 2 FADH2, 2 ATP and 4 CO2 molecules (waste product that diffuses out of the cell). The 6 NADH and 2 FADH2 molecules drive the next stage of aerobic respiration—the Electron Transport Chain.

Electron Transport Chain The Electron Transport Chain, linked with chemiosmosis makes up the second stage of aerobic respiration. Electrons are transferred from one molecule to another by several electron carrying molecules located in the membrane of the mitochondria. All steps occur in the cristae (inner membrane) Follow the steps in the diagram:

H+ are pumped back in by ATP synthase embedded in the membrane. http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm ATP is produced when NADH and FADH2 release hydrogen atoms (this regenrates NAD+ and FAD, which return to the Krebs Cycle to be reused) Each hydrogen atom gives up electrons and hydrogen ions (H+) The electrons released are at a high energy level and move down the chain. They lose energy as they move from molecule to molecule. The lost energy is used to pump the hydrogen ions from the matrix to the other side of the membrane. A concentration gradient of hydrogen ions across the membrane is created. H+ are pumped back in by ATP synthase embedded in the membrane. ATP is made from ADP and phosphates. Oxygen is the final electron acceptor and also accepts H+ ions to make water.

Efficiency of Cellular Respiration Through Aerobic Cellular Respiration, a maximum of 38 ATP molecules can be produced from one glucose molecule. 2 from Glycolysis 2 from Krebs cycle 32-34 from the Electron Transport Chain

To see how we get 38, follow along…. 2 ATPs directly from glycolysis 2ATPs directly from Krebs cycle Each NADH can generate 3ATPs from electron transport (30 total) Each FADH2 can generate 2ATPs from electron transport (4 total) http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

The actual number of ATP molecules generated through Aerobic Respiration varies from cell to cell. (36-38) Most eukaryotic cells produce only 36 molecules per glucose molecule because the active transport of NADH through a cell membrane uses up some ATP. When 38 ATP molecules are generated the efficiency is calculated as follows: Efficiency of Energy required to make ATP . Cellular Respiration = Energy released by oxidation of glucose = 38 x 7 kcal x 100% = 39% 686 kcal This is 20 times more efficient than glycolysis alone !!

Anaerobic Respiration If no oxygen is present, the Krebs Cycle and Electron Transport Chain are not utilized. The cell must have a way to keep glycolysis going. Glycolysis would stop without a cellular process that recycles NAD+ and NADH. Without such a process, glycolysis would quickly use up all the NAD+ in the cell. Glycolysis and ATP production would stop and the cell would die. Fermentation to the rescue 

Fermentation Fermentation is the chemical pathway that recycles NAD+ in the absence of oxygen. It keeps glycolysis going. No additional ATP is made. Therefore, you still have the 2% efficiency rate for energy release. Two types of fermentation: Lactic Acid Fermentation Alcoholic Fermentation

Lactic Acid Fermentation Pyruvic acid is converted by a specific enzyme into lactic acid. Two hydrogen atoms from NADH and H+ are transferred to pyruvic acid to form the lactic acid molecule. NADH is oxidized to NAD+ and reused to keep glycolysis going. http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

Occurs mostly in muscle cells during hard exercise. Lactic acid fermentation occurs in foods such as yogurt and cheese as well as certain animal cells. Occurs mostly in muscle cells during hard exercise. Muscle cells use up oxygen too fast and switch from aerobic to anaerobic respiration. Lactic acid builds up reducing the cells ability to contract. This causes fatigue, pain and cramps. http://www.burnthefatchallenge.com/wp/wp-content/uploads/2011/01/treadmill-300x300.gif Slow down!!! Allow the lactic acid time to diffuse back into the blood stream and to the liver where it is converted back into pyruvic acid.

Alcoholic Fermentation Converts pyruvic acid to carbon dioxide and ethyl alcohol. NAD+ is recycled in the same manner as before. http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm

Bakers use the alcoholic fermentation of yeast to make bread. CO2 is produced and trapped in the dough, causing it to rise. When the dough is baked, yeast cells die and the alcohol evaporates. You can’t get drunk from eating bread !!!

COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION Click to reveal COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION   PHOTOSYNTHESIS RESPIRATION FUNCTION   Production of Glucose   Oxidation of Glucose LOCATION   chloroplasts   mitochondria REACTANTS   6CO2 + 6H2O   C6H12O6 + 6O2 PRODUCTS   C6H12O6 + 6O2   6CO2 + 6H2O EQUATION    light 6CO2 + 6H2O C6H12O6 + 6O2  C6H12O6 + 6O2 6CO2 + 6H2O +ATP