CELLULAR RESPIRATION   Regents Biology

OBJECTIVES Upon completion of this unit students will be able to:   1. Explain why cellular respiration is important for living things. 2. Describe the role of ATP in energy transfer. 3. Differentiate aerobic and anaerobic respiration. 4. Describe glycolysis. 5. Explain the process of fermentation. 6. Describe the function of the Krebs cycle and the electron transport chain. 7. Compare the efficiency of aerobic vs. anaerobic respiration. 8. Relate muscle fatigue to oxygen debt.     KEY TERMS 1.                      ADP 2.                      aerobic respiration 3.                      anaerobic respiration 4.                      ATP 5.                      cellular respiration 6.                      electron transport chain 7.                      fermentation 8.                      glycolysis 9.                      Krebs cycle 10.               oxygen debt

OVERVIEW One of the fundamental differences between living and nonliving matter is living matter’s continual need for energy. The chemical bonds between atoms of food molecules provide the energy used by all living organisms to sustain life. RESPIRATION IS THE LIFE PROCESS IN WHICH ENERGY IS RELEASED FOR USE IN THE CELL. Once released, it becomes available to the cell in the operation of all other life functions. CELLULAR RESPIRATION IS A BIOCHEMICAL PROCESS THAT INCLUDES THE REACTIONS USED BY CELLS TO RELEASE ENERGY FROM ORGANIC MOLECULES SUCH AS GLUCOSE. The energy released as a result of these reactions is temporarily stored in the bonds of molecules of adenosine triphosphate (ATP). This energy may be released for use in cell processes when ATP is hydrolyzed (converted) to adenosine diphosphate (ADP) and phosphate (P). Like other reactions that occur in the cell, the reactions of respiration are controlled by ENZYMES. The following equation illustrates the reactions involving the formation of ATP:   ATP  ADP + P + energy The two forms of cellular respiration carried on by living things are known as “aerobic” (with oxygen) and “anaerobic” (without oxygen). The breakdown of materials in a cell is called catabolism. The synthesis of materials in a cell is called anabolism.

ENERGY ENERGY:THE ABILITY TO DO WORK Why do organisms need energy? TO PERFORM ALL LIFE FUNCTIONS Living things rely on CHEMICAL ENERGY stored in their food The foods most commonly broken down for energy are CARBOHYDRATES namely GLUCOSE Carbohydrates are ORGANIC COMPOUNDS Organisms can only use CHEMICAL ENERGY to carry out their life functions; food breakdown occurs in many CHEMICAL STEPS related to the formation of HIGH-ENERGY COMPOUNDS Where is the release of the energy stored in food accomplished? IN THE MITOCHONDRIA OF EACH CELL CELLULAR RESPIRATION: PROCESS BY WHICH ENERGY STORED IN FOOD IS RELEASED BY CELLS

STORAGE AND TRANSFER OF ENERGY The energy released during cellular respiration is not used directly, it must first be “packaged” in molecules called ADENOSINE TRIPHOSPHATE (ATP) STRUCTURE OF AN ATP MOLECULE:   The last phosphate group in ATP is a HIGH ENERGY BOND; when the third phosphate is detached from ATP and bonded to another compound, it transfers ENERGY TO IT. This transfer of chemical energy to another compound involving a phosphate group is called PHOSPHORYLATION (ADDING PO4 TO ANOTHER COMPOUND)

When one phosphate group is removed from ATP, the remaining molecule is called ADENOSINE DIPHOSPHATE (ADP) which is a compound that is in a LOWER ENERGY STATE THAN ATP   STRUCTURE OF AN ADP MOLECULE:

SOURCE OF ENERGY FOR ATP We know that during cellular respiration, food is broken down and chemicals are released. By the gradual breakdown of food, A 3RD PHOSPHATE IS ATTACHED TO ADP, THUS RETURNING IT TO ATP. ATP CAN BE USED THROUGHOUT THE CELL.

The most common food substance from which cells obtain energy is GLUCOSE GLUCOSE is therefore the starting point for cellular respiration and the energy in glucose is used to generate (make) ATP. From the energy in a single molecule of glucose, a cell can produce up to 36 MOLECULES OF ATP (1 GLUCOSE 36 ATPs)

TYPES OF RESPIRATION In cellular respiration, GLUCOSE BREAKS DOWN and energy stored in these bonds of the glucose molecule is extracted and used to form ATP FROM ADP There are two types of cellular respiration that may take place: AEROBIC AND ANAEROBIC ANAEROBIC RESPIRATION: CARRIED OUT IN ABSENCE OF O2; PARTIAL BREAKDOWN OF GLUCOSE; INEFFICIENT AEROBIC RESPIRATION: CARRIED OUT IN PRESENCE OF O2; COMPLETE BREAKDOWN OF GLUCOSE; VERY EFFICIENT

A. Glycolysis The initial steps of both aerobic and anaerobic respiration are the same in the process known as GLYCOLYSIS and occurs in the CYTOPLASM This involves PHOSPHORYLATION and two phosphate groups are attached to the glucose molecule. These steps REQUIRE energy. For each pyruvic acid molecule produced by glycolysis, two ATP are formed. Since the splitting of one glucose molecule produces two pyruvic acid molecules, a total of four ATP are formed per glucose molecule. So the net energy output of glycolysis is two ATP for each molecule of glucose.

Anaerobic Respiration A number of one-celled organisms, namely YEAST AND BACTERIA use anaerobic respiration as their primary mode of energy production Practical uses of anaerobic respiration: MAKING CHEESE, YOGURT; BREWING BEER; MAKING WINE There are two principal types of anaerobic respiration: 1.ALCOHOLIC FERMENTATION - the major products produced in this process ETHYL ALCOHOL and this process is primarily accomplished by THE AID OF ENZYMES   http://images.google.com/imgres?imgurl=http://www.bae.uky.edu/~snokes/BAE549thermo/microbio/metabo4.jpg&imgrefurl=http://www.bae.uky.edu/~snokes/BAE549thermo/microbio/metabolic.htm&h=111&w=577&sz=6&hl=en&start=88&tbnid=4q9RDLM1xt3HSM:&tbnh=26&tbnw=134&prev=

2. LACTIC ACID FERMENTATION - which produces LACTIC ACID   2. LACTIC ACID FERMENTATION - which produces LACTIC ACID Overworked human muscle cells that are DEPRIVED OF O2 will carry on anaerobic respiration. Results will be A LACK OF ATP PRODUCTION AND LACTIC ACID BUILD-UP = MUSCLE FATIGUE Both types of anaerobic respiration are considered INEFFICIENT because the end products of both CONTAIN ENERGY THAT IS NOT EFFECTIEVLY RELEASED BY THE CELL http://images.google.com/imgres?imgurl=http://www.bae.uky.edu/~snokes/BAE549thermo/microbio/metabo4.jpg&imgrefurl=http://www.bae.uky.edu/~snokes/BAE549thermo/microbio/metabolic.htm&h=111&w=577&sz=6&hl=en&start=88&tbnid=4q9RDLM1xt3HSM:&tbnh=26&tbnw=134&prev=

The reactions of anaerobic respiration are actually a series of reactions that progressively convert glucose to end products and energy. A more detailed study of the process reveals that glucose molecules are first converted to two molecules of an intermediate compound known as PYRUVIC ACID. To begin this conversion, the energy stored in two molecules of ATP is released. However, the fact that four molecules of ATP are formed in this process makes possible the net gain of two ATP. The following equation and diagram illustrate this process:

Krebs found that THE SERIES OF REACTIONS HAS A REPEATING CYCLE C. Aerobic Respiration The series of chemical reactions that begin with the 2-carbon compound formed from pyruvic acid is called the KREBS CYCLE/CITRIC ACID CYCLE Krebs found that THE SERIES OF REACTIONS HAS A REPEATING CYCLE   ONLY ONE ATP is produced directly by each turn of the Krebs cycle:   For each turn of the cycle, two molecules of CO2 and 4 pairs of hydrogen atoms are produced from one 2-carbon molecule (2C). Hydrogen is removed by coenzymes. Note that three water molecules are used during the Krebs cycle.

 Aerobic respiration begins with GLYCOLYSIS which is the SPLITTING OF A MOLECULE OF GLUCOSE INTO 2 MOLECULES OF PYRUVIC ACID AND THE NET OUTPUT OF 2 MOLECULES OF ATP The remaining steps of aerobic respiration take place inside the MITOCHONDRIA A mitochondrion has a double membrane. The inner membrane is deeply folded and has a very large surface area. Research indicates that most of the enzymes, coenzymes, and other special molecules needed for aerobic respiration are located on this membrane surface. It is the presence of these molecules in an organized pattern on the membrane that makes the entire process possible. http://www.steve.gb.com/images/science/mitochondrion.png

THE ELECTRON TRANSPORT CHAIN TO SUMMARIZE WHAT WE KNOW SO FAR: IN AEROBIC RESPIRATION, 2 ATP ARE PRODUCED BY GLYCOLYSIS AND 1 ATP IS PRODUCED BY EACH TURN OF THE KREBS CYCLE (2 ATP FOR EACH GLUCOSE) The remaining energy released by the breakdown of glucose is used to FORM ATP BY THE ELECTRON TRANSPORT CHAIN (ETC) In the ETC, a series of REDOX REACTIONS take place. At three places along the chain, MOLECULES OF ATP ARE FORMED Altogether, 32 ATP ARE PRODUCED BY THE ETC Since 2 ATP come directly from GLYCOLYSIS and 2 ATP from the KREBS CYCLE, aerobic respiration can produce a total of 36 ATP from each molecule of GLUCOSE

So what’s the deal with oxygen here So what’s the deal with oxygen here? The final step in this process involves oxygen. Oxygen combines with HYDROGEN to form WATER. This water is called THE WATER OF METABOLISM. A cell that can use oxygen from the environment for its respiration can EXTRACT THE ENERGY REMAINING IN THE END PRODUCTS OF GLYCOLYSIS This is why aerobic respiration is so much more efficient than anaerobic. In anaerobic respiration, or FERMENTATION, the only energy-yielding process is GLYCOLYSIS; the end products of fermentation have almost as much energy as THE GLUCOSE FROM WHICH THEY ARE MADE

Like anaerobic respiration, aerobic respiration is characterized by glycolysis and progressively converts glucose to end products and energy. Unlike anaerobic respiration, aerobic respiration uses molecular oxygen to release substantially more energy per glucose molecule metabolized. For this reason, aerobic respiration is a more efficient form of respiration. In general, the process of respiration may be illustrated as follows:   C6H12O6 + 6 O2  6 H2O + 6 CO2 + 36 ATP The net gain of ATP molecules in aerobic respiration is 36 making it 18 times more efficient than anaerobic respiration. The significance of aerobic respiration is that usable energy is stored in the chemical bonds of the ATP molecules.

MUSCLE FATIGUE AND OXYGEN DEBT Some organisms can FUNCTION BY ANAEROBIC RESPIRATION ALONE WHEN O2 IS NOT AVAILABLE. Examples: YEAST, HUMAN MUSCLE CELLS During periods of intense or prolonged activity, MUSCLE CELLS USE O2 FASTER THAN IT CAN BE SUPPLIED BY THE RESPIRATORY AND CIRCULATORY SYSTEMS When the oxygen supply gets too low, the ETC CANNOT FUNCTION AND THE KREBS CYCLE STOPS WORKING The muscle cells still undergo GLYCOLYSIS, and LACTIC ACID accumulates in the muscle cells and produces the sensation of muscle fatigue and reduces the ability for the cells to do their normal work. Cells require A PERIOD OF REST to recover to a normal condition. During this time, FRESH 02 allows for the lactic acid to be oxidized. The amount of oxygen needed to dispose of the lactic acid is OXYGEN DEBT

Electron Transport Chain (32) Kreb’s Cycle (2) + Electron Transport Chain (32)