CELLULAR RESPIRATION

Energy Energy is the ability to do work All living thing livings (organisms) need energy to live Directly or indirectly nearly all the energy for life comes from the Sun Some organisms make their own food (autotrophs) While others must obtain it from other organisms (heterotrophs)

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 this energy is released for use in the cell Once released, it becomes available to the cell in the operation of all other life functions Remember that we referred to all the chemical reactions in a cell as the cell’s metabolism.

Where Does All This Energy Come From? Complex carbohydrates are the major source of energy for most organisms But – before the energy in those carbohydrates can be used by cells, the carbohydrates are broken down into simple sugars such as glucose C 6 H 12 O 6 FYI: How much energy is in glucose? Lots One gram of the sugar glucose (C 6 H 12 O 6 ), when burned in the presence of oxygen, releases 3811 calories of heat energy.

The process where these glucose molecules are broken down to release energy is cellular respiration Cellular respiration is a series of enzyme catalyzed chemical reactions which produces ATP (adenosine triphosphate) Most of the processes that occur in cells use the ATP for their energy source

ATP ATP is an energy-transfer compound or “energy-carrier” Cell can use ATP because (in part) of it’s unique structure It makes ATP PERFECT for the storage and release of energy

~ High Energy Bond

The high energy bonds contain a large amount of energy ATP releases energy when the bond between the second and third phosphate groups is broken, forming a molecule called adenosine diphosphate (ADP) ATP and ADP can be interchanged by the addition or removal of a phosphate group Sometimes ADP becomes adenosine monophosphate (AMP) by losing an additional phosphate group but there is less energy released in this reaction

Overview of Cellular Respiration 6O 2 + C 6 H 12 O 6 6CO 2 + 6H 2 O + Energy

Cellular respiration occurs in 2 main parts Glycolysis and aerobic respiration The 1 st stage, glycolysis, is an anaerobic process Anaerobic metabolic processes do not require oxygen The 2 nd stage – aerobic respiration – includes the Krebs cycle and electron transport and is an aerobic process Aerobic metabolic processes require oxygen.

Glycolysis Glucose (6 carbon molecule) is broken down in the cytoplasm into two 3-carbon molecules called pyruvic acid It takes 2 molecules of ATP to split each molecule of glucose At the end of glycolysis, however, 4 molecules of ATP are produced C-C-C-C-C-C + 2ATPC-C-C + C-C-C + 4ATP Glucose + 2 ATP2 Pyruvic Acid + 4 ATP or Remember: This is occurring in the cytoplasm in the absence of oxygen

In the absence of Oxygen In some cells lacking the enzymes necessary for aerobic respiration Or In cells when oxygen is lacking, Anaerobic respiration will go to fermentation

Lactic Acid Fermentation Glucose is gradually broken down in a series of enzyme controlled reaction to lactic acid (anaerobic respiration) Glucose2 Lactic Acid + 2 ATP

Lactic Acid Fermentation Lactic acid is produced in animals and is associated with muscle fatigue when the muscle cells are using oxygen faster than the circulatory system can supply it. Lactic acid is also produced by some bacteria and is important in the production of cheeses, buttermilk, and yogurt As a result of anaerobic respiration, there is a net gain of 2 ATP

Another End Product of Anaerobic Respiration Depending on the organism (like yeast and some bacteria in the baking and brewing industries), anaerobic respiration can also produce the end products ethyl alcohol and carbon dioxide glucose enzymes 2 alcohol+ 2CO ATP

Aerobic Respiration Many of the enzymes involved in aerobic cellular respiration are located in the mitochondria In the process with the presence of oxygen, the chemical energy of glucose is released gradually in a series of enzyme-controlled reactions Aerobic respiration is much more efficient than anaerobic respiration

SUMMARY EQUATION Glucose + Oxygen  water + carbon dioxide + 36ATP or C 6 H 12 O 6 +6O 2 enzymes 6H 2 O+6CO 2 +36ATP

Krebs Cycle Glycolysis has a net result of 2 ATP and 2 pyruvate (pyruvic acid) In the presence of oxygen, pyruvate is transported into the mitochondrial matrix where it is converted to carbon dioxide. The series of reactions that does this called the Krebs cycle (or citric acid cycle) For each glucose molecule, there are two turns of the Krebs cycle The net yield from the Krebs is six carbon dioxide molecules & 2 ATP

The Electron Transport Chain The final step in the breakdown of glucose High-energy electrons and hydrogen ions produced in the Krebs cycle are used to convert ADP to ATP Electrons move along the mitochondrial membrane and are released H + ions are released and diffuse into the matrix Oxygen is the final electron acceptor (H + plus O = H 2 O one of the by-products) In total 32 molecules of ATP are formed for each molecule of glucose

Total ATP Production in Aerobic Respiration From Glycolysis 2 From the Krebs Cycle 2 From the Electron Transport Chain 32 GRAND TOTAL 36

Efficiencies Only 2 molecules of ATP are produce in anaerobic respiration While 36 molecules of ATP are produced in aerobic respiration

Prokaryotic cellular respiration Some prokaryotes also undergo aerobic respiration They do not, however, have a mitochondria Main difference – use of cell membrane as electron transport site The movement of pyruvate to mitochondria not necessary, saving prokaryotic cell two ATP molecules Increases net total of ATP to 38

During a race, runners rely on the energy supplied by ATP to make it to the finish line. To obtain energy, the body uses ATP already in muscles and new ATP made by lactic acid fermentation and cellular respiration At the beginning of a race, the body uses all three ATP sources, but stored ATP and lactic acid fermentation can only supply energy for a limited time

When the gun goes off in a footrace, the muscles of the runners contain only enough of this ATP for a few seconds of intense activity Before most of the runners have passed the e50- meter mark, that store of ATP is nearly gone At this point, their muscle cells are producing most of their ATP by lactic acid fermentation These sources can usually supply enough ATP to last about 90 seconds In a 200 or 300-meter sprint, this may be just enough to reach the finish line

What happens if the race is longer? For exercise longer than 90 seconds, cellular respiration is the only way to generate a continuing supply of ATP Cellular respiration release energy more slowly than fermentation, which is why even well-conditioned athletes have to pace themselves Your body stores energy in muscle and other tissues in the form of the carbohydrate glycogen These stores of glycogen are usually enough to last for 15 or 20 minutes of activity After that, your body begins to break down other stored molecules, including fats, for energy This is one reason why aerobic forms of exercise such as running, dancing and swimming are so beneficial for weight control

Comparing Photosynthesis and Cellular Respiration