Chemical energy and food 1 g of glucose (C 6 H 12 O 6 ) releases 3811 calories of heat when burned in the presence of oxygen FYI: 1 calorie is the amount of heat needed to raise the temp of 1g of H 2 0 1C FYI: the Calories listed on food packages are actually kilocalories (1000 calories) Glycolysis is the gradual release of energy in the presence or absence of oxygen

Cellular respiration Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen

Not so simple Cellular respiration must be regulated, otherwise all of the energy is released at once and that would be bad news Remember the sucrose/KClO3 demonstration ? 3 steps involved in cellular respiration

The 3 steps of cellular respiration  Step 1:Glycolysis the process in which 1 molecule of glucose is broken in half, producing 2 molecules of pyruvic acid, which is a 3-carbon compound  Step 2:ATP is utilized to get this process started (2 ATP molecules are used, 4 are produced; net gain of 2 ATP)  Step 3:NADH is used to pass energy on to other molecules

LEO the lion goes GER When electrons are gained, reduction occurs (GER) Gained electrons-> reduction (what is reduced is the positive charge) When electrons are lost, oxidation occurs (LEO) Lost electrons->oxidation

Fermentation Fermentation is the release of energy from food molecules without the presence of oxygen During fermentation cells convert NADH to NAD+ by passing high energy electrons back to pyruvic acid Fermentation is an anaerobic activity (does not require oxygen)

Alcoholic fermentation Yeasts and some other microorganisms use alcoholic fermentation, forming ethyl alcohol and CO2 as wastes Pyruvic acid + NADH--  alcohol + CO2 + NAD + Alcoholic fermentation produces CO 2, which can cause bread to rise

Lactic Acid Fermentation Pyruvic Acid can be converted into lactic acid This can cause discomfort in muscles after vigorous, unusual exercise Pyruvic acid + NADH -  lactic acid + NAD +

The Krebs cycle and electron transport Glycolysis releases only about 10% of the energy in glucose, leaving 90%. Cells use oxygen to accept electrons from pyruvic acid in an aerobic process When oxygen is crucial for a process, that process is aerobic (oxygen required)

The krebs cycle The Krebs cycle works to break down pyruvic acid into CO 2 in a series of energy extracting reactions. The Krebs cycle is also called the citric acid cycle because citric acid is formed in the first of the series of reactions hill.com/sites/ /student_view0/chapter2 5/animation__how_the_krebs_cycle_works__quiz_1_. html hill.com/sites/ /student_view0/chapter2 5/animation__how_the_krebs_cycle_works__quiz_1_. html

Krebs cycle (A) Krebs cycle begins when pyruvic acid produced during glycolysis enters the mitochondrion. 1 Carbon atom from pyruvic acid becomes part of a molecule of CO 2 2 of the 3 carbon atoms become part of coenzyme A for form acetyl-CoA. Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon molecule, producing a 6- carbon molecule (citric acid)

Krebs cycle (B) As the cycle continues, citric acid is broken down into a 4-carbon molecule, more CO 2 is released, and electrons are transferred to energy carriers. For each step in the Krebs cycle, a molecule of ATP is produced Krebs cycle products include CO 2 & ATP

Krebs cycle diagram Why is the Krebs cycle also knows as the citric acid cycle?

Electron transport (A) High energy electrons from NADH and FADH2 are passed into and along the electron transport chain. At the end of the electron transport chain is an enzyme that combines electrons from the electron chain with H and O ions to form water. Why do we need oxygen? Because Oxygen is the final acceptor of electrons in the electron transport chain, that’s why!

Electron Transport (B) When 2 high energy electrons are transported down the electron transport chain, their energy is used to transport H+ ions across the membrane of the mitochonria. This results in the 2 sides of the membrane being of opposite charges

Electron Transport (C) The movement of materials across the membrane of the mitochondria (H+, ATP synthases) allow for ADP to be transformed into ATP The transformation of ADP into ATP happens because a phosphate is attached to the ADP, thus it becomes ATP The energy to do this is provided by ATP synthase (a protein)

The Totals Glycolysis produces 2 ATP per glucose molecule When oxygen is involved, (Krebs Cycle & electron transport) results in 36 ATP per glucose molecules That is 18 times more energy from glucose when oxygen is present About 38% of the energy in glucose is made by the cell into ATP. The remaining 62% is lost (heat is the main place it’s lost). That is why you feel warm after exercise.

Energy and Exercise Quick energy is supplied by ATP in cells. After a few seconds that is used up, then cells are producing ATP by lactic acid fermentation. (about 90 seconds worth) After about 90 seconds, cells must produce ATP by cellular respiration. Cellular respiration produces ATP more slowly than fermentation, so a runner, for example, has to pace themselves to insure not running out of energy. Cellular respiration is good for a minutes, so then the body relies on other sources for energy, such as stored fats.

Photosynthesis and Cellular Respiration Photosynthesis “deposits” energy into cells. Cellular respiration “withdraws” energy from cells. Look at the chart on Pg. 232 in the Biology Text. Explain how Photosynthesis and Cellular respiration are similar. Explain how Photosynthesis and Cellular respiration are different. ( Lots of these!)