Chapter 9

 Hunger can present a variety of different symptoms in different people Ultimately, the cause is the same, your body has a need for food  Food provides living things with energy It is used as the chemical building blocks needed for growth and reproduction

 One gram of sugar (C 6 H 12 O 6 ) when burned in the presence of oxygen releases 3811 calories of heat energy!  Calorie – the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius Is represented as kilocalories (C) on food labels

 Cells don’t actually “burn” the glucose molecules Instead energy is gradually released  The releasing of energy starts with a processes called Glycolysis In the presence of oxygen, glycolysis proceeds to 2 other pathways In the absence of oxygen, glycolysis is followed by another pathway

 Cells don’t actually “burn” the glucose molecules Instead energy is gradually released  The releasing of energy starts with a processes called Glycolysis In the presence of oxygen, glycolysis proceeds to 2 other pathways In the absence of oxygen, glycolysis is followed by another pathway

 In the presence of oxygen, glycolysis is followed by the Krebs Cycle and Electron Transport Chan (ETC) They are included in the process of cellular respiration  Cellular Respiration – the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

 There are 2 sites where cellular respiration takes place 1. Glycolysis – in the cytoplasm 2. Krebs Cycle & ETC – in the mitochondria

6O 2 + C 6 H 12 O 6 -> 6CO 2 + 6H 2 O + Energy Oxygen + Glucose -> Carbon Dioxide + Water + Energy

 The process requires oxygen and food and gives off carbon dioxide, water and energy  This process occurs in multiple steps If there was only 1 step, all of the energy from glucose would be released at once Cells need to control energy usage by storing it and releasing it little bits at a time  This is done by creating ATP

 Glycolysis – the process in which one molecule of glucose is broken in half, producing 2 molecules of pyruvic acid, a 3 carbon compound  is the 1 st set of reactions in cellular respiration

 Even though glycolysis is an energy - releasing process, it requires energy to start it  2 molecules of ATP are used to start glycolysis, and ultimately when the process is over, 4 ATP molecules are produced *Glycolysis gives a net gain of 2 ATP molecules *

 One reaction of glycolysis moves 4 high energy electrons using an electron carrier NAD + NAD electrons -> NADH  With the use of NAD +, energy can be passed to other pathways of the cell

 Glycolysis is so fast that thousands of ATP’s can be produced in milliseconds!  The cell requires the use of NAD + to pass on the high energy electrons to keep NAD + free for more glycolysis to occur

1. Created energized ATP molecules 2. Passed on high energy electrons (w/ NADH) 3. Created pyruvic acid (which gets used in the Krebs Cycle)

 When glycolysis occurs and there is no oxygen present, it proceeds to the pathway of fermentation  Fermentation – process that releases energy from food molecules by producing ATP in the absence of oxygen  Anaerobic – does not require oxygen

 During fermentation, cells convert NADH to NAD + by passing the high energy electrons back to pyruvic acid Keeps NAD + free to accept more electrons Allows more ATP energy to be produced

1. Alcoholic Fermentation Done by some yeasts and microorganisms to produce alcohol and breads pyruvic acid + NADH -> alcohol + CO 2 + NAD +

2. Lactic Acid Fermentation Occurs in muscles during rapid exercise when the body cannot supply enough of oxygen to the tissues Lactic Acid Fermentation can produce ATP to supply muscles with additional energy Too much lactic acid buildup can cause a painful, burning sensation which is associated with muscle fatigue pyruvic acid + NADH -> lactic acid + NAD +

 In addition of supplying overused muscles with energy, lactic acid fermentation is also utilized for making different food products Done with the use of bacteria  Ex.) cheeses, yogurts, pickles, sauerkraut

 At the end of glycolysis, about 90% of the chemical energy that was available in the glucose is still unused It is trapped in high energy electrons and pyruvic acid  To extract the rest of the energy, the cell is going to use oxygen Because cellular respiration requires oxygen it is an aerobic process

 In the presence of oxygen, the pyruvic acid produced in glycolysis is passed to the second stage of cellular respiration, the Krebs Cycle  During the Krebs Cycle, pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions Because a molecule called Citric Acid is one of the first compounds formed, Krebs Cycle is also referred to as the Citric Acid Cycle

 As seen in glycolysis and photosynthesis, the Krebs Cycle also produces high energy electrons which require special electron carriers  Along with carbon dioxide as a product, the highly energized compounds NADH, ATP and FADH 2 are also produced

OR

 The Krebs Cycle’s highly energized electrons are passed to the ETC the energized carrier molecules NADH and FADH 2  The purpose of the ETC is to use the energized electrons to convert ADP into ATP

 How much energy does cellular respiration yield from 1 glucose molecule?  Remember, glycolysis had a net gain of 2 ATP molecules Which is all that can be made in the absence of oxygen (anaerobic)  With the addition of the Krebs Cycle and ETC, the cell can make an additional 34 ATPs for a grand total of 36 ATPs per glucose

 The 36 ATP molecules the cell makes per glucose represents about 38% of the total energy of glucose May not seen efficient, but the cell is more efficient at using chemical fuel than the average engine is at using gasoline fuel  The remaining 62% of glucose energy is released as heat Which is why the body feels warmer after vigorous exercise

 Quick Energy Cells contain small amounts of ATP made through glycolysis and cellular respiration  This ATP is enough to last about 90 seconds of intense activity After this small amount of ATP is used, lactic acid fermentation starts, causing lactic acid buildup in the muscles  The only way to rid the body of this is with oxygen, which is why heavy breathing starts soon after activity

 Long-Term Energy For exercise longer than 90 seconds, cellular respiration is the only way to generate a continuing supply of ATP Cellular respiration releases ATP more slowly than fermentation does  Why athletes have to pace themselves The body is also able to utilize carbohydrate glycogen in muscles and other tissues  Can supply energy for 15 to 20 minutes of activity