Chapter 9 Chemical Pathways Honors Biology

Energy in Food: What is the difference between a: calorie(lower case c) and Calorie (upper case C)? -A calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree C. -A Calorie is a kilocalorie, or 1000 calories For example, 1 gram of glucose releases 3811 calories, on a food label 3.8 Calories

Energy in Food:  The reason we eat is to get energy  We get carbohydrates from our food which are broken into Glucose Organisms cannot use glucose directly, it must be broken down into smaller units…… ATP  This process in living things begins with glycolysis. Cellular Respiration  If oxygen is present, glycolysis is followed by the Krebs Cycle and electron transport chain – This is called Cellular Respiration

 The equation for cellular respiration is exactly the opposite of photosynthesis.  Equation: 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O and energy

 Glucose needs to be broken down in small steps so that energy is not wasted.

 Definition: The process of breaking the glucose in half to form 2 molecules of pyruvate, a 3 carbon chain.  Uses 2 ATP to start reaction  Produces 4 ATP and 2 NADH  Occurs in the Cytosol (not mitochondria)

 Does not require oxygen  Very Fast – thousands of ATP produced in milliseconds  Stops when it runs out of NAD+ (electron carrier)  If oxygen is available: Cellular respiration starts  If oxygen is NOT available, to make more NAD+, your body goes through fermentation.  This way ATP can be made even without Oxygen.

 You have to use a little energy to make even more energy.  Like a bank, you put money in to earn interest.  Net ATP gained per glucose molecule=2 Animation Pyruvate molecules Glucose

 Fermentation is releasing energy in the absence of oxygen. It is an ANAEROBIC process.  Ultimately it allows NADH to be converted to NAD+, allowing glycolysis to continue.  There are two main types of fermentation  Alcoholic Fermentation  Lactic Acid Fermentation

 Alcoholic fermentation is found in Yeasts, and a few other microorganisms.  The equation is: Pyruvic acid + NADH  alcohol + CO 2 + NAD+ Note: Carbon Dioxide is also produced, so when yeast conducts fermentation, there is the release of carbon dioxide as well as alcohol.

 Alcoholic fermentation diagram

 Pyruvic acid from glycolysis can be converted to lactic acid.  This conversion regenerates NAD+ for glycolysis to continue  The equation is: Pyruvic acid + NADH  lactic acid + NAD+ Lactic acid fermentation is used by muscles when they run out of oxygen, ultimately causing soreness. Lactic acid is also created by unicellular organisms in the production of cheese, pickles, kimchi and other foods.

 Lactic Acid fermentation diagram

 In the Krebs Cycle, pyruvic acid is broken down into carbon dioxide.

 Where does it occur: Mitochondria  It requires oxygen – it is AEROBIC  It is also known as the Citric Acid Cycle

1. Pyruvic acid enters the mitochondria 2. One carbon becomes part of carbon dioxide and NAD+ becomes NADH 3. The other 2 carbons join coenzyme A to form acetyl-CoA 4. Acetyl-CoA adds to a 4-carbon molecule producing citric acid Animation

5. The citric acid is broken down to a 5- carbon molecule 6. Carbon dioxide is released and NAD+ becomes NADH 7. The 5-carbon compound is broken into a 4-carbon compound 8. Carbon dioxide is released and NAD+ becomes NADH, ADP also becomes ATP Animation

9. The 4-carbon compound is recycled, to be used again in the cycle 10. FAD is converted into FADH NAD+ is converted into NADH Animation So far, from 1 glucose Glycolysis produced: 2 NADH and 2 ATP Krebs Cycle produced: 8 NADH and 2 FADH 2 and 2 ATP

What happens to the Krebs cycle products? Carbon Dioxide is released to the atmosphere ATP is used for cellular activities NADH and FADH 2 are used in the electron transport chain to produce large amounts of ATP

 Uses the high energy electrons from the Krebs cycle to convert ADP into ATP

 Where does it occur: Inner membrane of the Mitochondria  It requires oxygen – it is AEROBIC

1. Electrons from the NADH are transferred to carrier proteins 2. These electrons transport H+ across the membrane 3. Electrons move down the chain, allowing additional H+ movement 4. At the end of the chain, oxygen accepts electrons, and left over H+, creating water Animation

5. The H+ buildup on the other side of the membrane creates a gradient 6. The H+ moves through ATP synthase, spinning the protein 7. Each rotation charges an ADP, attaches a phosphate, and creates ATP Animation

So far, from 1 glucose Glycolysis:2 ATP Krebs Cycle:2 ATP Electron Transport: 32 ATP Totals: 36 ATP from 1 glucose molecule This is 38% efficiency The rest of the energy is released as heat

Cells contains small amounts of ready ATP -About 5 seconds worth After that, your body uses lactic acid formation -This lasts for about 90 seconds -You breathe hard to get rid of the lactic acid buildup For exercise longer than 90 seconds, cellular respiration is used -This is a slow method to generate ATP -Glycogen (a form of carbohydrate) is used for the first minutes of cellular respiration -After that other molecules, such as fats, are broken down