Cellular Respiration

Honors Biology Chapter 9 Chemical Pathways Cellular Respiration

Energy in Food: What is the difference between a: calorie(lower case c) and Calorie (upper case C)? Basic Need for Energy • 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 Basic Need for Energy • This process in living things begins with glycolysis. • 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: An Overview:Cellular Respiration 6O2 + C6H12O6 6CO2 + 6H2O and energy

Glucose needs to be broken down in small steps so that energy is not wasted. Breaking Down Energy Slowly:

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) First Step: Glycolysis

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. Glycolysis

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 Why use ATP in Glycolysis if you want ATP? Glucose Animation Pyruvate molecules

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 Fermentation

AlcohlicfermentAtion

Alcoholic fermentation is found in Yeasts, and a few other microorganisms. The equation is: Pyruvic acid + NADH  alcohol + CO2 + 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

Alcoholic fermentation diagram Alcoholic Fermentation

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

Lactic Acid fermentation diagram Lactic Acid Fermentation

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

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

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

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

Krebs Cycle • The 4-carbon compound is recycled, to be used again in the cycle • FAD is converted into FADH2 • NAD+ is converted into NADH So far, from 1 glucose Glycolysis produced: 2 NADH and 2 ATP Krebs Cycle produced: 8 NADH and 2 FADH2 and 2 ATP Animation

Krebs Cycle

Krebs Cycle • What happens to the Krebs cycle products? Carbon Dioxide is released to the atmosphere ATP is used for cellular activities NADH and FADH2 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 Electron Transport Chain

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

Electron Transport Chain • Electrons from the NADH are transferred to carrier proteins • These electrons transport H+ across the membrane • Electrons move down the chain, allowing additional H+ movement • At the end of the chain, oxygen accepts electrons, and left over H+, creating water Animation

Electron transport chain

Electron Transport Chain • The H+ buildup on the other side of the membrane creates a gradient • The H+ moves through ATP synthase, spinning the protein • Each rotation charges an ADP, attaches a phosphate, and creates ATP Animation

Cellular Respiration totals 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

Energy use by humans • 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 15-20 minutes of cellular respiration • After that other molecules, such as fats, are broken down

Cellular Respiration