Cellular Respiration Cellular Respiration: Harvesting Chemical Energy Ppt from: aurumscience.com

Life Requires Energy Living cells require energy from outside sources Some animals, such as the giant panda, obtain energy by eating plants; others feed on organisms that eat plants

Energy flows into an ecosystem as sunlight and leaves as heat Photosynthesis uses sunlight to generate oxygen and glucose sugar. Cell respiration uses chemical energy in the form of carbohydrates, lipids, or proteins, to produce ATP.

ATP ATP stands for Adenosine Tri-Phosphate ATP is a molecule that serves as the most basic unit of energy ATP is used by cells to perform their daily tasks

ATP ATP can be broken down into a molecule of ADP by removing one of the phosphate groups. This releases energy. ADP can be remade into ATP later when the cell has food that can be broken down (i.e. glucose)

NADH NADH is a molecule that can “carry” H+ ions and electrons from one part of the cell to another. NADH is the “energized” version of this molecule that is carrying the H+ ion and two high-energy electrons. NAD+ is the “non-energized” version of this molecule that does not have the ion or the extra two electrons.

Adenosine triphosphate (ATP) LE 8-9 P P P Adenosine triphosphate (ATP) H2O P + P P + Energy i Inorganic phosphate Adenosine diphosphate (ADP)

LE 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO2 + H2O Simple sugars (Glucose) + O2 Cellular respiration in mitochondria ATP powers most cellular work Heat energy

Cell Respiration and Production of ATP The breakdown of organic molecules (carbohydrates, lipids, proteins) releases energy. Cellular respiration consumes oxygen and organic molecules and yields ATP Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6O2  6CO2 + 6H2O + Energy

Glycolysis Glycolysis is the first stage of cellular respiration. Occurs in cytoplasm. During glycolysis, glucose is broken down into 2 molecules of the 3-carbon molecule pyruvic acid. ATP and NADH are produced as part of the process.

ATP Production 2 ATP molecules are needed to get glycolysis started.

ATP Production Glycolysis then produces 4 ATP molecules, giving the cell a net gain of +2 ATP molecules for each molecule of glucose that enters glycolysis.

NADH Production During glycolysis, the electron carrier 2 NAD+ become 2 NADH. 2 NADH molecules are produced for every molecule of glucose that enters glycolysis.

Glycolysis Glycolysis uses up: Glycolysis produces 1 molecule of glucose (6-carbon sugar) 2 molecules of ATP 2 molecules of NAD+ Glycolysis produces 2 molecules of pyruvic acid (3-carbon acids) 4 molecules of ATP 2 molecules of NADH

Advantages of Glycolysis Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase. Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.

Movement to the Citric Acid Cycle Before the next stage can begin, pyruvic acid must first be transported inside the mitochondria. Pyruvic acid is combined with an enzyme called Coenzyme A. This enzyme helps with the transportation. Pyruvic acid + Coenzyme A make Acetyl CoA One more molecule of NADH is produced. This also releases one molecule of CO2 as a waste product.

LE 9-10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ Acetyl Co A Pyruvate CO2 Coenzyme A Transport protein

Krebs Cycle During the citric acid cycle, pyruvic acid produced in glycolysis is broken down into carbon dioxide and more energy is extracted.

Citric Acid Cycle Acetyl-CoA from glycolysis enters the matrix, the innermost compartment of the mitochondrion. Once inside, the Coenzyme A is released.

Citric Acid Cycle The molecule of acetate that entered from glycolysis joins up with another 4-carbon molecule already present. This forms citric acid.

Citric Acid Cycle Citric acid (6-carbon molecule) is broken down one step at a time until it is a 4-carbon molecule. The two extra carbons are released as carbon dioxide.

Citric Acid Cycle Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2. FADH2 has the same purpose as NADH – to transport high-energy electrons and H+ ions.

Citric Acid Cycle For each turn of the cycle, the following are generated: 1 ATP molecule 3 NADH molecules 1 FADH2 molecule

Citric Acid Cycle Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle. So each molecule of glucose results in two complete “turns” of the Krebs cycle. Therefore, for each glucose molecule: 6 CO2 molecules, 2 ATP molecules, 8 NADH molecules, 2 FADH2 molecules are produced.

LE 9-11 Pyruvic acid (from glycolysis, 2 molecules per glucose) CO2 Citric acid cycle Oxidation phosphorylation NAD+ CoA NADH ATP ATP ATP + H+ Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD+ FAD 3 NADH + 3 H+ ADP + P i ATP

Electron Transport Chain The electron transport chain occurs in the inner membrane of the mitochondria. Electrons are passed along the chain, from one protein to another. Each time the electron is passed, a little bit of energy is extracted from it. Electrons drop in energy as they go down the chain and until they end with O2, forming water

Electron Transport Chain NADH and FADH2 pass their high-energy electrons to electron carrier proteins in the electron transport chain.

Electron Transport Chain At the end of the electron transport chain, the electrons combine with H+ ions and oxygen to form water.

Electron Transport Chain Energy generated by the electron transport chain is used to move H+ ions (from NADH and FADH2) against a concentration gradient. This creates a “dam” of H+ ions in the outer fluid of the mitochondria.

The electron transport chain generates no ATP The chain’s function is to break the large free- energy drop from food to O2 into smaller steps that release energy in manageable amounts. The end result is a “reservoir” of H+ ions that can be tapped for energy, much like a reservoir in a hydroelectric dam.

Chemiosmosis The electron transport chain has created a high concentration of H+ ions in the outer fluid of the mitochondria. H+ then moves back across the membrane, into the inner fluid. H+ ions pass through a channel protein called ATP Synthase ATP synthase uses this flow of H+ to convert ADP molecules (low energy) into ATP (high energy)

LE 9-14 INTERMEMBRANE SPACE H+ A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient. H+ H+ H+ H+ H+ H+ A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob. H+ Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP. ADP + ATP P i MITOCHONDRAL MATRIX

Total ATP Production During cellular respiration, most energy flows in this sequence: glucose  NADH   electron transport chain chemiosmosis ATP About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 total ATP Remainder is lost as waste heat

Fermentation Cellular respiration requires O2 to produce ATP Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions) In the absence of O2, glycolysis can couples with a process called fermentation to produce ATP.

Types of Fermentation Fermentation consists of glycolysis + reactions that regenerate NAD+, which can be reused by glycolysis Two common types are alcohol fermentation and lactic acid fermentation

Alcohol Fermentation Yeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide. This process is used to produce alcoholic beverages and causes bread dough to rise. Pyruvic acid + NADH → Alcohol + CO2 + NAD+

Lactic Acid Fermentation Most organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid. Pyruvic acid + NADH  Lactic acid + NAD+

In lactic acid fermentation, pyruvate is reduced to NADH, the only end product is lactic acid. No carbon dioxide is released. Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce (out of breath) Result: Soreness!

Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration Most other organisms cannot survive in the long-run using glycolysis and fermentation, they require oxygen. These are obligate aerobic organisms.

LE 9-18 Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle

The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

Other Energy Sources Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate

LE 9-19 Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation

Video Review on ATP & Respiration https://www.youtube.com/watch?v=00jbG_cfGuQ&list=PL3EED4C1D684D3ADF&index=7&feature=plpp_video