How Cells Harvest Chemical Energy CELLULAR RESPIRATION How Cells Harvest Chemical Energy

CELLULAR RESPIRATION Cellular Respiration is the process animals use to turn food (glucose) into energy (ATP). The reactants of this reaction are glucose and oxygen. The products are carbon dioxide, water, and energy (ATP). Glucose = C6H12O6

THE EQUATION The overall equation for cellular respiration is: C6H12O6 + 6O2  6CO2 + 6H2O + ATP In words: Glucose + Oxygen  Carbon Dioxide + Water + Energy

THE EQUATION Where do we get glucose from? Food! Where do we get oxygen from? Breathing! What do we breathe out? Carbon Dioxide and Water!

THE REACTION Cellular Respiration is an AEROBIC process, which means that it only happens when OXYGEN is present. It happens in 3 stages: Glycolysis, the Kreb’s Cycle, and the Electron Transport System.

STEP 1: GLYCOLYSIS Glycolysis breaks down glucose (6 carbons) into 2 molecules of pyruvic acid (with 3 carbons each) It occurs in the cytoplasm of cells. (10 steps) 2 ATP are produced from each molecule of glucose. It also produces 2 NADH, which is an organic molecule that carries electrons (energy)

6.9 GLYCOLYSIS HARVESTS CHEMICAL ENERGY BY OXIDIZING GLUCOSE TO PYRUVIC ACID Figure 6.9A

STEP 2: THE KREB’S CYCLE Pyruvic acid diffuses into the inner matrix of the mitochondria, the location of the Kreb’s Cycle. Pyruvic acid is converted into Carbon Dioxide (1 carbon) and Acetyl COA in the transition step (an enzyme with 2 carbons). It then becomes CO2, which we breathe out. Each acetyl CoA is rearranged (oxidized) to release energy. The Kreb’s Cycle produces 2 ATP, 6 NADH, and 2 FADH2.

6.11 THE KREB’S CYCLE Acetyl CoA The Krebs cycle is a series of reactions in which electrons are transferred to NADH and FADH2 2 KREBS CYCLE CO2 Figure 6.11A

STEP 3: THE ELECTRON TRANSPORT SYSTEM (ETS) It is also called chemiosmosis, ETS, or ETC It consists of a series of reactions on the cristae, the inner membrane of the mitochondria. Electrons are released from NADH and FADH2, which release energy (called chemiosmosis). Hydrogen ions are pumped across the membranes in the mitochondria. Then they are pushed back through proteins, and ATP is synthesized. 34 ATP are produced during this part of the reaction.

ELECTRON TRANSPORT CHAIN Chemiosmosis in the mitochondrion Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

LET’S REVIEW Glycolysis: Where does it occur? How many ATP are produced? Kreb’s Cycle: Where does it occur? How many ATP are produced? ETS: Where does it occur? How many ATP are produced? Where does the carbon from glucose go? Where does the oxygen turn into?

An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Cytoplasmic fluid Mitochondrion Figure 6.8

6.14 REVIEW: EACH MOLECULE OF GLUCOSE YIELDS 38 MOLECULES OF ATP For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Cytoplasmic fluid Mitochondrion Electron shuttle across membranes KREBS CYCLE GLYCOLYSIS 2 Acetyl CoA 2 Pyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Glucose by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis by substrate-level phosphorylation by chemiosmotic phosphorylation Maximum per glucose: Figure 6.14

FERMENTATION: An alternative to Cellular Respiration Occurs when there is NO oxygen. ANAEROBIC Only glycolysis occurs (not Kreb’s or the ETS). This is how yeast converts pyruvic acid to alcohol (when making beer and wine). This also occurs in our muscles when we work out, then lactic acid is produced. Lactic acid fermentation in bacteria is also used to make cheese and yogurt.