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 = C 6 H 12 O 6

THE EQUATION The overall equation for cellular respiration is: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + 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 pyruvate (with 3 carbons each) It occurs in the cytoplasm of cells. 2 ATP are produced from each molecule of glucose. It also produces 2 NADH, which is an organic molecule that carries electrons (energy) It is exergonic, it does not require energy!

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

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 (an enzyme with 2 carbons). It then becomes CO 2, which we breathe out. It is an endergonic process, it requires energy! The Kreb’s Cycle produces 2 ATP, 6 NADH, and 2 FADH.

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

STEP 3: THE ELECTRON TRANSPORT SYSTEM (ETS) It is also called chemiosmosis, ETS, or ETC It consists of a series of reactions on the inner mitochondrial membranes (cristae). Electrons are released from NADH and FADH, which provide energy. 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.

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

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 Figure 6.8 High-energy electrons carried by NADH GLYCOLYSIS GlucosePyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion Cytoplasmic fluid

For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules 6.14 REVIEW: EACH MOLECULE OF GLUCOSE YIELDS 38 MOLECULES OF ATP KREBS CYCLE Electron shuttle across membranes Cytoplasmic fluid GLYCOLYSIS Glucose 2 Pyruvic acid 2 Acetyl CoA KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion 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.