CELL RESPRIATION CHAPTER 9

9–1CHEMICAL PATHWAYS Chemical Energy and Food Calorie – amount of energy needed to raise1 gram of water 1 0 Celcius. Cells release energy from glucose gotten from food. Process begins with glycolysis (splitting of a glucose molecule). If oxygen is present (aerobic), it leads to Kreb’s Cycle & Electron Transport Chain. If oxygen is not present (anaerobic), it leads to fermentation.

Glucose Glycolysis Krebs cycle Electron transport Fermentation (without oxygen) Alcohol or lactic acid CHEMICAL PATHWAYS

OVERVIEW OF CELLULAR RESPIRATION Cellular respiration (Rs) – process that releases energy by breaking down food molecules in the presence of oxygen. 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + Energy ( 36ATP) In words:6 oxygen + glucose yields 6 carbon dixoide + 6 waters + 36 ATP 3 stages of cell respiration Glycolysis Kreb’s Cycle Electron Transport Chain

Glucose Glycolysis Cytoplasm Pyruvic acid Electrons carried in NADH Krebs Cycle Electrons carried in NADH and FADH 2 Electron Transport Chain Mitochondrion Figure 9–2 – pg. 222 Cellular Respiration: an Overview – Cell respiration is a process that releases energy by breaking down food molecules in the presence of oxygen. Glycolysis takes place in the cytoplasm. Krebs cycle and electron transport chain take place inside the mitochondria. Mitochondrion

GLYCOLYSIS 1 st step in Rs Process in which one molecule of glucose is broken in half to produce two molecules of pyruvic acid and 2 ATP molecules. At the end, 4 ATP are made, however, 2 ATP are used in the beginning. Net ATP production during glycolysis is 2 (4-2 = 2) WHAT DOES GLYCOLYSIS BREAK DOWN? GLUCOSE

Glucose To the electron transport chain 2 Pyruvic acid Figure 9–3 Glycolysis – pg. 223 – Glycolysis is the first stage in cellular respiration. During glycolysis, glucose is broken down into 2 molecules of pyruvic acid.

FERMENTATION No oxygen after glycolysis, fermantation takes place (anaerobic) Fermentation releases energy from food molecules when there is no oxygen available. Two types of fermentation Alcoholic Lactic Acid

ALCOHOLIC FERMENTATION Performed by yeast Produces carbon dioxide and ethyl alcohol as waste products. Carbon dioxide causes bread to rise

LACTIC ACID FERMENTATION Pyruvic acid is converted to lactic acid Happens when mucles are used during rapid exercise. Not enough oxygen available and the body can’t produce the ATP needed. Buildup of lactic acid creates the painful burning sensation during hard exercise. Reason muscles feel sore after intense activity.

Glucose Pyruvic acid Lactic acid Figure 9–4 – pg. 225 Lactic Acid Fermentation – Lactic acid fermentation converts glucose into lactic acid. The first part of the equation is glycolysis. The second part shows the conversion of pyruvic acid to lactic acid.

9–2The Krebs Cycle and Electron Transport Introduction End of glycolysis, 90% of energy from glucose is unused. Oxygen – most powerful electron acceptor – required for the remaining steps of cell respiration. Energy-releasing reactions in the cell require oxygen and this is the reason we “breathe” or “respire”

KREBS CYCLE Oxygen is available, glycolysis is followed by Krebs Cycle. Named after Hans Krebs an English biochemist. During Krebs Cycle, pyruvic acid (from glycolysis) is broken down into carbon dioxide.

KREB’S CONT’D Begins when pyruvic acid enters the mitochondria Citric acid is broken down and CO 2 is released. Electrons are transferred to energy carriers (usually proteins) Each turn of the Krebs Cycle produces 1 ATP molecule. Krebs turns twice during respiration, producing 2 ATP overall. CO 2 released during Krebs is the source of all the CO 2 organisms breath out. WHY IS THE KREBS, CYCLE ALSO KNOW AS THE CITRIC ACID CYCLE? CITRIC ACID IS BROKEN DOWN INTO CO 2

Citric Acid Production Figure 9–6 The Krebs Cycle – pg. 227 – During the Krebs cycle, pyruvic acid from glycolysis is used too make CO 2, NADH, ATP AND FADH 2 Mitochondrion

ELECTRON TRANSPORT 3rd step in cell respiration Uses high energy electrons from the Krebs cycle to create ATP from ADP. Electrons are passed along an electron transport chain. Passed from 1 carrier protein to the next. Located on the interior membrane (cristae) of the mitochondria. At the end the electrons (H + ) combine with O to form water. Waste products of cell respiration.

Figure 9–7 Electron Transport Chain – pg. 228 – The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP into ATP. Electron Transport Hydrogen Ion Movement ATP Production ATP synthase Channel Inner Membrane Matrix Intermembrane Space Mitochondrion

THE TOTALS Glycolysis produces 2 ATP. Kreb’s Cycle produces 2 ATP Electron Transfer Chain produces 32 ATP Grand Total of Cell Respiration = 36 ATP See Fig page 229.

COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION Photosynthesis (P S ) & Cell Respiration (R S ) are opposite chemical reactions They are the reverse of each other P S removes CO 2 from the atmosphere R S puts it back P S releases O 2 and R S uses O 2 to release energy (ATP) from food. Products of P s are the reactants of R S. Products of R S are the reactants for P s. Cell respiration takes place in all eukaryotes and some prokaryotes. Photosynthesis takes place only in plants, algae and some bacteria. See Fig. 9-10, page. 232.

Flowchart – Steps of Cellular Respiration Glucose (C 6 H ) + Oxygen (0 2 ) Glycolysis Krebs Cycle Electron Transport Chain Carbon Dioxide (CO 2 ) + Water (H 2 O) Cellular Respiration