Cellular Respiration Unit 5: Plants, Photosynthesis, and Cellular Respiration
Overview! Organisms obtain energy (ATP) by breaking down (catabolic pathway, exergonic reaction) organic molecules (glucose) during cellular respiration. Sugar (Glucose)! ATP! Available Energy! The function of cellular respiration is to gather electrons from glucose and use their energy to create ATP.! Cellular respiration occurs in the cytoplasm and mitochondria. (ATP)
Anaerobic vs. Aerobic Respiration! Anaerobic oxygen (O 2 ) not required! Aerobic oxygen (O 2 ) required Cellular Respiration Oxygen unavailable Oxygen available Glycolysis (cytoplasm) Glycolysis (cytoplasm) Fermentation (cytoplasm): a) Lactic Acid Fermentation b) Alcohol Fermentation Aerobic Respiration (mitochondria): a) Krebs Cycle b) Electron Transport Chain (ETC) + Chemiosmosis
Aerobic Respiration! Aerobic cellular respiration occurs in two main parts: 1. Glycolysis! This stage is anaerobic, meaning that it doesn t require oxygen! 2. Aerobic Respiration! Aerobic mean that the process occurs with oxygen!! Includes the Krebs Cycle, Electron Transport Chain, and Chemiosmosis
Glycolysis! Glycolysis (glyco = sugar, lysis = to break) is the process of glucose being broken down in the cytoplasm of a cell.! What goes in?! Glucose (6-carbon sugar)! 2 ATP! What comes out?! 4 ATP total, a net of 2 ATP! 2 NADH (electron carriers)! 2 Pyruvate (3-carbon sugar)
Cellular Respiration: C 6 H 12 O 6 + 6 O 2! 6 CO 2 + 6 H 2 O + ATP (36) Goes IN C 6 H 12 O 6 Comes OUT 2 ATP 2 ADP 2 NAD+ Glycolysis 2 NADH 4 ADP 4 ATP (2 net) 2 Pyruvate Krebs Cycle Electron Transport Chain + Chemiosmosis
Between Glycolysis and the Krebs Cycle! After glycolysis, the cell is left with 2 pyruvate in the cytoplasm.! Prior to entering the Krebs Cycle, pyruvate firsts reacts with coenzyme A (CoA) to form a 2-carbon molecule called Acetyl CoA.! Also during this time, one carbon dioxide is released and one NADH (electron carrier) is formed.
Cellular Respiration: C 6 H 12 0 6 + 6 O 2! 6 CO 2 + 6 H 2 0 + ATP (36) Goes IN C 6 H 12 O 6 Comes OUT 2 ATP 2 ADP 2 NAD+ Glycolysis 2 NADH 4 ADP 4 ATP (2 net) 2 NAD+ 2 Pyruvate 2 NADH 2 CO 2 2 Acetyl CoA Krebs Cycle Electron Transport Chain + Chemiosmosis
The Krebs Cycle! After glycolysis, most of the energy from the glucose is still contained in the 2 pyruvate.! In the presence of oxygen, the pyruvate is transported into the mitochondria and converted to Acetyl CoA.! There it is broken down into carbon dioxide in a process known as the Krebs Cycle.
The Krebs Cycle! What goes in?! Pyruvate!Aceytl CoA! What comes out?! 4 CO 2! 6 NADH (electron carrier)! 2 FADH 2 (electron carrier)! 2 ATP
Cellular Respiration: C 6 H 12 0 6 + 6 O 2! 6 CO 2 + 6 H 2 0 + ATP (36) Goes IN C 6 H 12 O 6 Comes OUT 2 ATP 2 ADP 2 NAD+ Glycolysis 2 NADH 4 ADP 4 ATP (2 net) 6 NAD+ 2 FAD 2 ADP 2 NAD+ 2 Pyruvate 2 NADH 2 CO 2 2 Acetyl CoA 6 NADH 2 FADH 2 Krebs Cycle 2 ATP 4 CO 2 Electron Transport Chain + Chemiosmosis
Electron Transport Chain! This is the point at which most of the ATP of aerobic cellular respiration is produced.! The electrons carried by NADH and FADH 2 are brought to the ETC to convert ADP! ATP.! These electrons are release by NADH and FADH 2 to move along the mitochondrial membrane from one protein (cytochromes) to another.! This causes Hydrogen ions to be pumped across the mitochondrial membrane into the innermembrane space.! After the electrons have been passed down the chain they are accepted at the end by O 2 to make H 2 O.
Chemiosmosis! Because there are more Hydrogen ions (H+) in the innermembrane space, they want to diffuse back across the membrane into the matrix.! They move back across the membrane through an enzyme called ATP synthase.! ATP synthase turns ADP into ATP!
Fig. 9-16 H + H + Protein complex of electron carriers H + Cyt c H + Ι ΙΙ Q FADH 2 ΙΙΙ FAD ΙV 2 H + + 1 / 2 O 2 H 2 O ATP synthase NADH (carrying electrons from food) NAD + ADP + P i H + ATP 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation
Cellular Respiration: C 6 H 12 O 6 + 6 O 2! 6 CO 2 + 6 H 2 0 + ATP (36) Goes IN C 6 H 12 O 6 Comes OUT 2 ATP 2 ADP 2 NAD+ Glycolysis 2 NADH 4 ADP 4 ATP (2 net) 6 NAD+ 2 FAD 2 ADP 2 NAD+ 2 Pyruvate 2 NADH 2 CO 2 2 Acetyl CoA 6 NADH Krebs Cycle 2 FADH 2 2 ATP 4 CO 2 6 O 2 10 NADH 2 FADH 2 Electron Transport Chain + Chemiosmosis 10 NAD+ 2 FAD 32 ATP 6 H 2 O
Anaerobic Respiration! Some cells can function for short periods of time when oxygen levels are low or even exist without oxygen at all!! Recall, Glycolysis is an anaerobic process and occurs in the cytoplasm without oxygen.! If there is no oxygen after Glycolysis, the cell will carry out fermentation rather than aerobic cellular respiration.! Fermentation is the process in which NAD+ is regenerated, allowing cells to maintain Glycolysis and small amounts of ATP production in the absence of oxygen.
Fermentation! There are two main types of fermentation: 1. Lactic acid fermentation 2. Alcohol fermentation
1. Lactic Acid Fermentation! At the end of Glycolysis, pyruvate is left.! Lactic acid fermentation converts the pyruvate made during Glycolysis to lactic acid using special enzymes.! During Glycolysis NAD+ is converted to NADH. When Pyruvate gets converted to Lactic acid, NADH gets converted back to NAD+ so Glycolysis can be repeated.! This is what occurs in your muscle cells when you are at lacking oxygen. It is hypothesized that Lactic acid can cause your muscles to feel fatigued or sore.
1. Lactic Acid Fermentation
2. Alcohol Fermentation! This occurs in yeast (fungi) and some bacteria.! After Glycolysis, pyruvate is converted to ethanol and carbon dioxide.! This process also allows for NAD+ to be converted back to NADH.! This is why bread has holes in it!!!
Fig. 9-18a 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 NAD + 2 NADH + 2 H + 2 Pyruvate 2 CO 2 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation