Harvesting Energy: Glycolysis and Cellular Respiration

Sources of energy A. ATP B. Glucose

Cellular Respiration Cellular respiration is the name given to metabolic pathways in which cells harvest the energy from the metabolism of food molecules

Cellular Respiration Glucose breakdown is one of the main pathways of cellular respiration and occurs in 3 stages Glycolysis Krebs cycle Electron transport system

Harvesting energy from glucoseoverview A. Glycolysis occurs in the cytoplasm and splits glucose in half, producing 2 ATP B. In the mitochondria, an additional 34-36 ATP are produced C. In the absence of oxygen, fermentation occurs, producing only 2 total ATP per glucose

(cytoplasm) (mitochondrion) matrix intermembrane compartment Figure: 07-01 Title: A summary of glucose metabolism. Caption: Refer to this diagram as we progress through the reactions of glycolysis (in the fluid portion of the cytoplasm) and cellular respiration (in the mitochondrion). Glucose is broken down in stages, with various amounts of energy harvested as ATP along the way. The vast majority of the ATP is produced in mitochondria, justifying their nickname, “powerhouse of the cell.” (mitochondrion) matrix intermembrane compartment

The mechanism of cellular respiration A. Glycolysis 1. Occurs in the cytoplasm 2. Anaerobic, not really a part of aerobic respiration 3. Glucose molecule  2 pyruvic acid molecules (3 carbons)

Glycolysis Universal energy-harvesting process of life, very primitive Evolved early in life’s history Means “sugar-splitting” 6-C sugar glucose is split in half to make two 3-C compounds

(a) (b) pyruvate glucose fructose G3P bisphosphate Energy harvest Figure: 07-02 Title: The essentials of glycolysis. Caption: Glucose activation Energy harvest

Krebs Cycle Completes breakdown of glucose to single carbon molecules The process is aerobic (requires oxygen)

intermembrane mitochondrion compartment inner membrane outer membrane matrix cristae 1 (intermembrane compartment) 8 2 Figure: 07-03 Title: Cellular respiration. Caption: Cellular respiration takes place in mitochondria. A mitochondrion’s inner membrane separates the matrix (inner compartment) from the intermembrane compartment (between the inner and outer membranes). 7 (cytoplasm) 6 (inner membrane) 5 4 (matrix) 3 electron transport system (outer membrane)

Krebs cycle acetyl CoA pyruvate 1 Formation of acetyl CoA CO2 2 Krebs cycle CO2 acetyl CoA pyruvate Figure: 07-04 Title: The essential reactions in the mitochondrial matrix. Caption:

The mechanism of cellular respiration D. Electron transport and chemiosmotic ATP synthesis 1. Utilizes NADH and FADH2 formed in the previous steps

(intermembrane compartment) (matrix) 3 1 electron carriers (inner membrane) Figure: 07-05 Title: The electron transport system of mitochondria. Caption: 2 energy to drive synthesis (intermembrane compartment)

The mechanism of cellular respiration D. Electron transport and chemiosmotic ATP synthesis (cont.) 2. Electrons are released to electron transport system and provide energy for active transport of H+ ions from matrix to outside of inner membrane (intermembrane space) to form a membrane potential

The mechanism of cellular respiration D. Electron transport and chemiosmotic ATP synthesis (cont.) 3. Movement of H+ ions down concentration gradient provides energy to make ATP from ADP and Pi 4. The role of oxygen as the terminal electron acceptor

The mechanism of cellular respiration E. ATP yield (36–38 ATP per molecule of glucose) 1. 34 ATP produced by chemiosmotic synthesis (electron transport) 2. 4 ATP produced directly a. 2 ATP from glycolysis b. 2 ATP from Krebs cycle c. 2 ATP required for active transport of NADH from glycolysis into the mitochondria, in some cells

(cytoplasm) (mitochondrion) Figure: 07-07 Title: The energy harvest from the complete metabolism of one glucose molecule. Caption: (mitochondrion)

Fermentation—anaerobic process utilizing glycolysis to produce ATP A. Ethanol fermentation 1. Glucose  pyruvate  acetaldehyde  ethanol 2. Utilized by yeast in the absence of oxygen a. CO2 produced by fermentation allows bread to rise b. Ethanol utilized in production of beer and wine

Fermentation—anaerobic process utilizing glycolysis to produce ATP B. Lactate (lactic acid) fermentation 1. Glucose  pyruvate  lactate 2. Certain bacteria utilized in food production (sour cream, yogurt, sauerkraut, pickles, kimchee)

glucose pyruvate lactate (glycolysis) (lactate fermentation) Figure: 07-06UN01 Title: Lactate fermentation. Caption: glucose pyruvate lactate (glycolysis) (lactate fermentation)

Fermentation—anaerobic process utilizing glycolysis to produce ATP C. Fermentation and muscle performance

(cytoplasm) (mitochondrion) Figure: 07-E7-1 Title: How various nutrients yield energy. Caption: Fats, carbohydrates such as starches, and proteins can all be broken down into molecules that enter glycolysis or the Krebs cycle, where they are used to generate ATP. (mitochondrion)