RESPIRATION Prof Nirupama Mallick Agricultural & Food Engineering Department

The process of converting Food Energy into Chemical Energy (ATP). ATPs are used to power the metabolic processes. It is almost the reserve process of photosynthesis, which requires light energy for producing food, using carbon dioxide and producing oxygen. Respiration is the chemical process opposite of photosynthesis because it releases energy from food, and uses oxygen and produces carbon dioxide.

Photosynthesis vs Respiration Produces food Uses food Stores energy Releases energy Uses water Produces water Uses CO2 Produces CO2 Releases O2 Uses O2 Occurs in light Occurs at all time Only in cells containing chloroplasts Occurs in all cells

The Overall Equation for Respiration A common fuel molecule for cellular respiration is glucose Glucose Oxygen Carbon dioxide Water Energy

[Glucose loses electrons (and hydrogens)] Oxidation [Glucose loses electrons (and hydrogens)] Glucose Oxygen Carbon dioxide Water Reduction [Oxygen gains electrons (and hydrogens)]

What is ATP? Energy currency of the cell Adenosine Triphosphate 5-Carbon sugar (Ribose) Nitrogenous base (Adenine) 3 Phosphate groups The chemical bonds that link the phosphate groups together are Covalent high energy bonds When a phosphate group is removed to form ADP and P, small packets of energy are released. As ATP is broken down, it gives off usable energy to power chemical work and gives off some nonusable energy as heat.

What are the Stages of Cellular Respiration? Glycolysis Krebs Cycle Electron Transport Chain (ETC)/ Oxidative Phosporylation 9

Where Does Cellular Respiration Take Place? It actually takes place in two parts of the cell: Glycolysis occurs in the Cytoplasm or Cytosol Krebs Cycle & ETC Take place in the Mitochondria 10

Review of Mitochondria Structure About 1 micron diameter Smooth outer Membrane Folded inner membrane Folds called Cristae Space inside cristae called the Matrix Intermembrane space

Cellular Respiration - 2 2 34 Cellular Respiration

GLYCOLYSIS Glyco = sweet Lysis= splitting Embden-Meyerhoff-Parnas (EMP) Pathway Anaerobic (does not require Oxygen) 10 steps all occurring in cytosol or cytoplasm

GLYCOLYSIS

Glycolysis Summary Requires input of 2 ATP Takes place in the Cytosol (cytoplasm) Doesn’t Use Oxygen Requires input of 2 ATP Glucose splits into two molecules of Pyruvate or Pyruvic Acid Produces 2 NADH and 4 ATP Net Production: 2 NADH and 2 ATP 21

Pyruvic acid from glycolysis is first converted into Acetyl-CoA Pyruvate dehydrogenase

Net Production: 2 NADH Releases 2 CO2

Krebs cycle Krebs cycle- was discovered by Sir Hans Krebs Also called Citric acid cycle or Tricarboxylic Acid (TCA) cycle Requires Oxygen (Aerobic) Takes place in matrix of mitochondria

Krebs Cycle Summary Cyclical series of oxidation reactions Turns twice per glucose molecule Each turn of the Krebs Cycle also produces 3NADH, 1FADH2, 1ATP and 2CO2 Therefore, For each Glucose molecule, the Krebs Cycle produces 6NADH, 2FADH2, 2ATP and 4CO2 30

Electron transport chain (ETC) Discovered by Eugene Kennedy & Albert Lehninger (1948) Catalyzes a flow of electrons from NADH/ FADH2 to O2 1) direct transfer of electron as in the reduction of Fe3+ to Fe 2+ and Cu2+ to Cu+ 2) transfer as a hydrogen atom (H+ & e-) Electron transport is coupled with formation of proton gradient → used for ATP synthesis

Electron transport chain (ETC) Consists of 5 complexes: – Complex I (NADH dehydrogenase) – Complex II (Succinate dehydrogenase) – Complex III (Ubiquinone-Cytochrome bc1 complex) – Complex IV (Cytochrome oxidase) – Complex V (ATP synthase)

Electron transport chain (ETC) Complex I : NADH to Ubiquinone Complex II : Succinate to Ubiquinone Complex III :Ubiquinone to Cytochrome c Complex IV : Cytochrome c to Oxygen

Chemiosmosis The steps that transport protons from Intermembrane space to matrix establishing a proton chemiosmotic gradient. It is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to generate ATP.

ATP synthase F1 F0

ATP Synthesis Inner mitochondrial membrane is impermeable to protons. Proton can re-enter the matrix only through proton-specific channels (F0). The proton-motive force that drives protons back into the matrix provides the energy for ATP synthesis, catalyzed by the F1 complex associated with F0.

Electron Transport Chain Summary Occurs Across Inner Mitochondrial membrane Uses coenzymes NAD+ and FAD+ to accept e- from glucose NADH = 3 ATP’s FADH2 = 2 ATP’s 34 ATP Produced H2O Produced 40

Total number of ATP produced Glycolysis 4 ATP 2 molecules NADH 6 ATP Pyruvate DH complex TCA cycle 2 ATP 6 molecules NADH 18 ATP 2 molecules FADH2 4 ATP TOTAL ATP produced 40 ATP utilized in glycolysis 2 NET ATP PRODUCED 38

Fate of PYRUVATE in the absence of oxygen: Fermentation

Alcohol fermentation occurs in yeasts, and some bacteria NADH Pyruvate decarboxylase Lactate dehydrogenase NADH Alcohol dehydrogenase Alcohol fermentation occurs in yeasts, and some bacteria Lactic acid fermentation occurs in animal muscle cells, some fungi and bacteria to make yogurt

Fermentation Occurs when O2 NOT present (anaerobic) Requires NADH generated by glycolysis Called Lactic Acid fermentation in muscle cells, some fungi and bacteria, produces lactic acid) Called Alcoholic fermentation in yeast (produces carbon dioxide and ethanol) Net Gain: only 2 ATP 44

Cellular respiration can “burn” other kinds of molecules besides glucose Diverse types of carbohydrates Fats Proteins

Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Acetyl- CoA Krebs Cycle Glycolysis Electron Transport

Some commercial use of fermentation: wine and beer. Yeasts in the process of “budding” or reproducing.

Carbon dioxide in beer and cake- due to yeast fermentation