Cellular Respiration 101 by Leslie Patterson, M.S.

Definition Cellular respiration (oxidative metabolism) the metabolic process by which cells breakdown organic molecules, such as glucose, to release stored energy, and convert that energy into a usable form known as adenosine triphospate (ATP) Electron donor (oxidized: loses an electron) Electron tranport chain Electron acceptor (reduced: gains an electron) Once ATP is produced it can then be used to do cellular work such as biosysnthesis, locomotion, transport across cell membrane -besides glucose, amino acids, and fatty acids can be broken down to generate atp Cellular work-biosysnthesis, locomotion, transport across cell membrane To be considered cellular respiration the metabolic process must include an electron donor, electron tranport chain, and an electron acceptor. Electron (negative charge) Proton (+)

Two Forms of cellular respiration Aerobic respiration Meaning “requires oxygen” to produce ATP Oxygen (O2) is the final electron acceptor Anaerobic respiration Meaning “without oxygen” Uses an inorganic compound such as sulfate (SO4), nitrate (NO3), or sulfur (S), as the final electron acceptor in the production of ATP “Facultative anaerobes”-organisms that can use both oxygen and inorganic compounds as the final electron acceptor “Obligate anaerobes”- organisms that can only use inorganic compounds to respire Anaerobic respiration used by mainly prokaryotic organisms (Bacteria and archaea/ (lithothroph)) that live in environments devoid of oxygen. less electronegative substances such as sulfate (SO4), nitrate (NO3), and sulfur (S) Fermentation-uses the organic compound (pyruvate derivative) as a final electron acceptor, However, it can not be classified as respiration because it does not make use of the citric acid cycle or electron transport chain. Aerobic- meaning “requiring oxygen” Anaerobic- meaning “without oxygen”

Adenosine triphosphate (ATP) IS the energy currency cells use to perform work ATP is formed by the addition of an inorganic phosphate group (Pi) to adenosine diphosphate (ADP) to produce adenosine triphosphate (ATP) Substrate level phosphorylation – the direct transfer of (Pi) to ADP to form ATP from a reactive intermediate Oxidative phosphorylation – the indirect production of ATP through a series of reduction-oxidation reactions (electron transport chain) that forms a proton gradient across a cell membrane Why is it so powerful? Need to understand this better Substrate level phosphorylation Occurs in glycolysis and citric acid cycle ATP is produced from an enzyme-catalyzed phosphorylation reaction where ADP is the substrate. Oxidative phosphorylation Is the coupling of ATP synthesis with the oxidation of NADH and FADH2 and formation of electrochemical gradient (i.e. ATP is indirectly formed from the creation of electrochemical gradient—NOT directly) ATP is formed by a series of redox reactions ATP is powerful because it has high potential energy inpart because o fthe 4 negative charges clustered (in close relation to one another) in it’s three phosphate groups. The negative charges repel one another. Exergonic-reactions that release energy Endergonic-reactions that store energy

Aerobic Cellular Respiration Glycolysis Linkage Reaction Citric Acid Cycle (Krebs Cycle) Electron Transport Chain (ETC) *In respiration, glucose is oxidized and thus releases energy. Oxygen is reduced to form water. The carbon atoms of the sugar molecule are released as carbon dioxide (CO2). The third step defines the form of respiration (or the final electron acceptor in the electron transport chain) To function properly a final electron acceptor must be present. C6H12O6(Glucose) + 6O2(Oxygen)  6CO2(Carbon dioxide) + 6H2O(water) + Energy (ATP)

Glycolysis Occurs in the cytoplasm and does not require O2 Is the process through which one 6-carbon molecule of glucose is oxidized into two 3-carbon molecules of pyruvate The process requires two ATP to complete, but produces four ATP for a net gain of two ATP (substrate-level phosphorylation) Pgal-glyceraldehyde 3 phosphate What causes the split? NAD?__Nicotinamide adenine dinucleotide http://library.thinkquest.org/27819/media/glycolysis.gif

Link Reaction Occurs in the inner mitochondrial membrane Preparatory step for the citric acid cycle “Pyruvate decarboxylation” Removal of a carbon dioxide and hydrogen from pyruvate to form an acetyl group that combines with Coenzyme A (CoA) and forms acetyl-CoA Acetyl-CoA reacts with oxaloacetate to form citrate (the first compound in the citric acid cycle) Regulated by ATP and NADH Mitochondrial matrix Feedback inhibition Transuition of pyruvate to acetyl coa occurs in the enzyme complex pyruvate dehydrogenase which is locate in the inner mitochondrial membrane

Citric Acid Cycle (Krebs Cycle) Occurs in the mitochondrial matrix For every 1 acetyl-CoA that enters the cycle 3 molecules of NADH and 1 molecule of FADH2 2 molecules of CO2 1 molecule of ATP (substrate-level phosphorylation) At the end of the cycle oxaloacetate is regenerated and the cycle continues tricarboxylic acid cycle (TCA cycle) The citric acid cycle is an 8-step process involving 8 different enzymes. Throughout the entire cycle, acetyl-CoA changes into citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, and finally, oxaloacetate. The net energy gain from one cycle is 3 NADH, 1 FADH, and 1 ATP. Thus, the total amount of energy yield from one whole glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH, and 2 ATP. While the Krebs cycle is oxidative respiration, one more instance of substrate-level phosphorylation occurs as Guanosine triphosphate (GTP) is created from GDP by transfer of a phosphate group during the conversion of Succinyl CoA to Succinate. This phosphate is transferred to ADP in another substrate-level phosphorylation event. http://library.thinkquest.org/27819/media/krebs_cycle.gif

Electron Transport Chain (ETC) Occurs in the inner mitochondrial membrane Couples the oxidation of NADH and FADH2 to the creation of a proton gradient, which indirectly drives the production of ATP (oxidative phosphorylation) Oxidative phosphorylation produces ~26 ATP. ETC get’s rid of electrons and creates a proton gradient. Then as H+ ions push through the ATP synthase, 1 ATP is formed http://legacy.owensboro.kctcs.edu/gcaplan/Songbook/chemios.gif

Summary of Steps Aerobic respiration produces ~30 ATP Cytoplasm Mitochondrial Matrix & Inner Membrane Glucose Pyruvate Acetyl CoA 3. Citric Acid Cycle 4. Electron Transport Chain 1. Glycolysis 2. Linkage Reaction NADH NAD+ 2 ATP 26 ATP FADH2 O2 H2O FAD Aerobic respiration produces ~30 ATP 20 times more efficient than anaerobic respiration

Questions to consider How can the rate of cellular respiration be measured? Does cellular respiration differ in prokaryotes and eukaryotes? (hint: location) What type of regulators are in place for these processes? If no final electron acceptor is present, how does the cell handle the build up of NADH? (Is this considered cellular respiration?) How can the rate of cellular respiration be measured? When you study the equation for cellular respiration, you will see that there are at least three ways:1. Measure the amount of glucose consumed. 2. Measure the amount of oxygen consumed. 3. Measure the amount of carbon dioxide produced.

Electron Transport Chain (ETC) Occurs in the inner mitochondrial membrane Couples the oxidation of NADH and FADH to the creation of a proton gradient, which indirectly drives the production of ATP (oxidative phosphorylation) ETC get’s rid of electrons and creates a proton gradient. Then as H+ ions push through the ATP synthase, 1 ATP is formed http://legacy.owensboro.kctcs.edu/gcaplan/Songbook/chemios.gif