Overview cellular respiration

Catabolic Pathways Recall this is breaking down of complex molecules 2 types of pathways: –Fermentation – partial pathway requires no oxygen –Cellular respiration – oxygen is consumes

Anaerobic fermentation in yeast

Anaerobic fermentation humans

Cellular respiration is aerobic

Cellular Respiration Cellular respiration is the process of oxidizing food molecules, like glucose, to carbon dioxide and water. The energy released is trapped in the form of ATP for use by all the energy- consuming activities of the cell.ATP

Remembering ATP hydrolysis of the terminal phosphate of ATP yields between 11 and 13 kcal/mole of usable energy, depending on the intracellular conditions.

NAD+ and FAD 1. Each metabolic reaction in cellular respiration is catalyzed by its own enzyme. 2. As a metabolite is oxidized, NAD+ accepts two electrons and a hydrogen ion (H+); results in NADH + H+. 3. Electrons received by NAD+ and FAD are high-energy electrons and are usually carried to the electron transport system.

FAD and NAD

Respiration has four distinct stages: 1. Glycolysis 2. Krebs cycle 3. Electron transport chain 4. Oxidative phosphorylation

Glycolysis Glycolysis is the anaerobic catabolism of glucose.anaerobiccatabolism It occurs in virtually all cells. In eukaryotes, it occurs in the cytosol.cytosol C6H12O6 + 2NAD+ -> 2C3H4O3 + 2NADH + 2H+NADH

Glycolysis is enzyme driven Shockwave – observe the step by step process as you look at your book as well as the animation. i290/ASM/glycolysis.dcrShockwave i290/ASM/glycolysis.dcr Glycolysis glycolysis

Summary of yield The net yield from each glucose molecule is 2 NADH, 2ATP and 2 molecules of pyruvate An initial investment of 2 ATP yields 4 ATP and 2 NADH or a net gain of 2 ATP and 2 NADH

Energy from glycolysis

If molecular oxygen is present the pyruvate enters the mitochondria

Mitochondria Mitochondria are membrane-enclosed organelles distributed through the cytosol of most eukaryotic cells. organelles Their main function is the conversion of the potential energy of food molecules into ATP.

Mitochondria have: an outer membrane that encloses the entire structure an inner membrane that encloses a fluid-filled matrix between the two is the intermembrane space the inner membrane is elaborately folded with shelflike cristae projecting into the matrix. a small number (some 5–10) circular molecules of DNA

Prior to entering the Krebs Cycle, pyruvate must be converted into acetyl CoA. This is achieved by removing a CO2 molecule from pyruvate and then removing an electron to reduce an NAD+ into NADH. An enzyme called coenzyme A is combined with the remaining acetyl to make acetyl CoA which is then fed into the Krebs Cycle. The steps in the Krebs Cycle are summarized below:

Transition of pyruvate to acetyl CoA

We are now back at the beginning of the Krebs Cycle. Because glycolysis produces two pyruvate molecules from one glucose, each glucose is processes through the kreb cycle twice. For each molecule of glucose, six NADH2+, two FADH2, and two ATP.

To review Krebstca

Points to remember Each NADH made in the mitochondria yields 3 ATP NADH made in outside mitochondria yields 2 ATP FADH yields 2 ATP You will need this information as we discuss the electron transport chain.

Electron transport chain overview Krebstca (if can’t open go to bio home page at the bottom of page )Krebstca

Harvesting the nrg So far we have from glycolysis and the Kreb’s cycle: (per molecule of glucose) ATP by substrate phosphorylation NADH and FADH2 – (which account for most of the nrg stored from the metabolism of glucose )

Electron Transport Chain A collection of molecules found in the inner mitochondrial membrane

Key points Protons are translocated across the membrane, from the matrix to the intermembrane space Electrons are transported along the membrane, through a series of protein carriers Oxygen is the terminal electron acceptor, combining with electrons and H+ ions to produce water As NADH delivers more H+ and electrons into the ETS, the proton gradient increases, with H+ building up outside the inner mitochondrial membrane, and OH- inside the membrane.

/ /animations/electron_transpo rt/electron_transport.swfhttp:// / /animations/electron_transpo rt/electron_transport.swf (follow electron transport ) respiration info (go to electron transport chain)respiration info Animations (should be mcgraw hill)Animations

Key Points to remember 1. NADH and FADH2 donate electrons to the series of electron carriers in the ETC The final electron acceptor is Oxygen creating water as a by product of cell resp.

Points cont. Electron transport is coupled to ATP by chemiosmosis. Animation of Chemiosmosis during Aerobic RespirationAnimation of Chemiosmosis during Aerobic Respiration

Points cont. At certain steps along the chain, electron transfer causes electron carrying protein complexes to move Hydrogen ions from the matrix to the intermembrane space storing energy as a proton-motive force (hydrogen gradient) Animation of Chemiosmosis Proton PumpingAnimation of Chemiosmosis Proton Pumping

Points continued As hydrogen diffuses back into the matrix through ATP synthase, its exergonic passage drives the endergonic phosphorylation of ADP Electron transport system:Electron transport system (follow NADH and FADH2 as well as counting number of ATP made.)

Related Metabolic Pathways Without oxygen electronegetive oxygen to pull the electrons down the transport chain, oxidative phosphorylation ceases. Fermentation provides another avenue for the synthesis of ATP.

Fermentation 1. The oxidizing agent of glycolysis is NAD+, not oxygen. But glycolysis generates 2 ATP by oxidative phosphorylation. Fermentation regenerates ATP by transferring electrons are transferred to pyruvate.

The miracle of fermentation

Process of alcohol fermentation Fermentation consists of glycolysis plus reduction of pyruvate to either lactate or alcohol and CO2. NADH passes its electrons to pyruvate instead of to an electron transport system; NAD+ is then free to return and pick up more electrons during earlier reactions of glycolysis.

Alcohol fermentation pyruvate is first decarboxylated to yield a 2-carbon substance acetaldehyde. Acetaldehyde is then reduced as hydrogens are transferred from NADH to acetaldehyde to produce ethyl alcohol.

lactic acid fermentation pyruvate is used as the direct acceptor of the hydrogens removed from NADH. The end product is a molecule of lactic acid. Lactic acid [or lactate] is a common by-product of anaerobic respiration in muscle cells.

Advantage of Fermentation provides quick burst of ATP energy for muscular activity.

Disadvantage of Ferm. lactate is toxic to cells. lactate changes pH and causes muscles to fatigue. lactate is sent to liver, converted into pyruvate; then respired or converted into glucose. Two ATP produced per glucose molecule during fermentation

Go through this site and do review questions. Cell Respiration: Introduction General & Human Biology