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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. - PowerPoint PPT Presentation
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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.
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.
• It occurs in virtually all cells.
• In eukaryotes, it occurs in the cytosol.
• C6H12O6 + 2NAD+ -> 2C3H4O3 + 2NADH + 2H+
Glycolysis is enzyme driven
• Shockwave – observe the step by step process as you look at your book as well as the animation. http://instruct1.cit.cornell.edu/courses/biomi290/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.
• 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.
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 )
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.
• http://www.wiley.com/legacy/college/boyer/0470003790/animations/electron_transport/electron_transport.swf
• (follow electron transport )
• respiration info (go to electron transport chain)
• Animations (should be mcgraw hill)
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 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 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:
(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