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.

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 )

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