Ch 9: CellularCh 9: Cellular Respiration Respiration

The Big PictureThe Big Picture

Cellular respiration sole purpose is to Cellular respiration sole purpose is to produce ATP.produce ATP.

Its an exergonic (catabolic)reaction.Its an exergonic (catabolic)reaction.

Can be summarized as a whole as:Can be summarized as a whole as:Organic Compound+OxygenOrganic Compound+OxygenCO2+WaterCO2+Water +ATP + heat+ATP + heat

Glycolysis, Krebs Cycle, and Glycolysis, Krebs Cycle, and Oxidative PhosphorylationOxidative Phosphorylation

1. Glycolysis is the decomposition 1. Glycolysis is the decomposition of glucose to pyruvate (or pyruvic of glucose to pyruvate (or pyruvic acid)acid)

2. Krebs Cycle takes pyruvate (2 2. Krebs Cycle takes pyruvate (2 pyruvate per glucose molecule) pyruvate per glucose molecule) and yields electron acceptors and and yields electron acceptors and ATP.ATP.

3. Oxidative phosphorylation 3. Oxidative phosphorylation extracts ATP from NADH and extracts ATP from NADH and FADH2. FADH2.

Reminder on ATPReminder on ATP ATP (adenosine triphosphate) is a nucleotide ATP (adenosine triphosphate) is a nucleotide

with unstable phosphate bonds that the cell with unstable phosphate bonds that the cell hydrolyzes for energy.hydrolyzes for energy.

The cell taps energy stored in ATP by enzy-The cell taps energy stored in ATP by enzy- matically transferring terminal phosphatematically transferring terminal phosphate groups from ATP to other compounds.groups from ATP to other compounds.

The compound receiving the phosphate group The compound receiving the phosphate group is said to be is said to be phosphoralated phosphoralated and is more and is more reactive as a result.reactive as a result.

Cells use ATP to continue cellular work. But Cells use ATP to continue cellular work. But they must replenish the ATP supply to continue they must replenish the ATP supply to continue cellular work. Respiration does this.cellular work. Respiration does this.

Simply put – cellular respiration is a redox process that transfers hydrogen from sugar to oxygen.

• Valence electrons of carbon and hydrogen lose potential energy as they shift toward electronegative O.

• Released energy is used by cells to produce ATP.

Redox reactionsRedox reactions These are the energy-shuttling These are the energy-shuttling

mechansisms of metabolismmechansisms of metabolism

Partial or complete gain of Partial or complete gain of electrons=reduction electrons=reduction

Partial or complete loss of Partial or complete loss of electron=oxidationelectron=oxidation

They are always coupled…so in order They are always coupled…so in order for a material to lose an electron, for a material to lose an electron, another molecule must accept itanother molecule must accept it

The NAD+, NADH, FAD+, FADHThe NAD+, NADH, FAD+, FADH NAD+ and FAD+ are coenzymes that function in NAD+ and FAD+ are coenzymes that function in

the redox reactions and are found in all cells.the redox reactions and are found in all cells.

Traps energy-rich electrons from the organic Traps energy-rich electrons from the organic compound.compound.

NAD+= oxidized coenzymeNAD+= oxidized coenzyme

NADH= reduced coenzyme NADH= reduced coenzyme

Why isn’t glucose oxidized in one explosive Why isn’t glucose oxidized in one explosive step?step?

During oxydation of glucose, NADDuring oxydation of glucose, NAD+ + functions as an functions as an oxidizing agent by trapping energy-rich electrons from oxidizing agent by trapping energy-rich electrons from glucose. These reactions are catalized byglucose. These reactions are catalized by enzymes enzymes calledcalled dehydrogenases dehydrogenases which:which:

- Remove a pair of hydrogen atoms (2 e,2p) from - Remove a pair of hydrogen atoms (2 e,2p) from substrate.substrate.

- Deliver the two electrons and one proton to NADDeliver the two electrons and one proton to NAD++

- Release the remaining proton into the surrounding Release the remaining proton into the surrounding solution.solution.

Cellular Respiration

Glyclolysis (per glucose molecule)Glyclolysis (per glucose molecule) Takes place in cytosol.Takes place in cytosol. Mutiple steps (9 or 10 depending on Mutiple steps (9 or 10 depending on

source) in the process of decomposing source) in the process of decomposing glucose into pyruvate. Mg2+ ions are glucose into pyruvate. Mg2+ ions are cofactors to help.cofactors to help.

2 ATP go IN2 ATP go IN 4 ATP PRODUCED (so what is NET 4 ATP PRODUCED (so what is NET

gain?)gain?) 2 NAD+ go IN2 NAD+ go IN 2 NADH PRODUCED 2 NADH PRODUCED 2 Pyruvate (Pyruvic acid) PRODUCED2 Pyruvate (Pyruvic acid) PRODUCED

Glycolysis……….

- occurs whether O is present or not

- no CO2 is released as glucose is oxidized to pyruvate; all C in glu – cose can be accounted for in the 2 molecules of pyruvate.

- occurs in 2 phases

Glycolysis: Energy Investment Phase

- includes 5 preparatory steps in which glucose is split in two.

- consumes ATP….why? The cell uses ATP to phosphorylate the intermediates of glycolysis.

- End result of this phase is 2 molecules of glyceraldehyde phosphate (3 C

each) for each glucose molecule.

Glycolysis: Energy – Yielding Phase

- two 3 carbon intermediaries (PGAL) are oxidized becoming pyruvate.

- there’s a net gain of 2 ATPs by substrate phosphorylation

- 2 molecules of NAD+ are reduced to NADH

• Breaks down “Glucose” (6-carbon sugar) into 2 molecules of “Pyruvic Acid” (3-carbon compound)

•

Glycolysis

• The products are:

–2 Pyruvic Acid molecules

–2 ATP molecules

–2 NADH molecules

If Oxygen is present (Aerobic) ...“Krebs Cycle”… then to Electron Transport Chain

Glycolysis has 2 pathways…

If Oxygen is absent (Anaerobic) ……..

“Fermentation”occurs

KREBS Cycle (per pyruvate)KREBS Cycle (per pyruvate) Takes place in mitochondrial Takes place in mitochondrial

matrix.matrix. Pyruvate combines with CoA Pyruvate combines with CoA

(coenzyme A) to make acetyl CoA. (coenzyme A) to make acetyl CoA. This makes 1 NADH and 1 CO2.This makes 1 NADH and 1 CO2.

Acetyl CoA combines with OAA to Acetyl CoA combines with OAA to form citric acid. (8 steps yielding form citric acid. (8 steps yielding intermediate products). 3 NADH intermediate products). 3 NADH and 1 FADH2 are made and CO2 and 1 FADH2 are made and CO2 released. 1 ATP is made.released. 1 ATP is made.

How much total ATP then for the How much total ATP then for the Krebs cycle?Krebs cycle?

Junction between gly-colysis and Krebs CycleIs the oxidation of Pyru-vate to acetyl CoA.

- CO2 is removed from the carboxyl group of pyruvate changing it from a 3 carbon to a 2 carbon compound. CO2 is released.

- 2 NADH molecules are produced- Coenzyme A attaches to the acetyl group – very unstable-reactive

KREBS CYCLE(Aerobic Pathway)Krebs Cycle oxidizesthe remaining acetyl fragments of Acetyl –CoA to CO2.

- Energy released from this exergonic process is used to reduce co – enzymes, NAD and FAD, and phosphory – late ATP.How many ATPs areproduced here?

- 2 NADH molecules are produced- Coenzyme A attaches to the acetyl group – very unstable-reactive

ETC (Oxidative Phosphorylation)ETC (Oxidative Phosphorylation) Takes place in inner Takes place in inner

mitochondrial membranemitochondrial membrane Involves a passing of electrons Involves a passing of electrons

through a series of membrane through a series of membrane associated electron carriers in associated electron carriers in the mitochondria to ultimately the mitochondria to ultimately produce ATPproduce ATP

You shuffle electrons to pump You shuffle electrons to pump protons across the mitochondiral protons across the mitochondiral membrane against a membrane against a concentration gradient to help concentration gradient to help establish a proton gradientestablish a proton gradient

The ETC transports electrons from The ETC transports electrons from NADH and FADH2 along a transport NADH and FADH2 along a transport chainchain

The respiratory chain is composed of The respiratory chain is composed of 4 enzyme complexes and carriers 4 enzyme complexes and carriers called cytochrome c and ubiquinone called cytochrome c and ubiquinone (Q). The 1(Q). The 1stst two complexes shuttle two complexes shuttle the electrons of NADH + H+ and the electrons of NADH + H+ and FADH2 to Q. FADH2 to Q.

The third complex moves electrons The third complex moves electrons from Q to chytochrome c. from Q to chytochrome c.

The final complex passes electrons to The final complex passes electrons to OO22, an ultimate acceptor, an ultimate acceptor, which , which results in H20 as a by-productresults in H20 as a by-product

The chain is an energy converter The chain is an energy converter that pumps H+ across the that pumps H+ across the membrane. How? Certain membrane. How? Certain members along the electron members along the electron transport chain accept and transport chain accept and release protons along with release protons along with electrons. A gradient is created electrons. A gradient is created that is referred to as the that is referred to as the proton-proton-motive forcemotive force

Now this H+ has the capacity to Now this H+ has the capacity to do workdo work

The electron transport chain The electron transport chain made no ATP directly, but it did made no ATP directly, but it did ease the fall of electrons from ease the fall of electrons from food to oxygenfood to oxygen

So now, by So now, by chemiosmosischemiosmosis, it will , it will couple this electron transport couple this electron transport and energy release to and energy release to ATP ATP SynthaseSynthase

ATP SynthaseATP Synthase is an enzyme that is an enzyme that catalyses ATP from ADP and an catalyses ATP from ADP and an inorganic phosphateinorganic phosphate

Each NADH produces 3 ATPEach NADH produces 3 ATP Each FADH produces 2 ATPEach FADH produces 2 ATP

To summarize, for each glucose molecule…To summarize, for each glucose molecule… Glycolysis makes 2 NET ATP and 2 Glycolysis makes 2 NET ATP and 2

NADH andNADH and

2 pyruvate2 pyruvate 2 acetyl CoA = 2 NADH 2 acetyl CoA = 2 NADH

Krebs Cycle: 6 NADH, 2 FADHKrebs Cycle: 6 NADH, 2 FADH22, 2 ATP, 2 ATP

Since Since each NADH produces 3 ATPeach NADH produces 3 ATP during oxidative phosphorylation during oxidative phosphorylation and and each FADHeach FADH22 produces 2 ATP… produces 2 ATP…how many ATP total?how many ATP total?

Wait…but what if there is no oxygen?Wait…but what if there is no oxygen? What will be affected? Well now What will be affected? Well now

there is no electron acceptor to there is no electron acceptor to accept electrons at the end of accept electrons at the end of the ETC. NADH will accumulate. the ETC. NADH will accumulate. Once all NAD+ has been made to Once all NAD+ has been made to NADH, Krebs and glycolysis will NADH, Krebs and glycolysis will eventually stop.eventually stop.

We have to free NAD+ to allow We have to free NAD+ to allow glycolysis to continue! We must glycolysis to continue! We must release some NAD+ for use by release some NAD+ for use by glycolysisglycolysis

1.Alcoholic :

• Yeast & other microorganisms use this to produce alcohol & CO2 as wastes.

• Beer is a beverage made by alcoholic fermentation

2 TYPES: Alcoholic & Lactic Acid

FERMENTATION(Aanerobic Pathway)

Alcoholic FermentationAlcoholic FermentationCommonly done by yeast in an

anaerobic environment.1) Glycolysis is done as normal. And

then, to regenerate the NAD+… 2) Pyruvate 2) Pyruvate acetaldehyde acetaldehyde 3) Acetaldehyde3) Acetaldehyde ethanol…the ethanol…the

energy in NADH is used to drive this energy in NADH is used to drive this reaction and this will release NAD+. reaction and this will release NAD+. For each acetaldehyde, 1 ethanol is For each acetaldehyde, 1 ethanol is made and 1 NAD+ is produced. made and 1 NAD+ is produced.

Now we have made 2 ATP from Now we have made 2 ATP from glyocolysis for each 2 converted glyocolysis for each 2 converted pyruvatepyruvate

2.Lactic Acid:

– Exercise causes the body needs more oxygen for respiration to make more ATP

– Body resorts to lactic acid fermentation to make ATP

– Lactic Acid is also produced causing burning sensation in muscles

(Aanerobic Pathway)

Or…we can do Lactic Acid Or…we can do Lactic Acid FermentationFermentation

Lactic Acid FermentationLactic Acid Fermentation

Commonly done by: Muscle cells Commonly done by: Muscle cells during oxygen debt.during oxygen debt.

Same thing as before:Same thing as before:

- do glycolysis- do glycolysis

- but then to regenerate NAD+, a - but then to regenerate NAD+, a byproduct called lactate is made byproduct called lactate is made instead of instead of acetylaldehydeacetylaldehydeethanol.ethanol.

Diagram AssignmentDiagram Assignment You will diagram the major pathways to You will diagram the major pathways to

respiration in color in a way that is respiration in color in a way that is understandable to you. Use websites and understandable to you. Use websites and the book to help you form diagrams for the book to help you form diagrams for each section of respiration. each section of respiration.

It must be in color, complete, and have It must be in color, complete, and have

words on it to describe what is happening words on it to describe what is happening in the process for full credit.in the process for full credit.

Also must have an input/output chart by Also must have an input/output chart by each stage: glycolysis, krebs, + ETCeach stage: glycolysis, krebs, + ETC