Ch 9: RespirationCh 9: Respiration

The Big PictureThe Big Picture

Cellular respiration has the sole Cellular respiration has the sole purpose to produce ATP.purpose to produce ATP.

Its an exergonic reaction.Its an exergonic reaction. Can be summarized as a whole as:Can be summarized as a whole as:

Glucose + OxygenGlucose + Oxygen CO2 + Water+ ATP CO2 + Water+ ATP

Reminder on ATPReminder on ATP

ATP (adenosine triphosphate) is a ATP (adenosine triphosphate) is a nucleotide with unstable phosphate nucleotide with unstable phosphate bonds that the cell hydrolyzes for bonds that the cell hydrolyzes for energy.energy.

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

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

mechansisms of metabolismmechansisms of metabolism Gain a Proton or Electron=reduction Gain a Proton or Electron=reduction Loss of an Electron=oxidationLoss of an Electron=oxidation LEO GERLEO GER 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 NAD+ and FAD+ are coenzymes that functions in the redox reactions and functions in the redox reactions and is found in all cells. is found in all cells.

It traps energy-rich electrons from It traps energy-rich electrons from glucose or food.glucose or food.

NAD+= oxidized coenzyme (lost an NAD+= oxidized coenzyme (lost an electron)electron)

NADH= reduced coenzyme (gained a NADH= reduced coenzyme (gained a proton)proton)

Why glucose? CWhy glucose? C66HH1212OO66

It’s the energy source used most It’s the energy source used most often by living organisms. often by living organisms.

Keep in mind that fats and proteins Keep in mind that fats and proteins could also be considered but glucose could also be considered but glucose is the “hallmark” molecule to use in is the “hallmark” molecule to use in cellular respirationcellular respiration

Respiration is divided into three Respiration is divided into three parts: Glycolysis, Krebs Cycle, and parts: Glycolysis, Krebs Cycle, and

Oxidative PhosphorylationOxidative Phosphorylation

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

2. Krebs Cycle (oxidative phosphorylation) 2. Krebs Cycle (oxidative phosphorylation) takes pyruvate (1 pyruvate) and yields takes pyruvate (1 pyruvate) and yields electron acceptors and ATP.electron acceptors and ATP.

3. ETC (Oxidative phosphorylation) 3. ETC (Oxidative phosphorylation) extracts ATP from NADH and FADH2. extracts ATP from NADH and FADH2.

Glyclolysis (per glucose molecule)Glyclolysis (per glucose molecule)

Takes place in cytosol.Takes place in cytosol. There are 9 intermediate steps is the There are 9 intermediate steps is the

process of decomposing glucose into process of decomposing glucose into pyruvate. Mg2+ ions are cofactors to help.pyruvate. Mg2+ ions are cofactors to help.

One molecule of glucose goes INOne molecule of glucose goes IN 2 ATP go IN2 ATP go IN 4 ATP PRODUCED (so what is NET?)4 ATP PRODUCED (so what is NET?) 2 NAD+ go IN2 NAD+ go IN 2 NADH PRODUCED 2 NADH PRODUCED 2 Pyruvate (Pyrivic acid) PRODUCED2 Pyruvate (Pyrivic acid) PRODUCED

KREBS Cycle (per pyruvate)KREBS Cycle (per pyruvate) Takes place in mitochondrial matrix.Takes place in mitochondrial matrix. Pyruvate combines with CoA (coenzyme A) Pyruvate combines with CoA (coenzyme A)

to make acetyl CoA. to make acetyl CoA. This makes 2 NADH This makes 2 NADH and CO2.and CO2.

Acetyl CoA combines with OAA to form Acetyl CoA combines with OAA to form citric acid…which is why Krebs can also be citric acid…which is why Krebs can also be the Citric Acid Cycle. (7 intermediate the Citric Acid Cycle. (7 intermediate products). 6 products). 6 NADH and 2 FADH2 are NADH and 2 FADH2 are made and CO2 released. 2 ATP is made and CO2 released. 2 ATP is made.made.

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

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

membranemembrane Involves a passing of electrons through a Involves a passing of electrons through a

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

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

The ETC transports electrons from NADH The ETC transports electrons from NADH and FADH2 along a transport chainand FADH2 along a transport chain

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

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

The final complex passes electrons to The final complex passes electrons to O2, O2, an ultimate acceptoran ultimate acceptor, which results in , which results in H20 as a by-productH20 as a by-product

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

Now this H+ has the capacity to do Now this H+ has the capacity to do workwork

http://www.sci.uidaho.edu/bionet/biol115/t4_energy/etc.htm

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

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

ATP synthase is an enzyme that ATP synthase is an enzyme that actually MAKES ATP from ADP and actually MAKES ATP from ADP and inorganic phosphateinorganic phosphate

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

To summarize…To summarize… Glycolysis makes Glycolysis makes 2 NET ATP2 NET ATP and 2 NADH and 2 NADH 2 pyruvate2 pyruvate 2 acetyl CoA= 2 NADH 2 acetyl CoA= 2 NADH Krebs Cycle: 6 NADH, 2 FADH2, Krebs Cycle: 6 NADH, 2 FADH2, 2 ATP2 ATP

Since Since each NADH produces 3 ATPeach NADH produces 3 ATP during during oxidative phosphorylation and oxidative phosphorylation and each FADH2 each FADH2 produces 2 ATP…produces 2 ATP…how many ATP total?how many ATP total?

In Reality…In Reality…

It would appear we get 38 ATP. But we It would appear we get 38 ATP. But we don’t in reality. This is because glycolysis don’t in reality. This is because glycolysis only occurs in the cytoplasm and each only occurs in the cytoplasm and each NADH produced there must be transported NADH produced there must be transported into the mitochondria for oxidative into the mitochondria for oxidative phosphorylation. The transport of NADH phosphorylation. The transport of NADH across the mitochondrial matrix reduces across the mitochondrial matrix reduces the yield of these the yield of these NADH in glycolysis to NADH in glycolysis to only 2 ATP.only 2 ATP.

That means in reality 36 ATP only.That means in reality 36 ATP only.

Wait…but what if there is no Wait…but what if there is no oxygenoxygen

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

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

Alcoholic FermentationAlcoholic Fermentation Commonly 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 energy in ethanol…the energy in

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

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

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

Commonly done by: Muscle cells in Commonly done by: Muscle cells in an an oxygen debtoxygen 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 acetylaldehydeinstead of acetylaldehydeethanol.ethanol.