Cellular Respiration: Cellular Respiration: Harvesting Chemical Harvesting Chemical

EnergyEnergyChapter 9Chapter 9

Cells are open systemsCells are open systems Energy flows into most ecosystems as Energy flows into most ecosystems as

sunlight.sunlight. Photosynthetic organisms trap light Photosynthetic organisms trap light

energy and transform it into chemical energy and transform it into chemical bond energy.bond energy.

Cells use chemical bond energy to make Cells use chemical bond energy to make ATP.ATP.

Chemical elements essential for life are Chemical elements essential for life are recycled, but energy is not.recycled, but energy is not.

How do cells harvest chemical energy?How do cells harvest chemical energy?

““Spendable Energy”Spendable Energy”

Cellular respiration and fermentation Cellular respiration and fermentation are catabolic (energy-yielding) are catabolic (energy-yielding)

pathwayspathways FermentationFermentation -- An ATP-producing process in -- An ATP-producing process in

which both electron donors and acceptors are which both electron donors and acceptors are organic compounds; anaerobic process (without organic compounds; anaerobic process (without oxygen).oxygen).

Cellular respirationCellular respiration -- An ATP-producing process in -- An ATP-producing process in which the ultimate electron acceptor is an which the ultimate electron acceptor is an inorganic molecule, such as oxygen.inorganic molecule, such as oxygen.

Most efficient catabolic pathway is aerobic (with Most efficient catabolic pathway is aerobic (with oxygen).oxygen).

Carbohydrates, proteins and fats can all be Carbohydrates, proteins and fats can all be metabolized as fuel, but cellular respiration is metabolized as fuel, but cellular respiration is most often described as the oxidation of glucose: most often described as the oxidation of glucose:

CC66HH1212OO66 + 6O + 6O2 2 ——>6CO——>6CO22 + 6H + 6H22O + EnergyO + Energy (ATP + Heat)(ATP + Heat)

Cells must recycle the ATP they spend for Cells must recycle the ATP they spend for workwork

Respiration transfers the energy stored in food Respiration transfers the energy stored in food molecules to molecules to ATP.ATP.

ATP (adenosine triphosphate)ATP (adenosine triphosphate) -- Nucleotide with -- Nucleotide with unstable phosphate bonds that the cell unstable phosphate bonds that the cell hydrolyzes for energy; enzymes that catalyze hydrolyzes for energy; enzymes that catalyze this reaction are called ATPases.this reaction are called ATPases.

ATP + HATP + H22O O ADP + phosphate + energy ADP + phosphate + energy ADP + HADP + H22O O AMP + phosphate + energy AMP + phosphate + energy Removal of a phosphate yields 7 kcal of energy Removal of a phosphate yields 7 kcal of energy

per mole of ATP.per mole of ATP. Phosphate groups from ATP are transferred to Phosphate groups from ATP are transferred to

other compounds to do cellular work other compounds to do cellular work (phosphorylation); otherwise energy would be (phosphorylation); otherwise energy would be just be lost as heat.just be lost as heat.

Cells must recycle the ATP they spend Cells must recycle the ATP they spend for work (continued)for work (continued)

The compound receiving the The compound receiving the phosphate group from ATP is said to phosphate group from ATP is said to be be phosphorylated phosphorylated and becomes and becomes energized; enzymes catalyzing these energized; enzymes catalyzing these reactions are kinases.reactions are kinases.

Cells must replenish the ATP supply Cells must replenish the ATP supply to continue cellular work. Respiration to continue cellular work. Respiration provides the energy to regenerate provides the energy to regenerate ATP from ADP and inorganic ATP from ADP and inorganic phosphate.phosphate.

Addition of a phosphate group Addition of a phosphate group activates an enzymeactivates an enzyme

An Introduction to Redox An Introduction to Redox ReactionsReactions

Oxidation/reduction reactionsOxidation/reduction reactions -- Chemical -- Chemical reactions which involve a transfer of reactions which involve a transfer of electrons from one reactant to another electrons from one reactant to another ((redox redox for short); use of chemical energy for short); use of chemical energy in living things involves redox rxns.in living things involves redox rxns.

OxidationOxidation -- loss of electrons: -- loss of electrons: Fe Fe Fe Fe+3+3 + 3 e- (Iron has been + 3 e- (Iron has been

oxidized)oxidized) ReductionReduction -- gain of electrons: -- gain of electrons: O + 2 e- O + 2 e- O O-2-2 (Oxygen has been (Oxygen has been

reduced).reduced). LEO the lion says GER.LEO the lion says GER.

An Introduction to Redox An Introduction to Redox Reactions continuedReactions continued

Electron transfer requires both a donor Electron transfer requires both a donor and acceptor, so when one reactant is and acceptor, so when one reactant is oxidized the other is reduced: oxidized the other is reduced:

Fe + OFe + O22 Fe Fe22OO33 In this case, Fe is the In this case, Fe is the reducing agent or reducing agent or

reducerreducer; O is the ; O is the oxidizing agent or oxidizing agent or oxidizer oxidizer (has a high electronegativity)(has a high electronegativity)..

Transfer of electrons may not be Transfer of electrons may not be complete, but instead may just change complete, but instead may just change the degree of sharing in covalent bonds:the degree of sharing in covalent bonds:

CHCH44 + O + O22 CO CO22 + H + H22OO

Electron AcceptorsElectron Acceptors CC66HH1212OO66 + 6O + 6O2 2 ——>6CO——>6CO22 + 6H + 6H22O + O +

Energy Energy (ATP + Heat)(ATP + Heat) Hydrogens stripped from glucose are Hydrogens stripped from glucose are

not transferred directly to oxygen, not transferred directly to oxygen, but are first passed to a special but are first passed to a special electron acceptor.electron acceptor.

Nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide (NAD(NAD++ / NADH) / NADH) -- A -- A dinucleotide dinucleotide that that functions as a functions as a coenzyme coenzyme in the redox in the redox reactions of metabolism. reactions of metabolism.

Electron acceptors cont.Electron acceptors cont. Flavin adenine dinucleotide (FAD / Flavin adenine dinucleotide (FAD /

FADHFADH22)) – see NADH. – see NADH. NADNAD++= Oxidized coenzyme (net = Oxidized coenzyme (net

positive charge); NADH = Reduced positive charge); NADH = Reduced coenzyme (electrically neutral).coenzyme (electrically neutral).

CoenzymeCoenzyme -- Small nonprotein -- Small nonprotein organic molecule that is required for organic molecule that is required for certain enzymes to function. certain enzymes to function.

DinucleotideDinucleotide -- A molecule consisting -- A molecule consisting of two nucleotides.of two nucleotides.

NAD+ / FADNAD+ / FAD

Mitochondrion ReviewMitochondrion Review

Respiration: Respiration: an overviewan overview There are three metabolic stages of cellular There are three metabolic stages of cellular

respiration:respiration: 1. Glycolysis1. Glycolysis 2. Krebs Cycle2. Krebs Cycle 3. Electron transport chain (ETC)3. Electron transport chain (ETC)

Glycolysis Glycolysis occurs in the cytosol of the cell; occurs in the cytosol of the cell; splits glucose (6C) into two pyruvate (3C) splits glucose (6C) into two pyruvate (3C) molecules.molecules.

Krebs Cycle Krebs Cycle occurs in the mitochondrial occurs in the mitochondrial matrix; breaks down pyruvatematrix; breaks down pyruvate into carbon into carbon dioxide.dioxide.

Electron transport chainElectron transport chain is located at the is located at the inner membrane of the mitochondrion, where inner membrane of the mitochondrion, where ATP synthesis or ATP synthesis or oxidative phosphorylation oxidative phosphorylation takes place.takes place.

Glycolysis: Glycolysis: a closer looka closer look GlycolysisGlycolysis (Glyco = sugar; lysis = (Glyco = sugar; lysis =

break) Occurs whether or not break) Occurs whether or not oxygen is present; yields 2 ATP.oxygen is present; yields 2 ATP.

Overall reaction: glucose + 2 ATP Overall reaction: glucose + 2 ATP 2 pyruvate + 4 ATP2 pyruvate + 4 ATP

Substrate-level phosphorylationSubstrate-level phosphorylation -- -- ATP production by direct enzymatic ATP production by direct enzymatic transfer of phosphate to ADP.transfer of phosphate to ADP.

Glycolysis stepsGlycolysis steps Step 1: Step 1: Glucose enters the cell, and Glucose enters the cell, and

carbon six is phosphorylated as 1 ATP is carbon six is phosphorylated as 1 ATP is used. used.

Glucose Glucose glucose-6-phosphate glucose-6-phosphate Step 2Step 2: Rearrangement of glucose-6-: Rearrangement of glucose-6-

phosphate to its isomer, fructose-6-phosphate to its isomer, fructose-6-phosphate.phosphate.

Step 3: Step 3: Carbon one of fructose-6-Carbon one of fructose-6-phosphate is phosphorylated using another phosphate is phosphorylated using another ATP to form fructose-1,6-diphosphate. ATP to form fructose-1,6-diphosphate.

Glycolysis cont.Glycolysis cont. Step 4: Step 4: Aldolase Aldolase cleaves the 6-carbon fructose cleaves the 6-carbon fructose

into two 3-carbon sugars.into two 3-carbon sugars. Fructose-1,6-phosphate Fructose-1,6-phosphate 2 3- 2 3-

phosphoglyceraldehydephosphoglyceraldehyde Step 5: Step 5: Phosphoglyceraldehyde is Phosphoglyceraldehyde is

phosphorylated on carbon one; NADH is formed.phosphorylated on carbon one; NADH is formed. 2 3-phosphoglyceraldehyde + 2 NAD2 3-phosphoglyceraldehyde + 2 NAD++ 2 1,3 2 1,3

diphosphoglycerate + 2 NADHdiphosphoglycerate + 2 NADH Step 6:Step 6: ATP is produced by ATP is produced by substrate-level substrate-level

phosphorylation.phosphorylation. 2 1,3 diphosphoglycerate + 2 ADP 2 1,3 diphosphoglycerate + 2 ADP 2 3- 2 3-

phosphoglycerate + 2 ATPphosphoglycerate + 2 ATP

End of Glycolysis (really)End of Glycolysis (really) Step 7Step 7: Phosphate group on carbon three is : Phosphate group on carbon three is

transferred to carbon two.transferred to carbon two. 2 3-phosphoglycerate 2 3-phosphoglycerate 2 2- 2 2-

phosphoglyceratephosphoglycerate Step 8: Step 8: Enzymatic removal of a water Enzymatic removal of a water

molecule.molecule. 2 2-phosphoglycerate 2 2-phosphoglycerate 2 2- 2 2-

phosphoenolpyruvate + Hphosphoenolpyruvate + H22OO Step 9: Step 9: ATP is produced by substrate-level ATP is produced by substrate-level

phosphorylation; pyruvate formed.phosphorylation; pyruvate formed. 2 2-phosphoenolpyruvate 2 2-phosphoenolpyruvate 2 pyruvate 2 pyruvate

Glycolysis animationsGlycolysis animations http://www.northland.cc.mn.us/biologhttp://www.northland.cc.mn.us/biolog

y/Biology1111/animations/glycolysis.y/Biology1111/animations/glycolysis.htmlhtml

http://www.science.smith.edu/departhttp://www.science.smith.edu/departments/Biology/Bio231/glycolysis.htmlments/Biology/Bio231/glycolysis.html

http://student.ccbcmd.edu/courses/bihttp://student.ccbcmd.edu/courses/bio141/lecguide/unit6/metabolism/cellro141/lecguide/unit6/metabolism/cellresp/glycol_an.htmlesp/glycol_an.html