Today is Friday (!),November 10th, 2017

Pre-Class:

Take a deep breath in and out. No, that’s not respiration…that’s ventilation. Still, why do we need

oxygen? Exactly what does it do for us?

Also: How do you do?

In This Lesson:Cellular

Respiration(Lesson 2 of 3)

Today’s Agenda

• Respiration– Aerobic

• Glycolysis

• Pyruvate Oxidation

• Citric Acid Cycle

• Oxidative Phosphorylation

– Anaerobic

• Fermentation (Alcohol/Lactic Acid)

• Where is this in my book?– Chapter 9.

By the end of this lesson…

• You should be able to describe the aerobic and anaerobic respiration pathways by their inputs and outputs.

• You should know where the cell gets its ATP.

• You should be able to relate the mitochondrion’s structure with its function.

So what is it?• Think of cellular

respiration like a harvest of chemical energy.– Like Thanksgiving all the

time.

• This is where cells actually use the energy they have available (in the form of glucose, et cetera) to them to accomplish work.

• The goal?– PRODUCE ATP.

Cell “Work”Active Transport

Cell “Work”Movement of Proteins and Molecules

Cell “Work”Phosphorylation and Molecule Activation, Building Molecules

And ATP is…?

• You know how you can use money for all kinds of things? Money just facilitates some other activity? And you need it in the right form for your country?– The same goes for ATP. It’s used all over the place.

– Glucose is like a foreign currency. It needs to be exchanged.

• ATP is Adenosine Triphosphate.– It’s a modified nucleotide with 3 phosphates instead of 1.

• ATP = Adenine + Ribose + 3 Phosphate Groups

• ADP = Adenine + Ribose + 2 Phosphate Groups

• AMP = Adenine + Ribose + 1 Phosphate Group

– Adding phosphates is endergonic and requires energy.

– Removing them is exergonic and releases energy.

ATP

• What I’d like you to think about when you hear “ATP” is a giant chocolate bar:

http://savingmoneyplan.com/wp-content/uploads/2012/11/hersheys.jpg

ATP

Chocolate

• Chocolate is high in Calories.

– Therefore it’s got a lot of energy.

• Chocolate is high in sugar.

– It provides you with a boost when you eat it.

• Chocolate bars often are divided into squares or rectangles that you can eat one-at-a-time.

– You don’t need to destroy the whole bar to get something out of it.

ATP

• ATP has high-energy bonds.

– Your cell breaks off a phosphate and replaces those bonds with lower-energy bonds.

• ATP provides free energy when hydrolyzed.

• ATP can be reused.

– Like putting a square back on the chocolate bar.

• I wish I could do that.

Can chocolate be re-used?

Anyway…

• How does ATP actually store energy?

– Each phosphate group added to the adenosine molecule becomes progressively harder to “hold.”

• Remember, they have a -1 or -2 charge, so that’s a lot of negativity built up.

– The phosphates can “pop off” easily and release energy.

– This makes ATP a great energy donor.

O-

O – P – O O-

O-

O – P – O O-

O-

O – P – O O-

Energy

ATP

-OH

Anyway…

• How does ATP transfer energy?

• The hydrolysis of ATP to ADP releases energy.• ΔG = -7.3 kcal/mol

• Key: The “missing” phosphate is replaced by a hydroxyl from water.

• Key: The formation of this bond releases energy.

• Key: The other hydrogen ion (from water) goes to the phosphate.

O-

O – P – O O-

O-

O – P – O O-

O-

O – P – O O-

H-

The Catch

• As great as ATP is for energy transfer, it’s a particularly bad molecule for energy storage.

– It’s quite unstable and transfers its phosphate group too easily.

• A working muscle cell recycles over 10,000,000 ATP molecules every second.

ATP Production

• One energy source for production of ATP is the enzyme/channel protein ATP Synthase.

– Located in the mitochondrial membrane.

• H+ ions flow down the channel protein and power the enzyme like a hydroelectric dam.

– The question is…how do we turn it on? H+

catalytichead

rod

rotor

H+H+

H+

H+ H+

H+H+H+

H+

ADP P+

ATP

Inquiry Break

• Cellular Respiration – An Overview POGIL

• Go to the second STOP sign.

• IMPORTANT: The POGIL shows the “link reaction” – more on that later – as occurring in the intermembrane space. It doesn’t – it occurs in the matrix.

Back to “harvesting energy…”

• You should know the familiar equation for respiration:

– C6H12O6 + 6O2 6CO2 + 6H2O + ATP

• [glucose] + [oxygen] [carbon dioxide] + [water] + [energy]

• Before we really explore this in depth, keep something in mind:

– Respiration is, almost literally, burning calories.

– It’s like burning a piece of wood, only it happens in a lot of little steps instead of one big one.

• It even gives off heat, just not as much.

Respiration: Big Ideas

• As big molecules are broken into smaller ones…

• …bonds are broken…

• …and electrons are moved from one molecule to another…

• …“carrying energy” with them, which is:

– Stored in a new bond OR

– Released as heat OR

– Harvested to make ATP.

Respiration: Big Ideas• Therefore, quite a bit of respiration is made of redox

(reduction/oxidation) reactions.• Key: Reduction is a gain of electrons; oxidation is a loss of

electrons.• Key: The oxidized atom is the reducing agent and vice versa.• Key: Remember that with “OIL RIG:”

– “Oxidation Is Loss”– “Reduction Is Gain”

+ + +

e-

-e-

Loss of e- Gain of e- Oxidized Reduced

Reducing Agent

Oxidizing Agent

OIL RIG?

• The chem students sometimes prefer the mnemonic of “LEO goes GER:”

– Loss of electrons is oxidation.

– Gain of electrons is reduction.

• Use whichever you prefer.

Respiration: Big Ideas

• In living systems, electrons are moved with hydrogen atoms.

– Key: When you see H moving, you’re seeing electrons move too.

• Consider the overall respiration equation:

C6H12O6 + 6O2 6CO2 + 6H2O + ATP

The oxygen has gained hydrogens.

Reduction

Oxidation

The glucose will lose

hydrogens.

Oxidation and Reduction

• Oxidation:

– Removing H

– Loss of electrons

– Release of energy

– Exergonic

• Reduction:

– Adding H

– Gain of electrons

– Storage of energy

– Endergonic

Coupling Reactions

• I’m sure you remember that exergonic and endergonic reactions are coupled.– The energy released by the exergonic reaction is harnessed

for use in an endergonic reaction.

• C-C bonds are broken, but more importantly…

• Key: C-H bonds are broken to strip off H atoms.– C6H12O6 CO2 = oxidation of glucose fuel.

– O2 H2O = reduction of oxygen.

• Electrons are attracted to the more electronegative atom, which liberates potential energy.– In chemistry, F is the most electronegative, but it’s too strong

for living systems. O is the most electronegative for biology.• Which partly explains why fluoride ions are good in toothpaste.

Okay, let’s go…

• We’re ready to start learning the details of the respiration “story.”

• We’ll begin with two important “characters:”– NAD+

• Nicotinamide adenine dinucleotide, AKA niacin or Vitamin B3

– FAD• Flavin adenine dinucleotide, AKA riboflavin or Vitamin B2

• Key: These are each electron carriers and are responsible for moving H atoms around.

• I want you to think of these each as batteries.

Electron Carriers/Batteries

• Oxidized: NAD+ and FAD are the “drained” batteries:

• Reduced: NADH and FADH2 are the “charged” batteries:

• I’ll be using these symbols throughout the lesson.

A Closer Look at NAD+ and NADH

http://www.uic.edu/classes/bios/bios100/lectures/NADH01.jpg

Cellular Respiration Overview

• Aerobic Respiration

1. Glycolysis

2. Pyruvate Oxidation

3. Krebs/Citric Acid Cycle

4. Oxidative Phosphorylation

• Note: If oxygen is not around, many cells carry out fermentation following glycolysis.

Cytosol

Mitochondria

Warm-Up

• CrashCourse – ATP and Respiration – Part 1

Inquiry Break

• Cellular Respiration – An Overview POGIL

• Stop at the end of Page 4.

Quick Reminder:Mitochondrial Structure

• They have two bilayer membranes. From the outside in:– Outer membrane

– Intermembrane space

– Inner membrane

– Matrix

• The inner membrane has folds called cristae.

• Sketch it like you mean it.

http://course1.winona.edu/kbates/Bio241/images/figure-04-14.jpg

Glycolysis

• The name “glycolysis” literally means “splitting sugar.”

• In this process, glucose (6 carbons) is broken down into two pyruvate molecules (3 carbons).

• Key: It’s inefficient: 1 glucose molecule results in only 2 net ATP.

– The pyruvates can be broken down further for more energy.

• Glycolysis takes place in the cytosol. Why?

– Energy is needed by all cells, prokaryotic or eukaryotic, so it had to have evolved a long time ago, before eukaryotes.

Glycolysis: Evolution

• Because early cells had no organelles, and because the early atmosphere had no oxygen, life had to find a way to produce ATP anaerobically in the cytosol.

– Side note: “Cytoplasm” technically extends into the mitochondria, chloroplasts, and other organelles. Cytosol is the cytoplasm minus the organelles.

• Since all cells evolved from these early ones, glycolysis is like a homologous “structure” to us all.

Glycolysis: Input/Output

• Glycolysis is actually made up of ten (really 9.5) smaller reactions.

• Before we explore them, let’s get the input and output straight:

– Input

• Glucose (1)

• ATP (2)

– Output

• Pyruvate (2)

• ATP (4 total, 2 net)

• NADH (2)

The Detailed View

• I do not need you to memorize this.

• It’s useful, however, to see the pathway in full at least once to:

– see why the input/output is so.

– appreciate what’s happening.

• For clarity, enzymes are shown in italics and inputs/outputs are underlined.

• You are responsible for the inputs and outputs.

Glycolysis: Reactions [Detailed]

1. Hexokinase dephosphorylates ATP and adds the phosphate to glucose, creating glucose 6-phosphate. This also prevents glucose from exiting the cell.• -1 Glucose

• -1 ATP

2. Phosphoglucoisomerase converts glucose 6-phosphate to fructose 6-phosphate through a shape change.

3. Phosphofructokinase dephosphorylates ATP and adds the phosphate to fructose 6-phosphate, creating fructose 1,6-bisphosphate.• -1 ATP

Glycolysis: Reactions [Detailed]

4. Aldolase converts fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).– Isomerase converts the DHAP to G3P as well.– This means there are two G3P molecules and two of every

molecule moving forward.

5. NAD+ oxidizes G3P and then triose phosphate dehydrogenase adds an inorganic phosphate group to it, creating 1,3-bisphosphoglycerate (1,3-BPG).• +2 NADH

6. Phosphoglycerokinase removes the phosphate and phosphorylates ADP, creating 3-phosphoglycerate.• +2 ATP

Glycolysis: Reactions [Detailed]

7. Phosphoglyceromutase moves a phosphate group, creating 2-phosphoglycerate.

– Underachiever.

8. Enolase adds a double bond within the compound, creating phosphoenopyruvate (PEP).

9. Pyruvate kinase removes a phosphate group and phosphorylates ADP, creating pyruvate.

• +2 ATP

• +2 pyruvate

Glycolysis

http://cerebraldopamine.files.wordpress.com/2011/09/glycolysis_pathway.jpg

Quick Note

• I know I said you didn’t need to know the details of glycolysis, but it’s probably worth remembering G3P.

• It’s a 3-carbon sugar that will come up again in photosynthesis.

Pyruvate Oxidation: Input/Output

• Prior to entering the Citric Acid Cycle, pyruvate has to be oxidized.– Your book calls it “pyruvate oxidation” but it is also

known as the “link reaction” (especially by the POGIL).

• As usual, just know the inputs/outputs:– Input

• Pyruvate (2)

– Output• Acetyl CoA (2)

• NADH (2)

• CO2 (2) [waste]

Pyruvate Oxidation: Reactions [Detailed]

• First, the two charged pyruvate molecules enter the mitochondrion via active transport.– Both pyruvate oxidation and the citric acid cycle take place

in the matrix (inside the inner membrane).

• Enzyme complex pyruvate dehydrogenase complex:– Removes CO2, making acetate.

• (6 carbon glucose to 3 carbon pyruvate to 2 carbon fragment now)

• -2 Pyruvate

• +2 CO2 [waste]

– Oxidizes it and reduces NAD+ to NADH.• +2 NADH

– Adds Coenzyme A (sulfur-containing compound from a B vitamin), making acetyl CoA.• +2 acetyl CoA

Matrix

Pyruvate Oxidation

http://schoolworkhelper.net/wp-content/uploads/2011/02/pyruvate-oxidation.jpg

Citric Acid Cycle: Input/Output

• The products of pyruvate oxidation (acetyl CoA) feed the Citric Acid Cycle, also known as the Krebs Cycle.

• The Citric Acid Cycle is made of eight reactions but “turns” twice, once for each acetyl CoA input.

• Importantly, it is a cycle, meaning that it is continuously running like a revolving door.

• For both turns:– Input

• Acetyl CoA (2)

– Output• ATP (2)• NADH (6)• FADH2 (2)• CO2 (4) [waste]

Citric Acid Cycle: Reactions[Detailed]

1. Acetyl CoA loses its acetyl group to oxaloacetate, forming citrate.– Hence the name of the cycle (citrate is ionized citric acid).– -2 Acetyl CoA after both turns.

2. Citrate is made into isocitrate (isomer) by removing a water molecule and then adding one.

3. Isocitrate is oxidized by NAD+ and the resulting compound loses a CO2, becoming α-ketoglutarate.• +2 NADH after both turns.• +2 CO2 after both turns.

4. α-ketoglutarate loses another CO2 and is then oxidized by NAD+, forming succinyl CoA.• +2 NADH after both turns.• +2 CO2 after both turns.

Citric Acid Cycle: Reactions[Detailed]

5. CoA (in succinyl CoA) is replaced by a phosphate group which is then transferred to GDP (making GTP), which then is dephosphorylated as ADP becomes ATP. Meanwhile, succinyl CoA has become succinate.• +2 ATP after both turns.

6. Succinate is oxidized twice by FAD, making fumarate.• +2 FADH2 after both turns.

7. Water rearranges bonds in fumarate, making malate.8. Malate is oxidized by NAD+, making oxaloacetate. The

cycle can repeat as an acetyl group comes from another acetyl CoA.• +2 NADH after both turns.

Citric Acid Cycle

http://www.bio.miami.edu/tom/courses/protected/MCB6/ch12/12-10.jpg

So…

• How’s it going?

• I know, phew, right?

• Um…

• Well how’s your family?

• Good, good.

• Uh…

• Okay let’s just…let’s just keep going…

Review

• We’re about to go to the next step, but let’s recap a little bit.

– Cue marker joke.

– “Recap”…get it?

• From one glucose molecule:

• 6 CO2 [waste]

• 4 ATP (net)

• And…importantly…?

Review

• We have also built up:

– 10 NADH

– 2 FADH2

• All of that effort (charging the batteries) is now about to pay off.

• Cue oxidative phosphorylation.

http://fc08.deviantart.net/fs25/f/2008/092/5/f/IMA_FIRIN_MAH_LAZOR_by_Teh_Kenji.gif

Oxidative Phosphorylation

• Oxidative phosphorylation is technically broken into two phases:

– Electron Transport Chain

• Produces none of the ATP.

– Chemiosmosis

• Produces all of the ATP.

Oxidative PhosphorylationElectron Transport Chain

• All throughout this process, ΔG has been mostly positive, meaning our products to this point are high potential energy and are set to “fall” back down to lower energy.

• The cell will allow this to happen in short stages.– Not falling off a building…more like falling down stairs.

• This is called electron transport chain (ETC) and it takes place primarily within the inner membrane of the mitochondrion.– Remember, the inner membrane has lots of folds called

cristae that add surface area and make this even more efficient.

Electron Transport Chain [Simplified]

• NADH and FADH2 give up their electrons to a series of (mostly) enzyme complexes.– They also give up a proton or two (as in H+).

• Electrons eventually combine with O2 (the final electron acceptor) and some of those free protons to make H2O.

• The electron hot potato game causes protons to be pumped from the matrix into the intermembrane space, creating an electrochemical gradient.

Electron Transport Chain: Reactions [Detailed]

1. NADH gives up two electrons to Enzyme Complex I:– First to FMN (flavin mononucleotide), then to Fe-S, an iron-

sulfur protein.– Complex I is an integral membrane protein called NADH

Reductase.– NADH NAD+ + H+ + 2 e- (remember that H+)

• OR1. FADH2 gives up two electrons to Enzyme Complex II:

– Directly to Fe-S.– Complex II, stuck to the inside of the membrane like a G

protein, is called succinate dehydrogenase.– FADH2 FAD + 2 H+ + 2 e- (remember those 2 H+)

2. Next, the Fe-S passes the electrons to ubiquinone (abbreviated Q, also known as Coenzyme Q or CoQ).– Ubiquinone is not a protein and is hydrophobic, so it

moves around within the inner membrane.

3. Ubiquinone passes its electrons to Enzyme Complex III, called cytochrome reductase:– First to Cytochrome b (abbreviated Cyt b)…

– …then to another Fe-S protein…

– …then to Cyt c1…

Electron Transport Chain: Reactions [Detailed]

4. Complex III (specifically Cyt c1) then passes its electrons to Cyt c, which passes its electrons to Enzyme Complex IV, called cytochrome oxidase:– First to Cyt a…– …then to Cyt a3.

5. Now, at the end of our giant microscopic hot potato party, Cyt a3 passes its electrons to oxygen, the final electron acceptor.– Oxygen picks up a -2 charge, then two protons, making H2O.– Oxygen plays this role because it is quite electronegative.

• The electron transport chain has ended, but in the process we’ve liberated a buttload of potential energy.– And we have to pee, since we’ve also generated some water.

Electron Transport Chain: Reactions [Detailed]

Oxidative Phosphorylation

http://www.tokresource.org/tok_classes/biobiobio/biomenu/cell_respiration/c8_9x16_chemiosmosis.jpg

Electron Transport Chain: The Catch

• The catch: We haven’t made any ATP.

• The cell instead puts that liberated potential energy to use engaging in chemiosmosis:

– Making an H+ (proton) gradient across a membrane, in this case the mitochondrial membrane, to drive work.

– Simplified:

• H+ ions (protons) diffuse down their electrochemical gradient back into the matrix through ATP Synthase.

• ATP Synthase spins and makes ATP.

Oxidative Phosphorylation:Chemiosmosis

• Enzyme complexes I, III, and IV all pump hydrogen ions out of the mitochondrial matrix.

• This creates an electrochemical gradient:– The intermembrane space now has a buildup both of

protons and of positive charge.

• In a specialized form of facilitated diffusion, the mitochondrion lets these protons diffuse back into the matrix through ATP Synthase.– ATP Synthase is a membrane protein/enzyme complex.

– As protons diffuse, part of the protein spins (yes, spins), activating sites that generate ATP from ADP.

ATP Synthase

H+

catalytichead

rod

rotor

H+H+

H+

H+ H+

H+H+H+

H+

ADP P+

ATP

http://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Atp_synthase.PNG/300px-Atp_synthase.PNG

ATP Synthase

• ATP Synthase provides protons the only way back into the matrix.

• Think of the enzyme much like a waterwheel:

– The water (proton stream) turns the wheel (ATP Synthase’s rotor), generating power (ATP).

Oxidative vs. Substrate-Level Phosphorylation

• Notice something. We have now seen ATP generated both by an enzyme transferring a phosphate from another molecule, or through ATP Synthase putting ADP and Pi together.

• Biochemists distinguish these as follows:– Transferring P from another molecule = substrate-

level phosphorylation.• Krebs Cycle/Glycolysis

– Adding Pi through chemiosmosis = oxidative phosphorylation.• Chemiosmosis

Oxidative Phosphorylation:Input/Output

• After all this, we can look at oxidative phosphorylation’s inputs and outputs:– Input

• NADH (10)

• FADH2 (2)

• O2 (6)

– Output• ATP! (realistically 26-28 per glucose, though some sources

say upwards of 34 per glucose. Unlikely.)

• H2O (6) [waste]

• NAD+

• FAD

Did you notice something?

• Glycolysis is an anaerobic step.

• Pyruvate oxidation and the citric acid cycle don’t use oxygen directly.

• HOWEVER! Because they precede the ETC, they will not run without oxygen.

– Only the ETC actually needs oxygen.

Cell Respiration SummaryC6H12O6 + 6O2 6CO2 + 6H2O + ATP

• Reactants:– 1 C6H12O6

• 1 used in Glycolysis

– 6 O2• 6 used in Oxidative

Phosphorylation

• Products:– 6 CO2

• 2 from Pyruvate Oxidation

• 4 from Citric Acid Cycle

– 6 H2O• 6 from Oxidative

Phosphorylation

– 30 or 32 ATP [maximum]• 2 (net) from Glycolysis• 2 from Citric Acid Cycle• 26 or 28 from Oxidative

Phosphorylation

Cell Respiration Summary

C6H12O6 + 6O2 6CO2 + 6H2O

Oxid

ative P

ho

sph

orylatio

n

Glyco

lysis and

Oxid

ative

Ph

osp

ho

rylation

Glyco

lysis

Pyru

vate O

xidatio

nan

d C

itric Acid

Cycle

Closure

• Just kidding! We’re not done yet.

Inquiry Break

• Cellular Respiration – An Overview POGIL

• Stop at the end of Page 5 (STOP sign).

In a world…

• …without oxygen, like the world in which glycolysis originally evolved, there’s an issue:– We can’t run oxidative

phosphorylation, so the Krebs Cycle also doesn’t move.

– Alternatively, if you’re a prokaryote, you don’t have mitochondria, so that’s out too.

• Furthermore, glycolysis is not a cycle:– Input

• Glucose (1)• ATP (2)

– Output• Pyruvate (2)• ATP (4 total, 2 net)• NADH (2)

Problems and Solutions

• The Problems:1. We don’t have oxygen around for the end of the electron

transport chain.

2. NAD+ is ultimately responsible for creating ATP as it oxidizes G3P. It needs to be restored from NADH.

• The Solutions:1. Use a different molecule, like something with sulfur, to

accept electrons.• If so, this is anaerobic respiration.

• In anaerobic respiration, pyruvate oxidation and citric acid cycle occur in the cytosol, while the membrane used for oxidative phosphorylation is the cell membrane. Pretty cool.

2. Recycle NADH into NAD+ through fermentation.

Fermentation

• Two types of fermentation:– Alcohol fermentation oxidizes NADH through the

production of ethanol and CO2.• Utilized by bacteria and yeast (fungus).

• This explains winemaking, brewing, and bubbles in pizzas/bread.– Yeast farts!

– Lactic acid fermentation oxidizes NADH through the production of…lactic acid.• Utilized by fungi, bacteria, and animals.

• This explains cheese, yogurt, and not why your muscles are sore the next day after exercise.

Aside: Alcohol Fermentation in Nature

• BBC – Alcoholic Vervet Monkeys

Aside: Lactic Acid

• You may have heard that lactic acid leads to muscle soreness.

• Upon resumption of aerobic respiration, your muscles clear the lactic acid relatively quickly.

– So it’s not lactic acid.

• Some research suggests that short-term soreness is due to K+ ions, while longer-term soreness is due to micro-tears in muscle fiber.

Back to Fermentation

• Important stuff to note:– Fermentation creates no ATP on its own but allows

glycolysis to continue.

– Because the fermentation pathway yields only 2 net ATP, it’s inefficient for multicellular organisms.

– Obligate anaerobes (prokaryotes that don’t use oxygen) utilize fermentation regularly, but they’re single-celled.

– Facultative anaerobes (use oxygen only when available) utilize fermentation regularly as well.

– Humans and other eukaryotes mainly use it as backup for when the blood can’t deliver enough O2.• Aside: Brain cells can’t really do it. Strokes = dangerous.

Aside: Athletes

• So here’s a question for you – biomechanically, how do athletes have higher endurance than non-athletes?

• The answer, in part, appears to be efficiency of oxygen use.– Athletes simply get more oxygen dissolved into

their blood compared to the same volume breath from a non-athlete.

– This explains why “altitude training” helps make respiratory pathways even more efficient.

Warm-Up

• CrashCourse – ATP and Respiration – Part 2

Pseudo-Closure

• Whisper Down the Metabolic Pathway• I have written a short paragraph on respiration, but I’ve

broken it into 31 “cards.”– So each card has a fragment of a sentence or two.

• Your job, when you receive your card(s), is to arrange yourself in order with everyone else’s.– You have to hold onto your card, so get in line.

• This is challenging.• Hints:

– First figure out what yours is talking about.– Then think of what comes before and after it – go find those

people first.– If you’re the beginning or end, tell people so.

Last Topic: Versatility• Glycolysis accepts a lot of inputs; it doesn’t need to be

glucose.– Other molecules like starch just get broken down to glucose first.

• Proteins are not efficient sources of energy.– But when they are used, they must be hydrolyzed back to amino

acids.– The amino group becomes waste (ammonia, urea, or uric acid – it

goes in yo’ pee).– The carboxyl group and central carbon become a 2-carbon sugar

and is passed into respiration.

Last Topic: Versatility

• Triglycerides – great energy source that they are – have an interesting way of getting into the respiration pathway.

• The glycerol head enters the glycolysis pathway as G3P.

• The fatty acid tails are broken into 2-carbon fatty acids and enter the citric acid cycle as acetyl CoA.– Given that only two acetyl CoAs enter for each glucose, one

triglyceride provides a heck of a lot of “bang for your bond.”

Versatility: Fats and Carbs

• Fats generate 2x the ATP compared to carbohydrates.– They contain a lot of carbon atoms that are not

yet oxidized.

• On the other hand, carbohydrates are faster to use.– They contain carbon atoms that are partially

oxidized already.

– Less energy released than from fats, though.

Inquiry Break

• Cellular Respiration – An Overview POGIL

• “Finish him!”…I mean…“it.”

Cell Respiration Summary

GlycolysisPyruvate Oxidation

Citric Acid Cycle

Oxidative Phosphorylation

FermentationPyruvate Oxidation

Oxygen

Mitochondrial MatrixCytosol

O

S

No

Oxyge

n

Citric Acid Cycle

Oxidative Phosphorylation

Real Closure

• Keep in mind that actual people are behind these myriad facts.

• For example:

http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1978/mitchell.jpg

Peter MitchellChemiosmosis

http://media-2.web.britannica.com/eb-media/43/21043-004-D206E5D2.jpg

Hans KrebsCitric Acid Cycle

You?

?

Surprise!

• Oxidative Phosphorylation POGIL