chapters 9 & 10 cellular energetics cellular respiration & photosynthesis

CHAPTERS 9 & 10

CELLULAR ENERGETICS

Cellular Respiration &

Photosynthesis

• Which organelles are involved?• How does the shape of each

organelle facilitate its function?• What are the ultimate goals of

these two processes?– Cellular respiration– Photosynthesis

Growth, reproduction and dynamic homeostasis require that cells create and maintain internal environments that are different from their external

environments.Essential knowledge 2.B.3: Eukaryotic cells

maintain internal membranes that partition the cell into specialized regions.

a. Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface area where reactions can occur.

b. Membranes and membrane-bound organelles in eukaryotic cells localize (compartmentalize) intracellular metabolic processes and specific enzymatic reactions.

Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.

a.Autotrophs capture free energy from physical sources in the environment.

Evidence of student learning is a demonstrated understanding of each of the following:

1. Photosynthetic organisms capture free energy present in sunlight.

2. Chemosynthetic organisms capture free energy from small inorganic molecules present in their environment, and this process can occur in the absence of oxygen.

Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.

b.Heterotrophs capture free energy present in carbon compounds produced by other organisms.

Evidence of student learning is a demonstrated understanding of each of the following:

1. Heterotrophs may metabolize carbohydrates, lipids and proteins by hydrolysis as sources of free energy.

2. Fermentation produces organic molecules, including alcohol and lactic acid, and it occurs in the absence of oxygen.

✘✘ Specific steps, names of enzymes and intermediates of the pathways for these processes are beyond the scope of the course and the AP Exam.

Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.

c. Different energy-capturing processes use different types of electron acceptors.

To foster student understanding of this concept, instructors can choose an illustrative example such as:

• NADP+ in photosynthesis • Oxygen in cellular respiration

Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.

d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.

Evidence of student learning is a demonstrated understanding of each of the following:

1. During photosynthesis, chlorophylls absorb free energy from light, boosting electrons to a higher energy level in Photosystems I and II.

Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.

2. Photosystems I and II are embedded in the internal membranes of chloroplasts (thylakoids) and are connected by the transfer of higher free energy electrons through an electron transport chain (ETC). [See also 4.A.2]

3. When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thykaloid membrane is established.

4. The formation of the proton gradient is a separate process, but it is linked to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase.

5. The energy captured in the light reactions as ATP and NADPH powers the production of carbohydrates from carbon dioxide in the Calvin cycle, which occurs in the stroma of the chloroplast.

✘✘ Memorization of the steps in the Calvin cycle, the structure of the molecules and the names of enzymes (with the exception of ATP synthase) are beyond the scope of the course and the AP Exam.

• e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.

f. Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that harvest free energy from simple carbohydrates.

Evidence of student learning is a demonstrated understanding of each of the following:

1. Glycolysis rearranges the bonds in glucose molecules, releasing free energy to form ATP from ADP and inorganic phosphate, and resulting in the production of pyruvate.

2. Pyruvate is transported from the cytoplasm to the mitochondrion, where further oxidation occurs

3. In the Krebs cycle, carbon dioxide is released from organic intermediates ATP is synthesized from ADP and inorganic phosphate via substrate level phosphorylation and electrons are captured by coenzymes.

4. Electrons that are extracted in the series of Krebs cycle reactions are carried by NADH and FADH2 to the electron transport chain.

✘✘ Memorization of the steps in glycolysis and the Krebs cycle, or of the structures of the molecules and the

names of the enzymes involved, are beyond

the scope of the course and the AP Exam.

g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.:

1. Electron transport chain reactions occur in chloroplasts (photosynthesis), mitochondria (cellular respiration) and prokaryotic plasma membranes.

2. In cellular respiration, electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen. In photosynthesis, the terminal electron acceptor is NADP+.

3. The passage of electrons is accompanied by the formation of a proton gradient across the inner mitochondrial membrane or the thylakoid membrane of chloroplasts, with the membrane(s) separating a region of high proton concentration from a region of low proton concentration. In prokaryotes, the passage of electrons is accompanied by the outward movement of protons across the plasma membrane.

4. The flow of protons back through membrane-bound ATP synthase by chemiosmosis generates ATP from ADP and inorganic phosphate.

5. In cellular respiration, decoupling oxidative phosphorylation from electron transport is involved in thermoregulation.

✘✘ The names of the specific electron carriers in the ETC are beyond the scope of the course and the AP Exam.

h. Free energy becomes available for metabolism by the conversion of ATP→ADP, which is coupled to many steps in metabolic pathways.

CHAPTER 9

CELLULAR RESPIRATION:

HARVESTING CELLULAR ENERGY

PROTEINS ---> ATPLIPIDS ---> ATP

CARBS (glucose) ---> ATP

THE BIG PICTURE…ENERGY TRANSFERS OVERVIEW:

SUNLIGHT -->

PRODUCER -->

PRIMARY CONSUMER(HERBIVORE) -->

DECOMPOSERS -->

All release heat… all energyreturns to space eventually

RADIANT ENERGY(PHOTONS)

CHEMICAL ENERGY STORAGE(GLUCOSE)

CHEMICAL ENERGY(ATP)

(POWERS CELLULAR WORK)

HEAT

RADIANT ENERGY(PHOTONS)

CHEMICAL ENERGY(GLUCOSE)

CHEMICAL ENERGY(ATP)

(POWERS CELLULAR WORK)

HEAT

Metabolism? Anabolism? Catabolism?

• Metabolism is the sum total of all an organisms chemical reactions.

• Anabolism is the sum total of the RXNs requiring energy that synthesizes complex molecules from simpler ones.

• Catabolism is the opposite of anabolism.

THE HISTORY OF ENERGY USE

• The earliest organisms were PROKARYOTES- archaebacteria

• which lived 3.5 BYA• Got their energy from digesting organic

compounds in the water• Some of these creatures evolved into

autotrophic prokaryotes that made their own food via photosynthesis or chemosynthesis.

• Chemosynthesis- energy to synthesize carbohydrates comes from chemicals not light.

• Processes of glycolysis (breaking glucose to make ATP) and an ANAEROBIC (w/out oxygen) process evolved first...

• By 2.7 BYA oxygen had accumulated in the atmosphere (because of the photosynthetic bacteria that had evolved).

• By 2.0 BYA Eukaryotic cells had evolved w/ their high metabolic needs... Hence the evolution of aerobic respiration (uses oxygen as final electron acceptor).

Do chemosynthetic creatures still exist

today???• Yes, bacteria that

get their energy from hydrogen sulfide, ammonia, or ferrous ions, or minerals in stone.

• EATING AWAY at famous statues!

• Yes, creatures that live off hydrothermal vents on the ocean floor (far from sunlight!)

Methanobacteria- These bacteria inhabit wetlands, areas high in sewage and intestinal

tracts. They combine carbon dioxide and hydrogen, which frees the oxygen that they need to live and

produces methane as a byproduct.

Cellular Respiration

• Is the metabolic pathway(s) that create ATP for the organism for cellular work.

• The amount of ATP generated and particular “pathway” is influenced by the presence or absence of oxygen.

• Thus:1) Anaerobic Respiration (fermentation)2) Aerobic Respiration

Sequence of Events for incomplete anaerobic glucose

metabolism

1) Glycolysis (2 ATP)2) Fermentation (alcohol or lactic

acid)

*much energy is left over in the final products (alcohol or lactic acid)- not converted to carbon dioxide.

Sequence of Events for full glucose metabolism

(aka: aerobic respiration)1) Glycolysis (2 ATP)2) Oxidation of pyruvic acid to acetyl CoA

(lose CO2)3) Krebs Cycle (citric acid&ATP) (lose

CO2) 4) Electron Transport Chain5) ATP synthesis via chemiosmosis TOTAL ATP PRODUCTION IS 38ATP

STEP #1: GLYCOLYSIS

AEROBIC RESPIRATION

STEP #2: THE KREBS CYCLE

STEP 3: NADH & FADH2 CARRY ELECRONS TO ELECTRON TRANSPORT CHAIN -> CHEMIOSMOSIS

Notice…

• Aerobic Respiration yield of ATP is also called

• “Oxidative Phosphorylation”• What is oxidation?

REDOX: The Energy Rxnstransferring electrons

• Oxidation is the loss of electrons from one substance.

• Ex. Na -> Na+

NADH -> NAD+ , e-, e-, H+• Reduction is the addition of

electrons to another substance.• Ex. Cl -> Cl-

NAD+ plus (e-, e-, H+) -> NADH

• OIL RIG- • Oxidation is Losing• Reduction is Gaining

• LEO GER-• Losing electrons is OXIDATION• Gaining electrons is REDUCTION

CHARACTERISTICS

• Oxidation-reduction REDOX reactions are coupled.

• They transfer electrons from one reactant to another.

SUMMARY EQUATION FOR CELLULAR RESPIRATION

• C6H12O6 + 6 O2 -> 6 CO2 + 6 H20 + 38 ATP

• Oxidation: C6H12O6 -> 6 CO2

Glucose is oxidized Lost e- and hydrogens

• Reduction: 6 O2 -> 6 H20Oxygen is reducedGained e- and hydrogens

* Note- this does not happen DIRECTLY. Electrons are transferred via “electron carrier molecules”.

• Electrons fall from organic molecules to oxygen during cellular respiration.

• Organic molecules with an abundance of hydrogen are excellent fuels

• their bonds are a source of hilltop electrons with the potential to fall closer to oxygen.

Electrons from Hydrogen travel down electronTransport chain with Oxygen as the Electro-negative SINK for electronsSlowly releases energy --> forms water.

Protons form a concentration gradient… will result in ATP!!!

ENERGY CARRYING MOLECULES

(used for cellular work)

ATP&Coenzymes that are involved in the metabolic

pathways of respiration and photosynthesisNADHFADH2NADPHThese last three are called “electron carriers”

ATP ADENOSINE TRI-PHOSPHATE

ADP ATP“energy carrier molecule “

ATP

Energy isstored in the

bonds betweenphosphate

groups.

ATP

• : adenosine tri phosphate• : adenosine nucleotide

3 phosphate groups• : high energy bonds are between the

phosphates• : ATP releases energy by using a

phosphate group to phosphorylate other molecules thus degrading to ADP.

• : -7.3 kcal/mol

How is ATP regenerated?

1) SUBSTRATE LEVEL phosphorylation

2) OXIDATIVE PHOSPHORYLATIONChemiosmosis through ATP-synthase

Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis

NAD+ NADH

“electron carrier molecule “

NADH

NAD+/NADH is a coenzymeNAD+ accepts 2e- & H+

NADH is the ENERGY RICH formTHE OTHER H+ STICKS AROUND

FAD VV“electron carrier molecule “

FADH2

FAD/FADH2 is a coenzymeFAD accepts

2e- & 2H+

FADH2 is the ENERGY RICH

molecule

GLYCOLYSIS: BREAKING DOWN GLUCOSE

• Glycolysis happens in the cytosol of the cell.• Key Players:

enzymes- one at every stepATP- the goalADP + Pi

NAD+

NADH (a.k.a. NADH + H+)- w/ 2e-/H+PGAL- CCC-PPyruvic Acid(a.k.a. pyruvate)- CCC

Figure 9.8 The energy input and output of glycolysis

Glycolysis = breaking glucose

Energy Investment:1.2 ATP neededEnergy Payoff:1.2 NADH formed2.4 ATP formed3.2 pyruvate remainNET GAIN2,2,2

IMPORTANT EVENTS USED PRODUCED1. Glucose2. Add phosphate ATP ADP, Pi3. Add phosphate ATP ADP, Pi4. Split into 2 3Carbon

PGAL molecules5.2PGAL oxidized and 2NAD+ 2NADH, 2H+

NAD+ is reduced to NADH while phosphate is added to PGAL

6. ADP takes away Phosphate 2ADP 2ATP7. Water is taken out8. ADP takes away phosphate 2ADP 2ATP9. Pyruvic acid is created.

KNOWING THE DETAILS IS BEYOND THE SCOPE OF AP BIO

Glycolysis:phase 1- energy

investment

ENERGY INVESTMENT PHASE

Energy Payoff Phase

PHOSPHORYLATION BYREDOX NOT USING ATPNAD+ IS REDUCED

WHAT JUST HAPPENED?

• 1) one molecule of glucose is broken down into 2 molecules of pyruvic acid/ pyruvate.

• 2) two molecules of ATP are used but FOUR new molecules are generated, for a net gain of 2 ATP.

• 3) two molecules of NADH are formed.

FaculatativeAnaerobesUse oxygento make a lotof ATP when itis present.

Otherwise, regenerateNAD+ viafermentationand just liveoff the 2 ATPfrom glycolysis

The Next Step: When Oxygen is NOT around

Both molecules of pyruvic acid udergo fermentation in the absence of oxygen.

In animals: NADH (from glycolysis) is oxidized (releases hydrogen) while pyruvic acid is reduced (adds hydrogen). The new molecule is lactic acid.

In yeast: The three-carbon pyruvic acid molecule is broken into a 2 carbon compound (acetylaldehyde)and CO2 is released. NADH (from glycolysis) is oxidized (releases hydrogen) while the two carbon compound is reduced (adds hydrogen).

The new molecule is ethyl alcohol.

Fermentation only releases about3.5% of the kilocalaries available in glucose

What is the goal of fermentation?

• Regenerate NAD+ for glycolysis• It is needed at the beginning of the

energy payoff stage to phosphorylate the molecules.

Figure 9.x2 Fermentation

ALCOHOL FERMENTATION

Alcoholic fermentation

LACTIC ACID FERMENTATION

LACTIC ACID FERMENTATION

The end…

What are coupled reactions and how do they

work?

• Endergonic + Exergonic • Exergonic one lends energy to the

endergonic one.

• Aerobic respiration- the catabolism of pyruvate

• takes place in the mitochondrion • (requires O2)oxygen acts as the final

electron acceptor or oxidizing agent because it is reduced

• (very electronegative- acts like an electron sink)

Sequence of Events

1) Glycolysis2) Oxidation of pyruvic acid to

acetyl CoA (lose CO2)3) Krebs Cycle (citric acid)4) Electron Transport Chain5) ATP synthesis

Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle

Getting pyruvate into the Matrix

1) Carboxyl group of pyruvate is removed as 1 molecule of CO2.

2) Remaining 2 carbon molecule is oxidized to form ACETATE-> 2 e- and 1 H+ are transferred to NAD+ to form NADH.

3) CoenzymeA picks up ACETYL group-> acetyl-CoA

Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle

THE KREBS CYCLE1. Coenzyme A attaches acetyl

to OAA

2. Citrate/citric Acid formed

3. Decarboxylation

(CO2 released)

Redox- NADH formed

4. Decarboxylation

(CO2 released)Redox- NADH formed

5. ATP formed

6. Redox- FADH2 formed

7. Redox- NADH formed

OAA reformed

Figure 9.12 A summary of the Krebs cycle

THE KREBS CYCLE• Discovered by HANS KREBS in the 1930s (british-german)

1) Acetyl-CoA adds 2 carbon fragment to OAA- oxaloacetate which forms citrate/citric acid.

2) Citrate loses a CO2, compound is oxidized, NAD+ is reduced to NADH.

3) Another CO2 lost, compounds oxidized, NAD+ reduced to NADH.

4) CoA replaced by P ->GDP->GTP->ATP5) FAD is reduced to FADH26) H20 added, substrate oxidized, NAD+ reduced to NADH-

> OAA

Figure 9.11 A closer look at the Krebs cycle (Layer 1)

Figure 9.11 A closer look at the Krebs cycle (Layer 2)

Figure 9.11 A closer look at the Krebs cycle (Layer 3)

Figure 9.11 A closer look at the Krebs cycle (Layer 4)

• How many turns/glucose?• Two• NET RESULTS per glucose:• ATP?• Two• NADH?• Six• FADH2?• 2• CO2?• 4• WHAT HAPPENED TO Carbon, Oxygen, & Hydrogen of

GLUCOSE?• CO2 & NADH, FADH2

Figure 9.13 Free-energy change during electron transport

THE ELECTRON TRANSPORT CHAIN

• What is it?• Collection of molecules embedded in

the inner mitochondrial membrane.– Proteins (cytochromes)– Coeznymes (Q)

• Folds = cristae = increased surface area for more reactions!

• Moving electrons power the proton pumps

Main events:

NADH1) Dumps 2 electrons2) H+, NAD+ made

FADH21) Dump 2 electrons2) 2 H+, FAD made

The electrons pass down the ETC which is made of CYTOCHROMES- iron containing proteins that transfer electrons.

Final Step= attach to O2 & H+ to make water.

THE RESULTS

1) Exergonic flow of e- pumps H+ ions (protons) across membrane to Inter Membrane Space.

2) Ion gradient (H+/proton gradient) is created- this PROTON MOTIVE FORCE can do work.

CHEMIOSMOSISATP synthase = enzyme that makes ATP from ADP & P.

It is an ion pump in reverse.

When the ions enter ATP synthase it turns the protein rotor- causing change in shape of the enzyme.

Electron Transport Chain

Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis

Figure 9.16 Review: how each molecule of glucose yields many ATP molecules during cellular respiration

HOW MUCH ATP IS PRODUCED/glucose?

• Each NADH: 3 ATP (10x3=30 chemiosmosis)• Each FADH2: 2 ATP (2x2=4 chemiosmosis)• Total ATP from breakdown of glucose: • 4 glycolysis+2 Krebs Cycle+34 ETC= 40)• However, 2 are used during glycolysis so the

net amount is 38!• And some ATP is used to shuttle NADH into

the matrix that is created by glycolysis.

Figure 9.20 The control of cellular respiration 

GLYCOLYSIS

THE KREBS CYCLE

ELECTRON TRANSPORT CHAIN

LAB #5 Cell RespirationNext Class

• Extra credit to set up tomorrow during 7th period. You can only earn this extra credit once, but you are welcome to help if you just want to prep for the lab.

• Don’t forget to do the LAB BENCH exercise and write your prelab notes.