1. Enduring Understanding 2.A
BIG IDEA II Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis.
Enduring Understanding 2.A
Growth, reproduction and maintenance of the organization
of living systems require free energy and matter.
Essential Knowledge 2.A.2
Organisms capture and store free energy for use in biological processes.

2. Essential Knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.
Learning Objectives:
(2.4) The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy.
(2.5) The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy.

3. Autotrophs capture free energy from physical sources in the environment.
Photosynthetic organisms capture free energy present in sunlight.
6CO2 + 6 H2O + light energy  C6H12O6 + 6 O2 + 6 H2O
carbon dioxide + water + light energy  sugar + oxygen + water
Chemosynthetic organisms capture free energy from small inorganic molecules present in their environment, and this process can occur in the absence of oxygen.
6H2S + 6 H2O + 6 CO2 + 6 O2  C6H12O6 + 6 H2SO4
hydrogen sulfide + water + carbon dioxide + oxygen  sugar + sulfuric acid

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

5. Heterotrophs capture free energy present in carbon compounds produced by other organisms.
Heterotrophs may metabolize carbohydrates, lipids and proteins by hydrolysis as sources of free energy.
C6H12O6 + 6 O2  6CO2 + 6 H2O + energy (ATP + heat)
organic compounds + oxygen  carbon dioxide + water + energy
Fermentation produces organic molecules, including alcohol and lactic acid, and it occurs in the absence of oxygen.
C6H12O6  yeast  2 CH3CH2OH + 2 CO2 + heat
sugar  yeast  ethanol + carbon dioxide + heat

6. Heterotrophs capture free energy present in carbon compounds produced by other organisms.
Figure 9.19 Pyruvate as a key juncture in catabolism
Glycolysis is common to fermentation AND respiration.
The end product of glycolysis is pyruvate…represents a fork in the catabolic pathways of glucose oxidation. In a cell capable of both respiration and fermentation, pyruvate is committed to one of those two pathways, usually depending on the presence of oxygen.
The Evolutionary Significance of Glycolysis
Glycolysis occurs in nearly all organisms
Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

7. The Role of Electron Acceptors in Energy-Capturing Processes
Different energy-capturing processes use different types of electron acceptors:
NADP+ in photosynthesis
Oxygen in cellular respiration
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions.
In oxidation, a substance loses electrons, or is oxidized
In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
The electron donor is called the reducing agent
The electron receptor is called the oxidizing agent

8. Catabolic Pathways & ATP Production
Catabolic Pathways yield energy by oxidizing organic fuels.
Several processes are central to cellular respiration and related pathways.
The breakdown of organic molecules is exergonic:
Fermentation is a partial degradation of sugars that occurs without O2.
Aerobic respiration consumes organic molecules and O2 and yields ATP.
Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2.
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9. Cellular Respiration
Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is ultimately used to synthesize ATP
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10. Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced:
GLUCOSE loses electrons.
Oxygen accepts electrons.
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11. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
In cellular respiration, glucose and other organic molecules are broken down in a series of steps.
Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that harvest free energy from simple carbohydrates.
Electrons from organic compounds are usually first transferred to NAD+, a coenzyme.
As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration.
NICOTINAMIDE ADENINE DINUCLEOTIDE
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
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12. The Stages of Cellular Respiration: A Preview
Cellular respiration has three stages:
Glycolysis (breaks down glucose into two molecules of pyruvate) – occurs in cytosol
The citric acid cycle (completes the breakdown of glucose) – occurs in mitochondrial matrix
Electron Transport/Oxidative Phosphorylation (accounts for most of the ATP synthesis) – occurs across inner membrane of mitochondria
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13. Figure Review: how each molecule of glucose yields many ATP molecules during cellular respiration:

14. Review Questions from yesterday’s learning:
How are the equations for photosynthesis and chemosynthesis different (details)
What type of reaction is it when organisms break down sugars?
What types of reactions transfer electrons? (Compare the reactions)
Name the three steps in cellular respiration.
What is the net ATP production?

15. Mitochondria Structure & Function
Mitochondria have a DOUBLE MEMBRANE that allows COMPARTMENTALIZATION within the mitochondria and is important to its function.
OUTER MEMBRANE is smooth, but INNER MEMBRANE is highly convoluted, forming folds called cristae.
Cristae contain enzymes important to ATP production; cristae also increase the surface area for ATP production.

16. Visual Overview of Cellular Respiration

17. Term Comprehension: Substrate-Level Phosphorylation
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation.
Some ATP created during cell respiration is made by direct enzymatic transfer of a phosphate group from a substrate to ADP.
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18. Glycolysis http://highered. mcgraw-hill
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.
Glycolysis harvests chemical energy by oxidizing glucose to pyruvate – it is the first stage of cellular respiration.
Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate.
Glycolysis occurs in the cytoplasm and has two major phases:
Energy investment phase
Energy payoff phase
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19. Glycolysis Glycolysis occurs WITH or WITHOUT oxygen.
The first step is the phosphorylation of glucose (glucose molecule gains 2 inorganic phosphates) – this ACTIVATES the glucose to split.
The second step is the splitting of glucose – breaking it down into (2) 3-carbon molecules called pyruvic acid.
This process is achieved by stripping electrons and hydrogens from the unstable 3-C molecules (as well as the borrowed phosphates).
2 ATPs are needed to produce 4 ATPs (energy investment and energy payoff phases).
A second product in glycolysis is 2 NADH, which results from the transfer of e- and H+ to the coenzyme NAD+.
Occurs in the cytoplasm
Net of 2 ATPs produced
2 pyruvic acids formed
2 NADH produced

20. 10 Steps of Glycolysis 2 Phases:
---Energy investment phase (use 2 ATP)
---Energy payoff phase (create 4 ATP)

21. Energy investment phase
Fig. 9-8
Energy investment phase
Glucose
2 ADP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
4 ATP
formed
2 NAD e– + 4 H+
2 NADH
+ 2 H+
During the energy investment phase, the cell actually spends ATP.
This investment is repaid with interest during the energy payoff phase, when ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by electrons released from the oxidation of glucose.
THE NET YIELD FROM GLYCOLYSIS, PER GLUCOSE MOLECULE, IS 2 ATP plus 2 NADH.
2 Pyruvate + 2 H2O
Net
Glucose
2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used
2 ATP
2 NAD e– + 4 H+
2 NADH + 2 H+

22. The “Intermediate” Step
The pyruvate produced during glycolysis is transported from the cytoplasm to the mitochondrion, where further oxidation occurs.
The conversion of pyruvate to acetyl CoA is the junction between glycolysis (step 1) and the Krebs cycle (step 2).
If oxygen is present, Pyruvate (3 C each) from glycolysis enters the mitochondrion.
Using Coenzyme A, each pyruvate is converted into a molecule of Acetyl CoA (2 C each).
What happened to the other carbon from each molecule of pyruvate?
CO2 released!
NAD+ is reduced to form NADH

23. CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Pyruvate
Fig. 9-10
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+ 2 1 3
Acetyl CoA
Pyruvate
Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the citric acid cycle
Pyruvate is a charged molecule, so it must enter the mitochondria via active transport (with the help of a transport protein).
1st: Pyruvate’s carboxyl group (-COO) is removed and given off as CO2 waste.
2nd: Remaining 2 carbon fragment is oxidized (loses electrons) – these are picked up by NAD to form NAHD (stored energy).
3rd: Coenzyme A is attached to the remaining acetate – represents high potential energy that can enter into the Krebs cycle.
Coenzyme A
CO2
Transport protein

24. The Citric Acid Cycle http://highered. mcgraw-hill
In the Krebs cycle, carbon dioxide is released from organic intermediations ATP is synthesized from ADP and inorganic phosphate via substrate level phosphorylation and electrons are captured by coenzymes.
The citric acid (Krebs) cycle completes the energy-yielding oxidation of organic molecules – and its events take place within the mitochondrial matrix.
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn.
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25. Pyruvate CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle 2
Fig. 9-11
Pyruvate
CO2
NAD+
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle 2
CO2
Figure 9.11 An overview of the citric acid cycle
In the presence of oxygen, the pyruvic acid produced during glycolysis passes to the second stage of cellular respiration: the Krebs Cycle.
During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
Every time you exhale, you expel the CO2 produced by the Krebs cycle.
Figure 9.12 A closer look at the citric acid cycle
The citric acid cycle has eight steps, each catalyzed by a specific enzyme
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate – THUS CALLED “CITRIC ACID CYCLE”
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle
The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain
FADH2
3 NAD+
FAD 3
NADH
+ 3 H+
ADP + P i
ATP

26. Term Comprehension: Oxidative Phosphorylation
The process that generates most of the ATP during cellular respiration is called oxidative phosphorylation because it is powered by redox reactions of an electron transport chain.
Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration.
ATP synthesis can be powered by the flow of H+ back across mitochondrial membrane (chemiosmosis)
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27. What is the literal translation of glycolysis and why is it an appropriate name?
How many ATP are used and created from the process of glycolysis?
What is the intermediate product made in the citric acid cycle?
How many cycles are involved in the completion of the citric acid cycle?
What are the electron carriers which are produced in the first two portions of cellular respiration?

28. Chemiosmosis & Electron Transport http://highered. mcgraw-hill
Following the Krebs cycle, the electrons captured by NADH and FADH2 are passed to the electron transport chain:
The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP to ATP.
Every time 2 high energy electrons transport down the ETC, their energy is used to transport H+ across the inner membrane of the mitochondria…this creates a + charge on the inside of the membrane and a – charge in the matrix of the mitochondria.
As a result of this charge difference, H+ ions escape through channel proteins called ATP synthase causing it to rotate.
Each time it rotates, the enzyme ATP synthase grabs a low energy ADP and attaches a phosphate, forming high-energy ATP.
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29. NADH 50 2 e–
NAD+
FADH2 2 e–
FAD
Multiprotein
complexes  40
FMN
FAD
Fe•S 
Fe•S Q

Cyt b
Fe•S 30
Cyt c1 IV
Free energy (G) relative to O2 (kcal/mol)
Cyt c
Cyt a
Cyt a3 20
Figure 9.13 Free-energy change during electron transport
The electron transport chain is in the cristae of the mitochondrion. Most of the chain’s components are proteins. The carriers alternate reduced and oxidized states as they accept and donate electrons. Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O.
Electrons are passed from NADH or FADH2 through a number of proteins on the ETC including cytochromes (each with an iron atom) to O2
The electron transport chain generates no ATP
The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts e– 10 2
(from NADH
or FADH2)
2 H+ + 1/2 O2
H2O

30. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.
Electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen.
The passage of electrons is accompanied by the formation of a proton gradient across the inner mitochondrial membrane, with the membrane separating a region of high proton concentration from a region of low proton concentration.
The flow of protons back through membrane-bound ATP synthase by chemiosmosis generates ATP from ADP and inorganic phosphate (Pi).

31. INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Cata- lytic knob ADP
Fig. 9-14
INTERMEMBRANE SPACE H+
Stator
Rotor
Internal
rod
Figure 9.14 ATP synthase, a molecular mill of CHEMIOSMOSIS
Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the innermembrane space
H+ then moves back across the membrane, passing through channels in ATP synthase
ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP
This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work
Cata-
lytic
knob
ADP + P
ATP i
MITOCHONDRIAL MATRIX

32. The Pathway of Electron Transport:
Fig. 9-16 H+ H+ H+ H+
Protein complex
of electron
carriers
Cyt c V Q
 
ATP synthase 
2 H+ + 1/2O2
H2O
FADH2
FAD
NADH
NAD+
ADP + P
ATP i
(carrying electrons
from food)
Figure 9.16 Chemiosmosis couples the electron transport chain to ATP synthesis
The Pathway of Electron Transport:
The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis
The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work H+ 1
Electron transport chain 2
Chemiosmosis
Oxidative phosphorylation

33. During cellular respiration, most energy flows in this sequence:
Fig. 9-17
CYTOSOL
Electron shuttles
span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Glycolysis
Oxidative
phosphorylation:
electron transport
and
chemiosmosis 2
Pyruvate 2
Acetyl
CoA
Citric
acid
cycle
Glucose
+ 2 ATP
+ 2 ATP
+ about 32 or 34 ATP
Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration
During cellular respiration, most energy flows in this sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about ATP
About
36 or 38 ATP
Maximum per glucose:

34. Fermentation/Anaerobic Respiration
Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen
Most cellular respiration requires O2 to produce ATP
Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP
Anaerobic respiration uses an electron transport chain with an electron acceptor other than O2, for example sulfate
Fermentation uses phosphorylation instead of an electron transport chain to generate ATP
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35. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis
Two common types are alcohol fermentation and lactic acid fermentation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

36. Fig. 9-18
2 ADP + 2 Pi
2 ATP
Glucose
Glycolysis
2 Pyruvate
2 NAD+
2 NADH 2
CO2
+ 2 H+
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2 Pi
2 ATP
Glucose
Glycolysis
In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2
Alcohol fermentation by yeast is used in brewing, winemaking, and baking
In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation

37. Fermentation and Aerobic Respiration Compared
Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate
The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration
Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule
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38. The Anaerobes
Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2
Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes
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39. The Versatility of Catabolism
Glycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways.
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration.
Glycolysis accepts a wide range of carbohydrates.
In addition to carbohydrates, heterotrophs may metabolize lipids and proteins by hydrolysis as sources of free energy.
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40. Citric acid cycle Oxidative phosphorylation
Fig. 9-20
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle
Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA)
Fatty acids are broken down by beta oxidation and yield acetyl CoA
An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate
Anabolism:
The body uses small molecules to build other substances
These small molecules may come directly from food, from glycolysis, or from the citric acid cycle
Citric
acid
cycle
Oxidative
phosphorylation

41. Feedback inhibition is the most common mechanism for control
Fig. 9-21
Glucose
AMP
Glycolysis
Fructose-6-phosphate
Stimulates +
Phosphofructokinase – –
Fructose-1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Figure 9.21 The control of cellular respiration via feedback mechanisms:
Feedback inhibition is the most common mechanism for control
If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down
Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway
Citric
acid
cycle
Oxidative
phosphorylation

42. What do you know….
Glycolysis
Kreb Cycle
ETC
Fermentation Pathways

43. Overview of Cellular Respiration
A. Glycolysis – *takes place in cytosol
*breaks glucose into 2 molecules of pyruvate
*produces a net of 2 ATP’s
B. Krebs cycle - *takes place in mitochondrial matrix
*makes a derivative of pyruvate into carbon dioxide
C. ETC and Oxidative Phosphorylation –
*takes place in inner membrane of mitochondrion
*accepts e-’s from A and B via NADH
*at end, e-’s are combined with H+ and oxygen to form water
*forms a net of 34 ATP’s
D. Fermentation Pathways *takes place in cytosol
*2 types: Alcoholic and Lactic Acid Fermentation
*stores most of the energy in chemical bonds
*no production of ATP

44. Energy Coupling
H2O
Following cellular respiration or fermentation, free energy becomes available for metabolism by the conversion of ATPADP, which is coupled to many steps in metabolic pathways.