1. CHAPTER 6 How Cells Harvest Chemical Energy
Modules 6.1 – 6.7

2. How is a Marathoner Different from a Sprinter?
Long-distance runners have many slow fibers in their muscles
Slow fibers break down glucose for ATP production aerobically (using oxygen)
These muscle cells can sustain repeated, long contractions

3. Sprinters have more fast muscle fibers
Fast fibers make ATP without oxygen— anaerobically
They can contract quickly and supply energy for short bursts of intense activity

4. The dark meat of a cooked turkey is an example of slow fiber muscle
Leg muscles support sustained activity
The white meat consists of fast fibers
Wing muscles allow for quick bursts of flight

5. INTRODUCTION TO CELLULAR RESPIRATION
Nearly all the cells in our body break down sugars for ATP production  used by all cells to do work.
Most cells of most organisms harvest energy aerobically, like slow muscle fibers
The aerobic harvesting of energy from sugar is called cellular respiration, occurs in mitochondria
Cellular respiration yields CO2, H2O, and a large amount of ATP

6. 6.1 Breathing supplies oxygen to our cells and removes carbon dioxide
Breathing and cellular respiration are closely related
BREATHING O2
CO2
Lungs
CO2
Bloodstream O2
Muscle cells carrying out
CELLULAR RESPIRATION
Sugar + O2  ATP + CO2 + H2O
Figure 6.1

7. 6.2 Cellular respiration banks energy in ATP molecules
Cellular respiration breaks down glucose molecules and banks their energy in ATP
The process uses O2 and releases CO2 and H2O
Glucose
Oxygen gas
Carbon dioxide
Water
Energy
Review: 2nd law of thermodynamics, wasted energy is lost to each system as random KE (heat).

8. The efficiency of cellular respiration (and comparison with an auto engine)
Energy released from glucose banked in ATP
Energy released from glucose (as heat and light)
Gasoline energy converted to movement
100%
About 40%
25%
Burning glucose in an experiment
“Burning” glucose in cellular respiration
Burning gasoline in an auto engine
Figure 6.2B

9. 6.3 Connection: The human body uses energy from ATP for all its activities
ATP powers almost all cell and body activities
Body maintenance
Breathing, digesting food, temperature and blood circulation
Voluntary activities require additional energy input and utilize calories at a faster rate then simple body maintenance
Total expenditure = 2200 kcal a day
Table 6.3

10. BASIC MECHANISMS OF ENERGY RELEASE AND STORAGE
6.4 Cells tap energy from electrons transferred from organic fuels to oxygen
Glucose gives up energy as it is oxidized
Loss of hydrogen atoms
Energy
Glucose
Gain of hydrogen atoms
Figure 6.4

11. Movement of H represents electron transfer
1 glucose molecule contains more energy than a cell needs to use for a single job
** Look at equation at the bonds of reactants and products in cellular respiration
Movement of H represents electron transfer
Don’t see e-’s
CR is a series of steps, coupling exergonic with an endergonic reaction
** Review coupling: Glucose breakdown (exergonic – energy released) -> ATP synthesis (endergonic – energy stored)

12. Some of the energy that is released is stored in the phosphate bonds of ATP
Coupling of the release of energy of ATP, an exergonic reaction, to provide energy to drive endergonic reactions
At each step, electrons move from chemical bond in a molecule where they have more energy to a bond where they have less energy.
Oxygen atoms are the ultimate (final) electron acceptors. When these oxygen atoms bind with the hydrogen atoms carrying the electrons, they form water molecules with relatively low-energy covalent bonds.

13. Dehydrogenase and NAD+
6.5 Hydrogen carriers such as NAD+ shuttle electrons in redox reactions
Enzymes remove electrons from glucose molecules and transfer them to a coenzyme
OXIDATION
Dehydrogenase and NAD+
REDUCTION
Figure 6.5

14. Oxidation reactions involve electron loss and are exergonic half
Reduction reactions involve electron gain and are the endergonic half
LEO-GER “Loss of Electrons, Oxidation; Gain of electrons, reduction
Each step in glucose breakdown includes small redox reaction
Enzyme = dehydrogenase and coenzyme = NAD+
Glucose oxidized, NAD+ reduced forming NADH

15. Dehydronase removes H+’s from given molecule (glucose)
NAD+ picks up a H+ to become NADH
Electron carrier
Got reduced (gained electrons)
Some H+ goes into solution

16. 6.6 Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen
NADH delivers electrons to a series of electron carriers in an electron transport chain
NADH with less potential energy then glucose
Gets oxidized and NADH  back to NAD+ w/ H+’s passed down chain
ETC song
As electrons move from carrier to carrier, their energy is released in small quantities
Energy released and now available for making ATP
ELECTRON CARRIERS of the electron transport chain
Electron flow
Figure 6.6

17. Energy released as heat and light
In an explosion, 02 is reduced in one step
Energy released as heat and light
Figure 6.6B

18. Ultimate electron acceptor is oxygen
Small amounts of energy released that can build ATP
ETC
In eukaryotic cells found in mitochondrial membrane
In prokaryotic cells found in plasma membrane

19. 6.7 Two mechanisms generate ATP
Cells use the energy released by “falling” electrons to pump H+ ions across a membrane
The energy of the gradient is harnessed to make ATP by the process of chemiosmosis
The electron transport temporarily produces PE in the form of an increase of H+. ATP synthases use the PE to generate ATP by H+ flow through them
High H+ concentration
ATP synthase uses gradient energy to make ATP
Membrane
Electron transport chain
ATP synthase
Energy from
Low H+ concentration
Figure 6.7A

20. Organic molecule (substrate) New organic molecule (product)
ATP can also be made by transferring phosphate groups from organic molecules to ADP
Enzyme
Adenosine
Organic molecule (substrate)
This process is called substrate-level phosphorylation
NO membranes or ETC involved
Adenosine
New organic molecule (product)
Figure 6.7B

21. Chemiosmosis – requires membranes (ETC)
Substrate- level – requires no membranes (Glycolysis or Krebs)
Not as efficient = less ATP made

22. Black-Eyed Peas – Cellular Respiration Song

23. 6.8 Overview: Respiration occurs in four main stages
STAGES OF CELLULAR RESPIRATION AND FERMENTATION
6.8 Overview: Respiration occurs in four main stages
Cellular respiration oxidizes sugar and produces ATP in three main stages
Glycolysis occurs in the cytoplasm
The Krebs cycle (matrix) and the electron transport chain (cristae) occur in the mitochondria
Chemiosmosis occurs following ETC

24. An overview of cellular respiration
All interconnected, all with some ATP synthesis
High-energy electrons carried by NADH
GLYCOLYSIS
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
KREBS CYCLE
Glucose
Pyruvic acid
Cytoplasmic fluid
Mitochondrion
Figure 6.8

25. 6.9 Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid
Occurs in all cells, under all conditions (aerobic and anaerobic); animals, plants, fungi
Glucose
Pyruvic acid
Figure 6.9A

26. PREPARATORY PHASE (energy investment)
Steps – A fuel molecule is energized, using ATP.
Glucose 1 3
Details of glycolysis
Net result is 1 6C molecule split into 2 3C molecules
Each of 9 steps different enzme
Reactants include glucose, ADP, phosphate and NAD+
ATP to get things started
Look at overall reactants and products
Step 1
Glucose-6-phosphate 2
Fructose-6-phosphate 3
Fructose-1,6-diphosphate
Step A six-carbon intermediate splits into two three-carbon intermediates. 4 4
Glyceraldehyde-3-phosphate (G3P)
ENERGY PAYOFF PHASE 5
Step A redox reaction generates NADH. 5
1,3-Diphosphoglyceric acid (2 molecules) 6
Steps – ATP and pyruvic acid are produced.
3-Phosphoglyceric acid (2 molecules) 6 9 7
2-Phosphoglyceric acid (2 molecules) 8
2-Phosphoglyceric acid (2 molecules) 9
Pyruvic acid
(2 molecules per glucose molecule)

27. 6.10 Pyruvic acid is chemically groomed for the Krebs cycle
Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle
Pyruvic acid is an intermediate or a bridge
oxidized
Pyruvic acid
Acetyl CoA (acetyl coenzyme A)
waste
High-energy for Krebs
CO2
Figure 6.10

28. Compare the amount of chemical energy in glucose versus the two pyruvic acid molecules
Glucose with more energy than pyruvate. Why?
Look at the number of bonds

29. How will the NADH be used to make ATP
Chemiosmosis, NADH will carry electrons to the ETC

30. 6.11 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules
Acetyl CoA
The Krebs cycle is a series of reactions in which enzymes in the matrix strip away electrons and H+ from each acetyl group
Look at products and reactants and net energy production
What is usable now or later?
Needed to restart cycle 2
KREBS CYCLE
CO2
Not immediate
Not immediate
immediate

31. Alpha-ketoglutaric acid
2 carbons enter cycle
Oxaloacetic acid 1
Citric acid
CO2 leaves cycle 5
KREBS CYCLE 2
Malic acid 4
Alpha-ketoglutaric acid 3
CO2 leaves cycle
Succinic acid
Step
Acetyl CoA stokes the furnace
Steps and
NADH, ATP, and CO2 are generated during redox reactions.
Steps and
Redox reactions generate FADH2 and NADH. 1 2 3 4 5
Figure 6.11B

32. Official first step of Krebs
Formation of citric acid
A molecule of 2-carbon CoA joined with 4-carbon oxaloacetic acid
Results in 6-carbon citric acid

33. 6.12 Chemiosmosis powers most ATP production
The electrons from NADH and FADH2 travel down the electron transport chain to oxygen
Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes
In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP

34. ELECTRON TRANSPORT CHAIN
Chemiosmosis in the mitochondrion (inner membrane, cristae)
Net energy production = 32 ATP per glucose (only if O2 is available
Protein complex
Intermembrane space
Electron carrier
Inner mitochondrial membrane
Electron flow
Mitochondrial matrix
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
Figure 6.12

35. Advantage of membranes in general as related to membrane in mitochondria
Increased surface area
Increases amount of ETC/ATP synthases

36. Cyanide, carbon monoxide ELECTRON TRANSPORT CHAIN
6.13 Connection: Certain poisons interrupt critical events in cellular respiration
Rotenone
Cyanide, carbon monoxide
Oligomycin
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
Figure 6.13

37. 6.14 Review: Each molecule of glucose yields many molecules of ATP
For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules
Review – second chance at Black-eyed Peas
Cytoplasmic fluid
Mitochondrion
Electron shuttle across membranes
KREBS CYCLE
GLYCOLYSIS
2 Acetyl CoA
2 Pyruvic acid
KREBS CYCLE
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
Glucose
by substrate-level phosphorylation
used for shuttling electrons from NADH made in glycolysis
by substrate-level phosphorylation
by chemiosmotic phosphorylation
Maximum per glucose:
Figure 6.14

38. Compare glycolysis vs. Krebs
2 ATP + 2 NADH
Krebs (based on 2 CoA molecules)
2 ATP
6 NADH
2 FADH2

39. Overall review
4 ATP from glycolysis and Krebs by substrate-level phosphorlyation
40% glucose converted to ATP
Each NADH = 3 ATP (ETC/Chemiosmosis)
Each FADH2 = 2 ATP (ETC/Chemiosmosis)
Maximum yield per glucose is 38 ATP, but may be less due to energy used to shuttle NADH from glycolysis in cytoplasm to mitochondria

40. 6.15 Fermentation is an anaerobic alternative to aerobic respiration
Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP
But a cell must have a way of replenishing NAD+

41. In alcoholic fermentation, pyruvic acid is converted to CO2 and ethanol
This recycles NAD+ to keep glycolysis working
released
GLYCOLYSIS
2 Pyruvic acid
2 Ethanol
Glucose
Figure 6.15A
Figure 6.15C

42. In lactic acid fermentation, pyruvic acid is converted to lactic acid
As in alcoholic fermentation, NAD+ is recycled
Lactic acid fermentation is used to make cheese and yogurt
Responsible for muscle soreness after working out
GLYCOLYSIS
2 Pyruvic acid
2 Lactic acid
Glucose
Figure 6.15B

43. Different types of bacteria
Strict anaerobes
Require anaerobic conditions and are poisoned by O2
Facultative anaerobes
Can make ATP by fermentation or chemiosmosis depending on if O2 is available or not

44. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS
6.16 Cells use many kinds of organic molecules as fuel for cellular respiration
Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis
Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle
Fats are broken up and fed into glycolysis and the Krebs cycle

45. ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
Pathways of molecular breakdown
Food, such as peanuts
Polysaccharides
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
Pyruvic acid
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
Glucose
G3P
Acetyl CoA
KREBS CYCLE
GLYCOLYSIS
Figure 6.16

46. Pathways (look at draw and follow arrows for each of the following)
Polysaccharides  convert to glucose, then 3 stages plus intermediate
Proteins  convert to Pyruvic acid, Acetyl CoA, or Kreb’s cycle and then continues depending on the point of entry
Fatty acids  acetyl CoA to Kreb’s
Glycerol  G3P (glycolysis intermediate)

47. Fat due to the large amount of (H+)’s result in the most ATP produced
More than starch/sugar

48. 6.17 Food molecules provide raw materials for biosynthesis
In addition to energy, cells need raw materials for growth and repair
Some are obtained directly from food
Others are made from intermediates in glycolysis and the Krebs cycle
Biosynthesis consumes ATP
Can produce molecules that are not actually present in the original food

49. ATP needed to drive biosynthesis Cells, tissues, organisms
Biosynthesis of macromolecules from intermediates in cellular respiration
ATP needed to drive biosynthesis
GLUCOSE SYNTHESIS
KREBS CYCLE
Acetyl CoA
Pyruvic acid
G3P
Glucose
Amino groups
Amino acids
Fatty acids
Glycerol
Sugars
Proteins
Fats
Polyscaccharides
Cells, tissues, organisms
Figure 6.17

50. 6.18 The fuel for respiration ultimately comes from photosynthesis
All organisms have the ability to harvest energy from organic molecules
Plants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis
Converts CO2 and H2O into organic compounds using light energy
Figure 6.18