1. Cellular Respiration: Harvesting Chemical Energy
Chapter 9

2. Energy in Natural Systems
Energy stored in organic molecules (food) ultimately comes from the sun

3. Catabolic Pathways and ATP
Organic compounds have potential energy because of the arrangement of their atoms
Compounds in exergonic reactions can be seen as fuels
Some of those fuels can be used to do cellular work and some is lost as heat

4. Catabolic Pathways and ATP
Aerobic Respiration – oxygen is consumed as a reactant along with the sugar
Most prevalent and efficient
Most eukaryotes and some prokaryotes
C6H  6CO2 + 6H2O + Energy (ATP + Heat)
Glucose is fuel used most often (can also be fueled by other carbs, lipids, etc.)
Exergonic reaction

5. Catabolic Pathways and ATP
Anaerobic Respiration – an item other than oxygen in consumed
Fermentation – catabolic process that partially degrades sugar without the use of oxygen
Yeast
Cellular Respiration – includes both aerobic and anaerobic respiration
These catabolic pathways regenerate ATP to complete cellular work

6. Redox Reactions
Redox reactions occur during a chemical reaction when one reactant transfers electrons to another reactant
Oxidation – the loss of electrons from one item (the electron donor is called the reducing agent)
Reduction – the addition of electrons to another (the electron acceptor is called the oxidizing agent)
Some redox reactions change the degree of sharing in covalent bonds

7. Redox Reactions

8. Redox Reactions
Those items that are more electronegative will be stronger oxidizing agents (ie. Oxygen)
Energy must be added to pull an electron away
More energy is required the more electronegative the atom
The move of an electron towards a more electronegative item decreases the amount of potential energy and releases chemical energy that can be put to work

9. Redox Reactions In biology, cellular respiration is a redox reaction
Glucose is oxidized to carbon dioxide
Oxygen is reduced to water
The oxidation of glucose transfers electrons to a lower energy state, liberating energy that is now available for ATP synthesis
Hydrogen is an excellent source for these electrons; therefore carbohydrates and fats are our best fuel sources

10. Respiration and Electrons
Cellular respiration oxidizes glucose and other organic fuels through several steps where each is catalyzed by an enzyme.
At key steps, electrons are stripped from the glucose via hydrogen atoms
Hydrogen is passed via an electron carrier (coenzyme) called NAD+ which acts as an oxidizing agent

11. Functioning of NAD+
NAD+ traps electrons via enzymes called dehydrogenases which remove Hydrogen atoms from the glucose (or other substrate) oxidizing it.
NAD+ receives 2 electrons and 1 proton (the other proton is released) creating NADH which helps to store energy for making ATP later

12. Electron Transport
Hydrogen atoms are harnessed via NADH for their electrons, but to help control the reaction between hydrogen (electrons) and oxygen an Electron Transport Chain is used.
Electron transfer from NADH to oxygen is exergonic
Electrons cascade down the chain from one carrier molecule to another; each step is slightly more electronegative

13. Cellular Respiration (Aerobic)
3 stages:
Glycolysis
The citric acid cycle / Krebs Cycle
Oxidative phosphorylation: Electron Transport Chain and chemiosmosis

14. Glycolysis Process of “splitting sugar” into 2 molecules of pyruvate
First the glucose is split into 2 3-carbon sugars which are then oxidized into pyruvate
Occurs in the cytosol
Begins cellular respiration (occurs in both aerobic and anaerobic pathways)

15. Glycolysis Can be split into 2 phases Energy Investment: uses 2 ATP
Energy Payoff: creates 4 ATP
uses substrate level phosphorylation
NAD+ gains electrons becoming NADH

16. Pyruvate and Acetyl CoA
Glycolysis only releases about ¼ of chemical energy stored in glucose. The rest is still in pyruvate.
In aerobic respiration, pyruvate will enter mitochondria and be converted to Acetyl CoA
Carboxyl oxidized releasing carbon dioxide
Two carbon fragment oxidized forming acetate and transferring electrons to NADH
Coenzyme A is attached to the acetate

17. Citric Acid Cycle / Krebs
Acetyl CoA has high potential energy
Pyruvate (2 per glucose) is broken down to 3 carbon dioxides
Produces 1 ATP per turn
Most energy is transferred to NAD+ and FAD
NADH and FADH2 are then transferred to the ETC

18. Electron Transport Chain
Collection of molecules embedded in the inner membrane of the mitochondria
Largely proteins, but also have prosthetic groups which are nonprotein compounds
Each component becomes reduced as it accepts electrons from its ‘uphill’ neighbor…. Each step down is more electronegative

19. Chemiosmosis
In the inner membrane of the mitochondria are many copies of the protein complex ATP synthase (ATP synthetase)
Enzyme that makes ATP from ADP
Power source for the ATP synthase is a difference in concentration of H+ on opposite sides of the mitochondrial membrane
This is chemiosmosis (referring to the flow of H+ across a membrane)

20. Chemiosmosis

21. Energy Yield

22. Anaerobic Respiration vs. Fermentation
Anaerobic Respiration – uses an electron transport chain, but does not use oxygen as a final electron acceptor
May use sulfate ion
Fermentation – harvests energy without using oxygen or an ETC
An extension of glycolysis that allows ATP to be continually made
Replaces NAD+ for glycolysis to continue

23. Fermentation Alcoholic – pyruvate is converted to ethyl alcohol
Releases carbon dioxide
Used in winemaking, brewing and baking
Bacteria (yeast)
Lactic Acid – pyruvate is reduced directly by NADH to form lactate
No release of carbon dioxide
Used to make yogurt and cheese
Fungi and bacteria

24. Beyond Glucose
Your body can use a variety of carbohydrates to complete cellular respiration
Must be broken down to glucose (monomer)
Proteins must be broken down to amino acids and amino groups must be removed
Fats broken into glycerol and fatty acid
Fatty acid must go through beta oxidation to break down

25. Feedback Mechanisms in Cellular Respiration