1. Chapter 9: Cellular Respiration

2. Cellular Respiration Living cells require energy from outside sources
Organisms use glucose (C6H12O6) as their main energy source
Cellular respiration is the process of breaking down food molecules to release energy (as ATP)
Energy is released in the process of respiration when the cells of plants and animals convert sugar and oxygen into carbon dioxide and water

3. Respiration The breakdown of organic molecules is exergonic
Aerobic respiration consumes organic molecules and O2 and yields ATP (oxygen required)
Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 (no oxygen required)
Fermentation is a partial degradation of sugars that occurs without O2

4. 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)

6. Redox Reactions
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is used to make ATP
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)
In cellular respiration, the glucose is oxidized and O2 is reduced

7. NAD+
In cellular respiration, glucose and other organic molecules are broken down in a series of steps
Electrons from organic compounds are usually first transferred to NAD+ (nicotinamide adenine dinucleotide), a coenzyme
As an electron acceptor, NAD+ functions as an oxidizing agent
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
NADH passes the electrons to the electron transport chain

8. Electron Transport Chain
Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction
O2 pulls electrons down the chain in an energy-yielding tumble
The energy yielded is used to regenerate ATP

9. Stages of Cellular Respiration
Glycolysis - Anaerobic (breaks down glucose into two molecules of pyruvate)
Citric Acid Cycle - Aerobic (Kreb’s Cycle - completes the breakdown of glucose)
Oxidative phosphorylation - Aerobic (ETC - accounts for most of the ATP synthesis)

10. Mitochondria 1) Glycolysis Cytoplasm 2) Citric Acid Cycle
Matrix of mitochondria
3) Oxidative Phosphorylation (ETC)
Cristae of mitochondria

12. Step 1: Glycolysis “Splitting of sugar”
Breaks down glucose (C6H12O6) into two molecules of pyruvic acid - AKA pyruvate (C3H4O3)
Anaerobic
Occurs in the cytoplasm
NAD picks up H+ and electrons to form NADH2

13. STEP 1 - TWO Phosphates are attached to Glucose, forming a NEW Six-Carbon Compound.  The Phosphate Groups come From TWO ATP, which are Converted to ADP.
    STEP 2 - The Six-Carbon Compound formed in Step 1 is SPLIT into TWO Three-Carbon Molecules of PGAL.
    STEP 3 - The TWO PGAL Molecules are Oxidized, and each Receives a Phosphate Group Forming Two NEW Three-Carbon Compounds.  The Phosphate Groups are provided by Two molecules of NAD+ forming NADH.
    STEP 4 - The Phosphate Groups added in Step 1 and Step 3 are Removed from the Three-Carbon Compounds.  This reaction produces Two molecules of Pyruvic Acid.  Each Phosphate Group is combines with a molecule of ADP to make a molecule of ATP.  Because a total of Four Phosphate Groups were Added, FOUR MOLECULES OF ATP ARE PRODUCED.
TWO ATP Molecules were used in Step 1, but FOUR are Produced in Step 4.  Therefore, Glycolysis has a NET YIELD of TWO ATP Molecules for every Molecule of Glucose that is converted into Pyruvic Acid.  What happens to the Pyruvic Acid depends on the Type of Cell and on whether Oxygen is present

14. Glycolysis Summary Location: Cytoplasm Products 2 Pyruvates (3-C)
2 NADH
4 ATP total
** 2 ATP NET since 2 are used initially
Reactants
Glucose (6-C)
2 NAD+
2 ATP
Simple Summary
Summary total

15. Bridge Reaction
In the presence of O2, pyruvate enters the mitochondrion
Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis
In the mitochondria matrix…
1) Pyruvic Acid loses a C to form acetic acid (2-C)
2) The lost carbon binds with O2 making CO2
3)Acetic acid binds with Coenzyme-A forming Acetyl Co-A
The lost carbon binds with O2 making CO2

16. Step 2: The Kreb’s Cycle (Citric Acid Cycle)
Takes place within the mitochondrial matrix
There are 8 steps, each catalyzed by a specific enzyme
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate (4-C molecule), forming a 6-C molecule known as citric acid (citrate)
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle

17. Step 2: The Kreb’s Cycle (Citric Acid Cycle)
2 molecules of CO2 are released
NAD+ and FAD (flavin adenine dinucleotide - another ion carrier) pick up electrons and H+ becoming NADH and FADH2
The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain
The cycle generates 1 ATP, 3 NADH, and 1 FADH2 per turn
Recall that two molecules of pyruvate are formed during glycolysis resulting in two turns of the Kreb’s cycle for each glucose molecule!

19. Kreb’s Cycle Summary Products 8 NADH (2 from transition) Reactants
Location: Mitochondrial Matrix
Products
8 NADH (2 from transition)
2 FADH2
2 ATP
6 CO2 (2 from transition)
Reactants
2 Acetyl Co-A
Kreb’s Summary
Kreb's Summary 2

20. Step 3: Electron Transport Chain (ETC)
Aerobic process
Requires oxygen as the final electron acceptor
Takes place in the cristae of the mitochondria
A series of molecules that excited electrons pass along, to release energy as ATP
Most of the chain’s components are proteins, which exist in multiprotein complexes

21. Step 3: Electron Transport Chain (ETC)
Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food
These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
The carriers alternate reduced and oxidized states as they accept and donate electrons
Electrons drop in free energy as they go down the chain
They are finally passed to O2 (final electron acceptor), forming H2O

22. NADH and FADH2
Dump the electrons and protons they’ve gathered throughout glycolysis and the citric acid cycle
Again, oxygen is the final electron acceptor
O e H+  H2O
Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2
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
ETC uses chemiosmosis to generate large amounts of ATP

23. Chemiosmosis ETC Summary
Electron transfer in the ETC causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
H+ then moves back across the membrane, passing through channels in ATP synthase (enzyme that acts like an ion pump)
ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ADP
This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work
The H+ gradient is called the proton-motive force
ETC Summary

24. ETC

25. The bulk of ATP is made in the ETC!!
ETC Summary
Location: Cristae of Mitochondria
Reactants
10 NADH
2 FADH2
Product
34 ATP
Each NADH makes 3
Each FADH2 makes 2
The bulk of ATP is made in the ETC!!
Simpler ETC Summary
Best ETC Summary

26. Whole Respiration Process

27. Total ATP from 1 molecule of glucose in AEROBIC CONDITIONS
Total Energy
~38 ATPs per 1 glucose broken down
Total ATP from 1 molecule of glucose in AEROBIC CONDITIONS   
Stage ATP
+ 4 Total
Glycolysis NET (b/c 2 are used in the first step)
CA Cycle
ETC _________________
TOTAL  + 38
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 38 ATP

29. Fermentation 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
Fermentation uses phosphorylation instead of an electron transport chain to generate ATP
2 Types:
Lactic Acid Fermentation
Alcohol Fermentation

30. Lactic Acid Fermentation
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
As the lactate is produced in the muscles it leaks out into the blood and is carried around the body. If this condition continues the functioning of the body will become impaired and the muscles will fatigue very quickly. This point is often measured as the lactic threshold or anaerobic threshold or onset of blood lactate accumulation (OBLA). When oxygen becomes available the lactic acid is converted to pyruvic acid and then into carbon dioxide, water and ATP.
The process of lactic acid removal takes approx. one hour, but this can be accelerated by undertaking an appropriate warm down which ensures a rapid and continuous supply of oxygen to the muscles.

31. Lactic Acid Fermentation
Example: Burning feeling in muscles during a workout
From oxygen debt
Aerobic respiration cannot occur
Lactate builds up in muscles leaks into blood
As the lactate is produced in the muscles it leaks out into the blood and is carried around the body. If this condition continues the functioning of the body will become impaired and the muscles will fatigue very quickly. This point is often measured as the lactic threshold or anaerobic threshold or onset of blood lactate accumulation (OBLA). When oxygen becomes available the lactic acid is converted to pyruvic acid and then into carbon dioxide, water and ATP.
The process of lactic acid removal takes approx. one hour, but this can be accelerated by undertaking an appropriate warm down which ensures a rapid and continuous supply of oxygen to the muscles.

32. Alcohol Fermentation
In alcohol fermentation, pyruvate is converted to ethanol (type of alcohol) in two steps, with the first releasing CO2
Bacteria and fungi (yeast)
Alcohol fermentation by yeast is used in brewing, winemaking, and baking

33. Fermentation
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
Review

34. Role of Macromolecules
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration
Glycolysis accepts a wide range of carbohydrates
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

35. Regulation of Cell Respiration
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

36. Review Questions
Define cellular respiration and state its importance as a life process.
Differentiate between aerobic respiration, anaerobic respiration, and fermentation.
State and explain the chemical equation for cellular respiration.
Define oxidation and reduction and explain the idea of redox reactions.
Explain the use of NAD+ as a coenzyme.
Explain the electron transport chain (ETC).
Name the 3 major stages of cell respiration, along with their locations.
Explain glycolysis, stating the reactants, products, and major activities.
Explain the bridge reaction, stating the reactants, products, and major activities.
Explain the Kreb’s cycle, stating the reactants, products, and major activities.
Explain the ETC, stating the reactants, products, and major activities.
Explain the role of oxygen in the ETC.
Define chemiosmosis and explain its role in cellular respiration.
Differentiate between lactic acid fermentation and alcohol fermentation.
Differentiate between oblicate anaerobes and facultative anaerobes.
Explain the role of macromolecules in cellular respiration.
Explain how cell respiration is regulated.