Principles of Biology
Biology 101
Lake Tahoe Community College
Instructor: Sue Kloss
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Ch 9 – Cellular Respiration
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I. Cell respiration banks energy obtained from the food chain in ATP molecules.
A. C6H12O6 +O2 ---- CO2 + H2O + energy (ATP and heat)
II. Basic mechanisms of energy release and storage
A. cells use energy from electrons transferred from organic fuels to O2
1. energy is contained in the arrangement of electrons in chemical bonds
2. cell respiration taps the energy carried by the electrons in glucose
3. electrons are shuttled from molecules of hi energy to ones of low energy.
4. cell transfers energy from glucose to ATP
B. Hydrogen carriers like NAD+ shuttle electrons in redox reactions
1. oxidation-reduction, or redox
2. transfer requires donor and acceptor.
3. redox reaction: H + NAD+ -- NADH + H+
4. NADH is now an energy carrier w/ energy the cell can use
C. Redox reactions
1. Glucose is like an “electron bank”
2. NAD+ and dehydrogenase withdraw these electrons
3. NADH delivers electrons to an electron carrier molecule
4. NADH becomes NAD+ and is recycled in the cell
5. electron carrier gains electrons, which “Fall” down the cascade
6. electron carriers = electron transport chain
D. 2 mechanisms generate ATP
1. cells generate ATP by phosphorylation
2. chemiosmosis
3. substrate level phosphorylation
4. oxidative phosphorylation includes chemiosmosis
5. substrate level phosphorylation accounts for only a small % of the ATP a cell generates
III. Stages of cell respiration and fermentation
A. Respiration occurs in 3 main stages – Glycolysis, Krebs or Citric Acid Cycle, Oxidative Phosphorylation (ET&C)
1. it is continuous and all stages occur simultaneously
2. glycolysis and Krebs or Citric Acid cycle are exergonic
3. glycolysis occurs in the cell cytoplasm
4. Citric Acid or Krebs cycle in mitochondria
a. breaks pyruvic acid into CO2
5. small amt of ATP formed in CAC or Krebs cycle and glycolysis
6. main job of CAC and Glycolysis is to supply 3rd stage of respiration with electrons
7. 3rd stage of respiration is electron transport chain (etc)
a. etc obtains electrons from NADH
b. FADH2, reduced form of FAD
8. glycolysis and CAC are energy releasing stages - extract electrons from food molecules
a. glycolysis and CAC break these food molecules down
b. NAD+ and FAD temporarily capture the electrons and bring them to etc.
c. etc uses downhill flow of electrons from NADH and FADH2 to O2 to pump H+ ions across
membrane
d. this process stores the energy that the ATP synthase will use to make ATP
e. ATP synthase uses chemiosmosis of H+ ions diffusing down concentration gradient to
attach P to ADP
B. Glycolysis harvests chemical energy by oxidizing glucose into pyruvic acid
1. Glycolysis takes 10 chemical steps to turn glucose into pyruvic acid using substrate level phosphorylation
a. the Carbon skeleton of sugar is broken down
b. cell produces a net of 2 ATP molecules
c. 2 molecules of NAD+ are reduced to NADH
d. energy is consumed in the prep phase (2 ATP) and produced (4 ATP) in the energy payoff phase.
e. glycolysis is an ancient energy production system; all organisms use it.
g. 5% of energy in a glucose molecule is obtained from the 2 ATPs in glycolysis, 16% from NADH
less than 25% of energy stored in glucose is made available to a cell in glycolysis
2. Some details
C.
D.
E.
F.
a. ATP is needed to begin glycolysis
b. intermediates
c. the product of one step is the reactant for next step
d. 2 glyceraldehyde 3 phosphates (G3P) are produced at the end of the preparatory phase
e. ultimately, 2 molecules of pyruvic acid are formed for each glucose
Pyruvic Acid is groomed for CAC cycle
1. pyruvic acid diffuses from cytoplasm into mitochondria,
2. it must be altered (converted) to function in CAC.
a. it is oxidized while a molecule of NAD+ is reduced to NADH2
b. simultaneously CO2 is released, turning the substance to one with a 2 C skeleton
c. coenzyme A, a sulfer containing compound from Vitamin B, joins 2C compound to form
Acetyl CoA, hi energy fuel molecule
3. for each molecule of glucose that entered the cycle, 2 molecules of Acetyl Co A enter CAC.
CAC cycle completes oxidation of organic fuels, generates many molecules of NADH and FADH2
1. Coenzyme A helps 2C chain get into the cycle
2. each of these steps is catalyzed by a specific enzyme
3. the electrons are split off and used to reduce an electron carrier, the Cs are cast out as CO2
4. CAC cycle pays big energy dividends
5. each round of cycle produces one ATP by substrate level phosphorylation, 3 NADH, 2 FADH2.
6. Multiply that x 2 for each glucose molecule
Oxidative Phosphorylation
1. final stage of cell respiration is electron transport chain and chemiosmosis
2. mitochondria can use the energy stored in the H+ concentration to drive the reaction
3. electron transport chain of cell respiraton is built into the inner membrane.
a. all the folds of the christae provide increased surface area
4. electrons arrive having been carried by an NADH molecule.
a. Oxygen (O2) is the final electron acceptor
b. each Oxygen atom combines with 2 H’s to form H2O
5. Most carrier molecules are in the protein complexes which span the inner membrane
a. all carriers bind and release electrons in redox reactions
b. energy obtained from electron flow is used by protein complexes to actively transport H+
6. H+ ion gradient develops between the inner and outer membranes.
a. this concentration gradient stores potential energy
b. the H+ ions cross back to the other side via ATP synthase.
7. in this way, cell couples the exergonic proc. of chemiosmosis with the endergonic production of ATP
Fermentation is an anaerobic alternative to aerobic respiration
1. yeasts are fungi that typically perform aerobic respiration to obtain energy, 38 ATP/molecule of glucose
2. they can also survive anaerobically producing 2 molecules of ATP from a mol of glucose in glycolysis
3. this is very inefficient - in glycolysis, no O2 is necessary, but NAD+ is reduced to NADH
CHAPTER 9 OBJECTIVES
1. In general terms, distinguish between fermentation and cellular respiration.
2. Write the summary equation for cellular respiration. Write the specific chemical equation for the degradation of glucose.
3. Define oxidation and reduction.
4. Explain in general terms how redox reactions are involved in energy exchanges.
5. Diagram the role of NAD+ in cellular respiration.
6. In general terms, explain the role of the electron transport chain in cellular respiration.
7. Describe how the carbon skeleton of glucose changes as it proceeds through glycolysis.
8. Explain why ATP is required for the preparatory steps of glycolysis.
9. Identify the function of substrate-level phosphorylation and the reduction of NAD+ in glycolysis.
10. Diagram oxidation of pyruvate to acetyl CoA,; show molecules that are produced, and note how this process links glycolysis
to the citric acid cycle.
11. List the products of the citric acid cycle. Explain why it is called a cycle.
12. Describe how glucose is oxidized during cellular respiration.
13. Distinguish between substrate level phosphorylation and oxidative phosphorylation.
14. Diagram how the exergonic “slide” of electrons down the electron transport chain is coupled to the endergonic production of
ATP by chemiosmosis; where and how the cellular respiration electron transport chain creates a proton gradient.
15. Draw the structure and annotate with function of ATP synthase.
16. Summarize the net ATP yield from the oxidation of a glucose molecule.
17. State the basic function of fermentation.
18. Diagram the fate of pyruvate in alcohol fermentation and lactic acid fermentation.
19. Compare the processes of fermentation and cellular respiration.
Diagram the three stages of cellular respiration in the region of the eukaryotic cell where each stage occurs.
20. For each stange, include: reactants and products, relative amount of ATP produced, and electron shuttles in reduced AND
oxidized states.
21. Describe the evidence that suggests that glycolysis is an ancient metabolic pathway.