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Cellular Respiration: Harvesting Chemical
Energy
A. P. Biology
Chapter 9
Mr. Knowles
Liberty Senior High School
How is burning a candle like a
respiring cell?
So why don’t we just burn sugar?
It’s all about capturing energy!
Different Strokes for Different Folks!
• Autotrophy- “self-feeding,” when organisms use energy from light and CO2 to synthesize organic molecules.
• Heterotrophy- “other-feeding,” use already made organic molecules obtained from other organisms, living or dead.
Oxidative Respiration
C6H12O6 + 6O2 --> 6CO2 + 6H2O + ENERGY (ATP)
720 kcal of energy /mole glucose at cell conditions
Oxidative Respiration• Catabolism of glucose into
carbon dioxide and water, releasing 720 kcal/mol glucose.
• Is a Four Step Process = Glycolysis + Oxidation of Pyruvate + Krebs Cycle + Electron Transport Chain
Oxidative Respiration• Redox reaction that releases
energy by repositioning electrons closer to oxygen atoms.
• Uses ATP to trap energy and NAD+ and FAD+ to transport electrons.
ATP is the Energy Currency of the Cell
Adenosine Triphosphate-stores ~12kcal/mol
Adenine
Deoxyribose
PO4
PO4
PO4
Oxidative Respiration
• Energy is harvested from glucose in a series of gradual steps, using NAD+ as an electron carrier.
1. Glycolysis• Occurs with or without oxygen.• Two Step Process:
Modifying Glucose (Steps 1-4)Removing Groups that Provide Energy
(Steps 5 -9).
Making ATP During Glycolysis
• Substrate-level Phosphorylation - transferring PO4 directly to ADP --> ATP.
• Kinases- phosphorylates, adds PO4 group to a substrate. Ex. Hexokinase
Each Step Uses a Specific Enzyme
• Isomerases- change substrates into isomers. Ex. Glucose-->Fructose, Phosphoglucoisomerase.
Each Step Uses a Specific Enzyme
• Dehydrogenases- oxidizes substrates. Ex. G3PDH
At the End of Glycolysis!• Glucose + 2 ADP + 2 Pi + 2 NAD+ --> 2
Pyruvate + 2 ATP + 2 NADH + 2H+ + 2 H20
• Each ATP = 12 kcal/mole of energy.• Inefficient capture of energy, only 3.5 % of
available energy in glucose.• Most remains in pyruvate.
What would a food chain look like if organisms could only
perform glycolysis? Are they alive today?
Answer: The Archaebacteria 3.5 billion
years ago and TODAY!
AutotrophsL
ight
Glycolysis ONLY 3.5%
Efficiency1st Order
Heterotroph
2nd Order Heterotroph? ?
Without Kreb’s and ETC…
• Food chains were not very complex; few trophic levels.
• Could support very few animals with such poor efficiency.
2. Oxidation of Pyruvate
• Pyruvate + NAD+ + CoA --> Acetyl-CoA + NADH
• Acetyl-CoA can now enter the third step-Krebs Cycle.
3. Krebs Cycle• Oxidation of Acetyl-CoA.
• Produce 2 ATP by substrate-level phosphorylation.
• Many electrons harvested for the 4th Step (Electron Transport Chain).
• 6 NADH + 2 FADH
• All that remains of the glucose is 6 CO2.
4. Electron Transport Chain
• Convert the energy from the NADH and FADH made in the first three steps and make ATP.
• A series of transfers from transmembrane proteins that are progressively more oxidative.
• Eventually tranferred to oxygen --> reducing it to water.
H FADH2
FAD++
4H+
2H2O
Animation of Electron Transport Chain
ATP Synthase
Finally, ATP!!!!!
Factors that Affect Aerobic Respiration
• Respiration Rate- How much O2 can be taken in?
• Activity Level.• Size of the Organism.• Age and Gender.• Ectothermic vs. Endothermic Organisms
Ectotherms Have Slow Metabolisms
Are there options to aerobic respiration?
Anaerobic Respiration (Fermentation)- without oxygen.
What process can you do without oxygen?
Without Oxygen…
• Living cells can only make ATP by glycolysis.
• Only 2 ATP/molecule of glucose.
• May run out of NAD+.
Two Kinds of Fermentation• Alcoholic Fermentation- converts
pyruvic acid (from glycolysis) and converts it into:
1. CO2,2. Ethyl alcohol,3. NAD+
• Replaces NAD+ so glycolysis can continue.
Alcoholic Fermentaion
Let’s ferment?
Demo: Home made wine!
Fermentation in a Whale!
Show me Lactic Acid Fermentation!
Lactic Acid Fermentation
H3C--C—C--OH
O O
H
H3C--C—C—OH
OH O
Pyruvic Acid Lactic Acid
NADH (H+) NAD+
Lactic Acid Fermentation• Converts pyruvic acid (from
glycolysis) into two products:1. Lactic Acid2. NAD+
• Replaces NAD+ so glycolysis can continue.
So now what?
What do we do with all of the lactic acid after
anaerobic respiration?
The Cori Cycle, pp. 976-977. Ch. 44 (old text)
After Prolonged Exercise…• O2 consumption remains high.• Extra O2 is called Oxygen Debt.• Some of the O2 is used to convert
Lactic Acid CO2 + H2O + ATP (brain, heart, some muscle).
• Some of the O2 is used to convert Lactic Acid Glucose (Cori Cycle).
Anaerobic
Glycogen
Cor
i Cyc
le
The Two Fates of Lactic Acid
• With O2 (aerobic conditions):
1. Brain, heart and some muscle fibers can convert it into ATP.
2. Liver can convert into glucose by the Cori Cycle.
Hunters and Lactic Acid Build Up!
Video: Built for the Kill- Swamp a hunting
cormorant.
Without OxygenNo O2
Alcoholic Fermentation
Lactic Acid Fermentation
Metabolism in an Ectotherm!
Lactic Acid in a Crocodile
Video: National Geographic- Supercroc
Other sources of energy!
Proteins and Fats!
Primary Structure
Preparing Amino Acids for Metabolism
Deamination
H2N To Glycolysis or Kreb’s
A Glycerol
Three Fatty Acids
Energy from FatC-C-C-C-C-C-C-C
C-C-C-C-C-C-C-C
C-C-C-C-C-C-C-C
C
C
CGlycerol
3 Fatty Acids
Pyruvate Beta Oxidation
Beta Oxidation
• The catabolism of fatty acids.
• The breakdown of fatty acids into 2-carbon pieces. (Acetyl groups).
Beta OxidationC-C-C-C-C-C-C-C (Fatty Acid)
C-C-C-C-C-C C-C (Acetyl)
ATP
ADP + Pi
C-C-CoA (Acetyl CoA)
Coenzyme A
Kreb’s Cycle
NAD+ + FAD+
NADH + FADH
What happens to the respiration rate if you
limit the number of calories?
Video: Scientific Frontiers-Never Say Die
(Calorie Restriction)
