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But, in the presence of Oxygen….
2. Cellular Respiration
• A series of metabolic pathways involving 3
separate phases:
• Krebs cycle
• electron transport system
• oxidative phosphorylation
• Oxidizes pyruvate to ATP & CO2
• Text pg 117
• So why is ATP so important?
ATP
Energy released by the oxidation (controlled burning) of carbohydrates and fats,
and energy harvested by photosynthesis in green plants, are channeled into
making the molecule adenosine triphosphate (ATP).
ATP is a high energy compound considered to be the universal currency of
biological energy. On reaction of ATP with water under closely controlled
conditions, a high energy bond is ruptured releasing energy, and producing
adenosine diphosphate (ADP) and phosphate.
This release of energy is usually coupled to other biological processes, to do
work, for example, in the contraction of muscle and in the synthesis of the
essential macromolecules of life, nucleic acids and proteins. The ATP molecule
is then remade from the ADP and phosphate with further input of energy.
The synthesis of ATP is a central process in human nutrition. The energy in the food
we ingest is converted into ATP. Each day every one of us of makes, breaks down
and remakes in the mitochondria in our bodies an amount of ATP that is about the
same as our body weights. The energy in the ATP molecule powers all biological
processes. Thus, the synthesis of ATP is essential for life.
Where in the cell does this occur?
Mitochondria
• double membrane
bound organelle
• site of aerobic cellular
respiration
• source of cellular
energy
Mitochondria: Structure
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Outer membrane
Intermembrane space
Inner membrane (with folds called cristae)
Matrix
Text Pg. 68
The Mitochondrion
Outer Membrane
Intermembrane space
Inner Membrane
Matrix
Cristae
Outer Membrane
(& Intermembrane space)
• permeable to small molecules (to ~10,000 MW)
• contains transmembrane pores (porins)
which allow these molecules to pass
• composition of intermembrane space closely
matches cytoplasm
Inner Membrane
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highly folded into “cristae”
folds greatly increase surface area
relatively impermeable to solutes
surface facing matrix lined with small
lollipop-like particles (F1 particles)
F1 Particles
• about 9 nm in diameter
• 10,000 to 100,000 per
mitochondria
• face matrix side of inner
membrane
• contain ATP synthase
enzyme
• couples oxidation
reactions with
phosphorylation to
Plant chloroplast F1 particles (ATP synthase)
produce ATP
visualized at room temperature using atomic
force microscopy
F1 Particles = ATP Synthase
• Protein particles
which embed in inner
mitochondrial
membrane and face
matrix
• Actual site of ATP
production in
mitochondria
F1
F0
Matrix
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•
inner space of mitochondria
rich in proteins
contains ribosomes (70S) and DNA
derived from endosymbiotic prokaryote??
site of oxidative metabolism (Krebs cycle)
Krebs
KK
Cycle
ETC
ATP
KK
NADH
Krebs
KK
Cycle
NADH
ATP
KK
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•
10 enzymes act in sequence to:
Convert 1 Glucose (6C) --> 2 Pyruvate (3C)
2 ATP’s produced
2 NADH produced
Reactions occur in cytoplasm
Next…
Krebs
KK
Cycle
KK
Pyruvate moves to Mitochondria
and is oxidized to Acetyl-CoA
Glycolysis & A-CoA Production
glucose 6C
2 NADH
In Cytoplasm
In Mitochondria
pyruvate 3C
NADH
CO2
Acetyl CoA 2C
2 ATP
Next, Acetyl- CoA enters the Krebs Cycle
Text pg 123
acetyl CoA 2C
Oxaloacetate 4C
citric acid 6C
NADH
NADH
CO2
Malate 4C
Fumarate 4C
a-Ketoglutarate 5C
FADH2
Succinate 4C
ATP
NADH
CO2
Succinyl CoA 4C
Krebs Cycle
• Acetyl CoA from pyruvate oxidation is the
main input to cycle
• A-CoA combines with 4C oxalo-acetate to
form 6C citrate
• subsequent reactions produce molecules with
5C and 4C… causing the release of CO2
molecules each time
• Additionally, these reactions produce NADH,
FADH2 and ATP
Krebs Cycle
• For each A-CoA going into Krebs… 3 NADH,
1 FADH2, 1 ATP & 2 CO2 are produced
• The 2 CO2 molecules released in the cycle
convert 6C citrate back to 4C molecules and
result in 4C oxaloacetate to renew the cycle
• Note: 2 A-CoA are produced for each
glucose consumed!
Respiration and ATP
How many ATPs have we produced so far
from 1 glucose molecule?
• 2 ATP from glycolysis
• 2 ATP from Krebs Cycle
• Both termed substrate-level phosphorylation
• Krebs, so far, has doubled ATPs from Glycolysis
• But, not over yet..…
Remember the NADH
& FADH2 Produced?
And, the 2 NADH from Glycolysis
NADH, FADH2
Production in Mitochondria
• Each Pyruvate to Acetyl-CoA = 1 NADH
2 Pyruvates (from glucose) = 2NADH
• Each Acetyl-CoA in Krebs = 3 NADH & 1
FADH2
2 Acetyl-CoA = 6 NADH & 2 FADH2
Total NADH & FADH2
• 2 NADH from Glycolysis
• 2 NADH from Pyr oxidation
• 6 NADH from Krebs
• Plus: 2 FADH2 from Krebs Cycle
These Energy-Rich Molecules
pass on e- to an
Electron Transport Chain
Along this ETC, new ATP is synthesized from the
energy-rich NADH and FADH2 molecules…