Biology 107
Cellular Respiration
September 30, 2005
Cellular Respiration II
Student Objectives: As a result of this lecture and the assigned
reading, you should understand the following:
1.
Respiration occurs in two (2) stages: 1) the Krebs cycle (citric acid
cycle) and 2) the terminal electron transport chain.
2.
In eukaryotes these respiration reactions take place in
mitochondria.
3.
Some enzymes of the Krebs cycle are in the matrix of
mitochondria; other enzymes of the Krebs cycle and the enzymes
of the electron transport system are in the membrane of the
cristae of the inner membrane. The outer membrane is relatively
permeable, while the inner membrane restricts passage of most
molecules and ions, including protons (H+ ions).
Cellular Respiration II
4.
Compared to glycolysis, the Krebs cycle pays off big energy
dividends to the cell.
a. Each turn of the cycle makes 1 ATP molecule (by substrate
level phosphorylation) and 4 other energy-rich molecules
(3NADH and 1 FADH2).
b. Since two molecules of acetyl CoA are processed for each
glucose precursor, the total yield is 2ATP, 6NADH, and 2
FADH2 (compared to the total of 2ATP and 2NADH molecules
of glycolysis).
5.
No oxygen is required for the Krebs cycle.
Cellular Respiration II
6.
After the Krebs cycle is completed, glucose is completely
oxidized, but most of the energy is stored in electrons moved from
carbon atoms to the electron carriers NAD+ and FAD.
7.
In terminal electron transport, the high energy electrons stored in
the NADH and FADH2 carriers are passed step-by-step to
successively lower energy carriers embedded in the inner
membrane of the mitochondrion until the electrons are finally
accepted by the low energy level oxygen atom.
8.
As the electrons are passed down the electron transport chain, H+
are transported from the matrix across the inner mitochondrial
membrane to the intermembrane space and a concentration
gradient of hydrogen ions is produced.
Cellular Respiration II
9.
The theory of chemiosmotic coupling explains how the
concentration gradient of H+ is used to generate energy to make
ATP.
a. The enzyme complex ATP synthase synthesizes ATP using the
energy stored in the concentration gradient of H+ ions (i.e.,
protons) across the inner membrane, which is relatively
impermeable to H+.
b. The H+ ions tend to move down their concentration gradient
toward the matrix of the mitochondrion. Movement through the
ATP synthase is used to generate the ATP from ADP and
inorganic phosphate.
10.
The process of generating ATP from the electron transport chain
is called oxidative phosphorylation.
Cellular Respiration I
11.
Fats, complex carbohydrates, and proteins may be funneled into
glycolysis or the Krebs cycle. The most common convergent
point is acetyl CoA.
12.
In prokaryotic cells (which lack mitochondria) the oxidative
reactions are distributed between the cytoplasm and the plasma
membrane.
Aerobic Respiration Occurs in the Eukaryotic
Mitochondrion and Includes the Krebs Cycle
and the Electron Transport Chain/Oxidative
Phosphorylation
Pyruvate is Converted into Acetyl
CoA to Enter the Krebs Cycle
Pyruvate is Transported into the
Mitochondrion and Converted to
the 2-Carbon Acetyl CoA
Steps of the Krebs Cycle
General Organization
of the Electron
Transport Chain
Electron Transport Chain
Establishes a H+ Gradient Across
the Inner Membrane
The
Movement of
H+ Down Its
Concentration
Gradient
Generates
ATP
Summary of Cellular Respiration
Catabolic Pathways
Catabolic
Pathways
Example of
Regulation
Mechanisms
for Catabolic
Pathways