Biology 107
Cellular Respiration
September 28, 2005
Metabolism Review
Energy Flow
in
Ecosystems
ATP Supplies Energy for Cellular
Work
Modes of ATP Synthesis
Substrate Phosphorylation
Enzyme transfers a
phosphate group from a
substrate to ADP
Oxidative Phosphorylation
Reactions result in the
transfer of electrons to O2.
This transfer of energy is
used to phosphorylate ADP
with free Pi.
Cellular Respiration Involves
Oxidation-reduction Reactions
oxidation
C6H12O6 + 6O2
6CO2 + 6H2O
reduction
Electrons lose potential energy along the way
Exergonic Reactions – Advantage
of Multistep Process in Transfer of
Energy to ATP
Summary of Multistep Reactions
Used to Generate ATP in
Eukaryotic Cells
Glycolysis Energy Scorecard
Structure of NAD+/NADH
eeH+
H+
Early Steps in Glycolysis
Later Steps in Glycolysis
Substrate Phosphorylation
Summary of
Net Products
of Gycolysis
Two ATPs
Two water molecules
Two NADHs (+2H+)
Two pyruvates
The electrons in the
NADHs can yield ATPs
through the electron
transport system, and
the pyruvate can be
metabolized in the
Krebs cycle.
In the Presence of Oxygen,
Pyruvates Enter the Mitochondrion
and are Oxidized
In the Absence
of Oxygen,
Pyruvates are
Fermented to
Liberate NAD+
Lactic Acid Fermentation
Compared to Alcohol Fermentation
Summary
Cellular Respiration I
Student Objectives: As a result of this lecture and the assigned
reading, you should understand the following:
1.
Cell release chemical energy by means of an exergonic process
called cellular respiration, the aerobic harvesting of energy from
food molecules by cells.
2.
Cellular respiration is the energy-releasing chemical breakdown of
molecules and the storage of energy from that breakdown in a
form (e.g., ATP) the cell can use to perform work.
Cellular Respiration II
3.
Normally there is an oxidation of the organic molecule causing the
hydrogen atoms (electrons and their accompanying protons) to be
removed from the carbon atoms and eventually combined with
oxygen (which is thereby reduced).
4.
In cellular respiration, the electrons go from higher energy levels
to lower energy levels, and energy is released. This energy is
released over many steps as electrons move to successively
lower energy levels. Some of that energy is lost as heat; a portion
of that energy (40%) is captured in the terminal phosphate bonds
of ATP.
5.
The efficiency in living systems is due to the fact that energy
release occurs over the course of a series of controlled reaction
steps.
Cellular Respiration I
6.
The harvesting of energy involves the rearrangement of electrons
in chemical bonds. The common theme is that a cell transfers
energy from one molecule to another by coupling an exergonic
reaction (energy-releasing) to an endergonic reaction (energystoring). The energy released was stored in the specific
arrangement of a molecule's covalent bonds, and the energy
stored is in the new covalent bonds formed.
7.
In summary, cellular respiration rearranges electrons in chemical
bonds. These are redox reactions. Because an electron transfer
requires both a donor and an acceptor, an electron leaves one
molecule only when it contacts another molecule that attracts it
more strongly.
8.
In respiration, there are two main coenzymes derived from B
complex vitamins. First is NAD+ ,(nicotinamide adenine
dinucleotide) which in part is derived from B3, niacin. The second
coenzyme is FAD (flavin adenine dinucleotide), which in part is
derived from B2, riboflavin.
Cellular Respiration I
9.
Glucose supplies energy to form ATP by two related processes: 1)
glycolysis and 2) cellular respiration. The products of glycolysis
are reactants used in respiration.
10.
In glycolysis ("splitting of sugar"), the 6-carbon glucose molecule
is split into two 3-carbon molecules, pyruvate. The net energy
harvested from the glycolysis reactions is in the form of ATP and
NADH.
a. This production of ATP in glycolysis is by the direct, enzymemediated transfer of a phosphate group from a substrate to
ADP by the mechanism called substrate phosphorylation. This
is different from electron transport (oxidative) phosphorylation,
which requires oxygen and a transport system.
b. Glycolysis occurs in the cytosol and does not require oxygen
(i.e., it is an anaerobic process).
Cellular Respiration I
11.
In the presence of oxygen, the pyruvates are fed into the second
stage of energy capturing, cellular respiration.
12.
In the absence of oxygen, the pyruvate is converted to either
lactic acid or ethanol. This conversion process is known as
fermentation, and it produces no ATP. Fermentation is a
mechanism for cells to replenish the supply of NAD+ that the cell
is using in glycolysis.
13.
The reactions of glycolysis follow essentially the same routes in
prokaryotes and eukaryotes, except the products of fermentation
are more varied under anaerobic conditions.