Download Microbial Metabolism

Microbiology for the Health Sciences
Metabolism: the sum of
all chemical reactions
that occur in a living cell
in order that the cell
sustains its life’s
processes
Catabolism: decomposition
reactions in a living organism,
the breakdown of complex organic
compounds into simpler
ones. Catabolic reactions makes
ATP
Anabolism: all synthesis reactions
in a living organism; the
building of complex organic
molecules from simpler ones.
Anabolic reactions use ATP.
Catabolism and Anabolism coupled
rxns
1. Digestion
2. Movement of nutrients across cell membrane
3. The oxidation of glucose into two pyruvic acid
molecules
This is also known as Glycolysis.
4. The complete oxidation of pyruvic acid into
carbon dioxide (CO2) and the formation of ATP.
This is represented by the Kreb’s Cycle and the
Electron Transport system
Enzymes needed to speed up chemical reactions
Exoenzymes: enzymes the cell uses to break down large
molecules outside of cell so can be transported across cell
membrane
Naming of enzymes substrate/enzyme
Main nutrient groups:
◦ Carbohydrates
◦ Proteins
◦ Lipids
Amylase
Protease
Lipase
Passive Diffusion: moves down concentration gradient
(requires No Energy)
Facilitated Diffusion: moves down a concentration gradient
uses carrier molecule (requires No Energy)
Active Transport: movement against concentration gradient
(requires Energy)
Endocytosis: (Eukaryotes) substance engulfed by cell
membrane
[INSERT FIGURE 5.12]
Beginning of oxidation glucose
to two pyruvic acid molecules
1 glucose molecule contains 6
carbons. In glycolysis, glucose
is broken down to 2, 3 carbon
molecules called pyruvate
Uses 2 ATP
Make 4 ATP
Net Energy is 2 ATP
2 ATP added to glucose (6C) to energize it.
Through 10 steps glucose is converted to two
pyruvate (3C), with energy transferred to make 4
ATP (substrate phosphorylation).
Although glycolysis makes 4 ATP, the net ATP
production by this step is 2 ATP (because 2 ATP
were used to start glycolysis). The 2 net ATP are
available for cell use.
If oxygen is available to the cell, the pyruvate will
move into the plasma membrane (P) or the
mitochondria & aerobic respiration will begin.
[INSERT FIGURE 5.18]
Pyruvic acid loses 1 molecule of
carbon in form of carbon dioxide in
preparatory step for Kreb cycle = 2
carbon compound called acetyl CoA
Kreb cycle results in the complete
oxidation of acetyl CoA to carbon
dioxide and formation of ATP
Carbon dioxide eventually released
from cell
2 ATP equivalents produced
H left with it’s corresponding electron
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Requires 2 cycles to metabolize glucose
Acetyl Co-A (2C) enters the Kreb's Cycle &
joins with Oxaloacetic Acid (4C) to make
Citric Acid (6C)
Citric acid is oxidized releasing CO2 , free
H+, & e- and forming ketoglutaric acid (5C)
Free e- reduce the energy carriers NAD+ to
NADH and FAD+ to FADH2
Ketoglutaric acid is also oxidized releasing
more CO2 , free H+, & eThe cycle continues oxidizing the carbon
compounds formed (succinic acid, fumaric
acid, malic acid, etc.) producing more CO2,
NADH, FADH2, & ATP

H2O is added to supply more H+

CO2 is a waste product that diffuses out of
cells
H’s need to be moved to where can be
useful
Carrier molecules NAD+ and FAD+ act as
shuttles to move H’s to plasma
membrane
NAD can carry 1 H and FAD can carry 2 H
H and corresponding electrons released
into plasma membrane
H pumped out of membrane and electron
passed down carrier chain inside
membrane
Nicotinamide Adenine
Dinucleotide
NAD can carry 1 hydrogen
NADH
Flavin Adenine Dinucleotide
FAD can carry 2 hydrogen
FADH2

Continuation of Cellular
Respiration
◦ Electron transport
 Most significant production of
ATP occurs through stepwise
release of energy from series of
redox reactions known as an
electron transport chain (ETC)
 Consists of series of
membrane-bound carrier
molecules that pass electrons
from one to another and
ultimately to final electron
acceptor
 Energy from electrons used to
pump protons (H+) across the
membrane, establishing a
proton gradient
 Located in cristae of eukaryotes
and in cytoplasmic membrane
of prokaryotes
Excess protons outside
membrane create potential
energy due to high positive
charge on one side of
membrane
Protons used to synthesize ATP
Then protons, electrons and
final electron acceptor, oxygen,
combine with oxygen to form
water
Oxidative Phosphorylation
NADH and FADH2 carry protons (H+) and
electrons (e-) tothe electron transport chain
located in the membrane.
The energy from the transfer of electrons along
thechain transports protons across the membrane
and creates an electrochemical gradient.
As the accumulating protons follow the
electrochemical gradient back across the
membrane through an ATP synthase complex, the
movement of the protons provides energy for
synthesizing ATP from ADP and phosphate.
At the end of the electron transport system, two
protons, two electrons, and half of an oxygen
molecule combine to form water.
Since oxygen is the final electron acceptor, the
process is called aerobic respiration.
Net result = 34 ATP from the
Electron Transport System
Note:
4 ATP were formed from
glycolysis and kreb cycle
Total ATP formed in prokaryotes
is 38 for each glucose molecule
ATP synthase, also called complex,
is the final enzyme in the oxidative
phosphorylation pathway.
This enzyme is found in all forms
of life and functions in the same
way in both prokaryotes and
eukaryotes.
The enzyme uses the energy stored
in a proton gradient across a
membrane to drive the synthesis of
ATP from ADP and phosphate (Pi).
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Found in the inner mitochondrial membrane or cristae
Contains 4 protein-based complexes that work in sequence
moving H+ from the matrix across the inner membrane
(proton pumps)
A concentration gradient of H+ between the inner & outer
mitochondrial membrane occurs
H+ concentration gradient causes the synthesis of ATP by
chemosmosis
Process
Glycolysis
Kreb’s cycle
Electron
Transport System
Begin with
2 ATP, glucose
2 pyruvate
H+, corresponding
electrons
End with
4 ATP, 2 pyruvate
6 carbon dioxide, H+
Water
Net Energy
2 ATP
2 ATP equivalents
34 ATP
[INSERT TABLE 5.3]
Terminal electron acceptor something other
than oxygen
Such as: Nitrate, nitrite, sulfate, or carbonate
Releases energy from sugars or other organic
molecules (amino acids)
Does not require oxygen
Does not require kreb cycle or electron transport chain
Uses organic molecule as final electron acceptor
Produces only small amounts of ATP
Examples of end products are lactic acid or ethanol

Fermentation
◦ Sometimes cells cannot
completely oxidize glucose by
cellular respiration
◦ Cells require constant source of
NAD+ that cannot be obtained
by simply using glycolysis and
the Krebs cycle
 In respiration, electron
transport regenerates NAD+
from NADH
◦ Fermentation pathways provide
cells with alternate source of
NAD+
 Partial oxidation of sugar (or
other metabolites) to release
energy using an organic
molecule from within the cell
as an electron acceptor
[INSERT TABLE 5.4]
[INSERT FIGURE 5.22]