Metabolism of Bacteria

1. Ch 5
Microbial
Metabolism

2. Objectives:
• Differentiate between, anabolism, and
catabolism.
• Explain what is meant by oxidation–
reduction.
• Describe the chemical reactions of
glycolysis.
• Explain the products of the Krebs cycle.

3. Metabolism
The entire spectrum of chemical reactions
that carried out in the cell and hydrolyzed by
enzymes.
• Anabolism is related with the synthesis of
complex molecules and polymers from simpler
ones with consumption of energy.
• Catabolism is related with the breakdown of
polymers and molecules into simple forms
with the release of energy.

5. Energy Production:
Oxidation-Reduction Reactions
• Oxidation = removal of e
-
• Reduction = gain of e
-
Redox reaction =
oxidation reaction paired
with reduction reaction.

6. Oxidation-Reduction
In biological systems, the electrons are often
associated with hydrogen atoms.
Biological oxidations are often
dehydrogenations.

7. The Generation of ATP
Phosphorylation:
1. Substrate level phosphorylation: transfer of a
high-energy PO4
–
from another phosphorylated
compound to ADP.
2. Oxidative phosphorylation: transfer of electrons
from one compound (frequently NADH which acts
as an electron carrier)to another is used to
generate ATP by chemiosmosis.
3. Photophosphorylation: Associated with
photosynthesis), the electrons are obtained from
light-activated pigments

9. The energy generated by catabolic
reactions is utilized by the cells for:
 Biosynthetic processes
 Repair
 Transport of nutrients across the
cell membrane
 DNA replication
 Protein synthesis etc.

10.  Most of medically important
microbes are chemoheterotrophs
which catabolize organic compounds
(sugars, fats and proteins) to
release energy.
 The most common form of organic
compound used by microbes as
carbon and energy source are
complex carbohydrates.

11.  Complex carbohydrates
include:
• Starch
• Cellulose
• Oligosaccharides
• Tri and di- saccharides
made up of glucose units.
 These polymers are first
enzymatically broken down to
their monomer form, a six
carbon sugar called glucose.

12. Metabolic Pathways of Energy Production:
COH Catabolism
• Cellular respiration
– Aerobic respiration
– Anaerobic respiration
• Fermentation
The three steps of aerobic respiration
1.Glycolysis (oxidation of _____ to ______)
2.Krebs cycle (oxidation of acetyl CoA to ___)
3.Oxidative phosphorylation (e-
transport
chain)

13. Glucose is further broken
down by various pathways
with release of energy
which ultimately results in
the formation of energy
rich compounds like:
 ATP
 Reduced coenzymes (NADH, NADPH,
FADH2).

14. Embden-Meyerhof-Parnas (EMP) pathway
(Glycolysis)
 The most common pathway present in all
medically significant microbes.
 It is functional in the absence or presence
of oxygen.
 Involves ten enzyme-catalyzed reactions
located in the cytoplasm of the cells.
 Two reactions are energy driven and three
reactions release energy.

15.  Seven steps are reversible and three are
irreversible reactions involving (the pathways 1,
3, 10) hexokinase, phosphofructokinase and
pyruvate kinase.
 This pathway results in generation of pyruvate
(a 3-carbon sugar) and energy rich compounds
ATPs and NADPH.

18. TCA cycle
Under aerobic conditions pyruvate is further
catabolized into various intermediates via
enzymes of Krebs cycle, also called TCA cycle.
The latter cycle is present in many bacteria,
fungi, yeasts, algae and higher forms of
eukaryotic cells. Initially pyruvate is
decarboxylated to a two carbon compound as
shown under:

19. Acetyl CoA then enters TCA cycle by
combining with oxaloacetic acid to form citric
acid. The latter molecule is a six carbon
compound which gets converted into
oxaloacetic acid through a series of reduction
and decarboxylation reactions. The net
reaction of TCA cycle is as follows:

20.  TCA cycle is also a source of generating ATPs though in a
limited amount.
 TCA cycle should not be seen only as a catabolic pathway
but also as a major source of C4 and C5 intermediates which
are required for the synthesis of amino acids and
nucleotides.
 In contrast to fermentation reactions which occur in the
cytoplasmic matrix TCA cycle operates in the mitochondrial
complex in close proximity to respiratory cycle.
 The reduced coenzymes like NADH generated during TCA
cycle and other fermentation reactions produce ATPs once
they enter respiratory cycle.