microbiology

1. Metabolism ; The sum of chemical
reactions in a cell
• Catabolic reactions are used for breaking down nutrients
– Exergonic
– Often hydrolysis reactions
– Example: Oxidation of glucose to CO2 and H2O
• Anabolic reactions are used for biosynthesis of cellular
components
– Endergonic
– Often dehydration syntheses
– Example: Synthesis of starch from glucose
• The terms catabolic and anabolic are applied to metabolic
pathways; Series of chemical reactions

3. Microbial Metabolism
Why is energy needed?
 maintain the structural integrity of the cell by repairing any damage to its constituents
 synthesize new cellular components such as nucleic acids, polysaccharides and
enzymes
 transport certain substances into the cell from its surroundings for the cell to grow and
multiply
 cellular movement.
Adenosine triphosphate in metabolism
• Catabolic reactions are coupled to dehydration synthesis of ATP from ADP and
phosphate
• Hydrolysis of ATP to ADP and phosphate is coupled to anabolic reactions

5. Central to the metabolic processes of any cell are enzymes.
Enzymes
Various Types of Prokaryotic
Energy Production Processes
 Fermentation
 Anaerobic Respiration
 Aerobic Respiration
 Lithotrophy: Lithotrophs are a diverse group of organisms using inorganic substrate to obtain
reducing equivalents for use in biosynthesis or energy conservation via aerobic or anaerobic
respiration
 Photoheterotrophy: Uses light for energy and cannot use carbon dioxide as their sole
carbon source.
 Anoxygenic photosynthesis: the phototrophic process where light energy is captured and
converted to ATP, without the production of oxygen
 Methanogenesis: Methanogenesis or biomethanation is the formation of methane by
microbes known as methanogens

6. Enzyme Structure
 Apoenzyme
 Protein
 Allosteric site
 Cofactor
 Metal ions
 Cu
 Zn
 Mg
 Fe
 Ca
 Co
 Mn
 Coenzyme
 Vitamins
 CoA
 NAD
 NADP
 FAD
 FMN
Create Holoenzyme with active site

7. Major classes of enzymes
Enzyme classification

8. Enzymes can be stopped
• Conditions that disrupt the 3D shape
• Acidic, alkaline, high salt, high temperature, etc.
• These conditions thus affect growth of cell also.
• Inhibitory molecules affect enzymes
• Competitive inhibitors
• Fit in active site but are not changed; prevent normal
substrate from binding, prevent reaction.
• Non-competitive inhibitors
• Bind permanently to active site or other site which
changes molecular shape; prevents reaction.
• Allosteric inhibitor: temporary binding, regulates.

9. Competitive Inhibition
 Both the substrate and the
inhibitor fit into the active
site, but the inhibitor isn’t
altered by the enzyme. As
long as the inhibitor is in
the active site, the
substrate cannot enter the
active site and react. The
more inhibitor molecules
that are present, the more
often one of them occupies
the active site

10. Allosteric sites
In allosteric site, inhibitor is not reacted, but causes a shape change in the
protein. The substrate no longer fits in the active site, so it is not
chemically changed either.

11. Competitive Inhibitors -compete
for the active site
 1. Penicillin
– competes for the active site on the enzyme
involved in the synthesis of the pentaglycine
crossbridge
 2. Sulfanilamide (Sulfa Drugs)
– competes for the active site on the enzyme that
converts PABA into Folic Acid
 Folic Acid - required for the synthesis of DNA and RNA

12. Non-competitive Inhibitors - attach to
an allosteric site

13. Enzyme lowers the activation energy

14. Environmental factors affect enzyme activity
Temperature
pH

15. Substrate concentration
Under conditions where the active sites of an enzyme population are not saturated, an
increase in substrate concentration will be reflected in a proportional rise in the rate of
reaction.
The Michaelis—Menten equation relates the rate of a reaction to substrate
concentration, [S]:
v = Vmax[S]
[S] + Km
Values of Vmax and Km are more easily determined experimentally by plotting the
reciprocals of [S] and V to obtain a straight line

16. Enzyme activity is influenced by substrate
concentration. The initial rate of reaction (vo)
is proportional to substrate concentration at
low values of [S]. However, when the active
sites of the enzyme molecules become
saturated with substrate, a maximum rate of
reaction (Vmax) is reached. This cannot be
exceeded, no matter how much the value of
[S] increases. The curve of the graph fits the
Michaelis–Menten equation. Km is the value
of [S] where v = Vmax
2 .
Some enzymes do not obey Michaelis–Menten kinetics. The activity of allosteric enzymes is
regulated by effector molecules which bind at a position separate from the active site. By
doing so, they induce a conformational change in the active site that results in activation or
inhibition of the enzyme. Thus effector molecules may be of two types, activators or inhibitors.

17. Principles of energy generation
How enzyme-catalysed reactions are involved in the cellular capture and utilisation of
energy.
The ‘cash’ of cellular metabolism is a compound called adenosine triphosphate (ATP).
ATP has a structure very similar to the nucleotides found in RNA, except it has two additional
phosphate groups

18. Oxidation Reduction reaction
As the lactate is oxidised, so the NAD+ in the coupled reaction is reduced.
It is said to act as the electron acceptor. NAD+/NADH is generally involved
in catabolic reactions, and NADP+/NADPH in anabolic ones.

19. Catabolic pathways in heterotrophs. Pathways for the catabolism of
proteins, nucleic acids and lipids as well as carbohydrates can all feed
into the tricarboxylic acid cycle

20. Embden–Meyerhof pathway, glycolysis is used for the metabolism of simple sugars
not just by microorganisms, but by most living cells
Entner–Doudoroff pathway, producing a mixture of pyruvate and glyceraldehyde-
3-phosphate
One molecule each of ATP, NADH and NADPH per molecule of glucose degraded
pentose phosphate pathway, sometimes known as the hexose monophosphate
shunt is an other option for glucose metabolism

22. The pentose phosphate pathway. Operating simultaneously with
glycolysis, the pathway serves as a source of precursors for other
metabolic pathways. The metabolic fate of intermediates is indicated in
italics. Circled numbers next to each molecule denote the number of
carbons