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CHAPTER 2
Major Metabolic Pathway
Major Metabolic Pathway
Introduction to metabolism and
bioenergetics.
Glucose metabolism: Glycolysis and TCA
cycle,
Respiration.
Metabolism of nitrogenous compounds
and hydrocarbons.
Overview of biosynthesis for small and
macromolecules, anaerobic and autotrophic
metabolism
.
Major challenges in bioprocess development:
 To select an organism that can efficiently
make a given product
Before 1980 only naturally occurring organisms
were available (wild type organism).
With the advent of genetic engineering, it is
possible to remove or add genes to an
organism to alter its metabolic functions in a
predetermined manner (metabolic
engineering)
It is important to understand the metabolic
pathways in natural organisms either to use
them directly or to metabolically engineer
them to make a desired, novel product.
OR
Metabolic Pathways
Metabolism: a complete set of chemical
reactions that occur in living cells, allowing
cells to grow and reproduce, maintain their
structures, and respond to their
environments.
Characteristics of metabolism:
1. Varies from organisms to organism
2. Effected by environmental condition.
Even the same species may produce different product when
grown under different nutritional and environmental
regulation.
Example: Saccharomyces cerevisiae (baker’s yeast)
Condition
Product
anaerobic
ethanol
aerobic
Yeast cells
aerobic (high glucose conc.) ethanol
This indicates metabolic regulation not only by oxygen , but
also by glucose. This effect is known as the Crabtree effect.
Therefore, control of metabolism is important in bioprocess.
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Glucose
produce energy to the cell
requires energy
glycogen
-Living cell require energy for biosynthesis,
transport of nutrient, motility and
maintainance.
-Energy is obtained from the catabolism of
carbon compounds (carbohydrate)
-Carbohydrates are synthesized from CO2
and H2O in the present of light by
photosynthesis.
It is the part of biochemistry concerned with the
energy involved in making and breaking of
chemical bonds in the molecules found in
biological organisms.
Bioenergetics
Sunlight
Autotrophs
or heterotrophs
Photosynthesis by autotrophs :
CO2 + H2O → carbohydrates
Catabolism
generating energy,
e.g ATP
Anabolism
requiring energy
Autotrophs and Heterotrophs
•Organisms are divided into autotrophs and
heterotrophs according to their energy pathways.
•Autotrophs are those organisms that are able to
make energy-containing organic molecules from
inorganic raw material by using basic energy
sources such as sunlight. Plants are the prime
example of autotrophs, using photosynthesis.
•All other organisms must make use of food that
comes from other organisms in the form of fats,
carbohydrates and proteins. These organisms which
feed on others are called heterotrophs.
Three major categories of metabolic reactions:
(I) degradation of nutrients (II) Biosynthesis of small
molecules (III) Biosynthesis of large molecules
• Energy is mainly stored or transferred by
adenosine triphosphate (ATP) ~
(contains high-energy phosphate bonds)
• Other energy carrying compounds
include GTP, UTP and CTP.
Glucose Catabolism
Glucose
Glycolysis or
Embden-Meyerhof-Parnas (EMP)
Aerobic metabolism
Anaerobic metabolism
Fermentation: ethanol,
acetic acid, lactate.
Tricarboxylic acid (TCA)
or (Krebs)
or (Citric acid cycle)
(pyruvate is converted to CO2 +NADH)
Oxidative phosphorylation
Glucose (6C) is broken down into 2 PGAL's (3C)
This requires two ATP's
2 PGAL's (3C) are converted to 2 pyruvates
This creates 4 ATP's and 2 NADH's
The net ATP production of Glycolysis is 2 ATP's
Respiration
• Respiration reaction sequence is also known
as electron transport chain
• oxidative phosphorylation- forms ATP
• Electron carried by NADH + H+ and FADH2 are
transferred to oxygen via a series og electron
carriers, forming ATP
• NADH + H+ results in 3 ATP
• FADH2 results in 2 ATP
Why 36 ATP?
•Glycolysis: 2 ATP
•Krebs Cycle: 2 ATP
•Electron Transport Phosphorylation: 32 ATP
•Each NADH produced in Glycolysis is worth 2 ATP (2 x 2
= 4) - the NADH is worth 3 ATP, but it costs an ATP to
transport the NADH into the mitochondria, so there is a
net gain of 2 ATP for each NADH produced in gylcolysis
•Each NADH produced in the conversion of pyruvate to
acetyl COA and Krebs Cycle is worth 3 ATP (8 x 3 = 24)
•Each FADH2 is worth 2 ATP (2 x 2 = 4)
•4 + 24 + 4 = 32
•Net Energy Production: 36 ATP
Control sites in aerobic glucose metabolism
• Several enzyme in glycolysis and Krebs cycle are
regulated by feedback inhibition.
• In glycolysis,
phosphofructokinase
fructose-6-phosphate + ATP
fructose-1,6diphosphate + ADP
• At high ATP/ADP ratios,phosphofructokinase is
inactivated
• Effect of Oxygen concentration- Pasteur effect
• Inhibition is important to alter cellular metabolism
Relation of Pasteur effect with glycolysis, Krebs cycle and electron transport chain?
Reading Assignment
• Metabolism of nitrogenous compounds
• Nitrogen fixation
• Metabolism of hydrocarbons
Hydrocarbon Catabolism
• Hydrocarbon: C & H
Aliaphatic hydrocarbon
e.g. octane, C8H18
polyethylene –HC=CHAromatic hydrocarbon
naphthalene
naphthalene
• Metabolism of hydrocarbon
Requires oxygen
Hydrocarbons are converted to acetyl-CoA which is
metabolized by TCA cycle.
Challenges : low solubility in aqueous solution.
available microorganisms are limited
Pseudomonas, Mycobacteria
Nitrogen Compounds Catabolism
• Nitrogen compounds can be used for C, N and energy
sources
• Proteins → peptides → amino acids → converted to
other amino acids or organic acids and ammonia by
deamination.
- organic acids: acetyl-CoA into TCA cycle, lipids
- amino acids: proteins, other amino acids or enter
TCA cycle
- ammonium: amino acid, protein, nucleic acids
• Nucleic acids → ribose/deoxyribose, phosphoric acid
and purine/pyrimidine
- sugar: glycolysis and TCA
- Phosphoric acid: ATP, lipids, nucleic acids
- bases: nucleic acids, urea, acetic acids
Anaerobic metabolism
Compare with
aerobic pathway?
Electron acceptor
Autotrophic metabolism
• Heterotropic growth – organic molecules
serve ac C source
• Autotrophs- obtain C from CO2
• Calvin cycle or Calvin-Benson cycle :provide
building blocks for autotrophic growth
• Energy: light (photoautotrophs) or chemicals
(chemoautotrophs)
Photosynthesis
Glycolysis and TCA
Phases in photosynthesis
• 2 phases:
1. Light phase
H 2O  NADP   Pi  ADP  oxygen  NADPH  H   ATP
2. Dark phase
CO2  NADPH  H   ATP  1 / 6 glu cos e  NADP   ADP  Pi
The overall reaction:
6CO2 + 6H2O + light → C6H12O6 + 6O2.
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