CHAPTER 2

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 Metabolic Pathway

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

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.

Metabolic Pathways

Even the same species may produce different product when grown under different nutritional and environmental regulation.

Example: Saccharomyces cerevisiae (baker’s yeast)

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.

Characteristics of metabolism:1. Varies from organisms to organism2. Effected by environmental condition.

Condition Product

anaerobic ethanol

aerobic Yeast cells

aerobic (high glucose conc.) ethanol

Glucose glycogen

~ produce energy to the cell

~ requires energy

-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

Photosynthesis by autotrophs :CO2 + H2O → carbohydrates

Anabolism requiring energy

Catabolismgenerating energy,e.g ATP

Autotrophsor heterotrophs

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

Aerobic metabolismAnaerobic metabolism

Tricarboxylic acid (TCA)or (Krebs)or (Citric acid cycle)(pyruvate is converted to CO2 +NADH)

Oxidative phosphorylation

Glycolysis orEmbden-Meyerhof-Parnas (EMP)

Fermentation: ethanol, acetic acid, lactate.

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

•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

Why 36 ATP?

Control sites in aerobic glucose metabolism• Several enzyme in glycolysis and Krebs cycle are regulated

by feedback inhibition.• In glycolysis,

fructose-6-phosphate + ATP fructose-1,6- diphosphate + ADP• At high ATP/ADP ratios,phosphofructokinase is inactivated• Effect of Oxygen concentration- Pasteur effect • Inhibition is important to alter cellular metabolism

phosphofructokinase

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 hydrocarbone.g. octane, C8H18

polyethylene –HC=CH-- Aromatic hydrocarbon

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 limitedPseudomonas, Mycobacteria

naphthalene

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

2.Dark phase

The overall reaction:6CO2 + 6H2O + light → C6H12O6 + 6O2.

ATPHNADPHoxygenADPPOH i2 NADP

PiADPNADPecosglu6/1ATPHCO2 NADPH

1

4

5

2

6

3