Biosynthetic studies and Basic Metabolic Pathways 

T. Y. B. Pharm (Sem –V)

Unit -I

What is Biosynthesis?

Biosynthesis is a process of forming larger organic compounds from small subunits within a living organism.

Biosynthesis is mainly done by enzymes.
Biosynthesis is also known as anabolism since simple compounds are joined together to form macromolecules by enzymes.

As an example, photosynthesis occurs inside the chloroplast.
The light energy is converted into chemical energy during photosynthesis.
The larger molecule glucose is biosynthesized from water and CO2 by photosynthetic organisms.(ATP, Enzyme, Cofactors).
Photosynthesis

Two sets of reactions:

Light Harvesting:

converts light energy to chemical energy (ATP, NADPH) Reduce NADP+ to NADPH
Generate ATP from ADP by photo phosphorylation
Splits H2O and  produces O2 as by product.

Carbon Fixing:

Uses ATP and NADPH from light reactions to fix CO2 into sugar
The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules.






What is the Difference Between Synthesis and Biosynthesis?

Biosynthesis of Primary Metabolites

Living plants are solar-powered biochemical & biosynthetic laboratory which manufactures both primary & secondary metabolites from air, water, minerals and sunlight.

Metabolites are organic compounds synthesizes by organisms using enzyme-mediated chemical reactions called metabolic pathways. OR

The reaction sequence occurring with in the organism in an orderly & regulated way known as metabolic pathways.
Example:
          


The primary metabolites like sugars, amino acids & fatty acids that are needed for general growth & physiological development of plant which distributed in nature & also utilized as food by man.

The secondary metabolites such as alkaloids, glycosides, Flavonoids, volatile oils etc are biosynthetically derived from primary metabolites.
Biosynthetic reactions are replica of common organic reactions like catalytic reactions, phosphorylation, hydride transfer, oxidation, elimination, acylation, alkylation, reduction, condensation, rearrangement etc.



             Fig.Plant metabolism

Metabolism & Metabolic Pathways:
Cell Metabolism: Process by which living cell process nutrient molecule & living state.
Metabolic Pathway: 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.
Living cell require energy for biosynthesis, transport of nutrient, motility and maintenance.
Energy is obtd. from the catabolism of carbon compd (carbohydrate).
Carbohydrates are synthesized from CO2, and H2O in the present of light by photosynthesis.
          
Types of Metabolism:
Catabolism: Metabolic reactions in the cell that degrade a substrate into smaller / simpler products.
                              produce energy to the cell

         Glucose → CO2
Anabolism: Metabolic reactions that result in the synthesis of larger /more complex molecules.
                               requires energy
                              glucose to glycogen 

Major Metabolic Pathways:

Cellular respiration:
Glycolysis
Anaerobic respiration
Kreb's cycle / Citric acid cycle, TCA cycle
Oxidative phosphorylation
Creation of energetic compounds from non-living matter:
Photosynthesis (plants, algae cynobacteria)
Chemosynthesis (some bacteria) 

Other pathways occurring in (most or) all living cell:
Fatty acid oxidation (Beta-oxidation)
Gluconeogenesis
HMG-COA reductase pathway (isoprene prenylation)
Pentose phosphate pathway (hexose monophosphate)
Porphyrin synthesis (or heme synthesis) pathway
Urea cycle 
Metabolites
Metabolites are the intermediates & products of metabolism.
The term metabolite is usually restricted to small molecules.
A primary metabolite is directly involved in the normal growth, development and reproduction.
A secondary metabolite is not directly involved in those processes, but usually has important ecological function. 

Importance of photosynthesis in formation of primary metabolites

Photosynthesis is the process where plants convert sunlight into energy, then store it as carbohydrates, sugars, such as glucose.

Photosynthesis may be the most important process in ecosystems, both brings in energy needed within the ecosystem, & produce oxygen (0) needed for cellular respiration, and the production of more ATP.
Photosynthesis has three basic steps:
1. Energy is captured from the sunlight.
2. Light energy is converted into chemical energy in the form of ATP and NADPH.
3. Chemical energy is used to power the synthesis of organic molecules (e.g. carbohydrates) from CO2.  

Photosynthesis

H2O+ light+ ADP + P ---> O2+ ATP+ e-

After the above steps occur in photosystem II , the electron is finally sent to photosystem I, where the following happens.  
 e- +NADP+ H --->NADPH

Now there are two high energy molecules, fully charged and ready to be used. Plants Make more energy that it needs immediately, so the NADPH and ATP are used to make glucose as follows:   

CO2+ ATP+ NADPH ---> C6H12O6

This happens in Calvin cycle.

Calvin Cycle

The Calvin cycle is the last step in photosynthesis.
The purpose of the Calvin Cycle is to take the energy from photosystem I and fix carbon. Carbon fixation means building organic molecules by adding carbon onto a chain. The following formula summarizes the Calvin cycle.
C5+ CO2+ ATP + NADPH   -----➜        C6H12O6

Where C5; is a five carbon molecule, such as pyruvate, when is recycled as glucose is synthesized.

The first step in the Calvin cycle is for the 3C5 to bind with 3CO2,
producing a six 3-carbon organic molecules (6C3).

Next, 6ATP and 6NADPH energizes the binding of a C3 to make a 6-carbon molecule (C6), glucose.
The remaining 5C3 continues moving through the Calvin cycle, being tuned back into the starter C5 organic molecule.  

Carbohydrate Utilization

Storage carbohydrate such as the starch of plants or the glycogen of animals is made available for energy production by a process.

As a result of this, the energy-rich carbohydrate is eventually oxidized to C02 and H2O.

During the process, the hydrogen atoms liberated are carried by coenzymes into the cytochrome system, in which energy is released in stages, with the possible formation of ATP and ADP and inorganic phosphate.
Eventually the hydrogen combines with oxygen to form water.

The overall reaction of glucose in terms of ADP and ATP is

C6H12O6+ 6CO2 + 38 ADP + 38P (inorganic) 6H2O + 6CO2+ 38 ATP      



Thank you

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