Biosynthesis: An Enzymatic Process | Zoology Optional Notes for UPSC PDF Download

Understanding Biosynthesis

Anabolic Process of Metabolism

• Biosynthesis is an anabolic process within metabolism, focusing on the construction of larger, more complex molecules from simpler components.

• Sugar Biosynthesis:
  • Occurs through processes like the Calvin cycle in plants or gluconeogenesis.
• Protein Synthesis:
  • Achieved through translation.
• Lipid and Cholesterol Biosynthesis:
  • Essential for cellular structure and function.

Importance of Biosynthetic Products

• Cellular Activity: Biosynthetic products are essential for sustaining various cellular activities.
• Growth and Development: Integral for the growth and development of living organisms.
• Survival: Vital for the overall survival of organisms.

Research and Applications

• Biosynthesis is a significant area of scientific research.
• Involves in vitro synthesis using chemicals and recombinant methods in microorganisms utilizing enzymes and substrates.

Examples of Biosynthesis

• Definition: Involves the synthesis of biological compounds through non-light-dependent processes.

2. Photosynthesis

• Definition: Complex organic matter synthesis using water, carbon dioxide, light energy absorbed by chlorophyll, accessory pigments, and inorganic salts.

3. Nucleic Acid Synthesis

• Process: Involves the synthesis of RNA and DNA, essential for genetic information.

4. Amino Acid Synthesis

• Process: Synthesis of amino acids, which are further used to construct peptides and proteins.

5. ATP Synthesis

• Process: Production of adenosine triphosphate (ATP), serving as a primary energy source for cellular activities.

Biosynthesis encompasses a diverse range of processes, each playing a vital role in the intricate web of life processes and sustaining living organisms.

Key Features of Biosynthesis

1. Anabolism at Its Core

• Biosynthesis is fundamentally an anabolic process, focusing on the construction of complex macromolecules from simpler compounds.

2. Multi-Step and Multi-Enzymatic Process

• Biosynthesis involves a series of multistep and multi-enzymatic processes.

3. Organelle Involvement

• Occurs in one or multiple cell organelles, contributing to the synthesis of various cellular components.

4. Energy-Driven Process

• Biosynthesis is an energy-driven process, utilizing chemical energy obtained through the hydrolysis of high-energy phosphate groups, such as ATP.

5. Enzymatic Catalysis

• Multiple enzymes catalyze biosynthetic reactions, reducing activation energy and accelerating the rate of the reaction.
• Enzymes often require cofactors like metal ions or coenzymes for proper functioning.

6. Monomer Synthesis

• Biosynthesis involves the synthesis of monomers essential for constructing macromolecules.
• Examples include the synthesis of amino acids for protein formation and nucleotides for DNA and RNA synthesis.

7. Feedback Regulation

• Biosynthesis is meticulously controlled at each step through enzymatic activities regulated by feedback mechanisms.

Various Biosynthetic Processes 

Sugar Biosynthesis or CO₂ Fixation

• Importance:
  • Crucial for primary producers like plants to fix atmospheric carbon dioxide and form organic compounds, especially sugar.
• Steps:
  • Carboxylation or CO2 Fixation:
    • CO2 is fixed by RuBP (Ribulose bisphosphate) to form 3-PGA (3-phosphoglycerate) using the enzyme RuBisCO.
  • Reduction:
    • 3PGA is reduced to triose phosphates (G3P and DHAP), which further convert to Fructose, Glucose, Starch, or Sucrose.
  • Regeneration:
    • RuBP is regenerated to continue the cycle.

Gluconeogenesis

• Definition:
  • The synthesis of glucose from non-carbohydrate precursors, occurring in microorganisms, plants, fungi, and animals.

Protein Biosynthesis

• Translation Process:
  • Protein synthesis through translation from mRNA involves charging or aminoacylation of tRNA catalyzed by aminoacyl tRNA synthetase.

Steps:

• Initiation:
  • Ribosome binds to mRNA at the start codon, and initiator tRNA binds to the ribosome.
• Elongation:
  • Polypeptide chain elongation through peptide bond formation between the growing chain and the new amino acid carried by tRNA.
• Termination:
  • Binding of a release factor to stop codons terminates translation, releasing the polypeptide chain from the ribosome.

Biosynthesis encompasses a spectrum of processes, each contributing to the intricate fabric of life's molecular architecture.

Biosynthesis of Biomolecules

Amino Acid Biosynthesis

Amino Acid Classification
Essential vs. Non-essential:

• Humans cannot synthesize all amino acids.
• Non-essential amino acids are synthesized in the body.
• Essential amino acids must be obtained through diet.

Non-Essential Amino Acids

• Source:
  • Synthesized from various metabolic intermediates, such as those in the citric acid cycle.
• Examples:
  • Glutamate, Glutamine, Arginine, Proline.

Synthesis Pathways

1. Glutamate Synthesis:

   • Amination of α-ketoglutarate catalyzed by glutamate dehydrogenase.
   • Equation: ketoacid + glutamate ⇌ amino acid + α-ketoglutarate

2. Oxaloacetate Pathway:

   • Synthesis of lysine, methionine, asparagine, threonine, isoleucine.
   • Transamination of oxaloacetate to form aspartate.

3. Phosphoenolpyruvate (PEP) Pathway:

   • Synthesis of phenylalanine, tryptophan, tyrosine.

4. 3-Phosphoglyceric Acid (3PGA) Pathway:

   • Serine, glycine, cysteine synthesis.

5. Pyruvate Pathway:

   • Alanine, valine, leucine synthesis.

Nucleic Acid Biosynthesis

DNA Synthesis

• Location:

  • Takes place in the nucleus.

• Process:

  • Semiconservative replication catalyzed by DNA polymerase.

RNA Synthesis (Transcription)

• Enzyme:
  • RNA polymerase catalyzes the transcription process.

Nucleotide Structure

• Composition:
  • Nitrogenous bases, pentose sugar, phosphate.

Lipid Biosynthesis

Fatty Acid Synthesis

• Location:

  • Occurs in the cytoplasm.

• Initiation:

  • Begins from Acetyl-CoA using NADPH.

• Enzyme:

  • Catalyzed by fatty acid synthase.

Triglyceride Synthesis (Lipogenesis)

• Formation:
  • Three fatty acids combine with glycerol.

Phospholipid Synthesis

• Constituents:
  • Glycerol, two fatty acids, and a phosphorylated third hydroxyl group.

Cholesterol Biosynthesis

• Source:

  • Synthesized from Acetyl-CoA in the liver and intestines.

• Precursors:

  • Isopentenyl pyrophosphate, dimethylallyl pyrophosphate.

• Pathways:

  • Mevalonate pathway in animals, non-mevalonate pathway in plants and bacteria.

• Roles:

  • Precursor for Vitamin D and steroid hormones.

Regulation and Control

• Genetic and Neuroendocrine Control:

  • Strict regulation to produce specific and required compounds.

• Importance:

  • Errors in biosynthetic pathways may lead to disorders.

Fat Synthesis in Plants

• Glycerol Formation:

  • From dihydroxyacetone phosphate, an intermediate of glycolysis.

• Steps:

  1. Reduction of dihydroxyacetone phosphate to α–glycerophosphate.
  2. Oxidation of NADH2.
  3. Hydrolysis by glycerol phosphatase, forming glycerol.

• Fatty Acid Synthesis:

  • Long-chain saturated fatty acids synthesized from acetyl–CoA.

Biosynthesis is a tightly regulated process crucial for maintaining the balance of biomolecules, and its dysregulation can have profound effects on cellular functions.