BIOL214 Protein Metabolism 1 Notes

BIOL214 Overview

  • Course Title: Biochemistry of Energy and Metabolism: Protein Metabolism Including the Nitrogen Web

  • Instructor: Prof. Ronald Sluyter

  • Subject Coordinator Contact: rsluyter@uow.edu.au

  • Textbook Reference: Lehninger Principles of Biochemistry, 8th Edition, Chapters 18 and 22

Metabolic Pathways

  • Key Metabolic Pathways Include:

    • Glycan Biosynthesis

    • Biodegradation of Xenobiotics

    • Nucleotide Metabolism

    • Carbohydrate Metabolism

    • Lipid Metabolism

    • Amino Acid Metabolism

    • Energy Cofactors and Vitamins Organization

Learning Objectives

  • Understand the importance of nitrogen in biology.

  • Explain nitrogen fixation and its impact.

  • Describe how ammonia (NH3) is incorporated into biomolecules.

  • Discuss the regulation and biosynthesis of amino acids.

  • Identify roles of amino acids in various biochemical processes:

    • Energy production

    • Neurotransmitter and hormone synthesis

    • Glutathione synthesis

    • Nitric oxide synthesis

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Importance of Nitrogen in Biochemistry

  • Nitrogen is a major element in:

    • Nucleic acids and proteins (amino acids)

    • Various cofactors (e.g., NAD, FAD, biotin)

    • Small hormones (e.g., epinephrine)

    • Neurotransmitters (e.g., serotonin)

    • Defense chemicals (e.g., amanitin from the death-cap mushroom)

Biochemistry of Molecular Nitrogen

  • Atmospheric Nitrogen (N2):

    • Comprises 80% of Earth's atmosphere but is largely unusable due to strong N≡N bond.

    • Transformation: N2 + 3 H2 → 2 NH3 (Ammonia)

  • Nitrogen Fixation:

    • Process by which nitrogen-fixing bacteria convert N2 → NH3.

    • Symbiosis examples:

      • Plants (e.g., Rhizobium with legumes)

      • Animals (e.g., spirochaetes with termites)

The Nitrogen Web

  • Nitrogen moves through a complex web rather than a cycle:

    1. Fixation: N2 → NH3/NH4+

    2. Nitrification: NH3 → NO2–/NO3–

    3. Denitrification: NO3–/NO2– → N2

    4. Anammox: Anaerobic oxidation of ammonia to N2

    5. Assimilation: Plants & microbes → NH3/NH4+

Ammonia Incorporation into Biomolecules

  • Key Entry Points: Glutamate and glutamine

  • Key Reactions:

    • NH4+ + ATP → Glutamine via glutamine synthetase

    • α-Ketoglutarate + Glutamine → 2 Glutamate via glutamine synthase

  • Importance:

    • Glutamine is crucial for amino acid biosynthesis.

Regulation of Glutamine Synthetase

  • Role: Central in converting NH3 to glutamine

  • Regulation Mechanisms:

    • Allosteric inhibition by end products

    • Adenylylation modification, influenced by glutamine and ATP

Transamination

  • Definition: Transfer of an amino group catalyzed by aminotransferases using PLP as a cofactor.

  • Uses glutamate as a nitrogen storage molecule, essential for other amino acid biosynthesis.

Amino Acid Biosynthesis (Anabolism)

  • Sources of Nitrogen: Glutamate or glutamine

  • Carbon Skeletons: Derived from glycolysis, citric acid cycle, and pentose phosphate pathway.

  • Essential Amino Acids: Must be obtained through diet.

    • Examples include histidine, isoleucine, leucine, etc.

  • Non-essential Amino Acids: Synthesized from six metabolic precursors.

Feedback Regulation in Biosynthesis

  • Mechanisms:

    • Inhibition of committed steps and feedback by end products

    • Enzyme multiplicity for control in branched pathways

Roles of Amino Acids

  • Key Functions:

    • Energy production (TCA cycle, gluconeogenesis, ketogenesis)

    • Synthesis of proteins, nucleotides, neurotransmitters, etc.

    • Production of antioxidants (e.g., glutathione)

    • Nitric oxide synthesis from arginine

Summary

  • Nitrogen fixation is crucial for biological activity.

  • Glutamate and glutamine are key in nitrogen incorporation.

  • Essential amino acids must come from diet, while non-essential can be synthesized.

  • Multiple regulatory pathways serve to control amino acid biosynthesis and metabolism.