Rucete ✏ Lehninger Principles of Biochemistry In a Nutshell
1.2 Chemical Foundations
This chapter introduces the chemical basis of biochemistry, highlighting the universality of chemical processes in all living organisms and the central role of carbon-based molecules.
Biochemical Unity and Essential Elements
• Fundamental biochemical processes, such as glucose breakdown, are remarkably similar across diverse organisms, reflecting a universal evolutionary origin.
• Fewer than 30 of over 90 naturally occurring elements are essential for life, with hydrogen, oxygen, nitrogen, and carbon comprising over 99% of the mass of most cells.
• Trace elements are required in minute amounts but are critical for the function of specific proteins and enzymes.
Structure and Diversity of Biomolecules
• Carbon's bonding versatility enables the formation of complex molecules with various sizes, shapes, and functions.
• Biomolecules are primarily carbon compounds modified by functional groups such as hydroxyl, amino, carbonyl, and carboxyl groups.
• The arrangement of these functional groups and their three-dimensional geometry determine the molecule's chemical personality and reactivity.
Universal Small Molecules and Metabolome
• All cells contain a universal set of small organic molecules (amino acids, nucleotides, sugars, and carboxylic acids) involved in central metabolic pathways.
• These molecules are highly water-soluble, polar or charged, and are conserved across all forms of life.
• Secondary metabolites, found in specific organisms like plants, play unique roles beyond the universal set; the total collection of small molecules in a cell is called the metabolome.
Macromolecules and Supramolecular Complexes
• Major cellular constituents include macromolecules: proteins (amino acid polymers), nucleic acids (nucleotide polymers), and polysaccharides (sugar polymers).
• Macromolecules can form larger supramolecular assemblies like ribosomes and cellular membranes through noncovalent interactions.
• Each class of macromolecule serves specific functions: proteins as enzymes and structural elements, nucleic acids for genetic information, polysaccharides for energy storage and structure, and lipids for membranes and signaling.
Stereochemistry: Configuration and Conformation
• The function of biomolecules depends not only on their covalent structure but also on their three-dimensional arrangement (stereochemistry).
• Stereoisomers have the same molecular formula but different spatial arrangements, often around double bonds (cis/trans isomers) or at chiral centers (enantiomers and diastereomers).
• Biological molecules are usually found in only one of their possible stereoisomeric forms due to the stereospecificity of enzymes.
• Conformation refers to the spatial arrangement of atoms that can change via rotation around single bonds, without breaking covalent bonds.
Stereospecificity in Biochemical Interactions
• Biochemical interactions are often highly stereospecific, requiring a precise fit between molecules (e.g., enzyme-substrate, receptor-ligand).
• The biological activity of molecules depends on both their configuration (fixed arrangement) and conformation (rotational flexibility).
• Only one stereoisomer is typically biologically active, as shown in examples like amino acids, glucose, and pharmaceutical agents.
In a Nutshell
The chemical unity of life is rooted in the versatile bonding of carbon and the presence of universal small molecules and macromolecules. Proteins, nucleic acids, and polysaccharides are polymers built from simple subunits whose sequence and structure determine biological function. Stereochemistry is essential for molecular recognition and activity, making most biochemical reactions and interactions highly specific. Despite the diversity of life, these chemical foundations are conserved across all organisms.