Foundations of Biochemistry

Introduction to Biochemistry

Biochemistry is the study of the molecular structure and chemical processes that are fundamental to all living organisms. It seeks to explain the molecular logic of life by identifying the universal principles that underlie biological diversity. Biochemistry provides essential insights for fields such as medicine, agriculture, and nutrition, but its primary focus is understanding the molecular basis of life.

• Definition: Biochemistry describes the structure, function, and interactions of biological macromolecules.

• Applications: Insights from biochemistry are applied in health, disease treatment, biotechnology, and environmental science.

• Central Principle: The molecular logic of life refers to the universal chemical principles that govern all living systems.

Cellular Foundations

Universal Features of Cells

All cells, whether prokaryotic or eukaryotic, share certain structural and functional features. These include the presence of genetic material, a plasma membrane, and cytoplasm containing various biomolecules and organelles.

• Nucleus or Nucleoid: Contains genetic material (DNA and associated proteins). In eukaryotes, the DNA is enclosed within a nuclear membrane; in prokaryotes, it is found in the nucleoid region without a membrane.

• Plasma Membrane: A tough, flexible lipid bilayer that is selectively permeable to polar substances. It contains membrane proteins involved in transport, signal reception, and enzymatic activity.

• Cytoplasm: The aqueous cell contents and suspended particles and organelles. It is the site of many metabolic reactions.

• Supernatant (Cytosol): The soluble portion of the cytoplasm, containing enzymes, RNA, monomeric subunits, metabolites, and inorganic ions.

• Pellet (Organelles and Particles): Includes ribosomes, storage granules, mitochondria, chloroplasts, lysosomes, and endoplasmic reticulum.

Classification of Organisms by Energy and Carbon Source

Organisms can be classified based on their source of energy and carbon for cellular synthesis.

• Phototrophs: Obtain energy from light.

• Chemotrophs: Obtain energy from the oxidation of chemical compounds.

• Autotrophs: Use carbon dioxide (CO2) as their carbon source.

• Heterotrophs: Use organic compounds as their carbon source.

Examples:

• Photoautotrophs: Plants, cyanobacteria (use light and CO2).

• Photoheterotrophs: Purple and green bacteria (use light and organic compounds).

• Chemoautotrophs: Sulfur and hydrogen bacteria (use inorganic fuels and CO2).

• Chemoheterotrophs: Most non-photosynthetic eukaryotes (use organic compounds for both energy and carbon).

Structural Features of Bacterial Cells

Bacterial cells have unique features that distinguish them from eukaryotic cells, though they share some universal characteristics.

• Nucleoid: Contains a single, long, circular DNA molecule.

• Ribosomes: Smaller than eukaryotic ribosomes but perform the same function—protein synthesis from mRNA.

• Pili: Provide adhesion to other cells or surfaces.

• Flagella: Propel the cell through its environment.

• Cell Envelope: Structure varies with the type of bacteria and may include a cell wall and outer membrane.

Example: The Gram stain differentiates bacteria based on cell envelope structure: Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have an outer membrane and a thinner peptidoglycan layer.

Additional info: Cyanobacteria are Gram-negative and possess an extensive internal membrane system with photosynthetic pigments. Archaea have a pseudopeptidoglycan layer instead of peptidoglycan.