Introduction to Biochemistry
Cell and Its Biochemical Organization
The cell is the universal functional unit of life, divided into two main types: prokaryotes and eukaryotes. Prokaryotes are simple, single-cell organisms like bacteria without compartmentalized cytosol, whereas eukaryotes contain membrane-bound organelles and include plants and animals.
Importance of the Cell
- Basic unit of structure and function in humans.
- Contains diverse subcellular organelles specialized for various functions.
- Diseases can arise from organelle dysfunction.
- Cell cycle governs growth and division; apoptosis is vital for development and injury repair.
Molecular Composition of Cell
- Water: 70-75% of cell weight, solvent for biochemical reactions.
- Organic compounds: 25-30%, including proteins, nucleic acids, carbohydrates, lipids, and low molecular weight metabolites.
- Inorganic compounds: electrolytes vital for cellular homeostasis.
Eukaryotic Cell Structure and Functions
Eukaryotic cells comprise plasma membrane, nucleus, cytoplasm, and various organelles:
- Cell Membrane: Lipid bilayer with proteins; controls substance flow and cell communication.
- Nucleus: Contains genetic material; regulates cell functions.
- Mitochondria: Energy production centers; involved in metabolism and apoptosis.
- Lysosomes: Contain digestive enzymes; involved in cellular cleanup.
- Peroxisomes: Process reactive oxygen species to protect cells.
- Endoplasmic Reticulum and Golgi Apparatus: Synthesize and process proteins and lipids for cellular use and export.
- Cytoskeleton: Provides structure, facilitates movement and transport within cells.
Transport Across Cell Membranes
- Passive diffusion: movement along concentration gradients without energy.
- Facilitated diffusion: carrier-mediated but still energy-independent.
- Active transport: carrier-mediated against concentration gradients, energy-dependent (e.g., Na+/K+ ATPase).
- Macromolecule transport by endocytosis and exocytosis.
Energy-Rich Compounds and Signal Transduction
- ATP and other nucleotides store energy in phosphate bonds.
- Hydrolysis of high-energy bonds releases energy for cellular processes.
- cAMP acts as a second messenger, mediating hormonal signals via G-proteins and protein kinase cascades.
- Regulatory mechanisms modulate these signaling pathways to maintain cellular homeostasis.
Detailed Notes:
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