BIOCHEM 1-2

• Living matter is composed mainly of six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, constituting about 90% of the dry weight of the human body
• Water accounts for about 70-75% of the weight of the cell, with other cellular constituents either dissolved or suspended in water
• Organic compounds, accounting for 25-30% of the cell weight, include nucleic acids, proteins, polysaccharides (carbohydrates), and lipids
• Proteins account for 10-20% of the weight of the cell, while nucleic acids account for 7-10% of the cell weight
• Polysaccharides usually account for 2-5% of the cell weight, and lipids about 3%, with higher content in adipocytes or fat cells
• Other low molecular weight organic compounds may account for 4% of cell weight, including monosaccharides, amino acids, fatty acids, purine and pyrimidine nucleotides, peptides, hormones, vitamins, and coenzymes
• Carbohydrates, including sugars and starches, provide a ready, easily used source of food energy for cells and are classified as monosaccharides, disaccharides, or polysaccharides
• Lipids, a large and diverse group of organic compounds, are insoluble in water but dissolve in other lipids or organic solvents
• The most abundant lipids in the body are triglycerides, phospholipids, and steroids
• Triglycerides are the body's most abundant and concentrated source of usable energy, stored chiefly in fat deposits beneath the skin and around body organs
• Phospholipids, present in cell membranes, allow cells to be selective about what may enter or leave
• Cholesterol, the most important steroid molecule, is used to form vitamin D, some hormones, and bile salts
• Proteins account for over 50% of organic matter in the body and have varied functions, with amino acids as their building blocks
• Proteins can be fibrous/structural or globular/functional, with enzymes being functional proteins that act as biological catalysts
• Enzymes are very specific in their activities, each controlling only one or a small group of chemical reactions and acting only on specific molecules
• Nucleic acids make up genes, providing the basic blueprint of life, with DNA replicating itself before cell division and providing instructions for building every protein in the body
• RNA carries out orders for protein synthesis issued by DNA
• Inorganic compounds like cations (sodium, potassium, calcium, etc.) and anions (chloride, phosphate, etc.) account for the rest of the cell weight
• The cell is the universal functional unit of all forms of life, with the human body containing a wide variety of cells that differ in structure and function
• Eukaryotic cells aggregate to form tissues or organs, and in humans, they exist in large numbers of sizes and shapes to perform various functions
• The cell membrane, the outermost structure of the cell, separates the cell from its surroundings and is semi-permeable, allowing only selected compounds to pass through
• The table summarizes the four main types of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids, listing their chemical formula, monomer, and main function

  
• Cell membrane:

  • The outermost structure of the cell
  • It separates the cell from its surrounding
  • It is a lipid bi-layer consisting of proteins and small amounts of carbohydrates
  • Functions: semi-permeable, modification results in specialized structures like axons of nerves, microvilli of intestinal epithelium, and tails of spermatids
• Nucleus:

  • Control center of the cell
  • Contains genetic material (DNA) that acts as a blueprint for building the body
  • Functions: information center of eukaryotic cell, concentrated cellular DNA in the form of chromosomes
• Cytoplasm:

  • Cellular material outside the nucleus and inside the plasma membrane
  • Contains cytosol, organelles, and inclusions
  • Functions: site of most cellular activities, contains numerous enzymes, proteins, and solutes
• Mitochondria:

  • Ellipsoidal in shape
  • Functions as the powerhouse of the cell, responsible for producing energy in the form of ATP
  • More numerous and large in highly metabolically active cells
• Peroxisomes:

  • Small vesicles surrounded by a membrane, also called microbodies
  • Contain enzymes for H2O2 metabolism, including peroxidase and catalase
• Lysosomes:

  • Small vesicles in the cytoplasm, known as 'Suicidal bags' of the cell
  • Rich in hydrolytic enzymes that digest molecules brought into the cell by phagocytosis
  • Medical importance: involved in diseases like arthritis, muscular dystrophy, and cancer metastasis
• Ribosomes:

  • Tiny, dark bodies made of protein and ribosomal RNA
  • Actual sites of protein synthesis in the cell
• Golgi Apparatus:

  • Well-developed in cells involved in secretion
  • Processes materials for export, packages them as vesicles, and helps in the formation of organelles like lysosomes and peroxisomes
• Endoplasmic Reticulum:

  • System of fluid-filled tubules or canals in the cytoplasm
  • Rough ER is studded with ribosomes, functions in protein synthesis
  • Smooth ER functions in lipid metabolism and detoxification
• Cytoskeleton:

  • Filament-like structures made of proteins in the cytoplasm
  • Acts as the cell's "bones and muscles," providing an internal framework, supporting organelles, and facilitating intracellular transport and cell movements
• Cell Death:

  • Cells have a finite lifespan
  • Cell division and cell death are processes to maintain tissue volume
  • Types of cell death: necrosis (cell murder), apoptosis (genetically programmed cell death), atrophy (due to the absence of essential survival factors)