Molecules of Life: Carbohydrates

• Molecules of life are essential for survival and function of organisms
• They include carbohydrates, lipids (or fats), proteins, and nucleic acids
• These molecules are organic, containing carbon atoms, and are synthesized by living organisms

Carbohydrates

• Carbohydrates are a primary energy source for organisms
• They also act as structural components in cells
• Carbohydrates contain carbon, hydrogen, and oxygen
• The ratio is generally 1:2:1 (CH₂O)ₙ, where n is the number of carbon atoms
• Monosaccharides are the simplest form of carbohydrates, also known as simple sugars
• Glucose, fructose, and galactose are examples of monosaccharides
• Disaccharides consist of two monosaccharides joined by a glycosidic bond
• Sucrose (table sugar) and lactose (milk sugar) are common disaccharides
• Polysaccharides are complex carbohydrates composed of many monosaccharides linked together
• Starch, glycogen, and cellulose are important polysaccharides
• Starch serves as an energy storage molecule in plants
• Glycogen functions as an energy storage molecule in animals
• Cellulose is a structural component of plant cell walls

Lipids

• Lipids are for energy storage, insulation, and forming cell membranes
• They are hydrophobic, which means they are insoluble in water
• Lipids consist of carbon, hydrogen, and oxygen, but with a lower proportion of oxygen compared to carbohydrates
• Triglycerides (fats and oils), phospholipids, and steroids are the main types of lipids
• Triglycerides are a glycerol molecule attached to three fatty acid chains
• Saturated fats contain fatty acids with single bonds between carbon atoms and are typically solid at room temperature
• Unsaturated fats contain fatty acids with one or more double bonds between carbon atoms and are usually liquid at room temperature
• Phospholipids are similar to triglycerides, but one fatty acid is replaced by a phosphate group
• They form the basic structure of cell membranes, with a hydrophilic (phosphate) head and hydrophobic (fatty acid) tails
• Steroids have a structure of four fused carbon rings
• Cholesterol, testosterone, and estrogen are examples of steroids that serve various functions in the body

Proteins

• Proteins perform many functions in living organisms
• These functions include catalyzing reactions, transporting molecules, providing structural support, and regulating cellular processes
• Proteins are made of amino acids, containing carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur
• Amino acids are linked by peptide bonds to form polypeptide chains
• A protein can consist of one or more polypeptide chains folded into a specific three-dimensional structure
• A protein's structure determines its function
• Enzymes are proteins that act as biological catalysts, speeding up chemical reactions in cells
• Antibodies are proteins that recognize and bind to foreign substances (antigens) in the body, helping to fight off infections
• Structural proteins, such as collagen and keratin, provide support and shape to cells and tissues

Nucleic Acids

• Nucleic acids store and transmit genetic information in living organisms
• There are two main types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)
• Nucleic acids are polymers made up of nucleotides
• Each nucleotide consists of a pentose sugar, a phosphate group, and a nitrogenous base
• DNA contains the sugar deoxyribose
• RNA contains the sugar ribose
• DNA uses the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T)
• RNA uses uracil (U) instead of thymine
• DNA is a double-stranded molecule that forms a double helix structure
• RNA is typically single-stranded
• DNA carries the genetic instructions for the development, functioning, and reproduction of all known living organisms
• RNA plays various roles in gene expression, including carrying genetic information from DNA to ribosomes (messenger RNA or mRNA) and functioning as structural and catalytic components of ribosomes (ribosomal RNA or rRNA)
• Transfer RNA (tRNA) is involved in protein synthesis by bringing amino acids to the ribosome

Importance of Water

• Water is crucial for life, supporting biological processes through its properties
• It is a polar molecule, allowing it to form hydrogen bonds
• Water is an excellent solvent for polar and ionic substances, facilitating chemical reactions in cells
• Water has a high heat capacity, which helps to regulate temperature in organisms and environments
• It also has a high heat of vaporization, providing a cooling effect through evaporation
• Water is cohesive and adhesive, aiding in the transport of water and nutrients in plants and animals

Organic vs. Inorganic Molecules

• Organic molecules contain carbon and are generally associated with living organisms
• Inorganic molecules do not contain carbon-hydrogen bonds and are usually simpler in structure than organic molecules
• Organic molecules include carbohydrates, lipids, proteins, and nucleic acids, which are essential for life's processes
• Inorganic molecules like water, salts, and minerals are also vital for life, but they do not contain carbon-hydrogen bonds
• Carbon's ability to form stable bonds with other elements, including itself, allows for the creation of diverse and complex organic molecules
• This ability is the foundation for the complexity and variety of life

Macromolecules and Polymers

• Many molecules of life are large polymers called macromolecules
• Polymers are large molecules formed by joining smaller repeating units (monomers)
• Carbohydrates, proteins, and nucleic acids are examples of macromolecules that are polymers
• Lipids are not true polymers because they are not formed by the repeated linkage of a single type of monomer
• Monosaccharides are the monomers of carbohydrates
• Amino acids are the monomers of proteins
• Nucleotides are the monomers of nucleic acids
• Polymers are synthesized through dehydration reactions, where water molecules are removed as monomers are joined
• Polymers are broken down into monomers through hydrolysis reactions, where water molecules are added to break the bonds

Functional Groups

• Functional groups are specific groups of atoms attached to carbon skeletons, giving properties to organic molecules
• Common functional groups include hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH₂), and phosphate (-PO₄H₂)
• The properties and reactivity of organic molecules are largely determined by the presence and arrangement of functional groups
• The hydroxyl group makes a molecule polar and more soluble in water, while the carboxyl group makes a molecule acidic
• Functional groups can participate in chemical reactions and are involved in the formation of larger, more complex molecules

Isomers

• Isomers are molecules with the same molecular formula but different structural arrangements and properties
• Structural isomers differ in the arrangement of their atoms
• Geometric isomers differ in the arrangement of atoms around a double bond
• Enantiomers are mirror-image isomers that cannot be superimposed
• Isomer structures can result in different biological activities and functions
• Glucose and fructose are structural isomers with the same molecular formula (C₆H₁₂O₆) but different arrangements of atoms, leading to different properties and tastes

Self-Assembly

• Self-assembly is a process where molecules spontaneously organize into ordered structures without external intervention
• This process is driven by intrinsic properties of the molecules, such as their shape, charge, and hydrophobicity
• Self-assembly plays a crucial role in the formation of biological structures
• Examples include the formation of lipid bilayers in cell membranes, the folding of proteins into their specific three-dimensional shapes, and the assembly of viruses from their protein and nucleic acid components
• Self-assembly is essential for the efficiency and accuracy of biological processes

Central Dogma of Molecular Biology

• The central dogma of molecular biology describes the flow of genetic information within a biological system
• DNA is transcribed into RNA, and RNA is then translated into protein
• DNA replication ensures the faithful transmission of genetic information from one generation to the next
• Transcription is the process by which the information in DNA is copied into RNA
• Translation is the process by which the information in RNA is used to synthesize proteins
• This unidirectional flow of information is fundamental to understanding how genes determine traits and functions in living organisms