Organic Compounds, Carbohydrates

• Organic compounds are fundamental to life and are defined by their carbon-based structures.
• The diversity and complexity of organic molecules depend on carbon's capacity to create stable covalent bonds with itself and other elements.
• Living organisms consistently possess four primary classes of organic compounds: carbohydrates, lipids (or fats), proteins, and nucleic acids.

Carbohydrates

• Organisms use carbohydrates as their primary energy sources and as structural components.
• Sugars, starches, and fibers are examples of carbohydrates.
• Monosaccharides are the most basic carbohydrates, often referred to as simple sugars; glucose and fructose are examples.
• Cells use glucose as a primary energy source.
• Fruits are a common source of fructose.
• Disaccharides are formed when two monosaccharides are joined by a glycosidic bond; sucrose and lactose are examples.
• Glucose and fructose combine to form sucrose (table sugar).
• Glucose and galactose combine to form lactose (milk sugar).
• Polysaccharides are complex carbohydrates composed of numerous monosaccharides, including starch, glycogen, and cellulose.
• Plants store glucose as starch.
• Animals store glucose as glycogen, which is present in the liver and muscles.
• Plant cell walls contain cellulose as a structural element.

Lipids

• Lipids are hydrophobic molecules utilized for cell membrane structure, insulation, and energy storage.
• Lipids include fats, oils, phospholipids, and steroids.
• Fats (triglycerides) are composed of three fatty acids and one glycerol molecule.
• Saturated fats are solid at room temperature (e.g., butter) and lack double bonds in their fatty acid chains.
• Unsaturated fats have one or more double bonds in their fatty acid chains and are liquid at room temperature (e.g., olive oil).
• Phospholipids resemble fats but have a phosphate group in place of one fatty acid.
• They are essential parts of cell membranes, creating a lipid bilayer with hydrophobic tails and hydrophilic heads.
• Steroids have a structure made up of four connected carbon rings, such as cholesterol and testosterone.
• Animal cell membranes contain cholesterol, a precursor to steroid hormones.
• The steroid hormone testosterone is a sex hormone.

Proteins

• Proteins are made of amino acids, they are complex molecules that carry out a wide range of cellular tasks.
• These consist of catalysing reactions (enzymes), giving structural support, transporting molecules, and protecting against disease (antibodies).
• Each amino acid, the building block of proteins, has a unique side chain (R-group), a carboxyl group, and an amino group.
• Polypeptide chains are created when amino acids are joined by peptide bonds.
• A protein's structure is arranged into four tiers:
• Primary structure defines the sequence of amino acids.
• Secondary structure defines local folding patterns (e.g., alpha-helices and beta-sheets) that are held together by hydrogen bonds.
• Tertiary structure defines the overall three-dimensional structure of a protein, which is influenced by interactions between R-groups.
• Quaternary structure defines the arrangement of multiple polypeptide chains in a protein with multiple subunits.
• Enzymes are proteins that function as biological catalysts, accelerating chemical reactions by lowering the activation energy.
• They possess an active site where substrates attach and undergo a chemical reaction.
• Enzyme activity is susceptible to alterations in temperature, pH, and the presence of activators or inhibitors.

Nucleic Acids

• Cells use nucleic acids to store and transmit genetic information.
• The main types are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
• A sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base make up the nucleotides that make up nucleic acids.
• The bases adenine (A), guanine (G), cytosine (C), and thymine (T) are found in DNA.
• DNA is a double-stranded helix where A and T, and G and C, are paired.
• Genetic information is stored in DNA, which is essential for replication and transcription.
• The bases adenine (A), guanine (G), cytosine (C), and uracil (U) are present in RNA.
• RNA is typically single-stranded.
• RNA performs a variety of functions in gene expression, including mRNA carrying genetic information from DNA, rRNA creating ribosomes, and tRNA controlling gene expression.