The Molecules of Life

ORGANIC COMPOUNDS ORGANIC COMPOUNDS Living organisms are composed of organic compounds. An organic compound is essen0ally a compound that contains carbon and is found in living things (certain excep0ons exist, including CO2 and carbonates). Carbon atoms can form four covalent bonds, allowing for a diversity of stable carbon compounds to exist. MONOMERS ® POLYMERS Complex organic molecules may be comprised of smaller recurring subunits called monomers. Monomeric subunits might not be iden0cal, but will share the same basic structural characteris0cs. Carbohydrates, nucleic acids and proteins are all composed of monomers. Lipids do not contain monomers, but may be comprised of dis0nc0ve subunits (e.g. triglycerides are made up of glycerol and three faIy acid chains). Nucleic Acid Carbohydrate Nucleo0des Monosaccharides Lipid (triglyceride) FaIy acids + Protein Monoglycerides Amino acids METABOLISM Metabolism describes the totality of chemical processes that occur within a cell in order to maintain life. These metabolic processes provide a source of energy for biological processes and enable the synthesis and assimila0on of cellular materials for use within the cell. Metabolic reac0ons can broadly be described as being either anabolic or catabolic: Anabolism: • Smaller compounds are combined to form larger compounds • In the case of organic compounds, this involves condensation • Water is released as a by-product of condensation reactions Catabolism: • Large compounds are broken down into smaller compounds • In the case of organic compounds, this involves hydrolysis • Water is required as an input for hydrolysis reactions H2O Monomers Polymer H2O Polymer Monomers TYPES OF ORGANIC MOLECULES There are 4 classes of organic compounds found in cells: carbohydrates, lipids, nucleic acids and proteins. • Carbohydrates: Used primarily as a short-term energy source (e.g. glucose), also involved in cellular structure (e.g. cellulose in plant cell walls) and signalling (membrane receptors are often glycoproteins) • Lipids: Primary component of cell membranes (e.g. phospholipids), also involved in structure (waxes), cellular signalling (steroid hormones) and as a long-term energy source (e.g. triglycerides) • Nucleic Acids: Function as a genetic blueprint for cellular activity – DNA serves as a master copy, while RNA functions as a transient copy that is used to synthesis proteins (via transcription and translation) • Proteins: Serve a wide variety of functions within a cell – including structure (e.g. collagen), signalling (e.g. peptide hormones), immunity (e.g. antibodies) and maintaining metabolic control (e.g. enzymes) CARBOHYDRATES Carbohydrates are comprised of monomeric units called monosaccharides. These subunits form ringed structures that are covalently combined by condensa0on polymerisa0on to form polysaccharides. Glucose is an example of a monosaccharide that is used as an energy source within the cell. It can form a variety of polymers; including glycogen (energy storage in animals), starch (storage in plants) and cellulose (structural component within plant cell walls). Ribose is another example of a monosaccharide that func0ons as a core component of all nucleic acids (RNA contains ribose, while DNA contains the modified form – deoxyribose). Ribose (Pentose / 5C) Glucose (Hexose / 6C) MONOSACCHARIDES Starch (Amylose) VS Glycogen POLYSACCHARIDES LIPIDS Lipids are non-polar compounds that typically include long chains of hydrocarbons called faIy acids. They do not contain monomers, but may be composed of disLnct subunits. Triglycerides consist of a glycerol subunit combined with three faIy acid chains (via condensa0on reac0ons) and func0on as a source of long-term energy storage within a cell. Phospholipids have only two faIy acid chains aIached to the glycerol, but include a polar phosphate group which makes the molecule amphipathic (possessing both hydrophilic and hydrophobic proper0es). Phospholipids func0on as the primary component of membranes. Steroids (such as cholesterol) do not consist of any subunits and are composed of four fused carbon rings. PHOSPHOLIPIDS Phosphate + fa,y acids (´2) TRIGLYCERIDE Glycerol + fa,y acids (´3) STEROIDS 4 ´ fused carbon rings NUCLEIC ACIDS Nucleic acids are composed of monomeric subunits called nucleoLdes. Each nucleo0de contains a nitrogenous base that is aIached to a backbone consis0ng of a sugar and a phosphate molecule. Nucleo0des are joined together by condensa0on polymerisa0on to form long polymeric chains. The bases protrude from the sugar-phosphate backbone to form a sequence that func0ons as a code for protein assembly. DNA func0ons as a master copy, while RNA serves as a transient copy that plays an ac0ve role in the manufacturing of proteins. Nitrogen Base Phosphate A C T G Pentose Sugar MONOMER (NUCLEOTIDE) POLYMERISATION PROTEINS Proteins are composed of long chains of monomers called amino acids. These amino acids are joined together via condensa0on polymerisa0on to form polypepLde chains. There are 20 different amino acids and their order in a polypep0de sequence determines the overall shape and biological proper0es of the resul0ng protein. As most polypep0de chains contain between 50 – 2000 amino acid residues, organisms are capable of producing a huge range of possible proteins with a wide variety of func0ons. Protein sequences are encoded by nucleic acids, and so proteins func0on to enact the gene0c instruc0ons of a cell. H H H O N C C OH R MONOMER (AMINO ACID) H H H O H H O N C C N C C R pep#de bond R OH POLYMERISATION (DIPEPTIDE) INORGANIC MOLECULES Organic compounds are formed from inorganic sources and may create inorganic by-products if digested. • All organic compounds contain carbon (C), hydrogen (H) and oxygen (O) in varying ratios • Nucleic acids and proteins always possess nitrogen (N), while nucleic acids also contain phosphorus (P) and proteins may contain sulphur (S) – depending on the specific amino acids present in a polypeptide. Inorganic molecules also play important roles in the func0oning of the cells that comprise living organisms. • Oxygen gas (O2) is required for aerobic cell respiration (producing ATP from the breakdown of glucose) • Carbon dioxide gas (CO2) is used by plants to synthesise vital organic molecules (like carbohydrates) • Water (H2O) comprises ~70% of the cell’s internal environment and functions as a transport medium • Trace minerals (e.g. Na+, K+, Cl–) are necessary for maintaining survival in multicellular organisms