2: Molecules of life Living things: Highly ordered: chemical, cellular, tissue, organ, organ system, and organelle. Organised into cells Able to reproduce themselves Are able to grow and develop Require nutrients and energy Respond to their environment (external stimuli) Evolve and are adapted to their environment Store and transmit information BIOLOGICAL MOLECULES Most (96.3) of living matter consists of carbon, oxygen, nitrogen and hydrogen. The larger amount of the 3.7 remaining is sulphur, phosphorus and calcium. Carbon is a versatile building block for molecules. WATER H 2 is a polar molecule (one side has a slight negative charge O and one side has a slight positive charge H) and essential for life. Hydrophilic: water repelling Hydrophobic: water lovingattracting Hydrogen bonding: Polarity of water results in hydrogen bonding (the attraction between H and an electronegative atom usually O or N). These hydrogen bonds are relatively weak. Because of Hbonding water is more structured than other liquids (surface tension, ice, thermal buffering). A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. pH + + pH represents the concentration of hydrogen ions (H ) in a solution. Acids increase [H ] in a solution while bases decrease it. So, as pH declines the [H ] increases. Acid: donates a proton. pH less than 7 Base: accepts a proton. pH more than 7 VALENCES The number of covalent (strong chemical) bonds an atom will form. The sharing of electrons between atoms to complete outer valence shell results in strong chemical bonds (covalent bonds). The nucleus of an atom is made up of protons and neutrons. The number of protons = atomic number. Carbon is the most versatile of building blocks for molecules as it has 4 valences. BONDING Covalent: sharing of electron pairs between atoms. Ionic: electrostatic force of attraction between 2 oppositely charged ions (cation and anion) Hydrogen: weak bond between a hydrogen atom and an electronegative atom (N,O or F) BIOLOGICAL MACROMOLECULES Monomers: a molecule that can be bonded to other identical molecules to form a polymer. Eg. Amino acids. Polymers: a substance built from a large number of sub units. Eg. proteins Cells join together small organic sub unit molecules to form larger molecules that fall into 4 classes: Carbohydrates: act as both food and building materials. Monosaccharides : simple sugars Disaccharides: 2 monosaccharide joined by a glycosidic linkage. Eg. Sucrose = glucose + fructose Polysaccharides: multiple monosaccharides. Eg. 4x a glucose= starch (storage) 4x b glucose= cellulose(structural) Lipids: diverse hydrophobic macromolecules which are not polymers. Created out of a glycerol linked to 3 fatty acids. Phospholipids have a hydrophilic head and 2 hydrophobic tails. Phospholipids selfassemble in water to create a phospholipid bilayer. Proteins: consists of one or more polypeptides folded and coiled into a specific arrangement. A polypeptide is made up of polymers of amino acids. Functions: structure, storage, transport, hormonal, receptors, contractionmovement, defence and enzymatic. Each protein has a specific 3D shape. Primary (amino acid sequence), secondary (helixbeta bleated sheet), tertiary, quaternary Nucleic acids: informational polymers. A nucleic acid strand is a polymer of nucleotides. DNA: determines the primary structure of a polypeptide. It is the genetic material we inherit. Made of a phosphate group, pentose sugar (deoxyribose) and a nitrogenous base (adenine, thymine, cytosine and guanine). DNA is double stranded.