The Chemical Context of Life 

The formation and function of molecules depend n chemical bonding between atoms 

- COVALENT BONDS: Occurs when valence electrons are shared by two atoms 

- ELECTRONEGATIVITY: a tendency to attract electrons of a covalent bond (unequal sharing) 

- NONPOLAR COVALENT: occurs when the electrons are shared equally 

    - little to no difference in electronegativity 

- POLAR COVALENT: occurs when electron are shared unequally 

    - one atom has greater electronegativity than the other, therefore "pulls" the electrons closer 

- IONIC BONDS: are ones in which two atoms attract valence electrons so unequally that the more electronegative atom steals the electron away from the less electronegative atom (considered weak) 

    -give or take one or more electrons 

- An ion is the resulting charged atom or molecule 

- ionic bonds occur because these ions will either positively (cation) or negatively (anion) charges and will be attracted to each other by these opposite charges (considered weak) 

- HYDROGEN BONDS: relatively weak bonds that form between the partial positively charges hydrogen atom of one molecule and the strongly electronegative atom of another molecule 

- VAN DE WAALS INTERACTION: very weak connections that are due to asymmetrical distribution of electrons 

Chemical reactions make and break chemical bonds 

- REACTANTS: the starting materials

- PRODUCTS: the ending material 

Water and its properties due to hydrogen bonding helps make life on earth possible. 

- The structure of water: 

    -key to special properties 

    -one atom of oxygen and two atoms of hydrogen covalently bonded together to form a molecule 

    - Water molecules are polar 

        - POLAR: opposite charges on opposite sides due to electron negativity 

        - OXYGEN: partial negative charge 

        -HYDROGEN: partial positive charge 

- COHESION: the linking of like molecules 

   -water molecule linked to another water molecule- creates surface tension 

- ADHESION: the clinging of one substance to another substance 

   -water getting attached to a glass

- CAPILLARY ACTION: caused by surface tension where water moves through a narrow channel against gravity 

- TRANSPIRATION: the movement of water molecules up plants ( through the xylem)

- SPECIFIC HEAT: the amount of heat it takes to raise/lower the temp of a substance by 1 degrees Celsius  

   - makes oceans relatively stable therefore, supports life 

- ice floats because it can form more hydrogen bonds 

   -less dense than water 

   -floats keeping large bodies of water from freezing 

-SOLVENT: dissolves another substance 

-SOLUTE: substance being dissolved 

           -SOLVENT+SOLUTE= SOLUTION 

-HYDROPHILLIC: water loving (polar molecules, ionic compounds, some proteins) 

-HYDRROPHOBIC: water hating (non-polar molecules, such as oil ) 

-The pH scale runs between 0 & 14 and measures the acidity of  aqueous solutions 

   -acids: the excess of H+ ions 

-BUFFERS: substances that minimize the change in pH constantly taking and releasing  ions to keep pH constant 

-CARBONIC ACID: a buffer in living system s 

   -moderates pH changes in blood and ocean 

-all organic compounds contain carbon and also most contain hydrogen 

-CARBON AND MOLECULAR DIVERSITY: carbon is unparalleled in its ability to form molecules that are large, complex and diverse 

-ISOMERS: molecules that have the same molecular formula, but differ in arrangement 

-FUNCTIONAL GROUPS: attached to the carbon skeleton have diverse properties 

    -the behavior of organic molecules is dependent on the identity of their functional groups  

Macromolecules are polymers built from their monomers 

-POLYMERS: long chains of molecules made of repeating subunits called monomers 

   -ex: starch is a polymer composed of glucose monomers

-DEHYDRATION REACTION: create polymers from monomers (anabolic) 

-HYROLYSIS: when water is added to split molecules (catabolic) 

   -this occurs in the reverse of dehydration reactions 

Carbohydrates serve as fuel and building materials 

-MONOSACHARIDES: the monomers of carbohydrates 

-POLYSACCHARIDES: the polymers of monosaccharides 

-Starch connects downward= storage of energy 

-cellulose connects up and down in structure 

-carbohydrates function for energy storage and structure 

-cellulose=major component in plant cell walls 

-chitin= found in exoskeleton of shells of anthropoids 

Lipids are a diversde group of hydrophobic molecules 

-they aren't polymers because they are assembled from a variety (not repeating units) of components 

    -ex: wax, oil, fats, and steroids 

-triglycerides are made up of a glycerol molecule and three fatty acid molecules 

    -fatty acids include hydrocarbon chains of various lengths. These chains are non-polar (hydrophobic) 

-SATURATED FATTY ACIDS: have no double bonds, solid when room temperature 

-UNSATURATED FATS: have some carbon double bond: results in kinks, liquid at room temperature , commonly produced by plants 

   -ex: corn oil and olive oil 

-Steroids are made of four rings that are fused together 

-proteins include a diversity of structures resulting in a wide range of functions 

-proteins are polymers made up of amino acid monomers 

-peptide bonds link amino acids 

   -they are formed by dehydration synthesis between the amino and carboxyl groups of adjacent monomers 

-protein shape is crucial to protein function, when protein does not fold properly, its function changes, this can be the result of a single amino acid substituion such as seen in the abnormal hemoglobin typical  or sickle cell disease 

-there are four levels of protein structure 

   -primary 

   -secondary

   -tertiary 

   -quaternary