Chapter 4: Carbon and the Molecular Diversity of Life 

Carbon: The Backbone of Life

• living organisms consists mostly of carbon-based compounds
• carbon in unparalleled in its ability to form large, complex, and varied molecules
    * makes possible the diversity of organisms that have evolved on Earth
• Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds

Concept 4.1: Organic chemistry is the study of carbon compounds

• organic chemistry: the study of compounds that contain carbon, regardless of origin
    * range from simple molecules to colossal ones, which as proteins

^^Organic Molecules and the Origin of Life on Earth^^

• Stanley Miller’s classic experiment, trying to model how life first began, demonstrated the abiotic synthesis of organic compounds
• experiments support the idea that abiotic synthesis of organic compounds, perhaps near volcanoes, could have been a stage in the origin of life
• the overall percentages of the major elements of life — C, H, O, N, S, P — are suite uniform from one organism to another
• because of carbon’s ability to form four bonds, these building blocks can be used to make an inexhaustible variety of organic molecules
• the great diversity of organisms on the planet is due to the versatility of carbon

Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atoms

• electron configuration is the key to an atom’s characteristics
• electron configuration determines the kinds and number of bonds an atom will form with other atoms
• we are carbon based, not silicon based because silicon holds onto other elements too strongly - can’t let go of elements easily when elements need to be used by the organism

^^The Formation of Bonds with Carbon^^

• carbon has 4 valence electrons, so it can form four covalent bonds with a variety of atoms, making large complex molecules possible
• in molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape
• when two carbon atoms are joined by a double bond, the atoms joined to the carbons are in the same plane as the carbons
• double bonds don’t allow carbons to freely rotate (not dynamic like single bonds)
• ==valence==: the number of covalent bonds an atom can form
    * number of unpaired electrons in the valence shell of an atom is generally equal to its valence
• the electron configuration of carbon gives it covalent compatibility with many different elements
• the valence of carbons and its most frequent partners (hydrogen, oxygen, and nitrogen) are the building code for the architecture of living molecules

^^Molecular Diversity Arising from Variation in Carbon Skeletons^^

• carbon chains form the skeletons of most organic molecules and they vary in length and shape
• variation in carbon skeletons is an important source of the molecular complexity and diversity of living matter

@@Hydrocarbons@@

• ==hydrocarbons==: organic molecules consisting of only carbon and hydrogen
• many organic molecules, such as fats, have hydrocarbon components
• but, hydrocarbons are not prevalent in most living organisms
• hydrocarbons can undergo reactions that release a large amount of energy
• fat is more efficient to break down than sugar

@@Isomers@@

• ==isomers==: compounds with the same molecular formula but different structures and properties
• ==structural isomers==: have different covalent arrangements of their atoms
• ==cis-trans isomers==: have the same covalent bonds, but differ in their spatial arrangements
• ==enantiomers== : isomers that are mirror images of each other
• cis-trans isomers require a double or triple bond and react differently in reactions
• enantiomers are important in the pharmaceutical industry as two enantiomers of a drug may have different effects
    * usually only one isomer is biologically active
• single bonded molecules will react the same, even if their bonds are rotated
• double-bonded or triple-bonded molecules will react different in reactions if their bonds are rotated

Concept 4.3: A few chemical groups are key to molecular function

• the properties of an organic molecule depend not only on the arrangement of its carbon skeleton but also on the various chemical groups attached to the skeleton
• a number of characteristic groups can replace hydrogens attached to skeletons of organic molecules

^^The Chemical Groups Most Important in the Processes of Life^^

• estradiol and testosterone are both steroids with a common carbon skeleton, in the form of four used rings
• these sex hormones differ only in the chemical groups attached to the rings of the carbon skeleton
• you would think estrogen and testosterone are a antagonist chemicals, but they’re actually pretty similar - only differ by groupings that they have

• ==functional groups==: the components of organic molecules that are most commonly involved in chemical reactions
• the number and arrangement of functional groups gives each molecule its unique properties

^^ATP: An Important Source of Energy for Cellular Processes^^

• ==Adenosine Triphosphate (ATP)==: an important organic phosphate that is the basis of life
• ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups
• ATP is made in the inner-lining of the mitochondria
• ATP is not a very stable molecule, allowing it to form ADP and release a phosphate group that then become inorganic