Carbon and the molecular diversity of life
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Carbon chains form skeletons of most organic molecules. Atoms of other elements can be ... link together into complex intricate molecular skeletons; and ...

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4-1 Carbon and the

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Carbon and theMolecular Diversity of Life


The Importance of Carbon

  • Compounds containing carbon are said to be organic compounds

  • Organic chemistry - specializes in study of carbon compounds.

  • Major elements of life include CHNOPS.

  • Carbon, bonded with these elements, accounts for the large diversity of biological molecules.


Stanley Millers 1953 experiment: the abiotic synthesis of organic compounds under early Earth conditions


Organic Compounds

Hydrogen and other elementscovalently bonded to carbon

Carbohydrates

Lipids

Proteins

Nucleic acids


Carbons Bonding Behavior

  • Outer shell of carbon has 4 electrons; can hold 8

  • Each carbon atom can form covalent bonds with up to 4 atoms


Molecular Shape

  • A molecules shape is usually very important to its function in the living cell.

  • When carbon forms single covalent bonds, four hybrid orbitals causes the bonds to angle toward the corners of an imaginary tetrahedron.


Shape of carbon molecule can vary with number of bonds and number of carbon atoms


Valences for the major elements of organic molecules

Valence equals number of covalent bonds an atom will usually form as well as the number of electrons required to complete the atoms valence shell


Carbon Skeletons

  • A carbon atom can also bond with other carbon atoms

  • Carbon chains form skeletons of most organic molecules. Atoms of other elements can be bonded to the skeletons at available sites

  • Chains vary in length and may be straight, branched, or arranged in closed rings

  • Hydrocarbons are organic molecules consisting only of carbon and hydrogen


Variations in carbon skeletons


Hydrocarbons

  • A major component of petroleum (fossil fuel)

  • Many of a cells organic molecules have regions consisting of only carbon and hydrogen

    • Fat molecules have long hydrocarbon tails attached to a non-hydrocarbon component

  • Both petroleum and fat are hydrophobic (C-H bonds are nonpolar)

  • HCs store relatively large amount of energy


The role of hydrocarbons in fat


Isomers

  • Isomers are compounds that have the same molecular formula but different structures, resulting in different properties

    • Butane and isobutane - have same molecular formula (C6H10), but differ in arrangement of carbon skeletons

  • Three types of isomers:

    • structural isomers,

    • geometric isomers, and

    • enantiomers


Three types of isomers


The pharmacological importance of enantiomers


Functional Groups

  • Atoms or clusters of atoms that are covalently bonded to carbon backbone

  • Give organic compounds their different properties

  • Components of organic molecules that are most commonly involved in chemical reactions

  • Behave consistently from one organic molecule to another:

    • Estradiol and testosterone sex hormones


A comparison of the functional groups of female (estradiol) and male (testosterone) sex hormones


Functional groups most important in chemistry of life

Hydroxyl group OH

Carbonyl group CO, COH

Carboxyl groupCOOH

Amino groupNH2,NH3+

Sulfhydryl groupSH

Phosphate groupOPO32-


The variation in locations of functional groups along carbon skeletons is a major source of molecular diversity.


Hydroxyl Group

  • A hydrogen atom is bonded to an oxygen atom, which is bonded to carbon skeleton (OH)

  • Alcohols - organic compounds containing hydroxyl groups

    • specific names usually end in -ol (ethanol)

    • usually drop covalent bond between oxygen and hydrogen in structural formula --OH or HO--


  • The hydroxyl group is polar due to electronegative oxygen atom drawing electrons to itself.

  • Therefore, water molecules are attracted to hydroxyl group, which helps dissolve organic compounds containing such groups.

    • Sugars owe solubility in water to presence of multiple hydroxyl groups.


Carbonyl Group

  • Consists of carbon atom joined to an oxygen atom by a double bond (CO)

  • Aldehyde - on the end of carbon skeleton

    • propanal - 3 carbon aldehyde

  • Ketone - not on end of carbon skeleton

    • acetone - 3 carbon ketone

  • Propanal and acetone are structural isomers


Carboxyl Group

  • Oxygen atom is double-bonded to carbon atom that is also bonded to a hydroxyl group (COOH)

  • Carboxylic acids(or organic acids) - are compounds containing carboxyl groups

    • formic acid (HCOOH) - simplest, one carbon; substance injected when ants sting

    • acetic acid - two carbons; gives vinegar sour taste


Why does a carboxyl group have acidic properties?

  • Carboxyl group is source of hydrogen ions (H+)

  • Covalent bond between O and H is so polar that the H tends to dissociate reversibly from the molecule as an ion (H+)


Amino Group

  • Nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton (NH2 and NH3+)

  • Amines - organic compound with amino group

    • glycine - has amino and carboxyl group, considered both an amine and a carboxylic acid

    • amino acid - has both amino and carboxyl groups (glycine)

  • Most cellular organic compounds have two or more functional groups


  • The amino group acts as a base.

  • Ammonia (NH3) can pick up a proton from surrounding solution. Amino groups of organic compounds can do the same

  • This process gives the amino group at charge of +1, its most common state within the cell


Sulfhydryl Group

  • Sulfur atom is bonded to an atom of hydrogen, (SH) resembles hydroxyl group in shape

  • Thiols - organic compounds containing sulfhydryls

  • Can interact to stabilize the structure of a protein


Phosphate Group

  • Phosphate ion is covalently attached by one of its oxygen atoms to the carbon skeleton OPO32-

    • Phosphate is an anion formed by dissociation of an inorganic acid called phosphoric acid (H3PO4). The loss of hydrogen ions by dissociation leaves the phosphate with two negative charges

  • Function to transfer energy between organic molecules


Review of the Chemical Elements of Life

Living matter consists mainly of carbon, oxygen, hydrogen, and nitrogen, with smaller amounts of sulfur and phosphorus.

These elements share characteristics of forming strong covalent bonds, a quality that is essential in the structure of complex organic molecules.


The chemical behavior of carbon makes it very versatile as a building block in molecular structure:

  • can form four covalent bonds,

  • link together into complex intricate molecular skeletons; and

  • join with several elements.


Carbon provides for the great diversity of organic molecules, each with special properties that emerge from the arrangement of its carbon skeleton and the functional groups attached to that skeleton.


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