Biology I - Chapter 4 - Functional Groups

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TAMU-T Fall 2012 Biology I with Dr. Linkins

Functional Group: Hydroxyl (-OH)

Structure: Hydrogen atom bonded with Oxygen atom
Compound: Alcohols (name usually ends in -ol)
Example: Ethanol (the alcohol present in alcoholic beverages)
Functional Properties: 1) Is polar as a result of electrons spending more time near the electronegative oxygen atom 2) can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars

Functional Group: Carbonyl (-C=O)

Structure: a carbon atom joined to an oxygen atom by a double bond
Compounds: 1) Ketones (if carbonyl group is within a carbon skeleton) 2) Aldehydes (if carbonyl group is at the end of the carbon skelton)
Example: Acetone (simplest ketone) Propanal (aldehyde)
Functional Properties: 1) ketones and aldehydes can be structural isomers with different properties 2) two major groups of sugar: ketoses and aldoses

Functional Group: Carboxyl (-COOH)

Structure: oxygen is double bonded to a carbon atom that is also bonded to an -OH group
Compounds: Carboxylic acids (aka organic acids)
Example: Acetic acid (gives vinegar its sour taste)
Functional Properties: 1) acts as an acid; can donate an H+ because the covalent bond between the O and H is so polar 2) Found in cells in the ionized form with a charge of 1- called a carboxylate ion

Functional Group: Amino (-NH2)

Structure: nitrogen atom bonded to 2 hydrogen atoms and to the carbon skeleton
Compounds: Amines
Example: Glycine (a compound that is both amine and carboxylic acid; compounds with both groups are called amino acids)
Functional Properties: 1) acts as a base 2) Found in cells in the ionized form with a charge of 1+

Functional Group: Sulfhydryl (-SH)

Structure: sulfur atom bonded to an atom of hydrogen
Compounds: Thiols
Example: Cysteine (an important sulfur containing amino acid)
Functional Properties: 1) two sulfhydryl groups can react, forming a covalent bond. This "cross-linking" helps stabilize protein structure (tertiary structure) 2) cross-linking of cysteines in hair proteins maintains the curliness or straightness of hair. Straight hair can be "permanently" curled by shaping it around curlers and then breaking and re-forming the cross-linking bonds

Functional Group: Phosphate (PO4)

Structure: phosphorus atom is bonded to 4 oxygen atoms, one oxygen is bonded to the carbon skeleton, two oxygens carry a negative charge, and the fourth is double bonded to the phosphorus atom
Compounds: Organic phosphates
Example: Glycerol Phosphate (takes part in many chemical reaction in the cell, provides backbone for phospholipids, and the most prevalent molecules in cell membranes
Functional Properties: 1) contributes negative charge to the molecule of which it is a part 2) Molecules with phosphate groups have the potential to react with water, releasing energy

Functional Group: Methyl (-CH3)

Structure: a carbon atom bonded to three hydrogen atoms, the carbon of a methyl group may be attached to a carbon or to a different atom
Compounds: Methylated compounds
Example: 5-methyl cytosine (a component of DNA that has been modified by addition of a methyl group
Functional Properties: 1) addition of a methyl group to DNA, or to molecules bound to DNA, affects expression of genes 2) arrangement of methyl groups in male and female sex hormones affects their shape and function

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