Bio 311C Functional Groups

Hydroxyl

-OH

Hydroxyl Key Properties

Polar; hydrogen-bond donor and acceptor; alcohol

Hydroxyl Biological Examples

Sugars, glycerol, serine side chain

Hydroxyl Form Near Neutral pH

-OH, usually uncharged

Hydroxyl Polarity

Moderately Polar

Hydroxyl Biological Interpretation

Often increase water interaction but do not guarantee that the whole molecule is soluble

Carbonyl

>C=O

Carbonyl Key Properties

Polar; aldehyde or ketone

Carbonyl Biological Examples

Open-chain sugars, acetone, peptide-bond

Carbonyl Form Near Neutral pH

>C=O, uncharged

Carbonyl Polarity

Moderately polar

Carbonyl Biological Interpretation

Has a strong bond dipole and accepts hydrogen bonds. Aldehydes, ketones, amide carbonyls

Carboxyl

-COOH / -COO^-

Carboxyl Key Properties

Acidic; often negatively charged near neutral pH

Carboxyl Biological Examples

Fatty acids, free amino acids, aspartate, glutamate

Carboxyl Form Near Neutral pH

Mostly carboxylate (-COO^-)

Carboxyl Polarity

Highly polar / ionic

Carboxyl Biological Interpretation

Usually negatively charged near neutral pH; interacts strongly with water, ions, and positively charged groups

Amino

-NH₂ / -NH₃₊

Amino Key Properties

Basic; often positively charged near neutral pH

Amino Biological Examples

Free amino acids, lysine side chain, some bases

Amino Form Near Neutral pH

Often protonated (-NH₃₊)

Amino Polarity

Highly polar / ionic

Amino Biological Interpretation

Many aliphatic amino groups are positively charged near neutral pH. Protonation depends on pKa and molecular environment

Phosphate

-OPO₃H^- / -OPO_3²⁺

Phosphate Key Properties

Acidic; negatively charged; group-transfer chemistry

Phosphate Biological Examples

ATP and other nucleotides, DNA, RNA, phospholipids

Phosphate Form Near Neutral pH

One or more negative charges

Phosphate Polarity

Extremely polar / ionic

Phosphate Biological Interpretation

Strongly hydrated and usually water-soluble. Its charge is important in ATP, nucleic acids, and phospholipids

Sulfhydryl

-SH

Sulfhydryl Key Properties

Reactive thiol; can form disulfide bonds

Sulfhydryl Biological Examples

Cysteine, coenzyme A, enzyme active sites

Sulfhydryl Form Near Neutral pH

-SH, usually uncharged

Sulfhydryl Polarity

Weakly polar

Sulfhydryl Biological Interpretation

Interacts with water less strongly than hydroxyl groups. Thiols can ionize or form disulfide bonds, depending on pH and molecular context

Methyl

-CH₃

Methyl Key Properties

Nonpolar; hydrophobic; affects shape and recognition

Methyl Biological Examples

Lipid tails, alanine side chain, methylated DNA

Methyl Form Near Neutral pH

-CH₃, uncharged

Methyl Polarity

Nonpolar

Methyl Biological Interpretation

Does not form hydrogen bonds with water and generally increases hydrophobic character