Biology chapter 3

Four major groups of biological molecules

1. Carbohydrates: sugars and sugar polymers; energy and structure

2. Lipids: mostly nonpolar molecules; energy storage, membranes, signaling

3. Proteins: amino acid polymers; enzymes, transport, movement, regulation

4. Nucleic acids: nucleotide polymers; information storage and transfer

Carbon Chemistry

▪ Carbon has four valence electrons and can form four covalent bonds.

▪ Carbon can bond to itself, forming chains, branches, and rings.

▪ Carbon skeletons can be modified by functional groups.

▪ This flexibility creates enormous molecular diversity.

Hydrocarbon skeletons

▪ Hydrocarbons contain only carbon and hydrogen.

▪ Carbon skeletons may be linear, branched, or ring-shaped.

▪ Single and double bonds change molecular shape and

flexibility.

▪ Many biological molecules are modified hydrocarbon skeletons

Functional groups

▪ Functional groups are small reactive groups of atoms that give larger molecules specific chemical properties.

▪ Common groups include :

▪ OH: Hydroxyl

▪ C=O: Carbonyl,

▪ OH-C=O: Carboxyl

▪ NH3: Amino

▪ PO34-: phosphate

▪ SH: Sulfhydryl

▪ Functional groups help determine how molecules interact with water and with each other.

Structural isomers

▪ Glucose and fructose both have the formula C₆H₁₂O₆.

▪ Glucose has an aldehyde group at the end of the carbon chain.

▪ Fructose has a ketone group inside the carbon chain.

▪ Same formula does not mean same function.

Stereoisomers

▪ Stereoisomers are mirror-image forms of a molecule.

▪ The same atoms are connected in the same order, but

arranged differently in space.

▪ Biological enzymes often recognize only one form.

▪ This is why molecular shape matters

Example: D-Glucose and L-Glucose

▪ Chiral centers have 4 different

substituents

▪ Enantiomers: arranged in a mirror

image

▪ Diastereomers: not mirror images

▪ Why is this important?

▪ D-glucose is recognized by our

enzymes and is metabolized to give us

energy (calories)

▪ L-glucose is not and thus hase zero

calories (artificial sugar)

Monomers vs polymers

▪ A monomer is a small molecular subunit.

▪ A polymer is a larger molecule built from repeating monomers.

▪ Carbohydrates, proteins, and nucleic acids are built by linking monomers.

▪ Lipids are a major biomolecule class, but most are not true polymers

Dehydration synthesis

▪ Synthesis via dehydration reaction to remove water.

▪ A covalent bond forms between monomers.

▪ This reaction builds larger molecules from smaller

subunits.

▪ Examples: glycosidic bonds and peptide bonds.

Hydrolysis

▪ Hydrolysis adds water to break a covalent

bond

▪ Digestion relies heavily on hydrolysis.

▪ Hydrolysis releases monomers that cells can

absorb and reuse.