Biological Science Core Vocabulary

Amino Acid

A biological molecule consisting of a central carbon ($\alpha$-carbon) bonded to a hydrogen atom, an amino group ($\text{--NH}_2$ or $\text{--NH}_3^+$), a carboxyl group ($\text{--COOH}$ or $\text{--COO}^-$), and a variable side chain (R-group).

Peptide Bond

A covalent $\text{C--N}$ bond formed between the carboxyl group of one amino acid and the amino group of another through a condensation reaction.

Primary Structure of a Protein

The unique sequence of amino acids in a polypeptide chain, stabilized by peptide bonds.

Secondary Structure of a Protein

Localized folding patterns within a polypeptide, most commonly $\alpha$-helices and $\beta$-pleated sheets, formed by hydrogen bonds between carbonyl and amino groups along the peptide backbone.

Tertiary Structure of a Protein

The overall three-dimensional shape of a single polypeptide chain, resulting from interactions involving R-groups, such as hydrogen bonds, hydrophobic interactions, van der Waals interactions, disulfide bonds, and ionic bonds.

Quaternary Structure of a Protein

The overall protein structure produced by combinations of two or more polypeptide subunits.

Molecular Chaperone

A specialized protein, such as $\text{Hsp90}$, that facilitates protein folding and prevents non-specific aggregation between unfolded polypeptides.

Prion

An altered, misfolded form of a normal protein that acts as an infectious agent by inducing other normal protein molecules to fold into the disease-causing shape.

Active Site

The specific region on an enzyme where substrate molecules bind and undergo a chemical reaction.

Aldose

A monosaccharide characterized by having a carbonyl group ($\text{C=O}$) located at the end of its carbon chain.

Ketose

A monosaccharide characterized by having a carbonyl group ($\text{C=O}$) located within the carbon chain.

Glycosidic Linkage

A covalent bond formed between two hydroxyl groups of monosaccharides via a condensation reaction.

Starch

A plant energy-storage polysaccharide made of $\alpha$-glucose monomers connected by $\alpha\text{-1,4-}$ and $\alpha\text{-1,6-glycosidic}$ linkages, consisting of unbranched amylose and branched amylopectin.

Glycogen

A highly branched energy-storage polysaccharide in animal liver and muscle cells composed of $\alpha$-glucose monomers joined by $\alpha\text{-1,4-}$ and $\alpha\text{-1,6-glycosidic}$ linkages.

Cellulose

A structural polysaccharide made of $\beta$-glucose monomers linked by $\beta\text{-1,4-glycosidic}$ bonds, providing structural support in the cell walls of plants and algae.

Chitin

A structural polysaccharide composed of N-acetylglucosamine ($\text{NAG}$) monomers with $\beta\text{-1,4-glycosidic}$ linkages, providing support in fungal cell walls and exoskeletons of arthropods.

Peptidoglycan

A complex structural polysaccharide in bacterial cell walls consisting of alternating $\text{N-acetylglucosamine (NAG)}$ and $\text{N-acetylmuramic acid (NAM)}$ residues cross-linked by peptide bonds.

Glycoprotein

A molecule consisting of a protein covalently linked to carbohydrate chains (oligosaccharides), functioning as a surface cell-identity marker.

Nucleotide

The monomer subunit

Amino Acid

An organic molecule consisting of a central $\alpha$-carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R-group).

R-group (Side Chain)

The variable portion of an amino acid core structure that determines its unique chemical properties and solubility.

Peptide Bond

The covalent $C-N$ bond formed between the carboxyl group of one amino acid and the amino group of another via a condensation reaction.

Primary Structure

The linear, unique sequence of amino acids in a polypeptide chain.

Secondary Structure

Local protein folding patterns, such as $\alpha$-helices and $\beta$-pleated sheets, stabilized by hydrogen bonds along the peptide backbone.

Tertiary Structure

The overall three-dimensional shape of a single polypeptide, stabilized by interactions among R-groups and between R-groups and the backbone.

Quaternary Structure

The overall protein structure resulting from the combination of two or more polypeptide subunits.

Molecular Chaperones

Specialized proteins, such as Hsp90, that assist in proper protein folding and prevent improper aggregation of unfolded polypeptides.

Prion

An altered, infectious misfolded form of a normal protein that can induce other normal protein molecules to adopt its disease-causing shape.

Active Site

The specific region on an enzyme where substrate molecules bind and undergo a chemical reaction.

Monosaccharide

The simplest sugar monomer with the general molecular formula $(CH_2O)_n$, serving as a building block for complex carbohydrates and a source of chemical energy.

Aldose

A monosaccharide featuring a carbonyl group ($C=O$) located at the end of its carbon chain.

Ketose

A monosaccharide featuring a carbonyl group ($C=O$) located within its carbon chain.

Glycosidic Linkage

A covalent bond formed between two hydroxyl groups of monosaccharides during a condensation reaction.

Starch

An energy storage polysaccharide found in plant cells, consisting of unbranched amylose ($\alpha$-1,4 linkages) and branched amylopectin ($\alpha$-1,6 linkages).

Glycogen

A highly branched energy storage polysaccharide composed of $\alpha$-glucose monomers found in animal liver and muscle cells.