Lecture 14: Proteins and Protein Structure

Vocabulary practice flashcards covering protein composition, functional categories, levels of protein structure, peptide bonds, and bond interaction strengths from Lecture 14.

Amino Acids

The basic building blocks of proteins, consisting of smaller units that attach to one another in long chains.

Proteins

Large, complex biomolecules made up of one or more polypeptide chains required for the structure, function, and regulation of the body's tissues and organs.

Enzymes

Proteins that function as control molecules to regulate biological processes and reactions.

Antibodies (Immunoglobulins)

Defence proteins that recognise and bind specific foreign molecules called antigens.

Actin and Myosin

Two contractile proteins whose interaction enables muscle contraction in the body.

Dipeptide

A peptide molecule formed by the linking of two amino acids.

Tripeptide

A peptide molecule formed by the linking of three amino acids.

Oligopeptide

A peptide molecule formed by linking $4\text{--}10$ amino acids together.

Polypeptide

A macromolecular chain formed by linking more than $10$ amino acids together; proteins consist of one or more of these chains.

Primary Structure

The specific sequence of amino acids in a polypeptide chain, determined by DNA and stabilized by covalent peptide bonds.

N-terminus (Head)

The starting end of a polypeptide chain containing a free amino group, marked as $+H_3N$, which begins with amino acid 1.

C-terminus (Tail)

The terminating end of a polypeptide chain containing a free carboxyl group, marked as $-COO^-$.

Disulfide Bond (Disulfide Bridge)

A strong covalent bond formed between the sulfur atoms of two cysteine amino acids in a protein, possessing a typical bond strength of $\sim 240\,kJ\,mol^{-1}$.

Secondary Structure

The localized folding of a polypeptide chain into $\alpha$ helices or $\beta$ pleated sheets, stabilized by hydrogen bonds.

Tertiary Structure

The overall three-dimensional folding and packing of a polypeptide chain into a specific shape, stabilized by hydrogen bonds, disulfide bridges, and hydrophobic interactions.

Quaternary Structure

The spatial arrangement and assembly of two or more polypeptide subunits into a larger protein molecule, stabilized by hydrogen bonds, disulfide bridges, hydrophobic interactions, and ionic bonds.

R Group (Side Chain)

The variable group on an amino acid (ranging from 1 to 20 atoms) attached to the central carbon that confers unique chemical properties to each amino acid.

Peptide Bond

A covalent $C-N$ bond created via dehydration synthesis linking the amino group ($-NH_2$) of one amino acid to the carboxyl group ($-COOH$) of another.

Polypeptide Backbone

The repeated core chain sequence of atoms ($N-C-C$) throughout a polypeptide, distinct from the variable side chains.

Direction of Polypeptide Synthesis

The unidirectional process whereby polypeptide chains grow exclusively from the N-terminus to the C-terminus.

Hydrophobic Contact

A weak noncovalent interaction between nonpolar side groups in proteins, with a typical strength of $\sim 1\text{--}5\,kJ\,mol^{-1}$.

Ionic Interaction

An electrostatic interaction between oppositely charged groups, with a typical strength of $\sim 20\text{--}80\,kJ\,mol^{-1}$, depending on the surrounding environment.

Amino acids

The basic building blocks of proteins, consisting of a central carbon, an amino group ($-NH_2$), a carboxylic acid group ($-COOH$), a hydrogen atom ($H$), and a unique side chain (R group).

Dipeptide

A peptide molecule formed by the linkage of $2$ amino acids.

Tripeptide

A peptide molecule formed by the linkage of $3$ amino acids.

Oligopeptide

A peptide chain formed by the linkage of $4$ to $10$ amino acids.

Polypeptide

A polymer formed by linking more than $10$ amino acids together; proteins in the body and diet are long polypeptides consisting of hundreds of amino acids.

Actin and myosin

Two contractile proteins whose physical interaction enables muscle contraction.

Antibodies (immunoglobulins)

Defense proteins that recognize and bind to specific foreign molecules called antigens.

Primary structure

The precise linear sequence of amino acids in a polypeptide chain, determined by DNA and stabilized by covalent peptide bonds.

Secondary structure

Localized, regular folding configurations of a polypeptide chain, specifically forming $\alpha$ helices or $\beta$ pleated sheets, stabilized by hydrogen bonds.

Tertiary structure

The overall three-dimensional folding of a single polypeptide chain into a specific shape, stabilized by hydrogen bonds, disulfide bridges, and hydrophobic interactions.

Quaternary structure

The assembly of two or more distinct polypeptide subunits into a larger functional protein complex, stabilized by hydrogen bonds, disulfide bridges, hydrophobic interactions, and ionic bonds.

N-terminus (Head)

The beginning of a polypeptide chain, marked by a free amino group ($+H_3N$).

C-terminus (Tail)

The end of a polypeptide chain, marked by a free carboxyl group ($-COO^-$).

Disulfide bond (disulfide bridge)

A strong covalent bond formed between the sulfur atoms of two cysteine amino acid residues in a protein, with a typical bond strength of $\sim 240\,kJ\,mol^{-1}$.

Hydrophobic contact

A non-covalent interaction that stabilizes protein folding, with a typical strength of $\sim 1\text{--}5\,kJ\,mol^{-1}$.

Hydrogen bond

A stabilizing non-covalent interaction found in secondary, tertiary, and quaternary protein structures, exhibiting a typical strength of $\sim 5\text{--}30\,kJ\,mol^{-1}$.

Ionic interaction

A non-covalent electrostatic interaction between charged residues, possessing a typical strength of $\sim 20\text{--}80\,kJ\,mol^{-1}$, depending on the surrounding environment.

Peptide bond

A covalent $C\text{--}N$ bond formed through a dehydration synthesis reaction that links the amino group ($-NH_2$) of one amino acid to the carboxyl group ($-COOH$) of another, releasing $H_2O$.

Polypeptide backbone

The repeating structural chain of a polypeptide consisting of the continuous atomic sequence $N\text{--}C\text{--}C$.

R group (side chain)

The variable chemical group attached to the central alpha-carbon of an amino acid (ranging from $1$ to $20$ atoms) that determines its unique chemical and physical properties.

Direction of polypeptide synthesis

The unidirectional process during translation in which polypeptide chains are assembled exclusively from the N-terminus to the C-terminus.

Glycine

A special-case amino acid whose side chain consists solely of a single hydrogen atom ($H$).

Cysteine

A special-case amino acid possessing a reactive sulfhydryl side group ($-CH_2\text{--}SH$) capable of forming stabilizing covalent disulfide bridges.