Protein Structure and Amino Acids

Structure of Proteins

• Proteins are polymers made up of many amino acids.
• Each amino acid acts as a monomer; together they form polypeptides.
• Peptide bonds connect each amino acid residue.

Amino Acid Structure

• An amino acid consists of a chiral carbon with a hydrogen, an amine group, a carboxyl group, and an R group.
• The nitrogen side represents the N-terminal; the carboxyl side is the C-terminal.
• Amino acids can undergo condensation reactions, losing water, to form peptide bonds.

Formation of Peptides

• A dipeptide is formed when two amino acids combine through a dehydration reaction, resulting in the loss of one water molecule.
• Peptide bonds are covalent and are strong, making them difficult to break.

Levels of Protein Structure

• Four levels of protein structure: primary, secondary, tertiary, and quaternary.

Primary Structure

• The primary structure is the specific sequence of amino acids in a protein.
• The sequence directly impacts the protein's shape and function.

Secondary Structure

• The secondary structure consists of localized shapes, primarily alpha helices and beta pleated sheets.
• Alpha helices are stabilized by hydrogen bonds between the NH group of one amino acid and the carbonyl group of another, with each turn involving about 3.6 amino acid residues.
• Beta pleated sheets are similarly stabilized by hydrogen bonds between different amino acids.

Tertiary Structure

• The tertiary structure is the three-dimensional folding pattern of a single protein subunit.
• This includes a combination of alpha helices and beta pleated sheets, as well as other structures.

Quaternary Structure

• The quaternary structure arises from the combination of multiple protein subunits.
• Hemoglobin is an example, consisting of four subunits: two alpha and two beta subunits, forming a complex quaternary structure.

Structure of Proteins

• Proteins are long chains of amino acids, known as polymers.
• Amino acids serve as monomers, linking together to form polypeptides.
• Peptide bonds are strong covalent connections linking each amino acid residue.

Amino Acid Structure

• Each amino acid features a chiral carbon bonded to a hydrogen atom, an amine group, a carboxyl group, and a unique R group.
• The nitrogen side indicates the N-terminal, while the carboxyl side denotes the C-terminal of the amino acid.
• Condensation reactions allow amino acids to lose water and form peptide bonds.

Formation of Peptides

• Dipeptides are formed by two amino acids joining through dehydration reactions, resulting in the elimination of one water molecule.
• Peptide bonds are robust and require significant energy to be broken.

Levels of Protein Structure

• Proteins have four distinct structural levels: primary, secondary, tertiary, and quaternary.

Primary Structure

• The primary structure refers to the specific linear sequence of amino acids in a polypeptide chain.
• The order of amino acids is crucial, as it directly influences the protein's overall shape and functionality.

Secondary Structure

• The secondary structure comprises local folding patterns, primarily alpha helices and beta pleated sheets.
• Alpha helices are stabilized by hydrogen bonds between the NH group of one amino acid and the carbonyl group of another, with each turn consisting of approximately 3.6 amino acids.
• Beta pleated sheets are also stabilized by hydrogen bonds and involve multiple amino acids across different strands.

Tertiary Structure

• The tertiary structure represents the three-dimensional shape of a single protein subunit.
• This structure results from the interplay of various secondary structures, as well as other unique motifs.

Quaternary Structure

• The quaternary structure forms when multiple protein subunits combine to create a functional protein complex.
• Hemoglobin serves as a prime example, made up of four subunits: two alpha and two beta, exhibiting a complex quaternary configuration.