Amino Acids and Protein Structure

Amino Acids and Protein Structure

• Proteins are biomacromolecules, constructed from amino acids, which carry out diverse functions.
• Learning objectives include listing protein functions, describing amino acid structure, calculating isoelectric points, identifying bonds forming proteins, recognizing protein structures (primary, secondary, tertiary, and quaternary), and explaining protein denaturation.
• Proteins are vital for numerous biological processes.
• Protein functions include catalysis (enzymes), transport, signalling, and structure.

Protein Functions

• Catalysis (enzymes): Enzymes increase reaction rates by lowering activation energy. For example, maltose is broken down to glucose in a fraction of a second, compared to taking 300 years without an enzyme.
• Transport: Proteins transport substances like oxygen (hemoglobin), lipids (lipoproteins), ions, water, and monosaccharides.
• Signalling: Hormones regulate metabolism, and receptors receive signals, initiating cellular responses.
• Structural elements: Cytoskeletons, muscles, hair, and nails are composed of proteins. Some proteins provide structure without direct function within the cell.

Protein Structure

• Proteins are built from amino acid sequences to form complex 3D structures.
• Ribosomes create protein structures via protein folding.
• There are four main protein structures: primary, secondary, tertiary, and quaternary.

Primary Structure

• The primary structure of a protein is its linear amino acid sequence.
• Amino acids are linked by peptide bonds.
• The order of amino acid sequences forms the polypeptide chain.

Secondary Structure

• Secondary structures are local configurations stabilized by hydrogen bonds between amino acid backbones. Common secondary structures are alpha-helices and beta-sheets.
• Secondary structures are frequently broken first during denaturation processes.

Tertiary Structure

• The tertiary structure is the overall 3D shape of a polypeptide chain. It's stabilized by various interactions (hydrogen bonds, disulfide bonds, ionic interactions, hydrophobic interactions, and van der Waals forces) between amino acid R groups.
• Hydrophobic amino acids are typically sequestered inside the protein, and hydrophilic amino acids tend to be on the exterior.

Quaternary Structure

• The quaternary structure describes the assembly of multiple polypeptide chains to form a functional protein.
• The subunits can be identical (homomultimers) or different (heteromultimers). These subunits typically make up the final, functional protein.

Amino Acids

• Amino acids contain an amino group (-NH2), a carboxyl group (-COOH), and a central carbon atom.
• Different variants of R-groups give rise to varying amino acid characteristics.
• There are over 300 different amino acids found in nature, but only 20 are commonly used to build proteins.
• Essential amino acids cannot be synthesized by animals and must be obtained from the diet.
• Amino acids have varying electrical charges (positive, neutral, and negative) and different solubility in water.

Denaturation

• Denaturation is the process by which a protein loses its 3D structure and function.
• Denaturation can be caused by factors like high temperature, extreme pH, organic solvents, heavy metals, and extreme chemical environments.
• Denaturation often leads to a loss of biological activity. The primary structure, comprised of peptide bonds, is unaffected during denaturation.

Renaturation

• Renaturation is the process in which a denatured protein regains its native, functional structure.
• Proteins can renature under ideal conditions.

Amino Acids and pH

• Amino acids are amphoteric; they can act as both acids and bases.
• Amino acids' behaviour depends on pH, because of their acidic and basic groups.
• The isoelectric point (pI) of an amino acid is the pH solution in which an amino acid carries no net charge.

This quiz explores the crucial role of amino acids in protein structure and function. You will learn about different types of protein structures, their functions such as catalysis and transport, and the significance of proteins in biological processes. Test your knowledge on protein denaturation and the bonds that form proteins.