Biochemistry: Amino Acids and Protein Structure

Amino Acids and Protein Structure

• Proteins are biomacromolecules made of amino acids.
• Proteins perform many crucial functions.
• Learning objectives for biochemistry course include listing protein functions, describing amino acid structure, calculating isoelectric point, recognizing protein structures, and explaining protein denaturation.

Learning Objectives

• List the functions of proteins.
• Describe amino acid structure.
• Calculate isoelectric points.
• Recognize the primary, secondary, tertiary, and quaternary structures in proteins.
• Explain protein denaturation.

Proteins

• Proteins are biomacromolecules composed of amino acids.
• They are responsible for various essential functions.

Protein Functions

• Catalysis (Enzymes): Increase the reaction rate of metabolic chemical reactions by decreasing activation energy.
• Transport: Transport molecules throughout the circulatory system or between cellular compartments (e.g., hemoglobin transports oxygen).
• Signalling: Hormones direct and regulate metabolism in the body. Receptors receive signals and play a role in cellular response.
• Structural Elements: Provide support and shape to cells and tissues (e.g., cytoskeleton, hair, nails).

Amino Acids

• Amino acids have a common structure with an amino group, a carboxyl group, a central carbon atom (alpha carbon), and a variable side chain (R group).
• Twenty standard amino acids are commonly found in proteins.
• Twenty-one possible amino acids.
• Different side chains create diverse properties among amino acids.
• Essential amino acids cannot be synthesized in the body and must be obtained from food.
• The 20 most common amino acids in proteins are directly encoded by DNA.
• Other amino acids can also be utilized.
• Amino acids are amphoteric, acting as both a base and an acid.
• The properties of amino acids are pH dependent; the charge of side chains change depending on the pH.
• The isoelectric point (pI) is the pH at which the amino acid has a zero net charge.

Protein Structure

• Proteins have different levels of structure.
• Primary: The linear sequence of amino acids.
• Secondary: Local folding patterns like α-helices and β-sheets stabilized by hydrogen bonding.
• Tertiary: The overall 3D structure of a single polypeptide chain stabilized by diverse interactions among amino acid side chains, including hydrogen bonds, hydrophobic interactions, ionic bonds, and disulfide bridges.
• Quaternary: The arrangement of multiple polypeptide chains into a larger functional unit and the formation of hetero or homodimers, homotrimers/tetramers, etc.
• Ribosomes are responsible for protein's 3D construction.

Peptide Bond

• Peptide bonds form between amino acids during protein synthesis.
• One molecule of water is released during this bond formation making it a dehydration reaction.
• Peptide bonds link amino acids in a specific linear sequence defining the primary structure of a protein, and they are preserved even after protein denaturation.

Denaturation

• Denaturation disrupts the secondary, tertiary, and sometimes quaternary structures of a protein.
• Primary structure (peptide bonds) remains intact.
• Denaturation results in a loss of biological activity.
• Factors that cause denaturation include high temperatures, changes in pH, organic solvents, and certain chemical agents.

Renaturation

• Proteins can sometimes regain their natural shape (native conformation) after denaturation under specific conditions.

Test your knowledge on the critical concepts of amino acids and protein structure essential for understanding biochemistry. This quiz will cover protein functions, amino acid structures, and various levels of protein organization. Delve into topics like isoelectric points and protein denaturation.