Introduction to Biochemistry BCH 201

Introduction to Biochemistry (BCH 201)

• This course covers introductory chemistry and protein classification.
• It includes protein structures: primary, secondary, tertiary, and quaternary.
• The course will also explore biological functions of proteins.
• Methods of protein isolation, purification, and identification will be examined.
• Basic principles of tests for proteins and amino acids will be discussed.

What are Proteins?

• Proteins are complex macromolecules composed of amino acids.
• Amino acids are the building blocks of proteins.
• An amino acid is a simple organic compound with a basic amino group (-NH2) and an acidic carboxyl group (-COOH), unique to each amino acid.
• Proteins come from various sources, including meat, fish, eggs, and dairy products, as shown in the images.

What are Amino Acids?

• Amino acids are the monomers that make up proteins.
• A specific number of amino acids link together through peptide bonds.
• There are 20 different amino acids.

Synthesis of Peptides or Peptide Bonds

• A peptide is a short chain made up of one or more amino acids.
• Peptide chains form when two or more amino acids are bonded together by peptide bonds.
• For each peptide bond formed, one water molecule is lost.

Peptides and Polypeptides

• Peptides can be categorized based on the number of amino acids: dipeptides (2), tripeptides (3).
• Polypeptides are peptides with more than ten amino acids.
• The peptide bond formed in proteins is a special amide bond.

What are Polypeptides?

• Polypeptides are long chains of amino acids joined by peptide bonds.
• One or more polypeptides form a protein.
• A polypeptide has an amino-terminal (N-terminal) end and a carboxyl-terminal (C-terminal) end.
• The sequence of amino acids is determined by the mRNA codons.
• The sequence of nucleotides in mRNA ultimately determines the sequence of amino acids in the polypeptide.

Properties of Proteins

• Solubility in Water: Proteins are generally soluble in water or dilute salt solutions.
• Denaturation and Renaturation: Proteins can be denatured by agents like heat, urea, radiation, pH, or chemical agents, causing the unfolding of polypeptide chains without hydrolysis. The denaturation of a protein affects its secondary and tertiary structures, but not its primary structure. Renaturation is the process where a denatured protein returns to its native state.
• Buffering Capacity: Proteins have buffering capacity, resisting slight changes in pH. The buffering capacity arises from the presence of amino and carboxylic groups in proteins.
• Coagulation: When proteins are denatured by heat, they form insoluble aggregates called coagulum. (e.g., albumins and globulins).
• Isoelectric Point (pI): The pH at which the overall charge of a protein is zero. At the pI, a protein will not migrate under an electric field.
• Molecular Weights: The molecular weight of a protein is determined by the total number of amino acids, with an average weight of 110 g/mol per amino acid, and range from 5000 to 10⁹ Daltons.
• Maximum absorption wavelength: Proteins absorb UV light at a maximum wavelength of 280 nm. Nucleic Acids absorb at 260 nm.

Post-translational Modifications

• Modifications (phosphorylation, glycosylation, ADP ribosylation, methylation, hydroxylation, and acetylation) occur after protein synthesis on the ribosome.
• These modifications alter the charge and interactions between amino acid residues, changing the protein's three-dimensional structure and function.

Protein Bonding

• Besides primary peptide bonds, secondary bonds contribute to protein structure stability.
• Hydrogen bonds form between electronegative atoms and hydrogen atoms in peptide linkages, stabilizing secondary structure.
• Ionic bonds arise between acidic and basic groups, aiding in protein-protein interactions, although weaker than hydrogen bonds.
• Disulfide bonds are covalent bonds formed between cysteine residues via oxidation. These bonds contribute significantly to tertiary structure stability.
• Hydrophobic and Hydrophilic Interactions: Hydrophobic R groups cluster together to minimize water interactions, while hydrophilic interactions lead to hydrogen bonding.

This quiz covers fundamental concepts in biochemistry, focusing on protein classification and structure. Explore the intricacies of amino acids, their roles, sources, and the methods used for protein isolation and purification. Test your understanding of the biological functions of proteins and amino acids.