Biomolecules and Proteins: Structure and Function in Anatomy & Physiology

Biomolecules

Definition and Major Elements

Biomolecules are organic molecules essential for life, forming the structural and functional basis of living organisms. They are primarily composed of covalently bonded carbon and hydrogen, and often contain oxygen, nitrogen, and sometimes phosphorus or sulfur.

• Organic molecules: Compounds containing carbon atoms bonded to hydrogen, often forming complex structures.

• Key elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulfur (S).

• Role: Biomolecules make up most of our bodies and are responsible for biological processes.

Main categories of biomolecules:

• Carbohydrates (e.g., starch): Provide energy and structural support.

• Lipids (e.g., triacylglycerol): Store energy, form cell membranes.

• Proteins (e.g., enzymes): Perform a wide range of functions, including catalysis, transport, and structural roles.

Proteins

Structure of Amino Acids

Proteins are polymers made from monomers called amino acids. Each amino acid has a central carbon atom bonded to four groups:

• Amino group (–NH2)

• Carboxyl group (–COOH)

• Hydrogen atom

• Variable side chain (R group): Determines the properties and identity of the amino acid

Peptide bonds connect the carboxyl group of one amino acid to the amino group of another, forming polypeptide chains through dehydration synthesis:

• Dehydration synthesis: Removal of water to form a covalent bond between amino acids.

Example equation for peptide bond formation:

• $\text{Amino acid}_1 + \text{Amino acid}_2 \rightarrow \text{Dipeptide} + H_2O$

Levels of Protein Structure

The structure of a protein determines its function. Proteins can vary in length from short peptides (10–50 amino acids) to large polypeptides (up to 10,000s of amino acids).

• Primary structure: The sequence of amino acids in a polypeptide chain.

• Secondary structure: Local folding patterns such as alpha helices and beta sheets, stabilized by hydrogen bonds.

• Tertiary structure: The overall three-dimensional shape of a single polypeptide, determined by interactions among R groups.

• Quaternary structure: The arrangement of multiple polypeptide chains into a functional protein (not shown in the images, but important for some proteins).

Key points:

• Amino acid sequence determines protein folding.

• Folding determines protein function.

• Complexity of folding increases with protein size and sequence diversity.

Protein Functions

Proteins perform a wide range of functions in cells and tissues, making them the most versatile biomolecules.

• Enzymes: Catalyze biochemical reactions (e.g., enzyme-substrate complex).

• Transport proteins: Move substances across cell membranes (e.g., carrier proteins).

• Structural proteins: Provide support and shape to cells and tissues.

• Signaling proteins: Transmit signals within and between cells.

• Defense proteins: Protect against pathogens (e.g., antibodies).

Examples:

• Enzyme-substrate complex: Enzymes bind substrates to convert them into products.

• Carrier proteins: Facilitate movement of molecules like ATP across membranes.

• Ribosome: A protein-RNA complex that synthesizes proteins.

Additional info: Protein structure and function are central topics in Anatomy & Physiology, as proteins are involved in nearly every cellular process, including metabolism, signaling, and structural integrity.