Biology 120 Notes (Part 5) Continuing the Discussion of Macromolecules

Key Point

• Each monosaccharide has a unique form and therefore function.

The Structure of Polysaccharides

• Glycosidic bonds (linkages) join monosaccharides together through dehydration reactions.

Other Common Monosaccharides

• Maltose (grain sugar), lactose (milk sugar), and sucrose (table sugar) are common monosaccharides found in everyday use.

• All are created via formation of covalent glycosidic linkages.

Polysaccharides

• Polysaccharides are a long chain of monosaccharides joined by glycosidic linkages.

• They may be branched or unbranched and may consist of multiple types of monosaccharides.

• Starch is a storage polysaccharide in plants. 1. Plants store sugar as starch. It is composed of glucose monomers in a helix.

• Glycogen is a highly branched storage polysaccharide in animals. 2. Animals store sugar as glycogen. It is stored in liver and tissue muscle cells.

• Cellulose is a structured polysaccharide in plants. Cellulose is a structural polymer. It makes up most of the plant cell walls.

Chitin: A Structural Polysaccharide

• Chitin is a structural polymer found in cell walls of fungi and exoskeletons of insects and crustaceans.

• Peptidoglycan is a structural polysaccharide. 5. Peptidoglycan is a structural polymer found in cell walls.

Protein Structures and Function

• Macromolecules are large molecules made of small molecules joined together.

• (Review: The four classes of organic macromolecules are: proteins, lipids, nucleic acids, and carbohydrates.)

Functions of Proteins

• They are a catalyst for enzymes.

• Collagen and keratin are part of the structure of proteins.

• Proteins transport hemoglobin and membrane proteins.

• Proteins defend against antibodies.

• Proteins signal hormones.

• Proteins assist in movement.

The Structure of Amino Acids

• Amino acids are protein monomers.

Most proteins are made from combinations of twenty amino acids.

The Nature of Side Chains

• The twenty amino acids differ only in their unique R-group, or side chain.

Polymerization of Amino Acids

• Amino acids are linked when a bond forms between a carboxyl group of one amino acid and an amino group of another.

• The resulting C-N bond is called a peptide bond.

What is the Difference Between Polypeptides and Proteins?

• Polypeptides are a chain of amino acids joined together with peptide bonds.

• Proteins are a polypeptide or multiple peptides that have a unique structure and function.

What Do Proteins Look Like?

• Proteins have unparallel diversity of size, shape, and chemical properties.

• Proteins serve diverse functions in cells because structure gives rise to function.

Proteins Have Four Basic Structures

• Proteins have four basic structures which are: primary, secondary, tertiary, and quaternary.

• The primary structure has a sequence of amino acids.

• The secondary structure occurs when polypeptides coil or fold in a certain way.

• It can look like an a-helix or B-sheet.

• The secondary structure is formed by hydrogen bonds.

Tertiary Structure

• Folding results in a final 3-D shape of a polypeptide.

• Globular proteins exhibit tertiary structure.

• The shape is held together by hydrogen bonds.

• Ionic bonds and covalent bonds occur between “R groups.”

Quaternary Structure

• Many proteins contain several distinct polypeptide subunits that interact to form a single structure.

• The bonding of two or more distinct polypeptide subunits makes up a quaternary structure.

Folding and Functioning

• Protein structuring is hierarchal.

• Quaternary structure is based on tertiary structure, which is based in part on secondary structure.

• All three of the higher-level structures are based on primary structure.

• Combined effects of primary, secondary, and tertiary structure, and sometimes quaternary structure allow for diversity in protein form and function.

Normal Folding is Crucial to Functioning

• A denatured (unfolded) protein is unable to function normally.

• For example, when an egg is cooked, it cannot go back to being an egg that has not been cracked.