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.

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