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.