Biology 107Biology 107

Macromolecules IIMacromolecules II

September 9, 2002September 9, 2002

Macromolecules IIMacromolecules II

Student Objectives:Student Objectives: As a result of this lecture and the assigned As a result of this lecture and the assigned reading, you should understand the following:reading, you should understand the following:

1.1. Proteins are biological polymers constructed from amino acid Proteins are biological polymers constructed from amino acid monomers. Each different protein has a unique structure and monomers. Each different protein has a unique structure and function, and protein diversity is based upon these different function, and protein diversity is based upon these different arrangements of a universal set of amino acids.arrangements of a universal set of amino acids.

2.2. There are seven major functional classes of proteins: 1) structural There are seven major functional classes of proteins: 1) structural proteins; 2) contractile proteins; 3) storage proteins; 4) defense proteins; 2) contractile proteins; 3) storage proteins; 4) defense proteins 5) transport proteins 6) signaling proteins 7) enzymes.proteins 5) transport proteins 6) signaling proteins 7) enzymes.

Macromolecules IIMacromolecules II

33.. Amino acids have the same basic structure, with the amino Amino acids have the same basic structure, with the amino group and carboxyl group bonded to a central C atom (the alpha group and carboxyl group bonded to a central C atom (the alpha C). This central carbon also has an attached H atom and a C). This central carbon also has an attached H atom and a chemical group called the "R" group. chemical group called the "R" group.

4.4. It is the "R" group that is the variable part of the amino acid and It is the "R" group that is the variable part of the amino acid and determines the specific properties of each of the 20+ amino acids determines the specific properties of each of the 20+ amino acids in proteins. in proteins.

5.5. Amino acids are linked together by dehydration synthesis, with Amino acids are linked together by dehydration synthesis, with the resulting covalent linkages called peptide bonds.the resulting covalent linkages called peptide bonds.

Macromolecules IIMacromolecules II6. The specific shape that determines a protein's function comprises 6. The specific shape that determines a protein's function comprises

four (4) successive levels of structure, each determined by the four (4) successive levels of structure, each determined by the previous level. previous level.

a.a. The primary structure is the sequence of amino acids The primary structure is the sequence of amino acids forming forming the polypeptide chain. the polypeptide chain.

b.b. The secondary structure consists of polypeptide chain coils The secondary structure consists of polypeptide chain coils or or folds held in place by hydrogen bonding between the - N - H folds held in place by hydrogen bonding between the - N - H

and the - C = O groups along the backbone of the chain. and the - C = O groups along the backbone of the chain. Coiling or folding of a polypeptide chain usually results in Coiling or folding of a polypeptide chain usually results in

one one of two repeating structures, either an alpha-helix or a beta-of two repeating structures, either an alpha-helix or a beta-pleated sheet. pleated sheet.

Macromolecules IIMacromolecules II

c.c. Tertiary structure is the overall 3-dimensional shape of a Tertiary structure is the overall 3-dimensional shape of a polypeptide; tertiary structure is maintained by bonding polypeptide; tertiary structure is maintained by bonding (hydrogen, ionic and covalent [disulfide bridges]) and hydrophobic (hydrogen, ionic and covalent [disulfide bridges]) and hydrophobic or hydrophilic interactions between the "R" groups of various or hydrophilic interactions between the "R" groups of various amino acids in the polypeptide chain.amino acids in the polypeptide chain.

d.d. Quaternary structure is produced by the bonding interactions of Quaternary structure is produced by the bonding interactions of two (2) or more polypeptide subunits. Quaternary structure is two (2) or more polypeptide subunits. Quaternary structure is maintained by hydrogen bonding, ionic interactions, and maintained by hydrogen bonding, ionic interactions, and hydrophobic interactions.hydrophobic interactions.

Structure of Amino Acids with Nonpolar “R” Structure of Amino Acids with Nonpolar “R” GroupsGroups

Structure of Amino Acids with Polar or Ionic “R” Structure of Amino Acids with Polar or Ionic “R” GroupsGroups

Primary Protein Primary Protein StructureStructure

Consist of sequence of amino acidsConsist of sequence of amino acids

Has a polarity – amino end (#1 amino Has a polarity – amino end (#1 amino acid of the chain) and carboxyl acid of the chain) and carboxyl endend

Dictates the other levels of folding Dictates the other levels of folding and structureand structure

Secondary Protein Structure

Bonds That Stabilize Tertiary StructureBonds That Stabilize Tertiary Structure

Quaternary Protein Structure

Summary of Levels of Protein StructureSummary of Levels of Protein Structure