Chapter 3- Protein Structure and Function
Protein type Role in Cell or Organism
Antibodies and Defence- destruction of disease-causing viruses and bacteria
Contractile and motor Movement
Enzymes Catalyze chemical reactions
Hormones Act as signals that help coordinate the activities of many cells
Receptor proteins Receive chemical signals from outside cell and initiate response
Structural proteins Provide support for cells and tissues; form structures such as hair, feathers,
cocoons and spider webs
Transport proteins Move substances across cell membrane and throughout body
-Amino acid structure: Carbon attached to 1)amino functional group (NH ) 2)c2rboxyl functional group
(COOH) 3)H 4)R-group (differentiates between amino acids)
-In water, NH 2ttracts proton, forms NH +3and carboxyl group loses proton to form COO-. The charges
on these functional groups:
1. Help amino acids stay in solution where they can interact with each other and other solutes.
2.Add to their chemical reactivity.
- Nature of side chains:
1. amino acids with non-polar side chains do not have charged or electronegative atoms capable
of forming hydrogen bonds with water. These R-groups are hydrophobic. Polar side chains are
hydrophilic, dissolve in water.
2. Influences their chemical reactivity.
Structural Isomers: Same atoms but differ in order in which covalently bonded atoms are attached.
Geometric isomers: Same atoms but differ in the arrangement of atoms or groups on either side of a
double bond or ring structure.
Optical isomers: Same atoms but differ in arrangement of atoms or groups around a carbon atom that has
4 different groups attached.
-Monomers link to form polymers. Called polymerization. Proteins are polymerized by amino acids.
-Polymers form by dehydration synthesis (loss of H2O molecule). Break apart by hydrolysis, addition of
water molecule. Peptide bond: Bond between carboxyl group of one amino acid and amino group of another. Electrons are
partially shared between the neighboring carbonyl functional group and peptide bond.
Residue: amino acids in polypeptide
Chain of peptide bonds (backbone): 1) the side chain present in each residue extend out from it 2) it has
directionality 3) it is flexible
-Oligopeptides: less than 50 amino acids.
More than 50 amino acids are called proteins.
Level Description Stabilized by
Primary The sequence of amino acids in a Peptide bonds
Secondary Formation of a-helices and B-pleated Hydrogen bonding between groups
sheets in a polypeptide along the peptide-bonded backbone
thus, depends on primary structure
Tertiary Overall 3-D shape of a polypeptide Bonds and other interactions between
(includes contribution from secondary R-groups, or between R-groups and the
structures) peptide-bonded backbone; thus depends
on primary structure
Quaternary Shape produced by combos of Bonds and other interactions between
polypeptides (thus combination of R-groups