HW #4 72-74, 83-87 (11-17) Flashcards
What are the levels of protein structure?
There are four levels of protein structure: primary, secondary, tertiary, and quaternary. Not all proteins have all four levels. For example only proteins with multiple polypeptide chains have quaternary structure.
Which groups on amino acids react to form a peptide bond?
Peptides are formed by reacting the carboxyl group of one amino acid with the amino group of another amino acid In a covalent (amide) bond. Proteins consist of polypeptide chains; the number of amino acids in a protein is usually 100 or more. The peptide group is planar; this stereochemical constraint plays an important role in determining the three dimensional structures of peptides and proteins.
Why is it important to know the primary structure?
Primary structure is the order in which the amino acids are covalently linked. The primary structure of a protein can be determined by chemical methods. The amino acid sequence (the primary structure) of a protein determines it’s three dimensional structure which in turn determines it’s properties. A striking example of the importance of primary structure is sickle cell anemia, a disease caused by a change in one amino acid in each of two of the four chains of hemoglobin.
Why is alpha helix so prevalent?
The alpha helix is stabilized by hydrogen bonds parallel to the helix axis within the backbone of a single polypeptide chain. The helical conformation allows a linear arrangement of the atoms involved in the hydrogen bonds, which gives the bonds maximum strength and thus makes the helical conformation very stable.
How is the beta sheet different from the alpha helix?
The arrangement of atoms in the beta pleated sheet conformation differs markedly from that in the alpha helix. The peptide backbone in the beta sheet is almost completely extended. Hydrogen bonds can be formed between different parts of a single chain that is doubled back on itself (intrachain bonds) or between different chains (interchain bonds). The hydrogen bonding between peptide chains in the beta pleated sheet gives rise to a repeated zigzag structure. The hydrogen bonds are perpendicular to the direction of the protein chain, not parallel to it as in the alpha helix.
