Proteins: Their Structure and Biological Functions. Biological Functions of Proteins. Proteins are the agents of biological function Enzymes - Ribonuclease Regulatory proteins - Insulin, PCNA Transport proteins - Hemoglobin Structural proteins - Collagen
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Proteins are the agents of biological function
Unrelated proteins assume similar structures to fulfill common functions
One or more polypeptide chains
it has two alpha chains and two beta chains
Amino acid composition provides some (limited) clues about protein structure-function
- Primary sequence
- Secondary local structures
- Tertiary overall 3-dimensional
- Quaternary subunit organization
All of the information necessary for folding the peptide chain into its "native” structure is contained in the primary amino acid structure of the peptide.
Frederick Sanger was the first - in 1953, he sequenced the two chains of insulin.
- real amino acid sequencing
- sequencing the corresponding DNA in the gene
Six atoms of the peptide group lie in a plane
The atoms of the peptide bond lie in a plane
Two degrees of freedom per residue for the peptide chain
Unfavorable overlap precludes some combinations of phi and psi
All these are local structures that are stabilized by hydrogen bonds
Composed of beta strands
(aka beta bend, tight turn)
If the sequence holds the secrets of folding, can we figure it out?
So, how do proteins fold?
What are they?
What are the relevant numbers?
for the interaction of nonpolar residues with the solvent
How do proteins recognize and interpret the folding information?
Some design principles
The Forces That Drive Folding
More design principles
A nonpolar helix in citrate synthase:
A polar helix in calmodulin:
An important insight into protein structure
Proteins may be "conjugated" with other chemical groups
What are the forces driving quaternary association?