Chemistry for life Lecture 17
Each polypeptide has a unique linear sequence of amino acids with a carboxyl end (C-terminus) and an amino end (N-terminus)
The function of a protein depends on its ability to recognize and bind to another molecule
Four levels of protein structure
The primary structure of protein is its unique sequence of amino acids
Secondary structure, found in most proteins consists of coils and folds in the peptide chain
Tertiary structure is determined by various interactions among various side chains (R groups )
Quaternary structure results when a protein consists of multiple peptide chains
Typical secondary structures are a coil called an alpha helix and a folded structure called a beta pleated sheet
Tertiary structure, the overall shape of the polypeptide results from the interactions between R groups, rather than interactions between back bone constituents, these interactions include hydrogen bonds, ionic bonds, hydrophobic interactions and van der waal interactions. Strong covalent bonds called disulfide bridges may reinforce the protein's structure
when two or more peptide chains form one macromolecule. Collagen is a fibrous protein consisting of three polypeptides coiled like a rope. Hemoglobin is a globular protein consisting of four polypeptides; two alpha and two beta subunits
Sickle cell disease, A change in primary structure;
A slight change in primary structure can affect a protein's structure and ability to function.
Sickle cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
The abnormal hemoglobin molecules cause the red blood cells to aggregate into chains and to deform into a sickle shape
What determines protein structure?
In addition to primary structure, physical and chemical conditions can affect structure, Alterations in pH, slat concentration, temperature or other environmental factors can cause a protein to unravel. This loss of a protein's native structure is called denaturation. A denatured protein is biologically inactive
Protein folding in the cell
It is hard to predict a protein's structure from its primary structure. Most protein's go through several stages on their way to stable structure.
Diseases such as Alzheimer's, Parkinson's and mad cow disease are associated with misfolded protein's
Scientists use X-RAY CRYSTALLOGRAPHY to determine a protein's structure, another method is nuclear magnetic resonance (NMR) spectroscopy, which does don require protein crystallization
Bioinformatics is another approach to prediction of protein structure from amino acid sequences
NMR
Nuclear Magnetic Resonance
High resolution, atomic level methodology for the determination of chemical and biochemical structures of molecules