BIOL 200 Lecture Notes - Lecture 25: Homotrimer, Hypervariable Region, Replisome
25 Jan 2017
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Document Summary
Quaternary structure: the number and relative positions of the subunits in multimeric domains ie: hemagglutinin ha is a homotrimer made of three identical polypeptides associated together. Dimmer, trimer, tetramer; homomultimer (subunits are identical), heteromultimer (subunits are different) Macromolecular assemblies: association at even higher levels; up to a megadalton in mass; contains tens to hundreds of polypeptide chains, sometimes also other biopolymers like nucleic acids (ie ribosomes have inside proteins made of polypeptides, all assembled) Examples of macromolecular assemblies: transcription initiation machinery, replisome, spliceosome, nuclear pore complex, components of replication fork (topoisomerase, polymerase, primase, helicase), proton pump. Evolution of proteins conserves structure and function, but not primary sequence. One can change amino acids without changing the structure; ie change leucine for isoleucine (both are hydrophobic) If a point mutation is made in a place that breaks alpha helix or beta sheets, the probability of having a functional protein is very low because whole structure will break.
