Cell Biology: Study of Mutants and Endomembranes

Study Notes

A mutant is an organism with one or more genes that encode abnormal proteins.
When a protein encoded by a mutant gene is unable to carry out its normal function, the cell carrying the mutation exhibits a characteristic deficiency.
Determining the precise nature of the deficiency provides information on the function of the normal protein.

Isolation of proteins from yeast has led to the identification of homologous proteins in mammals, pointing to the conserved nature of endomembrane systems.

Vesicles bud from the Endoplasmic Reticulum (ER) and travel to the Golgi complex, where they fuse with the Golgi cisternae.
The Golgi complex is involved in protein synthesis and secretion.

Cell-free systems don't contain whole cells and have provided information about the roles of proteins involved in membrane trafficking.
In Experiment 1, ribosomes and required ingredients were used to synthesize proteins, which were released into the aqueous fluid or trapped within the lumen of vesicles.
The microsomal membrane was not required for incorporation of amino acids into proteins but for sequestering proteins within the ER cisternal space.

Vesicle budding does not occur in the absence of coat proteins.
Liposomes incubated with purified proteins that comprise coats on the cytosolic surface of transport vesicles within the cell can induce vesicle budding.

Vesicles form by membrane budding, during which membrane proteins of the donor membrane are incorporated into the vesicle membrane.
Soluble proteins in the donor compartment are bound to specific receptors.
Vesicles transport materials from a donor compartment to a recipient compartment, such as the Golgi complex.