Cell Biology: Study of Mutants and Endomembranes

Study of Endomembranes

• 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

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

Biosynthetic Secretory Pathway in Yeast

• 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

• 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.

Liposomes without Coat Proteins

• 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.

Vesicle Transport

• 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.