extraction of pure proteins from cells

Overview of Protein Extraction
  The extraction of pure proteins from cells involves the isolation and purification of proteins of interest, which is essential because various proteins exist in a single cell, each with unique characteristics based on their primary structure.

Homogenization Process
  To purify proteins, they first need to be released from cells and subcellular organelles through a process called homogenization, which disrupts the cellular membrane (cell lysis). Common homogenization techniques include:
  1. Blending: Grind tissue with a suitable buffer using a blender to break open cells.
  2. Potter Elvehjem Homogenizer: A thick-walled test tube with a tight-fitting plunger for mechanical disruption.
  3. Sonication: Using sound waves to create pressure waves that deform the cell membrane and induce lysis.

Differential Centrifugation
  After homogenization, differential centrifugation is applied to separate cellular components. The ruptured cells are centrifuged multiple times to collect cell pellets, while unwanted materials can be discarded. The forces of gravity and adjustable spin speeds help to target specific proteins by accumulating smaller components at different layers.

Salting Out Technique
  Salting out uses salt (commonly ammonium sulfate) to reduce protein solubility. As salt concentration increases, it attracts water molecules, decreasing their availability to interact with proteins. This causes hydrophobic interactions among proteins to increase, leading to precipitation. Centrifugation is then used to collect the precipitated proteins, which can be further purified.

Recovery and Trade-Offs
  Percentage recovery is noted at each purification step, with salting out yielding approximately 48% recovery from the original sample. Although purification techniques can lead to some protein loss, they are designed to collect sufficient protein for further analysis, balancing purity and yield in the process.