 To perform in vitro analysis , a protein must be purified away from other cellular components . This process usually begins with cell <unk> , in which a cell 's membrane is disrupted and its internal contents released into a solution known as a crude lysate . The resulting mixture can be purified using <unk> , which <unk> the various cellular components into fractions containing soluble proteins ; membrane <unk> and proteins ; cellular organelles , and nucleic acids . Precipitation by a method known as <unk> out can concentrate the proteins from this lysate . Various types of chromatography are then used to isolate the protein or proteins of interest based on properties such as molecular weight , net charge and binding affinity . The level of purification can be monitored using various types of gel electrophoresis if the desired protein 's molecular weight and <unk> point are known , by spectroscopy if the protein has distinguishable spectroscopic features , or by enzyme assays if the protein has enzymatic activity . Additionally , proteins can be isolated according their charge using <unk> . 
