 Once formed , proteins only exist for a certain period of time and are then degraded and recycled by the cell 's machinery through the process of protein turnover . A protein 's lifespan is measured in terms of its half @-@ life and covers a wide range . They can exist for minutes or years with an average lifespan of 1 – 2 days in mammalian cells . Abnormal and or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable . 
 Once formed , proteins only exist for a certain period of time and are then degraded and recycled by the cell <a href='null_genetive' title='1'><mark>'s</mark></a>machinery through the process of protein turnover . A protein <a href='null_genetive' title='2'><mark>'s</mark></a>lifespan is measured in terms of its half @-@ life and <a href='uninflect' title='3'><mark>covers</mark></a> a wide range . They can exist for minutes or years with an average lifespan of 1 – 2 days in mammalian cells . Abnormal and or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable . 
Once formed , proteins only exist for a certain period of time and are then degraded and recycled by da cell  machinery through tdaprocess of protein turnover . A protein  lifespan is measured in terms of its half @-@ life and cover a wide range . They can exist fir minutes or years with an average lifespan of 1 – 2 dayz in mammalian cells . Abnormal and or misfolded proteins are degraded more rapidly either due to bein targeted fir destruction or due to bbeinunstable .