where do post translational modifications occur in the cell
Post-translational modification Post-translational modifications can occur on the amino acid side chains or at the protein's C- or N- termini.[1] They can extend the chemical repertoire of the 20 standard amino acids by modifying an existing functional group or introducing a new one such as phosphate. Phosphorylation is a very common mechanism for regulating the activity of enzymes and is the most common post-translational modification.[2] Many eukaryotic proteins also have carbohydrate molecules attached to them in a process called glycosylation, which can promote protein folding and improve stability as well as serving regulatory functions. Attachment of lipid molecules, known as lipidation, often targets a protein or part of a protein attached to the cell membrane.
Cell cycle The first phase within interphase, from the end of the previous M phase until the beginning of DNA synthesis, is called G1 (G indicating gap). It is also called the growth phase. During this phase, the biosynthetic activities of the cell, which are considerably slowed down during M phase, resume at a high rate. The duration of G1 is highly variable, even among different cells of the same species.[3] In this phase, the cell increases its supply of proteins, increases the number of organelles (such as mitochondria, ribosomes), and grows in size. In G1 phase, a cell has three options. (1) To continue cell cycle and enter S phase (2) Stop cell cycle and enter G0 phase for undergoing differentiation. (3) Get arrested in G1 phase hence it may enter G0 phase or re-enter cell cycle. The deciding factor is availability of nitrogens and storage of energy rich compunds at the deciding point called check point. This check point is called G1 cyclin or CG1. It causes transition of G1 to S phase. Once the check point of G1 phase is crossed, cell cycle will go uninterrupted till it is completed.