Final answer:
Phosphorylation involves adding a phosphate group to a protein, affecting its function, exemplified by ATP generation in glycolysis. Ubiquitination marks proteins for degradation, leading to their breakdown in the process of proteolysis.
Step-by-step explanation:
Phosphorylation is the process of adding a phosphate group to a molecule, typically a protein. This modification is crucial in signalling pathways and affects protein function. An example of phosphorylation is observed in metabolic reactions like glycolysis, where the enzyme phosphoglycerate kinase catalyses the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP, forming ATP. This specific form of phosphorylation is known as substrate-level phosphorylation.
On the other hand, ubiquitination is a process that tags proteins for degradation by adding ubiquitin molecules. This starts with ubiquitin activation through ATP hydrolysis, followed by its transfer to a protein substrate. This tagged protein is then directed towards the proteasome for proteolysis, where it is broken down and recycled. Proteolysis is a critical cellular process for maintaining protein homeostasis and regulating various biological functions.