All of the given answers are ways that a cell may regulate protein concentrations. Polyubiquination is a signal for the protein to be degraded by a proteasome. Gene silencing will prevent transcription, which will lower the amount of mRNA template that can be translated into a protein. RNAi will degrade specific mRNAs or prevent the translation of specific mRNAs into proteins.

Polyubiquination is a modification results from the binding of small ubiquitin residues to a protein. Polyubiquination of a protein signals damage or problems with functionality, and triggers the mechanisms that result in protein degradation. The polyubiquinated protein is then brought to a proteasome (a complex of proteins) that will degrade the protein.

Glycosylation involves the attachment of a carbohydrate complex to a protein. The identity of the carbohydrate is essential for determining the functional outcome of glycosylation, but generally results in signaling and transport labels for the protein. Glycosylation is not by itself a signal to be brought to either a proteasome or a lysosome.

E1, E2, and E3 all have unique activities that progress step-wise to activate ubiquitin and then attach those ubiquitins to mark a protein for degradation. Their functions are not redundant, nor do they activate acids, autophagosomes or ATP complexes over the course of their pathways. 

The correct answer is proteasome. Ubiquitination of a protein signals for the proteasome to degrade it and recycle the ubiquitin. Alternatively, the lysosome does degrade proteins, however, this process is independent of ubiquitin. The peroxisome is responsible for the degradation of fatty acids, certain amino acids, and reactive oxygen species. Hydrolysis simply refers to a chemical mechanism that splits apart a compound by the addition of water, it does not however, describe an organelle or cellular compartment that is reponsible for protein degradation. 

The correct answer is proteasome. There are two general protein degradation processes: the first involving the lysosome and the second involving the proteasome. Lysosomal protein degradation is non-selective and occurs during cell starvation. Degradation through the proteasome is dependent on ubiquitination of the target protein, and as such, ensures protein-specific degradation. 

The correct answer is recognition of ubiquitin by the proteasome. Ubiquitin-mediated protein degradation by the proteasome is a well characterized method of specific protein degradation. The protein targeted for degradation is phosphorylated, then ubiquitinated. The proteasome recognizes these distinct ubiquitin chains and degrades the protein. Protein degradation can also occur through the lysosome, but this is independent of ubiquitination and is less specific. The golgi complex is involved in protein folding and modification of recently translated amino acid chains. 

The correct answer is that proteolysis occurs in the lysosome but ubiquitin-mediated protein degradation is in the proteasome. Proteolysis-lysosomal degradation is non-selective and is activated upon cellular starvation. ubiquitin-mediated protein degradation is highly specific and functions to promote a wide range of cellular processes. 

Older proteins in our bodies need to be degraded once they become damaged or no longer necessary. One way that the cell tags these proteins is by adding a ubiquitin tag, which can then be recognized by a proteasome, leading to the proteins' deconstruction.