Nuclear import and export do not require post-translational modifications. The nuclear localization sequence or the nuclear export sequence is contained within the amino acid sequence itself (primary structure), and does not require and special modification.

For targeting to the proteasome, proteins must be ubiquinated. To target a protein to the lysosome the addition of a mannose-6-phosphate is commonly made. 

When considering a protein creating/secreting cell, the organelles that are responsible for packaging and secreting the proteins will be most important. Starting at the beginning, proteins will be translated using the ribosomes found on the rough endoplasmic reticulum. Those will then be sent to the golgi apparatus for proper packaging. Those packages will then be released from the cell. The smooth endoplasmic reticulum will not be a vital organelle for protein creation and secretion.

Mannose-6-phosphate is a post-translational modification found on proteins important to the functionality of the lysosome (such as acid hydrolases). Ubiquination is a signal for proteins to be brought to the proteosome and degraded. Myristoylation involves the addition of a fatty acid chain, and is often seen in proteins targeted to the plasma membrane. Acetylation is a common modification found on histones that can help make genes transcriptionally active. 

An isomerase is an enzyme that catalyzes the rearrangement of bonds in a single molecule. For example glucose-6-phosphate isomerase catalyzes the conversion of glucose-6-phosphate into fructose-6-phosphate during glycolysis.

A hydrolase catalyzes a hydrolytic cleavage reaction, a kinase catalyzes the addition of a phosphate group, and a polymerase catalyzes polymerization reactions.

The correct answer is ubiquitination. Ubiquitin is added to the substrate protein to target the protein for degradation by the proteasome, serving as an efficient mechansim to control cellular protein levels. Myristoylation, palmitoylation, isoprenylation, and glycosylation are all post-translational protein modifications that involve the addition of a 14-carbon saturated acid, a 16-carbon saturated acid, an isoprenoid group, and a glycosyl group, respectively. These modifications have diverse functions, however, do not initiate the degradation of the protein.  

While each of these molecules could potentially be bound to a protein as a post-translational modification, the only one listed that is a fatty acid is palmitate. Thus, this is the correct answer. 

The correct answer is adenosine triphosphate (ATP). In order to phosphorylate a substrate, kinases catalyze the hydrolysis of ATP to adenosine diphosphate (ADP) and inorganic phosphate. This released phosphate by the hydrolysis reaction is covalently added to an amino acid residue on the substrate. Nicotinamide adenine dinucleotide phosphate, flavin adenine dinucleotide, and nicotinamide adenine dinucleotide are proton carriers. Guanine nucleotide exchange factor aids in exchanging guanine diphosphate for guanine triphosphate in a substrate. 

The correct answer is all of the answers are cellular processes in which ubiquitination is involved. Post-translational ubiquitination of proteins initiates many cellular processes by altering protein activity and the proteins that interact with the ubiquitinated protein. 

A kinase is an enzyme that adds a phosphate group. Do not get this confused with a phosphatase. A phosphatase is an enzyme that removes a phosphate group. The other enzymes listed do not deal with the addition or removal of a phosphate group from a protein.

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.