A cis conformation is so rare due to steric clashes between side chains in different amino acid residues. The Van der Waals forces are simply to great for two side chains to occupy nearby spaces. However, proline is a very unique amino acid. Proline has a unique ring structure, in which its side chain is attached to its amino backbone group. Because of this, there is actually some steric clash in the trans conformation, in addition to the cis conformation. Overall, it is estimated that 10-30% of proline exists in the cis conformation, which is far greater than any other amino acid.

A Ramachandran plot, also referred to as a dihedral plot, tells us about what bond angles are favorable for an amino acid residue. The colored regions are favorable, while the uncolored (white) regions are not favorable. Additionally, each colored regions also corresponds to a different secondary structures (alpha helix, beta sheet, etc.).

These plots can't tell us much about the specific residue order within a polypeptide chain, or the energy required to break an amide bond.

In a globular protein, the amino acid chain can twist in a way that polar groups lie at the protein's surface. This allows the protein to interact with water and enhances the protein's solubility in water. This does not occur in fibrous proteins, so fibrous proteins are insoluble in water.

Actin chain growth occurs at the (+) end of the chain, and nucleotide hydrolysis promotes dissociation of actin chains. 2 microfilaments of G-actin monomers make 1 filament of F-actin. However, actin filament assembly is powered by ATP, not GTP. 

An O-linked glycoprotein is a protein that has a sugar attached to it. It is called O-linked because the sugar is attached to an oxygen atom on either a threonine residue or a serine residue within the protein.

The correct answer is a kinase. Kinases are enzymes that couple the hydrolysis of ATP to the addition of a phosphate group to its substrate.

Phosphatase enzymes basically function oppositely to how kinases work. Phosphatases use water to hydrolyze phosphate groups off of their substrate.

Isomerase enzymes function to interconvert the structure of molecules from one isomer to another. This means that the substrate will remain with the same molecular formula, but it will have a difference in the connectivity of its bonds.

Ligases are enzymes that work by joining two molecules together.

Oxidoreductases are enzymes that act by catalyzing oxidation and reduction reactions, which involve the transfer of electrons from one molecule to another.

The last step of glycolysis, which involves the conversion of phosphoenolpyruvate into pyruvate, is catalyzed by the enzyme pyruvate kinase, yielding one pyruvate molecule and 1 ATP. The other kinases are involved in different steps of glycolysis.

Kinases catalyze the attachment of phosphate groups to their substrates. Phosphatases specifically remove phosphate groups from their substrates, which is the opposite of the function of kinases. The other enzymes listed do not have functions that involve removal of phosphate groups. 

From it's name, we can assume that this kinase will add phosphate groups to its targets. The source of these phosphate groups is ATP. PKA has 2 catalytic, and 2 regulatory subunits. When PKA is activated, there is a conformational change that causes the regulatory subunits to fall off, and frees the catalytic (kinase) portions. When PKA is inhibited, the regulatory subunits bind to the catalytic subunits and prevent phosphorylation. PKA has many activators, but cAMP is one of the most robust and well studied activator. Therefore, cAMP binds to the regulatory subunits, but does not inhibit protein function.

Polar R-groups, namely free hydroxyl groups on serine, threonine, and tyrosine, are the usual targets for phosphorylation because they are nucleophilic and can react with the phosphate group. Other R-groups are not as reactive and therefore are not ideal sites for phosphorylation.