Question

1: Briefly describe how allosteric modulation changes the function of a protein?

2: Define a covalent bond and explain how it is a form of potential energy.

3: Explain why negative feedback loops are adaptive in the context of cellular respiration and provide an example of a negative feedback loop from cellular respiration.

Answer 1

ANSWER 1

Allosteric modulation has long been recognized as a general and widespread mechanism for the control of protein function. Modulators bind to regulatory sites distinct from the active site on the protein, resulting in conformational changes that may profoundly influence protein function. Allosteric modulators bind outside of the orthosteric site, most likely changing the three-dimensional receptor conformation and thus affecting receptor affinity and/or ligand-binding efficacy of a Protein. Positive allosteric modulators (PAMs) and negative allosteric modulators respectively increase and decrease protein ligand affinity and sensitivity.

ANSWER 2

A covalent bond consists of the simultaneous attraction of two nuclei for one or more pairs of electrons. The electrons located between the two nuclei are bonding electrons. In a covalent compound the electrons are shared between the atoms in the compounds. This "sharing" is not always equal, but it does not result in full excess electron charges residing on one atom compared to another. Instead the electrons are distributed about the entire molecule in such a way the minimizes their energy compared to their energies in the separate atoms.  The energy of the molecule is lower (more stable) than the energy of the separated atoms. The potential energy is function of distance between the two atoms that are "bonding". If there is a distance at which the energy is lower than the two separated atoms we say these two atoms form a chemical bond. The bond length is the distance at which the potential energy is a minimum. The bond strength is the difference in the energy at the minimum compared to the separated atoms.

ANSWER 3

Negative feedback mechanism is the mechanism in which final product if higher in amount is form it will restrict the enzyme function which has produce it. Negative feedback loops are adaptive in cellular respiration because it prevent overproduction of a particular substance and also avoid energy depletion as ATP breakdown unnecessarily.

One of the example of negative feedback loop in cellular respiration is glycolysis step

The last step in glycolysis is catalyzed by pyruvate kinase that is conversion of phosphoenolpyruvate into pyruvate by pyruvate kinase.If energy is not required by cell then pyruvate is converted into alanine. ATP act as negative regulator in this case. The regulation of pyruvate kinase involves phosphorylation by a kinase (pyruvate kinase), resulting in a less-active enzyme. Dephosphorylation by a phosphatase reactivates it. If ATP is less then, more pyruvate will be converted into acetyl CoA through the action of pyruvate dehydrogenase. If either acetyl groups or NADH accumulates, there is less need for the reaction, and the rate decreases. Pyruvate dehydrogenase is also regulated by phosphorylation: a kinase phosphorylates it to form an inactive enzyme, and a phosphatase reactivates it. The kinase and the phosphatase are also regulated.