#exergonic

[justinempire]

Exergonic | Justin Empire

Exergonic by Justin Empire, Dance music from London, UK on ReverbNation

Exergonic

[detritus-of-an-ap-bio-kid]

Endergonic reactions absorb energy from surrounding and excess energy making the free-energy change is positive (🔺G). They are non-spontaneous, anabolic reactions. Exergonic reactions release or lose energy, meaning the free-energy change is negative (-🔺G). ATP is what powers endergonic reactions, which occurs in photosynthesis. ATP removes a phosphate group from the membrane and attaches it to the reactant. This is called phosphorylation and forms ADP. The energy released from forming the ADP drives the exergonic reaction, starting cellular respiration.

[spellbiomentors]

Hey, I've memorized that polymerization happens 5' to 3', but what's the logic behind this? As long as a phosphate group of one RNA and an OH on another RNA are interacting, why would it matter which way they're facing?

Hey, the key to understanding is knowing two pieces of information: 1) Why reactions happen, and 2) What type of nucleoside the very first molecule in an mRNA chain is.

1.

When you drop a pencil, it will fall to the ground without you having to do anything—it has the lowest energy there. In the same way, reactions want to head to lower energy—they want the products to have lower energy than their reactants. This is what we call “energetically favorable.” The greater the energy difference between the products and reactants, the more this reaction wants to happen.

So, a polymerization reaction in which the next nucleoside is a triphosphate will want to happen more readily than a reaction in which the next nucleoside is a monophosphate or diphosphate. Phosphate groups are negatively charged, so the more phosphates a nucleoside has, the more they repel each other, and increase the energy of a molecule.

This is why when we join two RNA molecules together, we have to phosphorylate—add phosphate groups—to the second one, in order to make the reaction want to happen more.

2.

Let’s say that the very first nucleoside in a chain isn’t one that has been modified yet, so it’s just a plain old monophosphate, and that we only modify nucleosides with more phosphates when we want them to join the end of a chain. The following diagram shows why polymerization in one direction is more favorable than the opposite direction.