Replication, Regulation and Recombination

14 Dec 2020

We start off where we ended the last chapter. How does the form of the DNA able its function? Looking at in reverse the three functions a DNA performs - replication, regulation and recombination.

Replication - when a new cell is created how does the DNA get replicated?

Regulation - what prevents the dna from frenzied unabated replication. The lack of which we know now causes cancer. And also how does a single common genome code in cells enable cells across the body perform varied functions. To put in the author’s words - “Why is hemoglobin protein only found the RBC and not in our eyes”.

Recombination - how does DNA from parents get transmutes and progagate in progenies?

The key to all the three functions is the double helical structure and the fact that bases pairs come in pairs.

When it needs to replicate, the DNA sort of unzips/splits into two single strands and two copies of the original are formed - serving replication function.

Jacquet Monad was studying the exponential growth of e.coli bacteria when fed with glucose and lactose. On mixing both glucose and lactoss he observed the e coli would consume first one of the two sugars and then switch to consuming the second sugar. During the switch the growth of the bacteria would take a minor kink. Monad was interested in explaining why was only one sugar consumed at first and why was there a kink when it switched to consume the second sugar.

The eventually answer explaining the above phenomen opened doors to understand how regulation works in DNA. Based on the environments presented to the cell (sugar present in this case) the underlying DNA turns on and off the genes needed to build the proteins to break this sugar. Therefore when a new sugar enters the system, the corresponding genes necessary to make that protein are turned on.

The question then comes, how does the cell know of the current needs of the environment. As in how does it detect the presence of a certain sugar? The DNA comes to help again by having sugar sensing proteins which hold the key to unlocking the genes necessary to break and synthesize these sugars. Once unlocked more RNA messages would generate relevant enzymes to digest the sugar.

The genes therefore had in it information encoded not only about how to make the protein but also the circumstances/environment in which it is to be turned on.

Regulatory function should also encompasses a cells ability to able to limit the DNA’s splitting and exponential growth. A replicator protein (DNA polymerase) takes up this role. A bunch of environment variables like age of the cell, current nutrients available dictates its ‘on’ and ‘off’ toggle mechanism. Like every other protein in the cell the DNA polymerase is also an off-product on the genome code in DNA. The DNA- ‘god what a molecule’ has provided itself information with information on how to replicate.

Lastly how does the DNA transmute in its progenies and have both common and varied features from its parent organism? The simple transmution of single base pair can happen due to extragenous factors like exposure to x-rays or errors that can happen during replication. Where an A is switched to T.

The more promient transmutation, coined ‘recombination’ happens when parent chromosomes (one from the mother, one from father) intermix. A hybrid gene is produced by swapping large chunks of DNA picks a few genes from the mother chromosome and a few from the father chromosome.