If you view
a cell (animal or plant) under a microscope (low powered) you’ll observe each
individual cell with a thick dark dot inside them that’s the nucleus, which
bares our genetic code. In plants and animals the genetic code is carried in
the form of a double helix structure (imagine a twisted ladder) known as the Deoxyribonucleic acid or DNA. DNA generally are double stranded
but are seen as single strands in some viruses for example Parvoviridae (class
II viruses), but the two strand is more stable.
Prior to
replication, you need some basic idea about what forms the genetic messenger,
the DNA is made up of four smaller chemical molecule known as the nucleotide bases: adenosine (A), guanine (G), thymine (T),
cytosine (C) and uracil (U) (that is present in the RNA molecule
instead of the thymine base). Now, the beauty of all these bases are; they combine in a complementary
fashion which in simple terms mean adenosine pairs with thymine (A-T)/(uracil
pairs with adenosine (U-A) in case of RNA )and cytosine pairs with guanine
(C-G).
When a cell
generally replicates, the genetic material i.e, the DNA is copied to two
identical DNA molecules giving rise to 2 daughter cells. So, every time the
cell divides, the 2 daughter cells consists of the same genetic information/DNA
as the parent cell. When cell division begins, the DNA uncoils and one of the
DNA strand acts as the template to be copied. The DNA does not uncoil at any
random place but does so at a specific position that is called the origin.
For any process to take place preparation has to done, similarly for replication to happen the DNA has to be prepared, for this many enzymes and proteins aid in the process. Eventually, DNA polymerase a special enzyme assembles the new strand. The job of the polymerase enzyme is to add on the complimentary base pair to the template strands thus forging a new DNA strands for the daughter cells.
With this
you might get a general idea about how DNA replicates but this happens only during
cell division, but then, what does gene expression mean. Our genes carry the all
the necessary information to make a functional molecule that is the proteins. So, in simple terms gene
expression means generation of a functional protein from the genetic code. In
the beginning, the information contained in the DNA is transferred to mRNA
(messenger Ribonucleic acid) this process is called transcription. When transcription occurs, only that region of DNA that
needs to be transcribed unwinds, just as before complimentary base pairing occurs
and an enzyme know RNA polymerase
catalysis the formation of the mRNA. However, here only a single stranded
molecule is obtained once the mRNA is released. Next step involves the decoding of this
mRNA to form the proteins, which is termed as translation. Again, the mRNA strand is read according to the
genetic code, which links the DNA sequence to the amino acid sequence in proteins. This step here is what experts manipulate
to reverse engineer a DNA sequence from amino acid sequence. Each group of
three bases (U, A, G and C) in mRNA (remember we use U instead of T base pair
in case of RNA) forms a codon, and
each codon specifies a particular amino acid, a chain of such amino acids constitute
a protein. Proteins as we all know it, are the main culprits behind every
cellular function, they even aid in DNA replication and this how a gene is
expressed.
In simple
terms, DNA contains all the raw data, but the cell can’t comprehend it unless,
it’s broken down and converted into a form that it (cell) can understand and
thus deliver the desired result.
Evolution is the slow change to the DNA of a
species over many generations. This occurs due to natural selection meaning when a certain trait help the survival
and reproduction of an organism. Thus, helping the species better adapt in its environment and making
them much more likely to survive and pass on the genes that aided their success.
Hope this
article shed some light and cleared some concepts, although the processes
previously explained, do take place with much more technical finesse but I know you got
some gist about it and hopefully it helped.
