MOLECULAR GENETICS 6

 Central Dogma of Molecular Biology

Francis Crick in 1956 proposed the hypothesis of Central Dogma This explains the flow of genetic information in any biological system

Three major classes of biopolymers are involved in this flow: DNA, RNA and Proteins.

With these 3 categories of biopolymers, a total of 9 transfers can be possible which are grouped under the following categories:

1. General transfers: These transfers occur in most of the organisms
2. a) DNA -> DNA (Replication)
3.        b) DNA -> RNA (Transcription)
4.        c) RNA -> Proteins (Translation)

In this lesson, we will discuss about these General transfers in detail.

2. Special transfers: These occur in viruses where RNA is the genetic material
3. a) RNA -> RNA
4.         b) RNA -> DNA
5.         c) DNA -> Proteins
6. Unknown transfers: These transfers might be possible but yet not known
7. a) RNA -> RNA
8.     b) RNA -> DNA

       c) DNA -> Proteins

DNA Replication

Replication is the process of reproducing or creating a copy of something. In this topic, we will see how DNA creates a copy of itself.

Various hypotheses were proposed by various scientists regarding the replication model of DNA i.e. how DNA replicates. Some of these were:

• Semi-conservative DNA replication model
• Conservative DNA replication
• Dispersive DNA replication

 

Semi-conservative DNA replication model

Watson & Crick suggested the ‘Semi conservative DNA replication’ model. According to this model, the two strands of DNA separate.

Each strand act as template for synthesis of a new strand. The new strand is synthesized based on complementary base pairing with the template.

Each new DNA molecule = 1 parental strand & 1 one newly formed strand. 

This is how the original DNA molecule (1 copy) gives rise to two copies.

Conservative DNA replication

According to this model, Complete DNA molecule (and not just one strand) acts as a template for new synthesis.

Dispersive DNA replication

According to the Dispersive model, the new DNA is synthesized in short pieces. A part of the old strand is attached to the end of a part of newly synthesized strand.