Central Dogma and Gene Expression

1. Bacteria called Klebsiella pneumoniae can use an enzyme called reverse transcriptase to create new genes when infected with bacteriophages (viruses that attack bacteria).
2. This newly created gene produces a protein named Neo, which puts the bacteria in a dormant state, stalling the virus’s replication and protecting the bacteria.

Central dogma of molecular biology:

1. Central dogma of molecular biology explains how genetic information flows from DNA to RNA to proteins.
2. Gene expression is the process our cells use to convert instructions in DNA into proteins. This happens in two-stages called transcription (occurs in the nucleus, in eukaryotic organisms) and translation (occurs in cytoplasm).

1. Transcription: mRNA copies the sequence of a gene from DNA, and then leaves the nucleus and travels to cytoplasm. 
2. Translation: Using the template encoded by mRNA, translation is carried out by ribosomes, i.e., the information in the mRNA is used to synthesise proteins (building blocks of life). 

3. In prokaryotic cells (such as bacteria), which lack a nucleus, transcription and translation occur in the same cellular compartment, the cytoplasm. 
4. In eukaryotic organisms, transcription occurs in the nucleus, while translation occurs in the cytoplasm.

What’s Happening	Transcription	Translation	Reverse Transcription
The Gist	Copying DNA into RNA	Using RNA to make a protein	Making DNA from RNA (like rewinding a cassette tape!)
Where it Goes Down	Nucleus of the cell	Cytoplasm of the cell	Can happen in the cytoplasm
The Big Picture	First step to make proteins	Second step to make proteins	Not involved in making proteins directly
Who’s the Star	DNA	RNA (specifically, messenger RNA or mRNA)	RNA and a special enzyme called "reverse transcriptase"

Practice Question:

Q. Consider the following statements:

1. In eukaryotic organisms’ transcription and translation occur in the cytoplasm.

2. The process of translation is carried out by ribosomes.

3. Reverse transcription is the flow of information from DNA to RNA.

How many of the statements given above are correct?

(a) Only one

(b) Only two

(c) All three

(d) None

Ans: (a) (Only statement 2 is correct)

Q. ‘RNA interference (RNAi)’ technology has gained popularity in the last few years. Why?

(1) It is used in developing gene silencing therapies.

(2) It can be used in developing therapies for the treatment of cancer.

(3) It can be used to develop hormone replacement therapies.

(4) It can be used to produce crop plants that are resistant to virtual pathogens.

Select the correct answer using the code given below.

(a) 1, 2 and 4

(b) 2 and 3

(c) 1 and 3

(d) 1 and 4 only

Ans. a)

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