Genetics 6 Sections19 LessonsLifetime
Transcription Key Features & Facts
Transcription-Key Features and Facts
Before getting into the discussion that how the actual process of transcription takes place, first we have to get a good understanding of some key features, facts and some essential terms to understand.
After that we will be able to understand the actual process of transcription.
We will discuss the process of transcription in both prokaryotes and eukaryotes.
Key Features
The first question is that
How DNA makes a RNA copy?
To answer that question we will first go through some definitions.
DNA Replication
DNA replication is like printing a copy of all the pages of a book. The replication process occurs only at the time of cell division.
Transcription
Transcription can take place at any time but only certain selected regions of the DNA are copied. This is like taking xerox copy of particular page of the book.
The genetic information in DNA is transcribed (copied) to the messenger RNA (mRNA).
During transcription, the message from the DNA is copied in the language of nucleotides (4 letter language).
The mRNA then reaches the cytoplasm where it is translated into functional proteins.
During translation, the nucleotide sequence is translated to the language of amino acid sequence (20 letter language).
Q: What is the name of the enzyme that performs this action?
A: RNA Polymerase (RNAP).
Q: What it does?
A: RNA Polymerase adds nucleotides (ATP, UTP, CTP, GTP) to make a strand of RNA that is complementary to DNA.
Q: What is the Direction of synthesis?
A: It is always from 5’ to 3’.
Q: Only one strand is copied – which one?
A: Template strand (non-coding, anti-sense strand).
RNAP reads the template strand & synthesizes RNA that is identical to coding strand except it has ‘U’ instead of ‘T’.
Q: How does RNAP know where to begin transcribing?
The PROMOTOR sequences on DNA determines the start sites for RNAP.
RNAP has high affinity for them.
Facts about Transcription
All of the DNA is NOT transcribed.
RNAP initially finds and binds to the promoter, not the coding region.
Gene = dsDNA; but only one strand is used as template for transcription i.e. the template strand & is complementary to mRNA.
Coding strand is NOT used but is identical to mRNA (T replaces U) & has TATA sequence (CAAT box).