Question

Transcription definition?

Answer 1

@Frostbite

Answer 2

Oh you're here :D

Answer 3

"noun
noun: transcription; plural noun: transcriptions

a written or printed representation of something.
the action or process of transcribing something.
"the funding covers transcription of nearly illegible photocopies"
an arrangement of a piece of music for a different instrument, voice, or number of these.
"a transcription for voice and lute"
a form in which a speech sound or a foreign character is represented.
Biochemistry
the process by which genetic information represented by a sequence of DNA nucleotides is copied into newly synthesized molecules of RNA, with the DNA serving as a template."-source da internet

Answer 4

Part 1.
Transcription:
In essentially the synthesis of RNA using information from the DNA. In a common language we could say the new nucleic acids are written in different forms of the same language, and the information is simply "rewritten" (transcribed) from DNA to RNA. As DNA serve as a template, the RNA nucleotide sequence would be complementary to the DNA with the exception that thymine is replaced with uracil.

Simplified mechanism of transcription:
In a simple overview, an enzyme called the \(\textbf{RNA polymerase}\) separates the two stands of DNA and joins RNA nucleotides complementary to the DNA template stands, elongating the RNA polynucleotide. Like the DNA polymerase the RNA polymerase can only assemble the nucleotides in a 5' -> 3' direction, however unlike the DNA polymerase the RNA polymerase can start from scratch, and does not need a primer.

In the DNA there are sequences of nucleotides that mark where transcription of a gene begins and where it ends. The DNA sequences that determines where the RNA polymerase binds and initiate transcription is donated the \(\textbf{promoter}\)and the sequence where the transciption ends is called the \(\textbf{terminator}\) (differences in bacteria and eukaryotes here).

We usually donate the direction of the transcription as "downstream" and the other direction as "upstream". The terms are also used to describe the positions of nucleotide sequences within the DNA and RNA relative to each other. For example the promoter sequence is said to be upstream from the terminator. The part of the DNA sequence that is actually transcribed into RNA is called a \(\textbf{transcription unit}\).

Transcription within bacteria and eukaryotes got some significant differences. One of the most appearing is the fact bacteria only got 1 type of RNA polymerase, while eukaryotes got 3 types responsible for the transcription of multiple types of RNA.


Exercise 1:
What is the mRNA sequence of the coding stand: 5'-CTGAT-3'?

First of all we remember template stand is the one that is being transcribed so we first need to find the template stand. We do this by taking the complimentary base sequence:
Template stand: 3'-GACTA-5'

The RNA sequence would be complimentary and anti-parallel to the template stand with the exception that thymine is replaced by uracil:
mRNA: 5'-CUGAU-3'

And this is the sequence of the synthesized RNA. Notice the similarity between the coding stand and the mRNA stand:
5'-CTGAT-3' (coding)
5'-CUGAU-3' (mRNA)

The only difference is the T's have been replaced by U's. This can become practical when doing fast transcriptions and having the coding sequence.


Extended mechanism of transcription:
The process of transcription can be divided into three stages:
1) Initiation
2) Elongation
3) Termination

\Large\textbf{Initiation:}
The promoter of a gene includes within it a so called \(\textbf{start point}\) (the nucleotide where RNA synthesis actually begins) and typically extends dozens of nucleotides upstream from the start point. The RNA polymerase binds in a specific location and orientation on the promoter and therefore determines where transcription stats and which of the two stands of the DNA helix is used as template.

Certain sections of the promoter are especially important for the binding of the RNA polymerase. In bacteria, the RNA polymerase by it self specifically recognizes and binds the promoter. In eukaryotes however, a collection of proteins called \(\textbf{transcription factors }\) transcription factors mediate the binding of RNA polymerase and the initiation of transcription. Ones the transcription factors are attached to the promoter, the RNA polymerase II binds to the promoter. This complex consisting of transcription factors and RNA polymerase II bound to the promoter is called the \(\textbf{transcription initiation complex}\). A specific nucleotide sequence crucial for this formation is the \(\textbf{TATA box}\) within eukaryotes.

It should be noted that the transcription factors are proteins, like the RNA polymerase and is a specific example of the importance of protein-protein interactions for the controlling of eukaryotic transcription. Ones all the transcription factors and attached to the promoter and the polymerase is bound the polymerase unwinds the two DNA stands and then stats the transcription of the template stand.

\(\Large\textbf{Elongation:}\)
The RNA polymerase start moving along the DNA, it continues to untwist the double helix as it goes downstream exposing approximately 10-20 nucleotides before re-pairing. the RNA polymerase adds nucleotides to the 3' end of the growing RNA stand as it progressed downstream of the template DNA stand. Transcription progresses at a rate of approximately 40 nucleotides per seconds in eukaryotes.

A single gene can be transcribed simultaneously by several other RNA polymerases following each other. (An analogy would be a bunch of trucks in a convoy). By doing this it is possible to make the protein in large amounts.

\(\Large\textbf{Termination:}\)
The mechanism of termination differs greatly between bacteria and eukaryotes. In bacteria, transcription proceeds through a termination sequences in the DNA. The transcribed terminator (the RNA termination sequence), causes the polymerase to detach from the DNA and release the transcript which is the final mRNA. In eukaryotes, the RNA polymerase I transcribes a sequences on the DNA called the \(\textbf{polyadenylation signal}\) (AAUAAA) which is found in the precursor mRNA. About 10-35 nucleotides downsteam of the polyadenylation signal the RNA transcript is detached from the polymerase releasing the \(\textbf{pre-mRNA}\). The pre-mRNA undergoes what is called processing, before the sequence can be translated.

Answer 5

Exercises for you to do:
more complicated questions are donated with a *.

a) What is formed during transcription and from what?
b) What DNA stand is transcription done from?
c*) Compare the use of the template stand in transcription and replication.
d) In what direction is the RNA stand synthesized?
e) What is a promoter, and is it located at the upsteam or downsteam end of a transcription unit?
f*) Draw the required parts within the DNA to perform a transcription and their relative position to each other.
g) How does the drawing in e) change between eukaryotes and bacteria?
h) What enables the RNA polymerase to start transcribing a gene at the right place on the DNA in 1) a bacterial cell, 2) a eukaryotic cell.
i) How would it affect transcription of a gene if the TATA box sequence was changed because of X-rays?