RNA: Questions About Nirenberg, Introns & mRNA

  • Thread starter STAii
  • Start date
  • Tags
    Rna
In summary: I am a bit rusty on biochemistry.In summary, Marshall W. Nirenberg's experiment showed that even though the RNA molecule did not start with the codon for protein, the protein was still created. Introns were discovered during mRNA processing, and their presence is not related to protein translation, but rather for alternative splicing. Lastly, mRNA molecules are recycled after they are used, and are re-translated if they stay in the cytoplasm.
  • #1
STAii
333
1
Greetings.
I have a few questions about RNA.

1-In Nirenberg's experiment (building a protein from mRNA made only of U-U-U-U-U ...), how was the protein actually built if it didn't start with AUG (the starting Codon). If the codon AUG is not neccesary for starting the building of a protein, can you please explain how the building starts otherwise ?.

2-During mRNA processing, how are the introns identified ?

3-Why are the introns there from the first place ? If they are not translated to any protein, what is their usage ?
If they have no usage, is it possible that (with time, and evolution) that the introns will go from the original DNA molecule ?

4-As far as i understand, the DNA is transcripted to mRNA, which is then translated to a protein, how does the cell know when it should transceipt a certain part of DNA to mRNA and went it shouldn't (iow, when the protein that the mRNA builds is not needed).

5-Are mRNA molecules re-used after building the protein molecule (iow, if the mRNA stays in the cytoplasm, will it be re-translated .. and re-translted ... and re-translated .. ?).

Thanks in advance (that's all .. for now ).
 
Biology news on Phys.org
  • #2
Originally posted by STAii
Greetings.
I have a few questions about RNA.

1-In Nirenberg's experiment (building a protein from mRNA made only of U-U-U-U-U ...), how was the protein actually built if it didn't start with AUG (the starting Codon). If the codon AUG is not neccesary for starting the building of a protein, can you please explain how the building starts otherwise ?.

Can you point out where you got nirenberg's experirement. I don't know what you are takling about?

Originally posted by STAii
2-During mRNA processing, how are the introns identified ?

introns have a specific sequences at the 5' end, which is the donor, and at the 3' end, which is the acceptor. It goes like this
Exon-5'CG/AGGUA/GAGU---Intron-----T/CNAHN3'-Exon--
________Donor site______________Acceptor site

Originally posted by STAii
3-Why are the introns there from the first place ? If they are not translated to any protein, what is their usage ?
If they have no usage, is it possible that (with time, and evolution) that the introns will go from the original DNA molecule ?

Nobody knows why introns are there but it is observed that there is alternative splicing sites. There could be a different 5' end, 3' end or a different internal structure.

For example, Calcitonin has 2 polyadenylation signals which are tissue specific. In the thyroid the 1st signal will be used whereas in the brain the 2nd signal is used. The exon at 3' end is different.

Originally posted by STAii
4-As far as i understand, the DNA is transcripted to mRNA, which is then translated to a protein, how does the cell know when it should transceipt a certain part of DNA to mRNA and went it shouldn't (iow, when the protein that the mRNA builds is not needed).

There is region upstream of the gene that is called the regulator region. These region control the expression of the DNA. Regulation of the DNA is complex. There can be DNA-protein, DNA-DNA and DNA-RNA interaction that control the expression. For example, some protein are produce only in specific tissues and these protein have a role in promoting tissue specific gene and these gene are can only be express when the protein is present.

Originally posted by STAii
5-Are mRNA molecules re-used after building the protein molecule (iow, if the mRNA stays in the cytoplasm, will it be re-translated .. and re-translted ... and re-translated .. ?).

You are rigth, mRNA is recylce until it is degraded and many ribosomes (translation untis) can bind to the same mRNA strand.
 
  • #3
Ok, i will come back to questions 2-5. But for now, let me talk about 1.
It is weird that you don't know this experiment.
Marshall W. Nirenberg (b. 1927) is an American biochemist who shared the 1968 Nobel Prize in Physiology or Medicine for his work on deciphering the genetic code.
His experiment is also known as the "Poly-U" experiment.
Mainly, what he did is that he made an RNA molecule made only of Uracil units.
He then got 20 tubes, and put differnt kinds of Amino acids into the 20 tubes (and also he put Ribosomes, and Enzymes, and other stuff). He put one molecule of this Poly-U RNA into each tube.
He waited, then came back, and found that only one tube had protein made in it (the one with the amino acid phenylalanine).
Anyway, the point is that the protein was made although the RNA did not start with AUG (the starting codon).
 
  • #4
Well, although AUG is a predominant initiator codon, there are other possibilities such as GUG or CUG. You say the molecule was only composed of Us? This was a eukaryotic or prokaryotic system? Maybe there were impurities? I haven't heard of the experiment before either :S

You might be interested in going through the following tutorial, it is quite nice!
http://www.lsic.ucla.edu/ls3/tutorials/
 
  • #6
I have look at the paper publish by Nirenberg (http://profiles.nlm.nih.gov/JJ/B/B/D/K/_/jjbbdk.pdf). From what I read, it appears that they did not used all the ribosome sub-unit, they only used the 30S fraction or they added a lot 30S rRNA. I think that the start codon was not required because of the condition used during the experiement.
 
  • #7
Ok, for Q1, i got what i need (not only AUG is a starting codon).
Now, the other questions.
Q2
introns have a specific sequences
good till now
at the 5' end, which is the donor, and at the 3' end, which is the acceptor. It goes like this
Exon-5'CG/AGGUA/GAGU---Intron-----T/CNAHN3'-Exon--
________Donor site______________Acceptor site
You lost me ..

Q5
You are rigth, mRNA is recylce until it is degraded and many ribosomes (translation untis) can bind to the same mRNA strand.
So suppose that the cell does not need a certain protein anymore (or has enough of it after some time), the ribosomes will still build from that protein?
 
  • #8
For question 2 i gave you the sequence that is recognize as being the start and end of an intron. So the 5' end of the intron is start and the 3' end is the end. when the intron is cut out the 5' end will be donate to the 3' end which will accept it in order to connect the two exons

Originally posted by STAii

So suppose that the cell does not need a certain protein anymore (or has enough of it after some time), the ribosomes will still build from that protein?

Yeah the cell keeps on build the protein until there is no more mRNA but mRNA is very unsatble so it degraded rapidly.
 
  • #9
Does this help?
http://www.blc.arizona.edu/marty/411/Modules/Weaver/Chap14/Fig.1432.jpg [Broken]

let me find a better picture..
 
Last edited by a moderator:
  • #10
Basically, small nuclear ribonucleoprotein particles, snRNPs recognize signals (that Ian gave) at the intron/exon boundaries. These snRNPs cause conformational change of the RNA and cleavage.

Four different sites have been found:
5'splice site
3'splice site
branchpoint (in the middle)
polypyrimidine track (after the branchpoint)
 

What is the significance of Nirenberg in RNA research?

Nirenberg's work in the 1960s helped to decipher the genetic code, specifically the relationship between mRNA and amino acids. He developed a method for synthesizing RNA and used it to identify the codons that correspond to each amino acid. This was a critical step in understanding how proteins are made from the genetic code.

What are introns and how do they relate to mRNA?

Introns are non-coding sequences of DNA that are transcribed into pre-mRNA but are removed during mRNA processing. This process, known as splicing, results in a mature mRNA molecule that only contains the coding sequences, or exons. Introns play a role in regulating gene expression and increasing genetic diversity.

How does mRNA differ from other types of RNA?

mRNA, or messenger RNA, is a type of RNA that carries the genetic information from DNA to the ribosomes where it is used to make proteins. Unlike other types of RNA, such as tRNA and rRNA, mRNA is single-stranded and contains the genetic code for a specific protein.

Why is mRNA important in the central dogma of molecular biology?

According to the central dogma, genetic information flows from DNA to RNA to proteins. mRNA plays a crucial role in this process as it carries the genetic code from DNA to the ribosomes, where it is translated into a specific protein. This process is essential for the functioning of all living organisms.

How does RNA research impact our understanding of genetics and disease?

RNA research has greatly advanced our understanding of genetics and disease. It has helped us identify the genetic code and how it is translated into proteins, as well as the role of RNA in regulating gene expression. This has led to the development of new therapies for genetic diseases and a better understanding of how diseases arise at the molecular level.

Similar threads

  • Biology and Medical
Replies
15
Views
2K
Replies
1
Views
1K
  • Biology and Medical
Replies
5
Views
3K
  • Biology and Chemistry Homework Help
Replies
7
Views
2K
Replies
19
Views
4K
  • Biology and Medical
Replies
2
Views
5K
  • Biology and Chemistry Homework Help
Replies
2
Views
7K
  • Biology and Chemistry Homework Help
Replies
2
Views
2K
  • Biology and Medical
Replies
11
Views
5K
  • Biology and Medical
Replies
26
Views
7K
Back
Top