Types of mutations

Single base substitutions

A single nucleotide base becomes replaced by another. These single base changes are also called point mutations. If a purine (a, t) replaces a purine or a pyrimidine (c, g) replaces a pyrimidine, it is called a transition. If a purine replaces a pyrimidine or vice-versa, the substitution is called a transversion.

Missense mutations -


In a missense mutation, the new base alters a codon resulting in a different amino acid being incorporated into the protein chain. This is what happens in sickle cell anaemia. The 17th nucleotide of the gene for the beta chain of haemoglobin is changed from an 'a' to a 't'. This changes the codon from 'gag' to 'ggt' resulting in the 6th amino acid of the chain being changed from glutamic acid to valine. This apparently trivial alteration to the beta globin gene alters the quaternary structure of haemoglobin, which has a profound influence on the physiology and wellbeing of the individual.The picture on the right shows an example of a missence mutation, a substitution of 'a' in the second codon to 'g' leads to an amino acid substitution of glutamine (Q) to arginine (R).


Nonsense mutations -

In a nonsense mutation, the new base changes a codon that specified an amino acid into one of the stop codons (taa, tag, tga). This will cause translation of the mRNA to stop prematurely and a truncated protein to be produced. This truncated protein will be unlikely to function correctly. Nonsense mutations occur in between 15% to 30% of all inherited diseases including cystic fibrosis, haemophilia, retinitis pigmentosa and duchenne muscular dystrophy. The picture on the right shows an example of a nonsense mutation, where 'c' in the second codon is changed to 't'. In the normal nucleotide sequence the second codon 'cag' codes for glutamine (Q) whilst in the mutated second codon 'tag' codes for Stop leading to premature termination of the protein.


Silent mutations -


Silent mutations are those that cause no change in the final protein product and can only be detected by sequencing the gene. Most amino acids that make up a protein are encoded by several different codons (see genetic code). So, if for example, the third base in the 'cag' codon is changed to an 'a' to give 'caa', a glutamine (Q) would still be incorporated into the protein product, because the mutated codon still codes for the same amino acid. These types of mutations are 'silent' and have no detrimental effect.

Splice site mutations -


Introns must be spliced from mRNA to produce the correct protein. This process must be carried out very accurately and it is guided by the nucleotide signals at the splice sites. If a mutation alters these signals, the intron may not be removed and an incorrect protein will be produced.

ChandraMukhi -- Reloaded ( Part IX )

PART IX - RAJINI ON MISSION CHANDRALEKHA

Rajini arrived to LMRVSoft office from US, as soon as he got the SMS from Prabhu. Prabhu apprised him of the strange happenings that were happening over the recent few days at office. Staffs were under the impression that these could be the effect of the black magic of Chandralekha. Prabhu refused to buy this "black magic" logic...he He rather suspected this as Nayantara's handiwork in association with Neelambari to stop the organization's growth. However Rajini rubbished these claims by Prabhu, as he thought Nayan could have never thought of doing such things. Prabhu thought since Love is blind, Rajini did not want to look Nayantara as guilt.Rajini ran the latest virus scanners, anti-spyware in every system, but none of them showed any problems in the system. Rajini was clueless…. What could be the problem.... During day times the systems ran fine without any issues… but during nights, some weird things were happening from any of the system... The problem occurs only for a few while and there was no log or anything created in the system, for Rajini to analyze the reason behind such a behavior. Another thing Rajini noticed was a strange sound coming from Chandralekha's room in the nights.. If Rajini knocked the door of that room, the sound will stop..On a fine day, as Rajini was working in his laptop monitoring the company's network set up, suddenly he found a strange thing happening... A malicious application that bypassed the company's firewall system was transmitting through every systems... Alas!!, Rajini could not stop that application through any of his software... And it was actually going towards the company's Project server... God!! If it gains access to the project server, then it might erase the entire data in that server.... Rajini was quick to react to this danger... He ran to the server room where prabhu was working in the Project server system... Swiftly, he pushed Prabhu from the chair and unplugged the network cable... Every staff arrived at the server room hearing this huge noise that came as a result of Prabhu falling to the ground... A shocked Prabhu got off from the ground... Rajini apologized to him and explained to him why he disconnected the network cable from the server system... Prabhu was surprised... "From which system, this virus has originated, Any idea?", he enquired... Rajini paused for a moment and said... "Hmm... it has come Nayantara's laptop only"Everyone was surprised... Prabhu was very much angry... "I told u already rite... This girl is the reason for everything....".. Rajini replied... "O.K dont worry, I will take care of her".... Nayantara who was also present there,was shell shocked... "I did not do anything...Please believe me...", she requested everyone, but no one was believing her... Rajini took Nayantara along with her laptop and went inside the conference room... He locked the room from inside, so that people from outside could only hear some whip lash sound.... After a while.... Rajini came outside of the room, a worried Vijayakumar inquired "What happend, what happened to my dear daughter's laptop... Dude..dude.. She loves that laptop... she can't bear losing the laptop... ... I assure u, she had kept it protected from any virus or spyware.. Nothing would have entered it, Kindly dont do anything to her laptop or disconnect the internet connection... She can't live without G-Talk or orkut dude....", Vijayakumar broke into tears... Rajini looked at him with a straight face and replied... "Dont worry... I have just disconnected the network cable from that laptop and put her system in quarantine... Things would be alright now... O.K everyone get back to work", Rajini left that place as a confused Prabhu and Jyo look over..That night, the staffs in LMRVSoft left home early fearing Chandralekha effect, and so Rajini was alone in the office. He decided to take another look at the Chandralekha ‘s room…. The strange sound was coming again from Chandralekha’s room…. Rajini, this time, rather than trying to go inside or knocking the door, observed the room, the sound carefully…. After a while, he left the place and left for his home with a sense of having found something…. Next day morning Rajini comes to office late and Prabhu was highly tensed.

Rajini : hey Prabhu .. Good morning … Why are tensed ???

Prabhu : Everyone in our company started to resign …. They are very much afraid of the Chandralekha’s effect .. Got 10 resignation letters in the morning and had a call from the client

Rajini : What they were asking ??

Prabhu : I had put conference to u … where were you at that time ??

Rajini : Cool … Cool you have Jyo to do all the household chores .. for me I have to do myself. Went for having breakfast

Prabhu : He asked us to solve this issue …If we solve this problem they will make the payment it seems … Is the handwork of Antony ??? Is he involved in all these ??

Rajini : Silly … Antony doesn’t have that much guts to work on these

Prabhu : Then ….. is there anything called BLACKMAGIC ??

Rajini : Give me 2 days… I will work and solve the issue

Prabhu : ( Rajini laughs ) : Poruthuirunthu par

Rajini planned to stay in the office …

Everyone else in the office left …… Jyo was happily playing in the chandralekha’s system ….
Rajini tried to connect but he wasn’t able to do the same as there were some network problems.Rajini went near the room and happened to hear the clicks sounds from the keys …. He found out that some one has entered the room and started working in the system

( TO BE CONTINUED .... )