How genes encode proteins

The sequence of base pairs in a gene determines the protein product that gene can encodeThe genes are located on the DNA which is found in the nucleus of the cell. Protein synthesis happens outside the nucleus in the cytoplasm on the ribosomes. The processes that are involved in making proteins from our genes are called transcription and translation and the molecules that are involved in these processes are called DNA, mRNA, tRNA and proteins. The order of information transfer is DNA to mRNA to protein.

Transcription

Transcription is the process where messenger RNA (mRNA) molecules are synthesised from DNA molecules. Transcription takes place in the nucleus. During transcription only one of the strands of DNA corresponding to a gene (template strand) is copied into mRNA. This mRNA molecule will be complementary to the bases that compose the template strand. The mRNA molecules have short lives. They travel out to the cytoplasm where they direct the synthesis of a protein and then they are destroyed. Transcription depends on complementary base pairings. A pairs with U, T with A, C with G and G with C. Only one of the DNA molecules is transcribed and therefore the resulting mRNA molecule is single stranded. The amount of transcription of any given gene can be directly controlled by the cell. Once the mRNA molecules leave the nucleus and enter the cytoplasm, they are loaded onto the ribosomes. It is at the ribosomes that protein synthesis occurs by a process called translation. The ribosomes are composed of ribosomal RNA (rRNA) proteins and ribosomal proteins.

Translation

Translation is the process where mRNA molecules are translated into proteins at the ribosomes. The nucleotides of the mRNA molecule are read by the ribosome so that each set of three nucleotides called a codon, specifies a single amino acid. Therefore, the first three nucleotides of the mRNA will encode the first amino acid, the second three bases the second amino acid and so on. The rules by which the base sequence of the mRNA molecule is translated into the primary amino acid sequence of a protein are called the genetic code. There are 64 different possible codons (this is because there are 4 bases: A, U, C, G, and each codon has 3 bases, so 43 = 64) and 20 amino acids. Some codons code for the same amino acid and therefore the genetic code is said to be degenerate. No codon codes for more than one amino acid.Three of the codons do not specify the incorporation of any amino acids. These are known as the stop codons - UAA, UAG, UGA. They are found at the end of the mRNA coding sequence and they tell the ribosome to stop translating the message and release the protein. The mRNA is translated from the 5' end and read one codon at a time to the 3' end. Translation usually starts at a start codon (AUG) which codes for methionine. Each successive codon is read and the amino acid incorporated into the protein chain until a stop codon is encountered. The codons in a mRNA molecule do not directly recognise the amino acids that must be incorporated. Instead this process is directed by a group of adapter proteins called transfer RNAs (tRNAs). Every codon, except the stop codons, has its own tRNA molecule. A tRNA molecule has an anti-codon end, which is made of a set of three base pairs. These base pairs can base pair with the complementary codon in the mRNA. The 3' end of a tRNA molecule is attached to an amino acid. In the translation process, a ribosome reads a mRNA molecule codon by codon. At each codon, a tRNA molecule with an anti-codon complementary to that codon attaches to the mRNA. It brings with it the appropriate amino acid that is then incorporated into the growing polypeptide chain. Once the amino acid has been added, the tRNA molecule is released and the ribosome moves onto reading the next codon in the mRNA chain. This process continues until the ribosome reads a stop codon. At this point the ribosome releases the mRNA molecule and the completed protein. The tRNA molecule functions as an interpreter reading codons in the mRNA molecule and translating them into amino acids. In this way, the sequence of base pairs in a given gene determines the amino acid sequence of the protein.

ChandraMukhi -- Reloaded ( Part II )

PART - II - HISTORY OF CHANDRALEKHA
(At the food court)

Jyothika : Hey Rajini, it was a surprise to see u here today. We tried to reach your mobile yesterday but could not get you.. How you came here at the right time?

Rajini : hahaha... (laughs and turns to the screen and tells), When I come, how I come, nobody can guess, but whenever needed I would be right there".

Jyothika : OK OK, I know, Prabhu would have sms-ed you about the new venture we are upto.
Rajini : yeah yeah, i got his message.I have come to help you to set up the new office. I have a small work to be completed here, let's go to Siruseri today evening. Prabhu too would be there at that time

Jyothika : Anyway, Thank god u saved my code, otherwise they would have spoiled my entire work

Evening time..Prabhu, Jyothika and Rajini arrived in a car to inspect their newly acquired office, LMRV Software company. Since the doors were locked, Rajini went to the security cabin and asked for the key from the Chief Security, Vijayakumar. Vijayakumar inquired why he needed the key. Rajini informed him that Prabhu had acquired the company and soon he would resume the operations at LMRV Software Company. Vijayakumar was shocked. "LMRV Company???.......... You mean you had bought that one". Rajini "Yea yea..you are right...What is the matter?". Vijayakumar replied "Sir, that company is haunted. ".

All of them were surprised. "What do you mean" asked a puzzled Prabhu. Vijayakumar continued "yes sir, that company is haunted by some black magic. Dont you see that company remaining locked for months. There is a story behind it. ". Vijayakumar started narrating the story of the mystery behind the LMRV software company.”

"This is a MNC company which had its corporate head office at US. Some years ago, Mr.Babu was appointed Divisional Manager for Chennai office. Babu was a good administrator and an excellent manager. The company's profit increased multi fold under him and the company was getting some plum projects from major US companies.. While looking for a C resource, Babu came to know of one talented girl called Chandralekha…who came first place in the World level conference of Programmers held two years ago. She was just brilliant when it comes to 'C' and PERL programming. If she started coding in C, one can watch it the entire day, (the complexity of the code, very hard to understand for any others). Babu wanted to employ Chandralekha in his company, who he thought would be the best resource for a high risk project he got. But she was already working for HPTR Software Company though at a lower pay. Babu tried all his tricks to get Chandralekha in our company but Chandralekha was steadfast in her decision. Finally Babu pressurized the consultancy through which Chandralekha got into her company and made her join LMRV software company. Chandralekha was unhappy, but unable to do much about that, she started working here. At nights she would stay in the company, secretly doing coding for her old company and send it through internet to them. Babu found it one day when he was analyzing why there were so many Night Taxi requisitions from Chandralekha. He called the old Project Manager of Chandralekha, Mr.Arun to his company, and infront of Chandralekha he made the MD of HPTR company dismiss Arun. Chandralekha was also fired from LMRV Company and both of their names were blacklisted so that they would not be able to join in any other software company. The project that Chandralekha was involved in here was dropped and her computer, in which the entire code she had written was locked and shifted to the godown. Soon after this incident Babu went onsite, But those who were working here began to get affected by many problems, frequent virus attack, hacking attack etc., It was rumored that Chandralekha, as a measure of revenge, had employed some black magic here and the employees working in that company or the computers there would be get affected. It was beginning to show, as almost everyone encountered some or other serious problems in their official and personal life. Gradually, the employees shifted to other companies, and hence the head office was forced to shut down its operations in Chennai. The black magic of Chandralekha was still haunting the company. It could cause problems to anybody who enters this office".Vijayakumar finished this lengthyyyy flashback as Rajini and Prabhu completed another yawn. But Jyothika was keenly listening to this story.........

( TO BE CONTINUED .... )