Bacteria belongs to a group of organism that lacks cell nucleus and membrane bound organells. This group of organisms are termed as prokaryotes. Prokaryotes follows the central dogma of molecular biology first proposed by Francis Crick in 1958 to synthesize proteins from mRNA through a process called translation and the mRNA is being synthesized from the DNA by another process called Transcription. Temperature, nutrient availibity are some key factors that start the process of synthesizing proteins in response to these key factors. Example.
This paper will provide an explanation as to how bacteria decode the genetic information to produce proteins. Transription generates 3 kinds of RNA. Transfer RNA(tRNA) carries amino acid during protein synthesis, ribosomal RNA molecules come together to form ribosomes while mRNA bears the message for protein synthesis. In bacteria, mRNA often carries coding information of more than 1 gene therefore it is said to be polycistronic (DIAGRAM). MRNA is synthesized under the direction of DNA by RNA polymerase. This polymerase in its core enzyme form has 5 subunits.
A 6th subunit called the Sigma factor helps the core enzyme to recognise and bind to the promoter regions which are often found at -35 basepair and -10 basepair(also called Pribnow box) upstream of the transcription site. Upon binding, RNA polymerase unwinds the helical DNA and this open region becomes a open complex. There is a reason as to why the -10bp site is chosen. The hydrogen bonds between the nucleotides in the Pribnow box are weak and easily broken, forming the open complex. RNA polymerase progresses along the DNA unwound DNA strand and starts to synthesize mRNA in the 5` to 3` direction.
MRNA synthesized is thus complementary and anti parallel to the template DNA. Termination of transcription require a terminator. There are two kinds of terminator, rho-independent terminator which refers to a nucleotide sequence that when transcribed into RNA, forms hydrogen bonds within the single-strande RNA, this intrastrand bonds creates a hairpin-shape loop and causes RNA polymerase to stop transcribing and dissociate from the template strand. Another terminator depend on a protein called the rho factor which causes RNA polymerase to dissociate from the mRNA. Its exact mechanism remains unclear.
With the mRNA synthesized by the RNA polymerase using DNA of the bacteria as template, the mRNA are translated to amino acids which are linked covalently to form a polypeptide. Translation begins when a ribosomes binds to mRNA and tRNA molecules carry the amino acid correspending to the codons dictate by the mRNA to the ribosome so that the amino acid can be added to the polypeptide chain as the ribosome moves down the mRNA strand. Translation initiated by formation of initiation complex consisting of 30s and 50 sribosomal subunits, Formyl-methionyl tRNA and the mRNA. Proteins called intitial factors are also required to form the complex.
The two ribosomal subunits that come together to for, the complex are commonly refer to as the 70s ribosome. This 70s ribosome has two sites in which tRNA carrying amino acids can bind to. One is called the P site and A site. There is also an E site where tRNA are released. The initiating transfer t RNA carrying formylmethionyl binds to the P site, a tRNA that recognises the next codon ann carries the second amino acid moves in to the A site. The formylmethionie carried by the tRNA in the P site is then joined to the amino acid carried by the tRNA that just entered the A site by a peptide bonds.
The ribosome then advance a distance of 1 codon. The tRNA that carries the formylmethionie is released at the E site. A tRNA carrying the next amino acid now moves in through the A site where the anti codon matches the codon of the mRNA. The ribosome shift down a distance of 1 codon, the 2 amino acid on the tRNA in the P site are transferred to the new amino acid and the 2nd tRNA is released at the E site. This cycle is repeated. Elongation is terminated by a stop codon. Stop codon do not code for any amino acid.
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