Protein synthesis

Protein synthesis is the creation of proteins via transcription and then translation on a ribosome, involving RNA polymerase, primers,  mRNA, tRNA and rRNA. It occurs in both Eukaryotic and Prokaryotic cells although there are certain differences like splicing occurs in different places and of course there isn't a nucleus in prokaryotes so no movement between membranes is involved to get the mRNA strand out of the cell.

Transcription

Transcription is the copying of DNA in the nucleus into pre-mRNA. For a gene to be synthesised into a protein it needs certain pathways within cells to occur which causes binding of transcription factors to the promoter sequence on the DNA sequence.

Splicing

Splicing occurs in the nucleus by the use of a spliceosome looping out the introns then cutting them out and binding the exons together leaving a strand of only exons. This is the pre-mRNA maturing and turning into mRNA to leave the cell.

Translation

Componants involved

mRNA

mRNA is a copy made of the DNA by RNA polymerase II and spliced to take out all the introns. This is a single polynucleotide strand that have codons made up of Adenine, Guanine, Cytosine and Uracil and instead of a deoxyribose in the sugar phospate backbone there is a ribose molecule. 

tRNA

This is a single polynucleotide strand that folds back on itself to form hydrogen bond in the shape of a clover leaf. This molecule on one end has an anticodon which is complimentary to the codon on the the mRNA strand which it attaches to. On the other end there is a specific protein that is able to detach and form part of a polypeptide chain.

Ribosome

The Ribosome is the location of the translation of proteins, the Ribosome has 3 tRNA binding sites the P site which holds the tRNA molecule with the polypeptide strand, the A site which binds to the tRNA molecule with the next amino acid to by hydrolysed and the E site which holds the tRNA molecule to be discharged. The mRNA strand is attached to the tRNA strand by Hydrogen bonds and also attached to the ribosome.

The Mechanism

Once the mRNA strand has bound to the

Prokaryotes

In prokaryotes initiation of transcription is different from that of Eukaryotes, at -10 and -35 these sequences are located upstream of the start site of transcription. There are specific sequences at each site that enable a Sigma factor to bind. At -10 this is called the TATA box due to the sequence of bases being TATAAT and then at -35 it is normally TTGACA. This Sigma factor then in turn binds to the RNA polymerase forming a holoenzyme, this now allows transcription to begin.

When finishing the transcription

Eukaryotes

Tn Eukaryotes the initiation is similar to that of the prokaryotes