Transcription and Translation

(two main processes of genes linking to proteins)

Transcription is the synthesis of RNA under the construction of DNA. This takes place in the nucleus. An enzyme know as RNA polymerase attaches(initiation step) at the promoter or TATA box (start site) and unwinds the double strand of DNA. Then it begins to copy on the 3' end of the strand. Then in the elongation step the RNA strand elongates in the 5' to 3' direction. The terminator signals the polymerase to stop, however; the process continues for hundreds of nucleotides after. The pre-mRNA is cut off at the cleavage where a poly(A) tail is connected. Also a modified form of guanine is attached at the other end known as he 5' cap. Both of these additions are to protect the pre-mRNA from degradation.


Transcription process
Transcription process
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RNA splicing is a process that modifies the pre-mRNA cutting out parts that are not necessary. Introns are the portion that is taken out by the spliceocomes and the remaining portions are known as exons. These sliceosomes also rejoin the exons. Now the RNA strand is complete to move on to the next process.

Splicing process
Splicing process


Translation is directed by the modified RNA to synthesize a polypeptide. The function of transfer RNA is to transfer amino acids to a ribosome. The t-RNA has a nucleotide triplet called an anticodon which is complementary to the m-RNA's codon. The ribosomal unit that attach to the m-RNA is called a ribosomal RNA. Each ribosome has three binding sites for t-RNA: the P site, the A site, and the E site. The P site holds the t-RNA that carries the polypeptide chain. The A site holds the t-RNA that has the next amino acid to be added to the polypeptide chain. The E site is where the t-RNA is released from the ribosome. Initiation stage is when the m-RNA, t-RNA with the first amino acid, and the two ribosomal subunits come together. During the elongation stage amino acids are being added to the polypeptide chain. The termination stage occurs when i stop codon reaches the A site and then a release factor hydrolyzes th finished polypeptide chain which frees it from the ribosome.

Translation process
Translation process


The polypeptide chain begins to coil and fold which forms a functional protein.