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Polypeptide synthesis

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The complete set of genes in a cell is known as the genome while the full range of proteins a cell can make is the proteome. These are the steps that bridge these two realms.

 

Proteins are made up of amino acids linked by peptide bonds, therefore a protein may be referred to as a polypeptide (of course, some proteins such as haemoglobin have extra bits to them). All are encoded for by the information stored in DNA. Let’s see how exactly this happens.

 

Transcription: DNA to mRNA

 

In a process called transcription, mRNA is formed based on DNA. The bases on the coding strand of DNA are transcribed into a new molecule, mRNA, which is synthesised by the enzyme RNA polymerase.

 

 

Wanna see more detail?

 

 

As you can see, the DNA double helix unwinds, RNA polymerase anneals to the coding strand and recruits freely available bases (A, U, C, G) to build an mRNA strand.

 

Splicing: pre-mRNA to mRNA

 

In eukaryotes, genes contain non-coding sequences which must be removed before mRNA is used to produce proteins. These are called introns as opposed to exons which are coding sequences. Splicing therefore is the process of excising (cutting out) introns to be left with mRNA containing purely coding sequence

 

Translation: mRNA to tRNA

 

The resulting mRNA finally leaves the nucleus where the above business had been taking place, and arrives in the cytoplasm where the final step takes place. More specifically, in ribosomes. Each mRNA codon is matched against an anticodon on tRNA, which is matched to its respective amino acid. This binds to the next amino acid and so forth, until a polypeptide is made.

 

ATP is used in the process of binding each amino acid to tRNA.

 

 

Result: protein synthesis

 

Each gene codes for one polypeptide. Many proteins are made of multiple different polypeptides, and are hence coded for by multiple genes.

 

Enzymes themselves which are proteins an take part in metabolic processes have their synthesis controlled by DNA. Therefore, the effects of these products determine the phenotype of an organism.

 

Ok byeeeee

 

 

 

 

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