Proteins Are Important For Proper Cell Functioning
Living cells function through their proteins. On the other hand, each gene contains the instructions for building a particular protein. However, the information encoded in the must be converted into a form that can be recognized by the ribosomes, which act as cellular protein-making machines.
What Is The First Step Of Protein Synthesis?
The first step of protein synthesis is called transcription. The DNA transcription to mRNA is actually the first step of the protein synthesis. During the transcription step the instructions encoded in the DNA of the genes are transcribed into the nucleotide sequence code of a ribonucleic acid (RNA). Because this RNA molecule carries the protein synthesis instructions, or in other words a “message”, from the genes to the ribosomes, it is called messenger RNA (abbreviated as mRNA).
What Are the Products Of Transcription?
The majority of the coding genes are transcribed into messenger RNA. There are some exceptions, and some of the coding genes are transcribed into different types of RNA molecules that carry out quite different functions in the cell. Such types of RNA are ribosomal RNA (rRNA) and transfer RNA (tRNA) – they are both required for the successful completion of the protein synthesis process.
What Are The Phases Of Transcription?
During the translation each messenger RNA molecule is synthesized is using one of the DNA double helix strands as a template (the so called “template strand”). The transcription step can be divided into 3 distinct phases:
Each of these phases is regulated by various transcription factors and co-activators in order to guarantee that the correct mRNA molecule is transcribed.
Transcription Differs In Prokaryotes Compared to Eukaryotes
In eukaryotic cells, the genetic material in the form of a DNA is held in the cell nucleus. So, this is the compartment where the actual transcription occurs. The DNA molecules ar build of two anti-parallel strands (helixes), which are built of deoxyribose sugar and a phosphate linked together with strong phosphodiester covalent bonds. Each of the deoxyribonucleotides possess one of the four nitrogenous bases (adenine, guanine, cytosine and thymine) bound to the 1′ carbon atom of the deoxyribose. The the two strands are held together due to the weak hydrogen bonds acting between the complementary bases of opposing strands.
Transcription Process In Brief
The highly compacted DNA molecule is uncoiled and an enzyme called helicase disrupt the hydrogen bonds between two strands. Thus the double helix is “unzipped” within this region and makes possible the single nucleotide chain open to be copied. Another enzyme, called RNA polymerase attaches to the single strand containing the coding gene and starts to read the information encoded by the DNA strand from the 3-prime (3′) end to the 5-prime (5′) end. Thus, the enzyme actually synthesizes a single strand of mRNA in the 5′-to-3′ direction. The sequence of the mRNA is identical with the DNA structure, the only difference that the RNA molecules use the nucleotide uracil instead of thymine used by DNA. Once synthesized, the single stranded mRNA molecule can move to the cytoplasm through nuclear pores.
The transcription step differs in prokaryotic from the one in eukaryotic cells based on the subsequent steps that the transcript need to undergo. The first product in prokaryotes is the “normal” mRNA which does not need any post-transcriptional modifications. While in eukaryotes the first product is called primary transcript and it requires needs post-transcriptional modification. The post-transcriptional modification of eukaryotic mRNAs includes:
- capping with 7-methyl-guanosine
- poly-adenosine tailing
The resultant molecule is called heterophil nuclear RNA (hnRNA). Then, hnRNA then is directed to the spliceosome, where the introns (noncoding parts of the gene) are excised to produce the final mRNA.