Question

How does a cell synthesize a protein?

Answer 1

Protein synthesis in a cell

All cells carry their functions through their proteins. All components of protein function are defined by the exact composition, structure and conformation, which is encrypted within the DNA region (known as locus) encoding that protein. With the process of protein synthesis the biological cells generate new proteins.

Protein synthesis takes place in two steps:

Transcription and translation

Transcription - the information (sequence) encoded in the DNA is copied to a RNA molecule as one strand of the DNA double helix is used as a template. The RNA molecule is sent to the cytoplasm, which helps in bringing all components required for the actual protein synthesis together like amino acids, transport RNAs, ribosomes, etc. In the cytoplasm the protein polymers are “synthesized” through chemical reactions, which is why the process is known as “protein synthesis” or “protein biosynthesis”.

Translation - The RNA copy of the protein genetic information encoded in DNA molecule is formed in the nucleus and it is called messenger RNA or mRNA. Each mRNA encodes the information for a single protein and is much smaller in size compared to the DNA molecule. This allows mRNA molecules to exit the nucleus through nuclear pores. Once enters the cytoplasm, the mRNA could interact with ribosome, which assists as the cell’s assembler within the process of protein synthesis. The ribosome consists of proteins and ribosome RNA molecules or rRNA, which are organized in two subunits. The mRNA firstly binds to just one of the ribosome sub-units.

When the mRNA interacts with the big ribosome sub-unit, this activates the approach of another RNA molecule, called transfer RNA or tRNA. The tRNA molecule possess a specific sequence of 3-bases (anti-codon), which complement a corresponding sequence (codon) within the mRNA sequence. When it finds it, it attaches to the mRNA, as the other end of the tRNA is laden with an amino acid. The other sub-unit of the ribosome arrives at this point and a complete structure is formed. The first tRNA binds to a start codon, which is one and the same for all the proteins. As the complete ribosomal structure is formed, another tRNA molecule approaches. The next tRNA vary from the first one and is carrying another amino acid. the tRNA must have an anti-codon that matches the second codon of the mRNA. The two amino acids carried by the first two tRNAs are bind together with the assistance from the ribosome and using cellular energy in the form of ATP.

The above steps are repeated until there are uncoupled codon sequences on the mRNA, thus the chain of amino acids grows longer. Once the sequence of amino acids is successfully assembled in a protein, the two ribosome sub-units separate from each other and joined again for later use.

The process of protein synthesis takes place in multiple ribosomes simultaneously and all over the cytoplasm. A living cell can synthesize hundreds of different proteins every single second.

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