Synthesis of Protein

Protein synthesis is a complex biological process that takes place in cells, involving the transcription of DNA into RNA and the translation of RNA into proteins. 

This process is crucial for the maintenance, growth, and functioning of living organisms. 

• Transcription:

Transcription is the process in which the genetic information encoded in DNA is used to synthesize a complementary RNA molecule. It serves as a crucial step in protein production within cells.

The first step occurs in the nucleus of eukaryotic cells or the nucleoid region of prokaryotic cells. Here, DNA serves as a template for the synthesis of messenger RNA (mRNA).

RNA polymerase, an enzyme, recognizes and binds to the DNA at the beginning of a gene, which is a specific sequence of nucleotides that codes for a particular protein.

The RNA polymerase unwinds and separates the DNA strands.

One of the DNA strands, known as the template strand, is used to synthesise a complementary mRNA strand. RNA nucleotides (adenine, uracil, guanine, and cytosine) are added to the growing mRNA chain according to the base-pairing rules.

• mRNA Processing:

The newly synthesised mRNA, known as the primary transcript or pre-mRNA, undergoes several modifications before leaving the nucleus.

Introns, non-coding regions, are removed through a process called splicing, and the remaining coding regions, called exons, are joined together.

A modified 5′ cap is added to the beginning of the mRNA, and a poly-A tail is added to the 3′ end. These modifications protect the mRNA and facilitate its export from the nucleus.

• Translation:

Translation takes place in the cytoplasm, specifically on ribosomes, which consist of ribosomal RNA (rRNA) and protein.

The mRNA binds to a ribosome, and the process begins with the initiation phase. Initiation factors, along with a special tRNA (transfer RNA) molecule called the initiator tRNA, assemble the ribosomal subunits and the mRNA.

The ribosome moves along the mRNA in the 5′ to 3′ direction, and tRNA molecules bring amino acids to the ribosome in a sequence dictated by the mRNA codons (three-nucleotide sequences).

During elongation, the ribosome reads the mRNA codons and catalyses the formation of peptide bonds between adjacent amino acids, forming a polypeptide chain.

The process continues until a stop codon is reached, signalling the termination phase. Release factors facilitate the release of the completed polypeptide chain from the ribosome.

Protein Folding and Post-Translational Modifications

The newly synthesised polypeptide chain undergoes folding to attain its three-dimensional, functional structure.

Post-translational modifications, such as phosphorylation, glycosylation, and addition of lipid groups, may occur, further modifying the protein’s structure and function.

The mature protein is then transported to its specific cellular location, where it carries out its designated function.

Diversity in Protein Sizes

Proteins, vital for diverse cellular functions, exhibit a range of sizes. Consider them as molecular structures, where some proteins are small, such as insulin, composed of 51 amino acids, while others are large, like haemoglobin, consisting of 574 amino acids. The size diversity in proteins corresponds to variations in the number of these building blocks, influencing the structure and function of each protein. This spectrum of sizes enables proteins to fulfil a wide array of roles within cells, contributing to processes as fundamental as signalling, transport, and catalysis.

Genetic Mutation 

A mutation is a change in the DNA of an organism. It can happen by mistake during cell division or be caused by external factors like chemicals or radiation. Mutations can affect a single letter or a larger piece of genetic code. Sometimes they don’t cause problems, but they can also lead to genetic disorders or new traits.