The Biological Basis of Life: Protein Synthesis

Proteins are required for the structural integrity and function of all living organisms. Protein accounts for nearly half of the total dry weight of a cellular structure. A protein is an organic compound with many molecules. It is made up of amino acids linked together by peptide bonds.

Proteins are composed of 20 amino acids; however, the arrangement of these amino acids determines the protein’s structure and function. Protein synthesis is the process through which proteins are produced. It takes place inside the cell in biological systems.

Definition of Protein Synthesis

Protein synthesis is a step-by-step process that results in the generation of specific and various types of proteins.

This method requires DNA, RNA, and a variety of enzymes. The process begins with transcription (the creation of RNA over a DNA template), follows with translation (the actual synthesis of proteins), and concludes with post-translational activities like protein folding, alteration, and proteolysis.

When it occurs in prokaryotes, it starts in the cytoplasm. In eukaryotes, the process begins in the nucleus with the production of a transcript (mRNA) from the coding part of the DNA molecule. When the transcript comes out of the nucleus, it goes to the ribosomes, turning it into a muscle protein with a specific chain of amino acids.

The Process of Protein Synthesis

DNA serves as a template to create messenger RNA (mRNA) during transcription. The mRNA then exits the nucleus and travels to a cytoplasmic ribosome for translation.

The genetic code within mRNA is decoded and synthesised polypeptides during translation.

One way to simplify these two processes is to remember the foundational element of molecular biology: DNA > RNA > Protein.

Protein Synthesis Mechanism

I. Transcription

Transcription is the first step of molecular biology’s core dogma: DNA → RNA. It is the process by which genetic instructions contained in DNA are transferred to messenger RNA (mRNA). During transcription, a complementary strand of mRNA is converted into a strand of DNA.

Transcription Procedures

Transcription consists of three stages: initiation, elongation, and termination.

1. Initiation – It occurs when RNA polymerase attaches to the promoter region. This causes the DNA to unravel, allowing the enzyme to read the nucleotides on one of the DNA strands.
2. Elongation – It is the process of incorporating nucleotides into the mRNA strand. RNA polymerase reads unwound DNA and creates mRNA form complementary base pairs. The newly produced RNA is attached to the unwinding DNA for a brief period during this process. Adenine (A) in DNA interacts with uracil (U) in RNA.
3. Termination – In transcription, this is the point at which the RNA polymerase crosses over to the other side of a stop (termination) region in the gene. The mRNA strand is now complete and separates from the DNA.

mRNA Processing

In eukaryotes, the newly synthesised mRNA has not been ready to be translated into protein. Therefore, it must be processed further before leaving the nucleus.

This could be done by splicing, editing, and adding polyadenylation. These mechanisms alter the mRNA. This enables a single gene to produce several proteins.

• Splicing – It eliminates mRNA’s introns. Introns are sections of the genome that do not include any protein-coding sequences. Exons are the only remaining mRNA sections that code for proteins. Ribonucleoproteins are RNA-containing nucleoproteins. Small nuclear ribonucleoproteins regulate the splicing of pre-mRNA.
• Editing – It modifies many nucleotides in mRNA. Examples include the two distinct versions of the human protein APOB, which assists in the transport of lipids through the bloodstream and was created by editing. 
• Polyadenylation – It ends the mRNA with a “tail.” The tail is composed of an As string (adenine bases). It indicates the end of the mRNA. It is also a part of the process by which mRNA leaves the nucleus. Additionally, the tail shields mRNA from degradation by enzymes.

Translation

The amino acids are connected in a precise order via translation, according to the genetic code’s principles. Translation occurs in the cytoplasm containing ribosomes.

It is divided into four stages:

(1) The activation – The amino acid and the tRNA are covalently linked.

(2) Initiation – Initiation factors assist the small ribosomal subunit binds to the 5′ end of mRNA.

(3) Elongation – The following aminoacyl-tRNA in line interacts with the ribosome via GTP and is also an elongation factor.

(4) Termination – The ribosome’s A site is adjacent to a stop codon.

Post-translation

Proteolysis and protein folding are events that occur following protein synthesis. Proteolysis is the process by which proteases break muscle proteins. It removes amino acid residues from the N-terminal, C-terminal, or internal polypeptide regions.

Post-translational modification is the enzymatic modification of a polypeptide chain after translation and peptide ionic bonding. It is possible to alter the polypeptide’s ends and side chains to ensure that it is correctly positioned in the cell. A few post-translational methods include phosphorylation, acetylation, and hydroxylation among others.

Inhibiting the Synthesis of Proteins

The substances to inhibit protein synthesis prevent cell development by affecting the production of new proteins. It is frequently referred to as substances that work at the ribosome level, such as antibacterial drugs.

Drugs can be altered to target other stages of mRNA translation if resistance develops.

Synthesis of Muscle Proteins

Synthesis of muscle proteins is the activity through which muscle protein is synthesised. It is the process through which new bricks are added to the wall. Muscle protein degradation takes bricks out of the wall on the other side. Muscle proteolysis and muscle degradation are two often used terms for the breakdown of muscle proteins.

The muscles will expand if protein synthesis exceeds the amount of protein breakdown. 

Conclusion

Proteins are small molecules found inside cells that are necessary for the structure and function of the cell. We would die if our cells could not perform their functions without protein synthesis. Striated skeletal muscle comprises the most important part of the muscle. Muscle proteins are classified according to their histological structure.