Protein biosynthesis: how cells make proteins
Overview of protein biosynthesis: stages from genetic information to folded protein, core machinery (ribosomes, tRNA, amino acids), differences between prokaryotes and eukaryotes, and biological importance.
Protein biosynthesis is the cellular process that constructs proteins from amino acid building blocks. The term is sometimes used narrowly to mean translation, but more commonly it denotes a sequence of coordinated steps beginning with gene transcription and ending with a folded, functional protein. Cells obtain amino acids by dietary supply or internal synthesis, then assemble them into a polypeptide chain that adopts a specific protein structure. The overall activity — often called synthesis — is central to cell growth, signalling and metabolism.
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Stages of biosynthesis
The process can be conceptually divided into several stages. First, DNA is copied into RNA during transcription, producing a precursor messenger RNA. In many organisms that precursor undergoes processing: addition of protective ends and RNA splicing, which can remove noncoding segments and generate multiple mature mRNAs from a single gene. Next, the mature mRNA guides the ribosome in translating nucleotide codons into an amino acid sequence. Transfer RNAs bring specific amino acids to the ribosome, where peptide bonds join them into a growing chain.
Core components and molecular machines
Key molecular players include ribosomes (the macromolecular machines that read mRNA), messenger RNA (the genetic template), transfer RNAs (adapters that match codons to amino acids) and aminoacyl‑tRNA synthetases (enzymes that attach amino acids to their tRNAs). Molecular chaperones assist newly made chains to fold correctly, and enzymes perform post‑translational modifications such as phosphorylation or glycosylation that can modulate activity, stability or localization. Together, these components control the sequence, timing and quality of protein production.
Differences between cell types
Although the genetic code is nearly universal, the logistics of biosynthesis differ between cellular domains. In prokaryotes, transcription and translation are often coupled: ribosomes begin translating an mRNA while it is still being synthesized. In contrast, eukaryotes separate transcription (in the nucleus) from translation (in the cytoplasm), and they commonly process pre‑mRNA by adding caps and tails and by alternative splicing to create diverse protein isoforms. For example, genes in organisms such as Drosophila can be spliced in many ways to increase proteomic complexity.
Functional importance and applications
Accurate protein biosynthesis is essential for life: errors can produce nonfunctional or harmful proteins and underlie many genetic diseases. Because translation differs between bacteria and eukaryotes, it is a major target for antibiotics that selectively inhibit bacterial ribosomes. Biotechnological applications exploit cellular biosynthesis to produce therapeutic proteins, enzymes and vaccines. Research into the process also informs genetic engineering, synthetic biology and efforts to design proteins with new functions.
Notable facts and ongoing research
Several notable features make protein biosynthesis a rich field of study: the redundancy and near‑universality of the genetic code, the regulatory role of mRNA sequence elements, and the impact of post‑translational modification on protein behavior. Contemporary research explores ribosome dynamics, quality control pathways that recognize defective nascent chains, and technologies that harness translation for medical and industrial aims. For further reading, see introductory resources on proteins, detailed treatments of translation mechanisms, and reviews of transcription and splicing processes.
Brief links: Amino acids • Polypeptides • Folding and structure • Biosynthesis overview • Prokaryotic translation • Eukaryotic processing • Model organisms.
Transcription
→ Main article: Transcription
In the first step for protein biosynthesis in a cell, sections of genes on the double-stranded DNA are visited, read and transcribed into single-stranded RNA molecules. In this process, complementary nucleic bases of RNA building blocks (uracil, cytosine, guanine, adenine) are assigned to the present sequence of nucleic bases of DNA (adenine, guanine, cytosine, thymine). In the RNA transcript then linked to the strand, ribose occurs instead of deoxyribose and uracil instead of thymine. The genetic information is contained in the base sequence, a codogen on the DNA is transcribed to a codon on the messenger ribonucleic acid, or mRNA for short.
For the transcription of a gene, in addition to several other factors, an RNA polymerase is necessary as an enzyme that catalyzes the continuous assembly of the RNA polymer depending on the DNA template. The base-pairing ribonucleoside triphosphates (UTP, CTP, GTP and ATP) assigned to the template are linked to each other to form the polynucleotide of an RNA, in each case by splitting off two phosphate groups of the triphosphates. There may be different types of RNA polymerase for the transcription of genes that code for proteins by means of an mRNA and for that of other genes, for example for the formation of an rRNA or a tRNA.
In eukaryotes, transcription takes place in the nucleus; therefore, the mRNA must be exported from the nucleus to the cytosol, since translation is carried out there. Prokaryotes, on the other hand, do not have a nuclear compartment; transcription takes place here in addition to translation in the cytoplasm.
Post-transcriptional modification
→ Main article: Post-transcriptional modification
Splicing
In eukaryotes, after pure transcription, the non-coding introns contained in the resulting pre-mRNA must be excised so that only the required exons remain. This process is called splicing. Consensus sequences are used to recognize the introns. During splicing, different snRNPs bind in the region of the introns and exon-intron junctions. These lead to the cleavage of the phosphodiester bonds, forming the spliceosome, and thus to the excision of the introns. At the same time, the exons are ligated. Splicing also occurs in rRNA and tRNA.
Capping
Meanwhile, the so-called capping also takes place, in which the stability of the RNA is increased. In this process, a so-called 5'-cap structure is attached, whereby the 5' end of the pre-mRNA undergoing synthesis is converted into a structure known as a "cap", which protects the mRNA from digestion by 5'-exonucleases and phosphatases.
Polyadenylation
During polyadenylation, the poly(A) tails are attached to the newly formed 3' end of the RNA (up to 250 nucleotides long). This poly(A) tail facilitates the export of the mRNA into the cytoplasm and also protects the 3' end from enzymatic degradation.
RNA Edition
In RNA editing, one or more nucleic bases of the RNA molecule are changed (modified), inserted or deleted after transcription. For example, editing can result in a new stop codon on the mRNA that is located upstream of the previous one; translation then stops here and the shorter isoform of a protein is formed. RNA editing occurs only in some organisms, cells or cell organelles and is often restricted to particular nucleotide sequences.
See also: Processing
Questions and answers
Q: What is protein biosynthesis?
A: Protein biosynthesis is the process by which cells build proteins.
Q: Is protein biosynthesis a single-step or multi-step process?
A: Protein biosynthesis is a multi-step process.
Q: Which molecules are used to build proteins in cells?
A: Amino acids are used to build proteins in cells.
Q: Can amino acids be synthesised or only obtained through food?
A: Amino acids can either be synthesised or obtained through food.
Q: What is the role of RNA splicing in protein biosynthesis?
A: RNA splicing is involved in producing the final proteins by creating messenger RNAs.
Q: How are proteins produced after the transcription of polypeptide genes?
A: Proteins are produced by translation and RNA splicing after the transcription of polypeptide genes.
Q: Does protein biosynthesis differ between prokaryotes and eukaryotes?
A: Yes, protein biosynthesis differs between prokaryotes and eukaryotes, although some parts of the process are the same in both.
Related articles
Author
AlegsaOnline.com Protein biosynthesis: how cells make proteins Leandro Alegsa
URL: https://en.alegsaonline.com/art/79513
Sources
- doi.org : 10.1016/S0092-8674(00)80878-8
- pubmed.ncbi.nlm.nih.gov : 10892653