Gene to Protein

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:22 PM IST

Transcription, Translation Of Molecular Biology

The central dogma of molecular biology represents a framework for conceptualizing the transfer of information, which occurs within a biological system, from one structural unit to another. First codified by Francis Crick in 1958, this distinguished scientist went on to explain how information initiates its throw from DNA to RNA and then into proteins. Recent elucidation of this key biological principle lies at the foundation of modern biology and explains the processes through which the genetic code contained within DNA is eventually transcribed into an active protein through an mRNA molecule.

Gene to Protein - Transcription and Translation

Diagram: Replication, Transcription, Translation

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The Role Of Gene Expression In Cellular Function

Gene expression is the process whereby information contained in DNA is transcribed into an active functional product, thereby considered as a protein or RNA molecule. This process is central to cellular function and organismal development. In this case, appropriate gene expression does take place in such a way that homeostasis within the cellular and organism levels is held. Diseases, examined by cancer, arise from misexpression of genes.

An Overview Of Transcription And Translation

There are two major ways genes are expressed: transcription and translation. In essence, transcription is the process whereby a section of DNA gets copied into RNA—more specifically, mRNA. Copies of the mRNA then move the genetic information from the nucleus out into the cytoplasm to its counterpart, the ribosomes, for translation. For that reason, the ribosome will read the mRNA to synthesize a polypeptide chain for a functional protein in the process of translation.

Definition Of A Gene

It is defined as the linear sequence of nucleotides in DNA coding for the formation of certain proteins or an RNA molecule. It is the fundamental level of inheritable unit found in chromosomes in the cell nucleus.

Structure Of The Gene Found On The Chromosome

Promoter: A DNA region where RNA polymerase binds to start the transcription.
Coding Sequence: Gene region from which RNA is transcribed, and later, portions where protein synthesis takes place.
Terminator: The nucleotide sequence signalling the end of transcription.

Diagram: Gene

Types Of Gene

Protein-coding Genes: Information in these genes is for making proteins.
Non-coding Genes: It does not code for proteins, but can otherwise produce functional RNA molecules such as ribosomal RNA and transfer RNA.

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This flow of genetic information involves three major processes: replication, transcription, and translation.

Replication

Cellular conditions make a replica of the DNA molecule itself. This occurs just before the division of a cell so that, as the cell divides, each resulting cell will have a full complement of the genetic information of the parent cell.

Transcription

It refers to the process by which a gene is expressed. It refers to the formation of an RNA molecule for a gene. It is essentially carried out by RNA polymerases, which are enzymes.

Translation

In other words, translation is the synthesis of a protein from the mRNA transcript. A ribosome reads the sequence that occurs via mRNA, uses vitamins with the assistance of tRNA, and then synthesises a corresponding amino acid series that forms a polypeptide chain.

Transcription: From DNA To mRNA

Transcription is a process whereby RNA is created using a DNA template. The main purpose of the process is to enable the transfer of genetic paraphernalia from DNA to RNA, which can carry out the information for protein synthesis.

Transcription takes place in the eukaryotic nucleus and the cytoplasm of prokaryotic cells.

Initiation

The process is described as follows:

Role Of RNA Polymerase

RNA polymerase attaches to the DNA template and synthesises the RNA transcript—this process is termed RNA transcription.

Binding To The Promoter Region

RNA transcription is initiated by the binding of RNA polymerase at a special site on DNA called a promoter where this DNA sequence is called a gene.

Formation Of The Transcription Initiation Complex

The promoter region is the region at which the various transcription factors and RNA polymerases assemble to form a transcription initiation complex that starts the process of synthesising RNA.
In the process of elongation, the electron-microscopic structure of DNA is unwound by the RNA polymerase, giving the template strand of the DNA so that base-pairing with the RNA nucleotides can be achieved.
The RNA polymerase moves along the DNA template, adding RNA nucleotides that complement the DNA bases, which link to each other to form an mRNA molecule.

Role Of Transcription Factors

Transcription factors are proteins that assist the binding of RNA polymerase and initiate transcription

Termination

Termination in prokaryotes is brought about when the RNA polymerase transcribes a terminator sequence in the DNA; it is considerably more complex in eukaryotes, involving other proteins.

Transcription Termination

When the elongation process nears its end, the newly synthesized mRNA is released or terminated from RNA polymerase.

Post-transcriptional Modifications In Eukaryote

5' Capping

A transcription is initiated, and the 5' end of the mRNA is joined or capped with a modified guanine nucleotide that prevents the digestion of mRNA. It also has a significant role in ribosome binding to mRNA for translation.

Polyadenylation

The 3' end of mRNA is polyadenylated by the addition of a poly-A tail, which is believed to prevent degradation of the mRNA and also aids in the export of the mRNA from the nucleus.

Splicing

The non-coding regions (introns) are excised from the mRNA transcript and the coding regions (exons) are joined. This process is called splicing and a mature mRNA molecule is now ready for translation.

Translation: From mRNA To Protein

Translation is a precise process whereby the mRNA decoding pathway is used to translate a particular sequence of amino acids, which are induced to fold into a functional protein.

Location of the process

Translation takes place in the cytoplasm, in detail in the ribosomes.

mRNA (Messenger Ribonucleic Acid)

mRNA reads as the template for the synthesis of proteins. It translates the genetic information from DNA to the ribosome.
It is the specification in vivo of the amino acid sequence of polypeptide chains in the molecule of protein.

tRNA (Transfer RNA)

Molecules of this type carry amino acids to the ribosome and then learn the m-RNA anticodon that would match the code which is an encoded protein specifically.

Ribosomes (rRNA and Protein Complex)

The ribosomes, composed of rRNA and proteins, carry out the process by which the information contained in the mRNA molecule is used to build the protein.

Amino Acids

Building blocks of proteins are amino acids that are linked in a specific order that is encoded by the base sequence of the mRNA in the process of translation.

The Genetic Code

The genetic code is a set of rules whereby information encoded within the genetic material—in the form of DNA or RNA sequences—is translated into proteins by living cells. It is universal for almost all organisms and consists of nucleotide triplets called codons. Each codon corresponds to one amino acid or one of the signals 'stop' while synthesizing the protein.

Codons and Anticodons

Triplets of nucleotides of mRNA that code for the amino acids. The sequence of three nucleotides on the mRNA, which codes for a particular amino acid. Anticodons are the triplets of nucleotides on the tRNA molecules that are complementary to codons.

Initiator And Terminator Codons

Translation initiates with an initiator codon (AUG) and terminates with a terminator codon (UAA, UAG, UGA).

Redundancy And Universality Of Genetic Code

The genetic code is degenerate in the sense that more than one triplet code can code for one amino acid. It is, however, universal for almost all organisms.

Translation Steps

The steps of translation have been discussed below:

Initiation

Initiation occurs when the small ribosomal subunit attaches to the mRNA and a special initiator tRNA.
The small subunit is associated with the large subunit.

Elongation

During elongation, tRNAs bring amino acids to the ribosome in the order prescribed by the mRNA codons.
The actual polypeptide is elongated by peptide bonds that form between the amino acid residues.

Termination

Translation stops when the ribosome reaches a stop codon.
The ribosome releases the completed polypeptide, which will spontaneously fold into its final, functional conformation.

Frequently Asked Questions (FAQs)

1. What is the process of transcription and translation?

Transcription is the process in which a copy of the gene's DNA sequence is made into a complementary mRNA; translation is the process by which mRNA is translated into a protein.

2. What are the steps in transcription?

The steps involved are initiation, elongation, and termination, with post-transcriptional modifications taking place in eukaryotes.

3. How does the genetic code work?

The genetic code consists of the codons of the mRNA, which specify the amino acids of the protein. It is universal and redundant.

4. What are some differences in the main ways gene expression occurs between prokaryotes and eukaryotes?

The former occurs in the cytoplasm of prokaryotes, and those processes are not as complex as eukaryotic ones while the mechanisms controlling them differ.

5. How do mutations relate to gene expression?

Mutations alter the DNA sequence; hence, they cause changes in the processes of transcription and translation, which might lead to an occurrence of sickness.

6. How do codons and anticodons work together in translation?

Codons are three-nucleotide sequences in mRNA that specify particular amino acids or start/stop signals. Anticodons are complementary three-nucleotide sequences on tRNAs. During translation, tRNAs with matching anticodons bind to the codons on the mRNA, bringing the correct amino acids to the ribosome for incorporation into the growing polypeptide chain.

7. How does frameshifting affect protein synthesis?

Frameshifting is a process where the ribosome shifts its reading frame during translation, either forward (+1 frameshift) or backward (-1 frameshift). This can occur naturally in some genes or as a result of mutations. Frameshifting changes the grouping of nucleotides into codons, potentially leading to:

8. What is the role of the signal recognition particle (SRP) in protein targeting?

The signal recognition particle (SRP) plays a crucial role in targeting certain proteins to the endoplasmic reticulum (ER) in eukaryotes or the plasma membrane in prokaryotes. It recognizes and binds to the signal sequence of a nascent polypeptide as it emerges from the ribosome. The SRP then guides the ribosome-mRNA-nascent polypeptide complex to the ER membrane (or plasma membrane in prokaryotes), where translation continues and the protein is inserted into or translocated across the membrane.

9. How do chaperone proteins assist in protein folding during and after translation?

Chaperone proteins assist in protein folding in several ways:

10. How do internal ribosome entry sites (IRES) facilitate cap-independent translation?

Internal ribosome entry sites (IRES) are specialized RNA structures that allow ribosomes to bind directly to mRNA, bypassing the need for 5' cap recognition. They facilitate cap-independent translation by:

11. What is the role of the poly(A)-binding protein in translation?

The poly(A)-binding protein (PABP) plays several important roles in translation:

12. What is the role of RNA polymerase in transcription?

RNA polymerase is the main enzyme responsible for transcription. It binds to the promoter region of a gene, unwinds the DNA double helix, and synthesizes an RNA strand complementary to the template DNA strand. RNA polymerase moves along the DNA, adding nucleotides to the growing RNA chain until it reaches a termination signal.

13. How does the start codon differ from other codons?

The start codon, typically AUG, is unique because it signals the beginning of protein synthesis and codes for the amino acid methionine. Unlike other codons, which are read by regular tRNAs, the start codon is recognized by a special initiator tRNA that helps assemble the ribosome and begin translation.

14. How does the process of translation termination differ from elongation?

Translation termination differs from elongation in several ways:

15. What is the function of the Kozak sequence in eukaryotic translation initiation?

The Kozak sequence is a consensus sequence found in eukaryotic mRNA that helps identify the correct start codon for translation. It typically includes a guanine three bases before the start codon and an adenine immediately after it (GCCACCAUGG, where AUG is the start codon). The Kozak sequence enhances the efficiency of translation initiation by helping the ribosome recognize the correct start site, especially when multiple AUG codons are present in the 5' untranslated region.

16. How does the structure of the ribosome contribute to its function in translation?

The ribosome's structure is crucial to its function:

17. What is the significance of the Shine-Dalgarno sequence in prokaryotic translation?

The Shine-Dalgarno sequence is a ribosome binding site found in prokaryotic mRNA, typically 8-10 nucleotides upstream of the start codon. It is complementary to a sequence in the 16S rRNA of the small ribosomal subunit. This complementarity helps position the ribosome correctly on the mRNA, aligning the start codon with the P-site of the ribosome and facilitating the initiation of translation in prokaryotes.

18. Why is mRNA processing necessary in eukaryotes?

mRNA processing in eukaryotes is necessary to create a mature, functional mRNA molecule. This process includes adding a 5' cap and a 3' poly-A tail, which protect the mRNA from degradation and aid in its export from the nucleus and translation. Additionally, introns (non-coding regions) are removed through splicing, leaving only the exons (coding regions) in the mature mRNA.

19. How do introns affect gene expression?

Introns are non-coding sequences within genes that are transcribed into pre-mRNA but removed during mRNA processing. They can affect gene expression by:

20. How does alternative splicing contribute to protein diversity?

Alternative splicing allows a single gene to produce multiple mRNA transcripts and, consequently, multiple protein isoforms. This process involves the inclusion or exclusion of different exons or the use of alternative splice sites. It greatly increases the protein-coding potential of the genome without increasing the number of genes.

21. What is the role of the poly-A tail in mRNA?

The poly-A tail is a string of adenine nucleotides added to the 3' end of mRNA during processing. It serves several important functions:

22. How do eukaryotic and prokaryotic gene expression differ?

Eukaryotic and prokaryotic gene expression differ in several ways:

23. What is the significance of the genetic code being "degenerate"?

The genetic code is degenerate, meaning that multiple codons can code for the same amino acid. This redundancy provides a "buffer" against some types of mutations, as a change in the third base of a codon often doesn't change the amino acid it specifies. This helps maintain protein function even if small changes occur in the DNA sequence.

24. What is the significance of codon bias in gene expression?

Codon bias refers to the unequal use of synonymous codons in coding DNA. It is significant because:

25. What is the role of selenocysteine in protein synthesis, and how is it incorporated?

Selenocysteine is often called the "21st amino acid" and is found in some proteins in all domains of life. Its incorporation involves:

26. What is the central dogma of molecular biology?

The central dogma of molecular biology describes the flow of genetic information in cells. It states that DNA is transcribed into RNA, which is then translated into proteins. This process is fundamental to how genes are expressed and how traits are manifested in organisms.

27. How does RNA editing affect gene expression?

RNA editing is a process that alters the nucleotide sequence of RNA after transcription but before translation. It affects gene expression by:

28. What are the main components of the translation machinery?

The main components of the translation machinery include:

29. What happens when a stop codon is encountered during translation?

When a stop codon (UAA, UAG, or UGA) is encountered during translation, it doesn't code for an amino acid. Instead, it signals the end of the protein-coding sequence. Release factors recognize the stop codon and cause the ribosome to release the completed polypeptide chain and disassemble, terminating translation.

30. How does the structure of tRNA relate to its function?

tRNA has a cloverleaf-like secondary structure and an L-shaped tertiary structure. The anticodon loop at one end matches the codon on the mRNA, while the other end carries the corresponding amino acid. This structure allows tRNA to act as an "adapter" molecule, linking the genetic code (codons) to the amino acid sequence of proteins.

31. What is the role of aminoacyl-tRNA synthetases in translation?

Aminoacyl-tRNA synthetases are enzymes that attach the correct amino acid to its corresponding tRNA. Each synthetase is specific for one amino acid and its cognate tRNAs. This "charging" of tRNAs ensures that the genetic code is accurately translated into the correct amino acid sequence during protein synthesis.

32. How does the ribosome facilitate peptide bond formation?

The ribosome facilitates peptide bond formation through its peptidyl transferase activity. It positions the amino acids carried by tRNAs in the correct orientation and catalyzes the formation of a peptide bond between them. This occurs in the ribosome's large subunit, specifically in the peptidyl transferase center.

33. How does transcription differ from translation?

Transcription is the process of creating an RNA copy of a gene sequence, while translation is the process of creating a protein using the information in messenger RNA (mRNA). Transcription occurs in the nucleus (in eukaryotes) and uses DNA as a template, while translation occurs in the cytoplasm and uses mRNA as a template.

34. What is the role of GTP hydrolysis in translation?

GTP hydrolysis plays crucial roles in translation, providing energy and serving as a proofreading mechanism:

35. What is the significance of the reading frame in translation?

The reading frame is crucial in translation because it determines how the nucleotide sequence is grouped into codons. A shift in the reading frame (e.g., due to an insertion or deletion mutation) can completely change which codons are read, potentially resulting in a very different amino acid sequence or premature stop codons.

36. What is the significance of the 5' cap on eukaryotic mRNA?

The 5' cap is a modified guanine nucleotide added to the 5' end of eukaryotic mRNA during processing. It serves several important functions:

37. How do ribosomes cycle between active and inactive states?

Ribosomes cycle between active and inactive states through a process called the ribosome cycle. After completing translation of an mRNA, the ribosome dissociates into its large and small subunits. These subunits remain separate until they are recruited for another round of translation. Initiation factors help reassemble the ribosome on a new mRNA, activating it for another round of protein synthesis.

38. What is the difference between constitutive and regulated genes?

Constitutive genes are continuously expressed and typically code for proteins needed for basic cellular functions. Regulated genes, on the other hand, are expressed only under specific conditions or in response to certain signals. Their expression can be controlled at various levels, including transcription, mRNA processing, and translation.

39. How do antibiotics like tetracycline and erythromycin inhibit bacterial protein synthesis?

Antibiotics like tetracycline and erythromycin inhibit bacterial protein synthesis by targeting the bacterial ribosome: