The main difference between coding and noncoding DNA is that coding DNA represents the protein-coding genes, which encode for proteins, whereas noncoding DNA does not encode for proteins. Furthermore, coding DNA is made up of exons while the types of noncoding DNA include regulatory elements, noncoding RNA genes, introns, pseudogenes, repeating sequences, and telomeres. Moreover, the genes in the coding DNA transcribe, producing mRNAs, which subsequently undergo translation, producing proteins while noncoding DNA can undergo transcription, producing noncoding RNAs such as rRNAs, tRNAs, and other regulatory RNAs.
Coding and noncoding DNA are two main types of DNA, which occur in the genome. Generally, proteins encoded by coding DNA have structural, functional, and regulatory importance in the cell while noncoding RNAs are important for controlling gene activity.
Key Areas Covered
1. What is Coding DNA
– Definition, Structure, Function
2. What is Noncoding DNA
– Definition, Types, Function
3. What are the Similarities Between Coding DNA and Noncoding DNA
– Outline of Common Features
4. What is the Difference Between Coding DNA and Noncoding DNA
– Comparison of Key Differences
Key Terms
Coding DNA, mRNAs, Noncoding DNA, Regulatory Elements, rRNAs, Transcription, Translation, tRNAs
What is Coding DNA
Coding DNA is the type of DNA in the genome, encoding for protein-coding genes. Significantly, it accounts for 1% of the human genome. Actually, coding DNA consists of the coding region of protein-coding genes; in other words, exons. Also, all exons in a protein-coding gene collectively known as the coding sequence or CDS. However, in eukaryotes, the coding region is interrupted by introns. In the meanwhile, coding regions start from the start codon at the 5′ end and terminates with the stop codon at the 3′ end. Apart from DNA, RNA can also contain coding regions.
Figure 1: Protein Synthesis
Furthermore, the coding region of a protein-coding gene undergoes transcription to produce an mRNA. In the mRNA, the 5′ UTR and 3′ UTR flank the coding region. Also, the CDS in the mRNA transcript undergoes translation to produce an amino acid sequence of a functional protein. Therefore, proteins are the gene product of the coding DNA. For instance, they have structural, functional, and regulatory importance in the cell.
What is Noncoding DNA
Noncoding DNA is the other type of DNA in the genome, accounting for 99% of the human genome. Significantly, it does not encode for protein-coding genes. Thereby, it does not provide instructions for the synthesis of proteins. Generally, the types of noncoding DNA in the genome include regulatory elements, noncoding RNA genes, introns, pseudogenes, repeating sequences, and telomeres.
Regulatory Elements
The main function of regulatory elements is to provide sites for the binding of transcription factors to regulate the expression of genes. Usually, there are two types of regulatory elements; cis-regulatory elements and trans-regulatory elements. Normally, cis-regulatory elements occur close to the gene to be regulated while trans-regulatory elements occur distantly to the gene to be regulated.
Figure 2: Role of Regulatory Elements
Moreover, these regulatory elements include promoters, enhancers, silencers, and insulators. Generally, the protein machinery responsible for transcription binds to the promoter. Also, transcription factors, which activate gene expression bind to enhancers while those repress the gene expression bind to silencers. On the other hand, enhancer-blockers, which prevent the action of enhancers and barriers, which prevent structural changes, repressing gene expression bind to insulators.
Noncoding RNA Genes
For instance, noncoding RNA genes are responsible for the synthesis of noncoding RNAs rather than mRNAs. Basically, there are three types of noncoding RNAs; tRNAs, rRNAs, and other regulatory RNAs such as miRNAs.
Figure 3: Noncoding RNA
Significantly, the main function of the noncoding RNAs is to take part in translation and the regulation of gene expression.
Introns
Introns occur interrupting the coding region of protein-coding genes. Generally, they are removed after transcription by splicing exons to obtain an undisturbed coding region.
Pseudogenes
Pseudogenes are the genes, which lost their protein-coding ability. Also, they arise due to retrotransposition or genomic duplication of functional genes, and become “genomic fossils”.
Repeating Sequences
Repeating sequences include transposons and viral elements. However, they are mobile elements. Here, transposons undergo transposition as mobile DNA elements while viral elements or retrotransposons move by a ‘copy and paste’ mechanism through transcription.
Telomeres
Telomeres are repetitive DNA, which occurs at the end of chromosomes. They are responsible for preventing chromosomal deterioration during DNA replication.
Similarities Between Coding DNA and Noncoding DNA
- Coding DNA and noncoding DNA are the two types of DNA, which occur in the genome.
- Chromosomes contain both types of DNA.
- Genes occur in both types of DNA.
- Both types of DNA can undergo transcription to produce RNAs.
- They have a function in protein synthesis.
Difference Between Coding DNA and Noncoding DNA
Definition
Coding DNA refers to the DNA in the genome, containing for protein-coding genes while noncoding DNA refers to the other type of DNA, which does not code for proteins.
Percentage in the Genome
Coding DNA accounts only for 1% of the human genome while noncoding DNA accounts for 99% of the human genome.
Components
Coding DNA composes of exons while noncoding DNA composes of regulatory elements, noncoding RNA genes, introns, pseudogenes, repeating sequences, and telomeres.
Encoding for Proteins
Coding DNA encodes for proteins while noncoding DNA does not encode for proteins.
Resultants of Transcription
Coding DNA undergoes transcription to synthesize mRNAs while noncoding DNA undergoes transcription to synthesize tRNAs, rRNAs, and other regulatory RNAs.
The function of the Gene Products
Proteins encoded by coding DNA have structural, functional, and regulatory importance in the cell while noncoding DNA is important for controlling gene activity.
Conclusion
Coding DNA is the type of DNA in the genome, encoding for protein-coding genes. Generally, these genes undergo transcription to synthesize mRNA. In eukaryotes, the coding region of protein-coding genes is interrupted by introns, which are removed after transcription. However, mRNAs undergo translation to produce proteins. Significantly, proteins play a key role in the cell by serving as structural, functional, and regulatory components of the cell. In contrast, noncoding DNA is another type of DNA, representing around 99% of the genome. However, it contains genes for noncoding RNAs, including tRNAs, rRNAs, and other regulatory RNAs, which are important in the translation of mRNA. Besides, noncoding DNA includes regulatory elements, introns, pseudogenes, repeating sequences, and telomeres. Therefore, the main difference between coding DNA and noncoding DNA is the type of genes present and their gene products.
References:
1. “What Is Noncoding DNA? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, Available Here.
Image Courtesy:
1. “Gene structure eukaryote 2 annotated” By Thomas Shafee – Shafee T, Lowe R (2017). “Eukaryotic and prokaryotic gene structure”. WikiJournal of Medicine 4 (1). DOI:10.15347/wjm/2017.002. ISSN 20024436. (CC BY 4.0) via Commons Wikimedia
2. “TATA box mechanism” By Luttysar – Own work (CC BY-SA 4.0) via Commons Wikimedia
3. “DNA to protein or ncRNA” By Thomas Shafee – Own work (CC BY 4.0) via Commons Wikimedia
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