In all living entities, protein synthesis occurs in the ribosomes. The composition of ribosomes in prokaryotes is different from that of eukaryotes. Ribosomes comprise two components – the large and small subunits. Each of these subunits contains RNA – ribosomal RNA and various proteins. These subunits function as a unit at the time of synthesis of proteins. The rRNAs (ribosomal RNAs) are found at the core of the protein synthesis machinery.
The ribosomal RNA of the small subunits of ribosomes are called 16s rRNA. When this rRNA is transcribed from the DNA of chromosomes, it is called 16s rDNA. It is this same gene that is responsible for producing 16s rRNA through the process of transcription. We refer to the rRNA gene or the rDNA to assign the DNA in the genome which produces the ribosomal RNA.
Key Difference between 16s rRNA and 16s rDNA
- 16s rRNA forms a factor of the 30s subunit in ribosomes of prokaryotes, the transcribed single-stranded ribosomal RNA. In comparison, the 16s rDNA forms the gene coding for the 16s rRNA, the double-stranded chromosomal DNA.
16s rRNA
- In mitochondria, archaea, bacteria and even chloroplasts, the small ribosomal subunits comprise the 16s.
- These are types of rRNA involved in creating the small subunits of the ribosomes in prokaryotes.
- The size of these is around 1550 bp.
- They promote the association of the small subunits to the large subunits by interaction with the 23s rRNA in the larger subunits.
16s rDNA
- In prokaryotes, the ribosome is 70s, and the smaller subunit is 30s. The rRNA of the 30s subunit is referred to as 16s rRNA, while the 16s rDNA gene is the one coding for it. Consequently, this 16s rDNA is referred to as the 16s rRNA gene.
- These are double-stranded, chromosomal DNA comprising non-coding and coding sites.
- The transcription of 16s rDNA gene gives the 16s rRNA sequence.
- In prokaryotes, these form the universal sequence of DNA.
- As they are highly conserved in various species, they are functional as molecular markers in prokaryotes (phylogenetic studies).
Key Differences between 16s rRNA and 16s rDNA
The table below depicts the differences between 16s rRNA and 16s rDNA.
| These form the components of small 30s subunits of prokaryotic ribosomes. | In prokaryotes, these form the gene which encodes the 16s rRNA. |
| RNA nucleotides | DNA nucleotides |
| Single-stranded | Double-stranded |
| Has the sequence of coding only. | Has both non-coding and coding strands. |
| These bases are present in their nucleotide sequences. | These are not present in their bases in the nucleotide sequences. |
| These do not comprise these bases in their nucleotide sequences. | It contains these bases in their nucleotide sequences. |
| Promotes the association of large and small subunits by interaction with 23s rRNA subunits. | Significant to identify prokaryotes. |
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