16s rRNA vs 16s rDNA

In all the living entities, protein synthesis occurs in the ribosomes. The composition of ribosomes in prokaryotes is different from that of the eukaryotes. Ribosomes comprise 2 components – the large and small subunits. Each of these subunits comprises RNA – ribosomal RNA and various proteins. These subunits match a d 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 very 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, while 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, and the small ribosomal subunits comprise the 16s.
  • These are types of rRNA involved in the creation of the small subunits of the ribosomes in prokaryotes.
  • The size of these is about 1542 nt.
  • 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, which varies.
  • 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.

16s rRNA

16s rDNA

What are they?

These form the components of small 30s subunits of prokaryotic ribosomes

In prokaryotes, these form the gene which encodes the 16s rRNA

Composition

RNA nucleotides

DNA nucleotides

How many strands?

Single-stranded

Double-stranded

Sequences of coding

Has the sequence of coding only

Has both non-coding and coding strands

Uracil bases

These bases are present in their nucleotide sequences

These are not present in their bases in the nucleotide sequences

Thymine bases

These do not comprise these bases in their nucleotide sequences

It contains these bases in their nucleotide sequences

Function

Promotes the association of large and small subunits by interaction with 23s rRNA subunits

Significant to identify prokaryotes

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