140
produced from microbes are very much similar to traditional protein sources such as
meat, egg, fish and milk in terms of overall presence of nutrients (Upadhyaya
et al. 2016).
8.2 Microbial Protein Synthesis
Proteins synthesis is carried out by the ribosomes along with messenger RNA, produced from the transcription of DNA in the nucleus of eukaryotes however there is
no nucleus present in prokaryotes so both transcription and translation occur in the
cytoplasm. In the DNA, a series of codes are transcribed and translated to synthesize
proteins. Transcription proceeds with the opening of the DNA double helix with the
help of an enzyme called DNA helicase. Another enzyme, RNA polymerase equates
new bases to the DNA joining them in a long strand of mRNA. When the enzyme
completes the transcription the mRNA strand will be detached. This mRNA strand
is single stranded and only one side of the DNA strand is transcribed. mRNA does
not have the same base pairs as DNA, one of the base is replaced. Thymine in DNA
is replaced by Uracil (U) which bonds to Adenine, like thymine. The mRNA is
organized in codons. Each codon codes for an amino acid that forms the building
blocks of proteins. More than one codon can code for a single amino acid. Once
transcription is completed, produced mRNA is transported out of nucleus into the
cytoplasm to attach with a ribosome. Ribosome is an organelle which carries out
protein synthesis. Some ribosomes are free in the cytoplasm while others are
attached to the endoplasmic reticulum. The endoplasmic reticulum is an organelle
which helps in the correct folding of proteins and delivers it to other areas. Proteins
are synthesized by the process of translation. There are three steps to translation:
Initiation, Elongation and Termination.
The ribosome binds around the mRNA and then a tRNA (transfer RNA) joins to
a codon referred to as the start codon. In most cases, the start codon is AUG. tRNA
are molecules residing in the cytoplasm, each with their particular codon which
joins to corresponding codons on mRNA. tRNAs carry the amino acids which complement to that of the codon. The ribosomes are composed of two subunits, a larger
subunit and another smaller one. There are three sites present where tRNA can be
found at a given time while the protein is being synthesized. Next the ribosome
starts synthesizing protein. An amino acid which complements the mRNA code
begins to join in a strand, the ribosome moves on the strand in a direction of 5′–3′
until a STOP codon is found. As the ribosome moves on the mRNA the amino acid
from the first tRNA is released and binds to the amino acid on the next tRNA via a
peptide bond. This is why a chain of amino acids is termed as a polypeptide chain.
The ribosome achieves this with the aid of enzymes known as aminoacyl tRNA
synthase. Once the ribosome finds a stop codon (UAG, UAA, and UGA) it will
detach the polypeptide chain and fall off from the mRNA (Lewin et al. 2011).
A. K. Singh et al.
produced from microbes are very much similar to traditional protein sources such as
meat, egg, fish and milk in terms of overall presence of nutrients (Upadhyaya
et al. 2016).
8.2 Microbial Protein Synthesis
Proteins synthesis is carried out by the ribosomes along with messenger RNA, produced from the transcription of DNA in the nucleus of eukaryotes however there is
no nucleus present in prokaryotes so both transcription and translation occur in the
cytoplasm. In the DNA, a series of codes are transcribed and translated to synthesize
proteins. Transcription proceeds with the opening of the DNA double helix with the
help of an enzyme called DNA helicase. Another enzyme, RNA polymerase equates
new bases to the DNA joining them in a long strand of mRNA. When the enzyme
completes the transcription the mRNA strand will be detached. This mRNA strand
is single stranded and only one side of the DNA strand is transcribed. mRNA does
not have the same base pairs as DNA, one of the base is replaced. Thymine in DNA
is replaced by Uracil (U) which bonds to Adenine, like thymine. The mRNA is
organized in codons. Each codon codes for an amino acid that forms the building
blocks of proteins. More than one codon can code for a single amino acid. Once
transcription is completed, produced mRNA is transported out of nucleus into the
cytoplasm to attach with a ribosome. Ribosome is an organelle which carries out
protein synthesis. Some ribosomes are free in the cytoplasm while others are
attached to the endoplasmic reticulum. The endoplasmic reticulum is an organelle
which helps in the correct folding of proteins and delivers it to other areas. Proteins
are synthesized by the process of translation. There are three steps to translation:
Initiation, Elongation and Termination.
The ribosome binds around the mRNA and then a tRNA (transfer RNA) joins to
a codon referred to as the start codon. In most cases, the start codon is AUG. tRNA
are molecules residing in the cytoplasm, each with their particular codon which
joins to corresponding codons on mRNA. tRNAs carry the amino acids which complement to that of the codon. The ribosomes are composed of two subunits, a larger
subunit and another smaller one. There are three sites present where tRNA can be
found at a given time while the protein is being synthesized. Next the ribosome
starts synthesizing protein. An amino acid which complements the mRNA code
begins to join in a strand, the ribosome moves on the strand in a direction of 5′–3′
until a STOP codon is found. As the ribosome moves on the mRNA the amino acid
from the first tRNA is released and binds to the amino acid on the next tRNA via a
peptide bond. This is why a chain of amino acids is termed as a polypeptide chain.
The ribosome achieves this with the aid of enzymes known as aminoacyl tRNA
synthase. Once the ribosome finds a stop codon (UAG, UAA, and UGA) it will
detach the polypeptide chain and fall off from the mRNA (Lewin et al. 2011).
A. K. Singh et al.