ZOOHCC - 501: Molecular Biology (Theory)
Unit 4: Translation
Protein synthesis in prokaryotes takes place in two main steps:
transcription and translation.
Transcription:
The process begins when the enzyme RNA polymerase binds to the promoter
region of a DNA molecule. The DNA double helix is unwound and RNA
polymerase synthesizes a single-stranded mRNA molecule using one of the DNA
strands as a template. As the RNA polymerase moves along the DNA template,
the mRNA molecule lengthens and when the termination signal is reached, the
RNA polymerase dissociates from the DNA template. The mRNA molecules then
exit the nucleus and translocate into the cytoplasm. translation:
Ribosomes bind to mRNA molecules, and ribosomes read codons on the mRNA in
order. Ribosomes recruit the appropriate tRNA molecule with the specific
amino acid indicated by the codon. Amino acids are added to the growing
polypeptide chain and the ribosome moves to the next codon. This process
continues until the ribosome reaches the stop codon, at which point the
newly synthesized polypeptide is released. In prokaryotes, transcription and
translation can occur simultaneously because there is no nuclear envelope
separating the two processes. Therefore, when an mRNA molecule is
synthesized, it is immediately translated into a polypeptide chain by
ribosomes.
Protein involvement
Proteins play an important role in the process of protein synthesis in
prokaryotes. Here are some examples.
RNA polymerase: RNA polymerase is the protein enzyme involved in the
transcription of DNA into RNA. It binds to the promoter regions of DNA
molecules and catalyzes the formation of complementary strands of
RNA.
Ribosome: Ribosome is a large molecular complex of RNA and protein. They
are responsible for translating mRNA into polypeptide chains. Ribosomes have
three distinct sites, the A site, the P site, and the E site, where tRNA
molecules carrying specific amino acids bind and are used to assemble
growing polypeptide chains.
Transfer RNA (tRNA): tRNA molecules are small RNA molecules involved in the
translation of mRNA into polypeptide chains. Each tRNA molecule carries a
specific amino acid that is added to the growing polypeptide chain. The tRNA
molecule also has a sequence of three nucleotides called anticodons that are
complementary to the codons on the mRNA.
Initiation Factors: Initiation factors are proteins involved in the
initiation of translation. They help bring the ribosome and mRNA together
and also help place the first tRNA molecule in the correct position in the
mRNA.
Release Factors: Release factors are proteins involved in the termination
of translation. They recognize stop codons in mRNAs and release newly
synthesized polypeptide chains from ribosomes.
Briefly Explanation
The process of protein synthesis in prokaryotes is a complex molecular
process involving multiple steps including transcription and translation.
This is the process of using the genetic information encoded in DNA to
synthesize proteins, which are essential molecules that perform various
functions within the cell.
Transcription:
The first step in protein synthesis is transcription. This is the process
by which genetic information encoded in DNA is copied into single-stranded
RNA molecules known as messenger RNA (mRNA). Transcription takes place in
the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells. In
prokaryotes, transcription is initiated when the enzyme RNA polymerase binds
to the promoter region of a DNA molecule. The DNA double helix is unwound
and RNA polymerase synthesizes a complementary strand of RNA using one of
the DNA strands as a template. RNA polymerase adds nucleotides to the
growing mRNA molecule until it reaches a termination signal. At this point,
RNA polymerase dissociates from the DNA template. Newly synthesized mRNA
molecules exit the nucleus and travel to the cytoplasm.
translation:
The second step in protein synthesis is translation. This is the process of
using the genetic information encoded in mRNA to synthesize proteins.
Translation takes place in the cytoplasm of both eukaryotic and prokaryotic
cells.
In prokaryotes, translation may begin before transcription is complete. A
large molecular complex of RNA and protein, the ribosome binds to the mRNA
molecule and sequentially reads the codons on the mRNA. Ribosomes have three
distinct sites, the A site, the P site, and the E site, where tRNA molecules
carrying specific amino acids bind and are used to assemble growing
polypeptide chains. Each tRNA molecule carries a specific amino acid that is
added to the growing polypeptide chain. The tRNA molecule also has a
sequence of three nucleotides called anticodons that are complementary to
the codons on the mRNA. The ribosome moves to the next codon and adds the
appropriate amino acids until it reaches the stop codon. Upon reaching the
stop codon, the newly synthesized polypeptide is released from the
ribosome.
Regulations:
The process of protein synthesis in prokaryotes is regulated at various
levels. Transcription is regulated by the binding of regulatory proteins
called transcription factors to specific DNA sequences known as enhancers
and silencers. Transcription factors can either promote or repress gene
transcription. Translation is regulated by several mechanisms, including the
binding of regulatory proteins known as initiation factors to the mRNA
molecule, which aid in the binding of the ribosome to the mRNA. Another
regulatory mechanism is modification of the mRNA molecule itself. B. Removal
of introns by splicing. Coding sequences can change and affect mRNA
translation. Diploma:
The process of protein synthesis in prokaryotes is a complex molecular
process involving multiple steps and regulatory mechanisms. It is essential
for the function and survival of cells and organisms. Understanding the
process of protein synthesis in prokaryotes is important for many branches
of biology, including genetics, molecular biology, and biotechnology.
