Question

Describe the process of Transcription and Translation in prokaryotic cells needs to be very detailed. Also when does this occur?

Answer 1

Transcription in prokaryotes

Transcription process is defined as the process of synthesis of RNA under the direction of DNA, it is the process by which messenger RNA transcripts of genetic material in prokaryotes are produced, to be translated for the production of proteins. This process occurs in the cytoplasm alongside translation, Prokaryotic transcription and translation processes occurs simultaneously.

Transcription involves four steps:

1. Initiation. The DNA molecule unwinds and separates to form a small open complex. RNA polymerase binds to the promoter of the template strand.
2. Elongation. RNA polymerase moves along the template strand, synthesising an mRNA molecule. In prokaryotes RNA polymerase is a holoenzyme consisting of a number of subunits, including a sigma factor (transcription factor) that recognises the promoter.
3. Termination. In prokaryotes there are two ways in which transcription is terminated. In Rho-dependent termination, a protein factor called "Rho" is responsible for disrupting the complex involving the template strand, RNA polymerase and RNA molecule. In Rho-independent termination, a loop forms at the end of the RNA molecule, causing it to detach itself.
4. Processing. After transcription the RNA molecule is processed in a number of ways: introns are removed and the exons are spliced together to form a mature mRNA molecule consisting of a single protein-coding sequence. RNA synthesis involves the normal base pairing rules, but the base thymine is replaced with the base uracil.

This is followed by the process of translation.

Translation is the process by which mRNA is used to direct protein synthesis, and the subsequent post translational processing of the protein molecule.

In translation the mature mRNA molecule is used as a template to assemble a series of amino acids to produce a polypeptide with a specific amino acid sequence. The complex in the cytoplasm at which this occurs is called a ribosome.

Translation process involves four steps

1. Initiation. The small subunit of the ribosome binds at the 5' end of the mRNA molecule and moves in a 3' direction until it meets a start codon (AUG). It then forms a complex with the large unit of the ribosome complex and an initiation tRNA molecule.
2. Elongation. Subsequent codons on the mRNA molecule determine which tRNA molecule linked to an amino acid binds to the mRNA. An enzyme peptidyl transferase links the amino acids together using peptide bonds. The process continues, producing a chain of amino acids as the ribosome moves along the mRNA molecule.
3. Termination. Translation is terminated when the ribosomal complex reached one or more stop codons (UAA, UAG, UGA).
4. Post-translation processing of the protein which produces the end product of desired protein molecule.

As prokaryotes doesn't have a nucleus, there is no process of mitosis they don't have a cell cycle, so the process of Transcription and Translation occur as soon as they are produced and they start replicating their DNA, grow and metabolize until the DNA is replicated and then divide again.

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