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How does protein synthesis occur in cells?

Protein synthesis is the process by which cells build proteins, which are essential for various biological functions. It involves two main steps: transcription and translation.

Transcription

During transcription, the DNA sequence of a gene is copied into a molecule called messenger RNA (mRNA). This process takes place in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells. The steps involved in transcription are as follows:

1. Initiation: RNA polymerase, an enzyme, binds to a specific region on the DNA called the promoter. This signals the start of transcription.

2. Elongation: RNA polymerase moves along the DNA strand, unwinding it and synthesizing a complementary mRNA strand. The mRNA molecule is built by adding nucleotides that are complementary to the DNA template strand.

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3. Termination: Transcription ends when RNA polymerase reaches a specific DNA sequence called the terminator. At this point, the mRNA molecule is released.

Translation

Translation is the process by which the mRNA molecule is used as a template to synthesize a protein. It takes place in the ribosomes, which are located in the cytoplasm of both prokaryotic and eukaryotic cells. The steps involved in translation are as follows:

1. Initiation: The mRNA molecule binds to the small subunit of a ribosome. The ribosome scans the mRNA until it reaches a specific start codon (usually AUG). At this point, a tRNA molecule carrying the amino acid methionine binds to the start codon.

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2. Elongation: The ribosome moves along the mRNA molecule, reading the codons (three-nucleotide sequences) and bringing in tRNA molecules with complementary anticodons. Each tRNA molecule carries a specific amino acid. The ribosome catalyzes the formation of peptide bonds between adjacent amino acids, creating a growing polypeptide chain.

3. Termination: Translation continues until a stop codon is reached on the mRNA molecule. At this point, the ribosome releases the completed polypeptide chain, and the mRNA molecule is also released.

After translation, the newly synthesized protein undergoes further modifications, such as folding and post-translational modifications, to become functional. The process of protein synthesis is crucial for the growth, development, and maintenance of cells and organisms.

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