Proteins are synthesized inside cells through a process called protein synthesis or translation. This complex process occurs in two main steps: transcription and translation.

**Transcription:**
During transcription, the DNA sequence of a gene is transcribed into a complementary messenger RNA (mRNA) molecule. This process takes place in the cell nucleus. Here is a step-by-step explanation of transcription:

1. Initiation: RNA polymerase, an enzyme, recognizes and binds to the promoter region on the DNA molecule. This marks the beginning of the gene sequence that needs to be transcribed.

2. Elongation: RNA polymerase unwinds the DNA double helix and synthesizes a complementary mRNA molecule using the DNA strand as a template. The enzyme adds nucleotides one by one, forming a chain that is complementary to the DNA sequence.

3. Termination: Transcription continues until a termination signal is reached on the DNA template. At this point, RNA polymerase stops synthesizing the mRNA molecule, and it is released.

**Translation:**
After transcription, the mRNA molecule is transported out of the nucleus and into the cytoplasm. Translation, the second step of protein synthesis, occurs in the cytoplasm at a cellular structure called ribosomes. Here is a step-by-step explanation of translation:

1. Initiation: The mRNA molecule binds to a ribosome, which consists of two subunits. The ribosome recognizes a specific sequence on the mRNA called the start codon (usually AUG) and positions itself accordingly.

2. Elongation: Transfer RNA (tRNA) molecules, each carrying a specific amino acid, bind to the ribosome. The tRNA molecules have an anticodon that is complementary to the codon on the mRNA. As the ribosome moves along the mRNA molecule, tRNA molecules bring the corresponding amino acids, and the ribosome catalyzes the formation of peptide bonds between them. This process continues until a stop codon is reached.

3. Termination: When a stop codon is encountered on the mRNA, the ribosome releases the synthesized protein chain, and the translation process is complete.

In summary, proteins are synthesized inside cells through a two-step process called transcription and translation. Transcription occurs in the nucleus, where the DNA sequence of a gene is transcribed into mRNA. The mRNA molecule then travels to the cytoplasm, where translation takes place at ribosomes. During translation, the mRNA sequence is decoded, and amino acids are assembled into a protein chain. This process is fundamental to cellular functions and plays a crucial role in various biological processes.

in endoplasmic reticulum (in ribosomes)