Question

Steps of protein synthesis

Answer 1

Protein synthesis is the process by which cells create proteins, and it occurs in two main stages: transcription and translation. Here's an overview of the steps involved in each phase:

### 1. Transcription
**Location:** Nucleus (in eukaryotic cells)

**Steps:**
- **Initiation:**
- RNA polymerase binds to a specific region of the DNA (the promoter) and unwinds the DNA strands, making the template strand accessible.

- **Elongation:**
- RNA polymerase moves along the DNA template strand, synthesizing a single strand of messenger RNA (mRNA) by adding complementary RNA nucleotides (adenine pairs with uracil, and cytosine pairs with guanine).

- **Termination:**
- RNA polymerase continues until it reaches a terminator sequence, which signals the end of the gene. The newly synthesized mRNA strand is released.

- **Post-transcriptional modifications (in eukaryotes):**
- The mRNA undergoes capping (addition of a 5' cap), polyadenylation (addition of a poly-A tail at the 3' end), and splicing (removal of introns and joining of exons).

### 2. Translation
**Location:** Cytoplasm (on ribosomes)

**Steps:**
- **Initiation:**
- The mRNA binds to a ribosome. The ribosome scans the mRNA for the start codon (AUG), which is recognized by the initiator tRNA that carries the corresponding amino acid (methionine).

- **Elongation:**
- Transfer RNA (tRNA) molecules, each carrying specific amino acids, bind to their corresponding codons on the mRNA. The ribosome catalyzes the formation of peptide bonds between the amino acids, elongating the polypeptide chain.

- **Termination:**
- The process continues until the ribosome reaches a stop codon (UAA, UAG, or UGA) on the mRNA. Release factors bind to the ribosome, prompting it to release the completed polypeptide chain.

### 3. Post-translational modifications (if necessary)
- After synthesis, the polypeptide may undergo various modifications, such as folding, phosphorylation, glycosylation, or cleavage, to become a functional protein.

### Summary
In summary, protein synthesis involves transcribing DNA into mRNA in the nucleus and then translating that mRNA into a protein language in the cytoplasm using ribosomes and tRNA. This process is crucial for cellular function and the expression of genes.