What are the steps of protein synthesis starting with DNA?
Protein synthesis, also known as translation, is the process by which the instructions carried by DNA are used to create proteins. Protein synthesis can be broken down into two main steps: transcription and translation. Here are the steps starting with DNA:
1. Transcription: In this step, the DNA sequence that codes for a particular protein is copied into a molecule called messenger RNA (mRNA).
- The DNA double helix unwinds, and an enzyme called RNA polymerase binds to the DNA at a specific site called the promoter.
- The RNA polymerase moves along the DNA strand, synthesizing a complementary mRNA molecule by adding nucleotides that are complementary to the DNA sequence.
- The mRNA molecule is now an exact copy of the protein-coding region of the DNA (gene).
2. mRNA Processing: Before the mRNA can be used in translation, it undergoes a series of processing steps.
- In eukaryotic cells, the initial mRNA molecule undergoes several modifications, including removal of non-coding regions (introns) and joining of coding regions (exons) through a process called RNA splicing.
- A modified mRNA molecule, called mature mRNA, is produced that consists solely of coding regions.
3. Translation: In this step, the mRNA is used as a template to synthesize a protein.
- The mature mRNA molecule moves out of the nucleus and attaches to a ribosome in the cytoplasm.
- Ribosomes read the mRNA in groups of three nucleotides, called codons. Each codon codes for a specific amino acid.
- Transfer RNA (tRNA) molecules, carrying specific amino acids, bind to the codons on the mRNA through their complementary anticodons.
- As each tRNA molecule brings its amino acid to the ribosome, the amino acids are joined together, forming a polypeptide chain.
- The ribosome moves along the mRNA, reading each codon and adding the corresponding amino acid until it reaches a stop codon.
- Once the protein is complete, it undergoes further modifications, such as folding into its three-dimensional structure or adding chemical groups.
These are the basic steps involved in protein synthesis starting with DNA. It's important to note that these steps are slightly different in prokaryotic cells, which lack a nucleus and have other mechanisms for processing mRNA.