1. DNA as the Template:
- The blueprint for making RNA is stored within the DNA molecule.
- DNA contains the genetic code that dictates the sequence of amino acids in proteins, and ultimately controls cellular functions.
2. Transcription Factors:
- Special proteins called transcription factors bind to specific regions of DNA, called promoters, marking the starting point for RNA synthesis.
3. RNA Polymerase:
- The enzyme RNA polymerase then binds to the promoter and unwinds the DNA double helix, exposing the nucleotide bases.
- RNA polymerase uses one strand of the DNA as a template, reading the DNA sequence and building a complementary RNA molecule.
4. RNA Synthesis:
- RNA polymerase moves along the DNA template, pairing RNA nucleotides with their complementary DNA bases.
- Adenine (A) in DNA pairs with Uracil (U) in RNA, Guanine (G) pairs with Cytosine (C).
- This process continues until RNA polymerase reaches a termination signal on the DNA, marking the end of the gene.
5. mRNA Processing:
- The newly synthesized RNA molecule, called pre-mRNA, undergoes processing:
- Capping: A modified guanine nucleotide is added to the 5' end of the pre-mRNA, protecting it from degradation and aiding in ribosome binding.
- Splicing: Non-coding regions (introns) are removed from the pre-mRNA, leaving only the coding regions (exons) for protein synthesis.
- Polyadenylation: A string of adenine nucleotides (poly-A tail) is added to the 3' end, providing stability and aiding in transport out of the nucleus.
6. Transport to the Cytoplasm:
- Once processed, the mature mRNA molecule is transported out of the nucleus through nuclear pores and into the cytoplasm, where it can be translated into protein.
Types of RNA in the Nucleus:
- mRNA (messenger RNA): Carries the genetic code from DNA to ribosomes for protein synthesis.
- tRNA (transfer RNA): Delivers specific amino acids to the ribosome during translation.
- rRNA (ribosomal RNA): Forms part of the ribosome, the cellular machinery for protein synthesis.
- snRNA (small nuclear RNA): Involved in splicing and other RNA processing events.
In summary, RNA molecules in the nucleus are created by a process called transcription where DNA acts as a template and RNA polymerase builds a complementary RNA copy. This process ensures that the genetic information encoded in DNA is accessible to the ribosomes for protein synthesis.
