RNA Notes

When Watson and Crick discovered the double-helix structure of DNA, they realized that the structure alone couldn't explain how genes function.
Scientists later discovered ribonucleic acid (RNA), another nucleic acid, which helps put the genetic code into action.
Like DNA, RNA is a nucleic acid composed of a long chain of nucleotides.
Differences between DNA and RNA:
- The sugar in RNA is ribose, whereas DNA contains deoxyribose.
- RNA is generally single-stranded, unlike the double-stranded structure of DNA.
- RNA contains uracil (U) in place of thymine (T), which is found in DNA.

There are three main types of RNA:
- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)

An mRNA molecule is a copy of a portion of DNA that will be used to make a protein.
After being made in the nucleus, mRNA travels to the cytoplasm, where protein synthesis takes place.

Protein synthesis occurs on ribosomes, which consist of two subunits.
These subunits are composed of several molecules of ribosomal RNA (rRNA) and as many as 80 different proteins.

During protein synthesis, transfer RNA molecules (tRNA) carry amino acids from the cytoplasm to the mRNA.

The process of copying a base sequence from DNA to RNA is known as transcription.
Transcription is similar to DNA replication, but the product is an RNA molecule.
In transcription, segments of DNA serve as templates to produce complementary RNA molecules.
Transcription is carried out by an enzyme called RNA polymerase.
RNA polymerase first binds to DNA and separates the DNA strands.
It uses one strand of DNA as a template to assemble nucleotides into a complementary strand of RNA.
The ability to quickly copy a DNA sequence into RNA makes it possible for a single gene to produce hundreds or even thousands of RNA molecules.

RNA polymerase binds only to promoters, which are regions of DNA with specific base sequences that can bind to RNA polymerase.
Other regions of DNA cause transcription to stop when an RNA molecule is completed.