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Nucleic Acid Function: Gene Expression - P3
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Page last updated: 8/2015
What is RNA?
Ribonucleic acid, RNA, occurs as a single-stranded molecule in living organisms. It also differs from DNA in that RNA has the base Uracil (U), instead of Thymine (T).
Genetic information copied from DNA is used to build three types of RNA:
- Ribosomal RNA (rRNA)
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
Ribosomal RNA - The Protein Factories: Most of the RNA in cells is part of the structure of small cellular organelles known as ribosomes, the protein factories of the cells.
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What Does RNA Do?
Genetic Transcription: This is the process by which a DNA sequence is copied to produce a complementary RNA transcript. In other words, it is the transfer of genetic information from DNA to RNA; like DNA replication, but the nucleic acid RNA is made instead.
DNA is the only original copy of the genetic instructions that a cell has. Rather than use this original to direct the building of proteins, mRNA copies of the information are made that can travel to the ribosome to direct protein synthesis.
Genetic Translation:
Making proteins from instructions contained in the genetic code is called translation. The mRNA goes to a ribosome, where it is read in three nucleotide sections called codons.
Gene Expression Diagram Showing Transcription & Translation
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Messenger RNA - The Genetic Blueprint: Messenger RNA is a copy of the genetic information that was transcribed from the cell’s original blueprint, DNA. This copy of the genetic information is brought to the ribosome and used as instructions for building proteins.
Transfer RNA - The Amino Acid Suppliers: Transfer RNA is also part of the process of building proteins. Like a little truck, tRNA brings the amino acid to the ribosome. Which amino acid it brings depends on which was coded for in the mRNA instructions. At the ribosome, these amino acids are joined together to form proteins.
Each codon calls for a Transfer RNA molecule; tRNA are the "trucks" that bring the amino acids to the ribosome for protein synthesis. This is the Genetic Code! Once the entire mRNA molecule is translated, numerous amino acids have been brought to the ribosome and joined together to form a strand of protein.
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