Today in Biology we’ll start our last Unit of the semester… Protein Synthesis. Protein Synthesis is sometimes referred as the “Central Dogma” of Biology, meaning its the key idea. The key idea of protein synthesis is that DNA codes for our traits and that code is used to create proteins that actually are our traits. All other parts of biology either exist because of, or are incorporated with Protein Synthesis.
There are two major parts of protein synthesis:
- Transcription: Using DNA → to make RNA
- Translation: Using RNA → to make Protein
Today we’ll be focusing on Transcription and the stuff it makes, RNA.
RNA, or Ribonucleic Acid, is like the cousin of DNA. Looks similar, and has similar parts… but there are three key differences you should know:
- RNA is a single strand of Nucleotides (DNA is double stranded)
- RNA is made of Ribose sugar (DNA contains Deoxyribose)
- RNA’s 4 bases are A,C,G, and Uracil (replaces T)
There are three types of RNA
- mRNA – “Messenger”
- Carries the DNA message out of the nucleus
- tRNA – “Transfer”
- Transfers a single Amino Acid to the ribosome
- rRNA – “Ribosomal”
- Makes up the ribosome (2 parts)
To make RNA, the process of Transcription takes place in the Nucleus. An RNA Polymerase enzyme attaches to a section of DNA that codes for a protein. This section of DNA is known as a Gene. At the start of the Gene, there is a section of DNA called the Promoter that tells the polymerase where to start. The Polymerase then unwinds the DNA and begins adding RNA nucleotides to ONE SIDE of the DNA molecule; matching A to T, G to C, C to G, and U to A. This process will continue until the RNA Polymerase reaches the Terminiator, or a section of repeating DNA nucleotides which tells the Polymerase to let go of the DNA and newly formed mRNA.
Now, just like all of the DNA did not code for a Protein, not all of the mRNA codes either. The sections of Non-coding material are called Introns (they’re IN the way) and the coding sections are called Exons. The introns are spliced out and the exons are put back together. The finished mRNA molecule then leaves the nucleus through a nuclear pore.
So ends, this part of the story. But our mRNA’s journey is far from over. But we’ll save that story for another time!