Central Dogma Project

The central dogma is composed of transcription and translation. Transcription occurs in the nucleus while translation occurs in the cytoplasm. You can remember this since transcription has a "C" and translation has an "L." C comes before L in the alphabet so transcription occurs first. Transcription is when RNA polymerase attaches to DNA during DNA replication and produces a strand of RNA. In DNA, the nucleotide base pairs are made of thymine, adenine, guanine, and cytosine. Adenine and thymine pair up, guanine and cytosine pair up. However, there's no thymine. Instead, there's uracil. In mRNA, nucleotide triplets of three are called codons. In tRNA, there are also nucleotide triplets of three. There are called anticodons. However, anticodons do NOT code for amino acids. Instead, they bind to amino acids during translation. RNA processing is when RNA is prepared and packaged for translation. Introns are cut out while exons are kept. They are cut by spliceosomes which are made by snRNPs and other proteins. A polyA tail is also added along with a G cap or 5' cap. In translation, RNA exits the nucleus and enters the cytoplasm. tRNA molecules attach to amino acids during translation using anticodons. These molecules along with the ribosome form polypeptide chains. Ribosomes are what form polypeptide chains. They have an E, P, and A site and an exit tunnel from which the polypeptide chains exit from. tRNA molecules sit in the sites while mRNA goes through the ribosome. First, a tRNA molecule enters the molecule and sits in the A or attachment site. When another tRNA molecule comes along, it moves to the P site and the new molecule attaches to the A site. The polypeptide chain on the original tRNA molecule switches over to the new tRNA molecule. The original now exits the ribosome and the new tRNA molecule now has a longer chain. And the cycle will start over and continue until all the mRNA has been translated. Thank you for watching our video and good luck on the AP Biology Exam!