Gregorich SBI4U - Building the Blueprints

The Central Dogma (Francis Crick, 1956) is a fundamental concept in molecular biology that states that genetic information flows from DNA to RNA to proteins. This concept has two major steps: Transcription and Translation.

Transcription is the mechanism by which RNA is synthesized from a section of DNA, while Translation is the subsequent mechanism of by which proteins are synthesized from RNA.

Over the years, scientists have realized that the sequence of nitrogenous bases in DNA codes in Triplets (set of 3 nitrogenous bases- AKA. Codons) to one specific amino acid. The image to the right is the Genetic Code, a code specifying the relationship between nucleotide codons and amino acids. This code is redundant, which means that some Codons code for the same amino acid.

Reading the table:

Ex. 1- UUC

1st position U, second postion U, third position C --> Phenylalanine

Ex. 2- AGU

1st position A, second postion G, third position U --> Serine

It is important to realize the distinguishing features of RNA to understand Genetic Expression. DNA is a double stranded helix, containing a Deoxyribose sugar backbone and codes with Adenine, Cytosine, Guanine, and Thymine.

RNA on the other hand is a single stranded molecule that contains a Ribose sugar backbone and replaces the nitrogenous base Thymine with Uracil.

RNA has different 3 types, each with a unique function for genetic expression. mRNA (Messenger RNA) is what you would typically think of as RNA; the intermediary between DNA and proteins. It is translated by Ribosomes into proteins. tRNA (Transfer RNA) is a carrier molecule that binds to specific amino acids and adds them to the mRNA strand being synthesized. rRNA (Ribosomal RNA) is actually bound to proteins to make up the structure of a ribosome. We will look at these in greater detail as we learn Transcription and Translation.

Textbook Practice

p.310-318#3-6, 8-11