The Central Dogma of Biology: Definition & Theory

The Central Dogma of Biology: Definition & Theory
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  • 0:01 The Central Dogma of Biology
  • 0:50 Central Dogma Analogy
  • 2:41 DNA to RNA: Transcription
  • 3:54 RNA to Protein: Translation
  • 5:45 Proteins & Phenotypes
  • 6:33 Lesson Summary
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Lesson Transcript
Instructor: Katy Metzler

Katy teaches biology at the college level and did her Ph.D. work on infectious diseases and immunology.

The central dogma of biology describes the flow of information from gene sequence to protein product. In this lesson, learn how the processes of transcription and translation work in cells, and discover how crucial sequence information is at every step.

Definition of the Central Dogma of Biology

Sometimes, when we talk about people's appearances, special skills or behaviors, we say, 'It's in your genes.' It's true: the genetic information carried in your DNA sequence determines many things about you, such as the color of your hair, the shape of your eyes, your blood type, and even your susceptibility to certain diseases.

But, did you ever wonder how a particular sequence of the nucleotides, called A, C, G and T, can lead to noticeable physical characteristics? The central dogma of biology describes just that. It provides the basic framework for how genetic information flows from a DNA sequence to a protein product inside cells. This process of genetic information flowing from DNA to RNA to protein is called gene expression.

An Analogy of the Central Dogma

To start off, let's look at an analogy to make the central dogma more tangible. Let's say that you want to learn how to make a wooden dresser, but you don't know anyone who knows how to do that. Luckily, in your town, there is a really good library that has a section of books about woodworking. So you grab a pen and notebook and head to the library to look up a how-to guide.

When you get to the library, you search through the shelves until you find a book that has a good set of instructions for a dresser that you like. You whip out your pen and notebook and copy down (or 'transcribe') the instructions. Satisfied, you take your notes and head back home.

At home in your workshop, you have all the wood and tools you need to make the dresser. You follow the instructions and make a good-looking dresser, effectively 'translating' the written words into a physical object that you can use in your home. Tada!

This analogy has set the stage for us to understand the central dogma on a molecular level. The library represents the nucleus, and your workshop at home represents the cytoplasm. All of the books in the library represent the DNA, the genetic material of the cell, stored in chromosomes.

The instructions for the wooden dresser you chose represent a single gene. As you may know, each gene contains the instructions needed to make a single type of protein. The finished dresser, then, represents the protein product. The wood you used to make the dresser represents amino acids, which are the building blocks of proteins.

And, what about the notebook? It represents RNA, which is a smaller molecule that can move out of the nucleus into the cytoplasm, where proteins are made. Simply put, the central dogma states that DNA leads to RNA which, in turn, leads to protein.

DNA to RNA - Transcription

DNA sequence information is converted to RNA in a process called transcription, which is the first step of gene expression, where a segment of DNA is copied into RNA. This is analogous to copying down notes out of a library book. It's helpful to remember that transcribe and transcription come from words like scribe and script, which have to do with writing things down.

First, the double-stranded DNA molecule is partially 'unzipped' and an enzyme called RNA polymerase literally copies the gene's nucleotides one by one into an RNA molecule. Like DNA, RNA is made of a particular sequence of nucleotides. Unlike DNA, RNA has only a single strand, and is a more fragile and temporary molecule inside the cell. Very importantly, RNA is small and can easily exit the nucleus and go to the cytoplasm, where proteins are made.

Back to our analogy: it's very easy to carry your notes home from the library. You wouldn't want to have to build your dresser there in the library, and you certainly wouldn't want to take the library's entire permanent collection of books to your house!

RNA to Protein - Translation

The sequence encoded in the RNA molecule is decoded and converted into an amino acid sequence in a process called translation. In our analogy, this part is equivalent to building the dresser out of wood according to the written notes you brought home from the library. You can remember this word by remembering that translate means 'to convert things from one language to another.' In our analogy, we are translating between written words and a physical object. In the cell, we are translating between a nucleotide sequence and an amino acid sequence.

In the cytoplasm, the ribosome translates RNA sequence information into an amino acid sequence. Groups of three nucleic acids in the RNA, called codons, instruct the ribosome to place certain amino acids into the chain. For example, the RNA sequence AAG codes for the amino acid lysine, and the sequence GCG codes for alanine.

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