Using DNA to Identify an Amino Acid Sequence

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  • 0:04 Transcription & Translation
  • 0:33 Base Pairing
  • 1:18 Protein Transcription
  • 2:11 An Example
  • 3:15 Lesson Summary
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Lesson Transcript
Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

How does DNA determine the amino acid sequence of a protein? Complete this lesson to learn how the information stored in DNA is transformed into RNA and how this dictates the sequence of amino acids in a protein.

Transcription & Translation

We've learned in previous lessons that transcription is a process that converts the information in DNA into RNA. This allows the DNA to stay safely protected in the nucleus, while RNA acts as the middleman, sending messages to other parts of the cell. The new code is then translated into a string of amino acids.

But say you only had the DNA sequence. How would you know what amino acid sequence was being called for? Before we find out, let's do a little review of complimentary base pairing.

Base Pairing

RNA transcription occurs similarly to DNA replication. The DNA double helix is 'unzipped', then new, RNA nucleotides float in and find their complimentary base on the DNA. Then, the RNA nucleotides are joined together to make a single-stranded RNA molecule.

The complimentary binding is again similar to DNA, which you can see playing out in the table appearing here:

DNA Base RNA Base
C G
G C
T A
A U

If the DNA molecule has a guanine (G), the RNA will have a cytosine (C). If the DNA molecule has a thymine (T), the RNA will have an adenine (A).

One difference is that RNA does not use the T base. Instead, it incorporates uracil (U). Therefore, if the DNA molecule has an adenine (A), the RNA will have a uracil (U).

Protein Transcription

The finished RNA molecule, called the messenger RNA, leaves the nucleus and acts as a messenger, delivering information from the DNA in the nucleus to the ribosome in the cytoplasm. This information tells the ribosome which amino acid, or building block of protein, needs to be added to the protein being made.

The messenger RNA contains three-base sequences called codons, which tell the ribosome what specific amino acid needs to be added. All life on Earth uses the same genetic code to determine the amino acid sequence of a protein.

A helpful genetic code table showing all the possible codons and their respective amino acids is available. To use it, you find the row with the first base, the column with the second base, and then the find the entire codon within the box.

The first codon used in almost all proteins is 'AUG', a sort of starter codon that codes for the amino acid methionine (met).

An Example

To find out which amino acids are being coded by DNA, you have to sort of imitate the process in the cell.

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