What Is the Role of DNA in Protein Synthesis?

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  • 0:01 DNA & Protein Synthesis I
  • 0:59 Structure of DNA
  • 2:06 Why Cells Need mRNA
  • 2:58 DNA & Protein Synthesis II
  • 3:52 Lesson Summary
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Lesson Transcript
Dominic Corsini
Expert Contributor
Brenda Grewe

Brenda has 25 years of experience teaching college level introductory biology and genetics. She earned her PhD in Genetics from Indiana University.

What purpose does DNA serve inside the cell? How does DNA contribute to protein synthesis? Learn the answers to these questions and more in this lesson.

DNA and Protein Synthesis I

To begin, let's ask ourselves this question: 'What makes your biological characteristics different than those of your friends, parents, or siblings?' The answer is that your DNA is unique. DNA is the primary genetic material contained within your cells and in nearly all organisms. It's used to create proteins during protein synthesis, which is a multi-step process that takes the coded message of DNA and converts it into a usable protein molecule.

While that may sound confusing, the process can be broken down into simple steps. The first of these steps is the one that utilizes DNA and it's called transcription, which is the process of using DNA to create messenger RNA, also simply called mRNA. This mRNA is a molecule that carries DNA's coded instructions for making a protein. Let's break down the process of transcription below and further explore DNA's role in protein synthesis.

Structure of DNA

To understand the role of DNA in protein synthesis, we first need to understand the basic structure of DNA. DNA is constructed as a double helix. To picture this, think of a twisted ladder, as you can see in this image:

Structure of DNA

At the front of this image, the molecule is unwound, so you can see the bonding pattern of DNA's bases, which are the subunits of DNA it is built from. There are four bases - adenine, thymine, cytosine, and guanine - and each is usually represented by the first letter in their name: A, T, C, and G, respectively. When combined, these bases form your genetic code.

They are arranged on two different strands (the two sides of the twisted ladder). The code on one strand dictates the code on the opposite strand, because the bases pair up in a specific pattern. Adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). This pattern is important because it will serve as the template for making our mRNA molecule. But first, let's consider this question: 'Why must cells produce mRNA?'

Why Cells Need mRNA

So far we've learned that:

  1. DNA is the genetic material within cells.
  2. DNA is used to build protein.
  3. DNA is built like a twisted ladder.

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Additional Activities

DNA makes RNA makes Protein

As you have learned, DNA is the genetic material of your cells and holds the information for making all the different proteins of your body. The synthesis of proteins occurs in two sequential steps: Transcription and Translation. Transcription occurs in the cell nucleus and uses the base sequence of DNA to produce mRNA. The mRNA carries the message for making a specific protein out to the cytoplasm where translation occurs. Translation converts the information in a series of three letter words in the mRNA into a sequence of amino acids, the building blocks of proteins.

Transcription Activity

A strand of DNA is transcribed into a mRNA molecule with the sequence: AUGCUAGCCUUUGGC.

  1. What is the base sequence of the DNA strand from which the mRNA was transcribed?
  2. The mRNA has a series of three letter words (read left to right) that tell the translation machinery which amino acids to join together and their order. If translation begins at the left end of the mRNA, how many amino acids are specified by the mRNA?

Translation Activity

The genetic code table is shown below. There are 64 three letter words (called codons) altogether. Sixty-one codons specify amino acids of proteins. Because there are only 20 different amino acids in proteins, some codon are synonyms for the same amino acid.

  1. The codon table shows that AUG codes for the amino acid methionine. Are there any other codons that code for methionine?
  2. The second codon of the mRNA is CUA. Which amino acid does it code for?
  3. Complete the translation of the mRNA, writing the amino acid sequence from left to right.

Put It All Together

Suppose that a mutation occurred in the DNA so that codon 4 of the mRNA is changed from UUU to UUG.

  1. What is the mutation that occurred in the DNA? (Recall the base-pairing rules: A in DNA pairs with U in RNA.)
  2. What effect does that have on the amino acid sequence of the protein?

Suppose that in another individual, a different mutation occurs to change codon 3 of the mRNA from GCC to GCA?

  1. What change occurred in the DNA?
  2. What effect does that mutation have on the amino acid sequence of the protein?


Transcription Activity:

  2. 5 amino acids

Translation Activity:

  1. No, there is only one methionine codon.
  2. Leucine
  3. Methionine-Leucine-Alanine-Phenylalanine-Glycine

Put It All Together:

  1. A --> C
  2. Phenylalanine to Leucine
  3. G --> T
  4. None, both codons are for Glycine.

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