Preventing Errors in DNA

Lesson Plan - Get It!

Audio:

You have learned that DNA is a very important molecule in the structure and function of cells in this What is DNA? series.

If you missed a lesson or want a refresher in this What Is DNA? series, catch them in the right-hand sidebar under Related Lessons.

When small errors occur in the DNA molecule, it can have serious consequences for living creatures. Errors in DNA are called mutations because they make changes in the sequence.

• Do you notice how the mutated allele looks different from the original allele?

Alleles are genetic codes for specific traits. This mutation could cause someone to have a genetic disorder or have a different eye color.

DNA replicates very frequently, and this repetitive process can lead to mutations in the sequence. Think about if you had to say the alphabet one hundred times in three minutes.

• Do you think you would make a couple of mistakes?

The same process happens in DNA replication. Mutations can occur anywhere in the DNA sequence, and there are a couple different types.

Substitution mutations replace one base in the DNA sequence with another. These can impact the protein synthesis by changing the amino acid sequence, but they can also be silent mutations. Silent mutations do not change the protein, and therefore have no negative impact.

Observe the image below to see a substitution mutation:

_{Image by Lln.gyenes lfv, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.}

Insertion mutations are caused when extra base pairs are added to the DNA sequence. Notice how extra base pairs are added in the following image:

_{Image by Lln.gyenes lfv, via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.}

• How might these extra base pairs impact protein synthesis?

Possibilities include changes in the sequence of amino acids and the shortening of the entire protein.

Deletion mutations cause base pairs or sequences of bases to be removed from the DNA sequence. Notice how base pairs are removed in the following image:

_{Image by Bilal Hussain, via Wikimedia Commons, is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.}

Frameshift mutations can be caused by the insertion or deletion of base pairs, which changes the way amino acids are added to the protein during translation. This causes a shift that can result in significant changes to the protein.

Notice how the sequence of amino acids changes between the normal and frameshift sequence in the following image:

_{Image by Genomics Education Program, via flickr, is available under the Creative Commons Attribution 2.0 Generic (CC BY 2.0) license.}

Mutations occur randomly but can be caused by mutagens in the environment.

• What do you think mutagen means?

If you guessed "something that causes mutations," you guessed correctly!

Mutagens include sunlight that causes mutations leading to skin cancer. Tobacco products act as mutagens for mutations leading to gum, mouth, and lung cancer. Sugar and mushrooms are also mutagens, but must be consumed in very high concentrations to do damage!

Some mutations happen without any cause or trigger! Not all mutations are bad, but not all mutations are good. They create genetic diversity for organisms, which is one reason we all look so different from one another!

As you read a case study on mutations, A case study: sickle cell anemia provided by the University of California Museum of Paleontology, answer the following questions:

• What is sickle cell anemia?
• What kind of mutation causes sickle cell anemia?
• How are proteins impacted by changes in the DNA?
• What effects can be seen at the cellular level?
• What negative effects are visible at the whole organism level? Positive effects?

• What protection measures does the cell use to keep the DNA safe?

There are enzymes that act as spellcheckers, making sure the DNA replicates accurately. Enzymes are also used to help DNA transcribe to mRNA correctly. These processes help protect the valuable information stored in the genetic code!

• Which mutation do you think can cause the most damage? Why?
• How do mutations happen?
• What can the cell do to prevent mutations?
• Are all mutations bad for living creatures?

In the Got It? section, you will review types of mutations and cell protection measures.