MCAT Flashcards: Point Mutations

What are point mutations? Ken Tao is an MCAT expert and explains that a point mutation is a one nucleotide substitution in the DNA sequence. There are three types of point mutations. Silent mutations, missense mutations and nonsense mutations. Watch this video to better understand how they work.

Full Transcription

In this flashcard video, we’re going to go over point mutations.

A point mutation is a one nucleotide substitution in the DNA sequence. There are three types of point mutations. Silent mutations, missense mutations and nonsense mutations.

To better understand how they work, take a look at this whiteboard. You can see here that we have a codon – a three nucleotide sequence. And here, we have UAU which codes for the amino acid tyrosine. If we want to do a point mutation, we have to change one of these nucleotides. Let’s say we changed the third U to a C. That would give us UAC which also codes for tyrosine. Because this point mutation resulted in the same amino acid, this is what we call a silent mutation. However, if we were to substitute the second A for a U, that would give us UUU, which codes for phenylalanine. Because this codes for a different amino acid, we went from tyrosine to phenylalanine, this is called a missense mutation.

The last type of point mutation is called a nonsense mutation. And here you can see we have UAU, the original sequence that codes for tyrosine. If you replace the third U with an A you get UAA which is a stop codons.

Stop codons do not code for an amino acid and they terminate translation. So that means when you have a nonsense mutation, you’re going to end up with a truncated protein because you have a pre-mature stop codon.

OK, so those are the different types of point mutations that you need to know for the MCAT.