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DNA Sequences in the Human Genome

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  • 0:00 Human Genome
  • 0:35 Introns & Exons
  • 1:40 Unique Noncoding DNA &…
  • 2:34 Repetitive DNA
  • 3:20 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

In this lesson, you're going to learn that the human genome is not uniform and is in fact made up of many different types of DNA sequences, some functional and others not.

Human Genome

If you were to look at a piece of computer code, you would see that it's not uniform. Some of the code seems to repeat over and over again. Some code seems to be in one place and another. Other pieces of the computer code encode for a function like the start of a program.

Our human computer code, the human genome, is just like this in that it is not uniform. It too is made up of different kinds of code. Some of it is very important for different functions, while other parts of it do pretty much nothing.

So, let's take a close look at the different types of DNA sequences found in the human genome.

Introns and Exons

In a eukaryote, a sequence of DNA that codes for a polypeptide will be made up of something known as exons and introns, meaning the sequence of nucleotides will usually not be continuous and will instead be split up into segments.

These segments are called introns and exons. The introns are intervening sequences and the exons are the expressed regions. In other words, the exons are found in between the introns. Introns are noncoding segments of nucleic acid, while the exons are expressed and usually translated into an amino acid sequence.

To help you remember which is which, just look at the definition. The exons express themselves while the introns are just the intervening sequences.

Just one little note, in case you get confused when reading about exons and introns elsewhere. You need to know that the terms exons and introns are used to refer to RNA sequences and the DNA sequences that encode these sequences of RNA.

Unique Noncoding DNA and Promoters

Not all genes in eukaryotes code for proteins thanks to exons. Actually only about 1.5% of all genes in the human genome code for proteins or give rise to rRNA or tRNA, while introns account for about 20% of the DNA sequences in the human genome.

The rest of the genome is made up of things like unique noncoding DNA, such as pseudogenes, segments of inactive DNA that look like genes but lack any function. Meaning, they don't produce functional proteins anymore, likely as a result of mutations they accumulated over a long period of time. Unique noncoding DNA accounts for about 15% of the DNA sequences in the human genome.

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