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Non-Coding Regions of DNA: Sequences & Explanation

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  • 0:04 Non-Coding DNA Explained
  • 1:43 Specific Types of…
  • 3:19 Lesson Summary
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Lesson Transcript
Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

In biology we learn that DNA is the blueprint for life. However, 98% of your DNA does not code for proteins. This non-coding DNA has been called useless, worthless, in a word, 'junk DNA.' But is it really worthless? Read this lesson and find out.

Non-coding DNA

When people refer to coding DNA, they are specifically referring to DNA that encodes proteins. However, much of DNA does not encode proteins. This portion of DNA is what has been commonly called junk DNA, and it is anything but. Part of the non-coding DNA is made (or transcribed) into functional RNA molecules. These RNA molecules are used to make proteins. Some examples include transfer RNA, ribosomal RNA, and translation-controlling RNA.

Another function of non-coding DNA is to regulate gene transcription. These sections of DNA provide binding sites for proteins that can affect transcription. These are called regulatory sites. An important regulatory site common to all genes is a promoter region. This is a section of non-coding DNA where transcriptional proteins can bind. In addition, many genes can have additional regulatory sites. These sites bind proteins that enhance or inhibit transcription. In some cases of highly regulated genes, there can be both types of regulatory sites.

Finally, there are non-coding sequences that probably have a function, but it has not been determined yet. Why do we think they have a function? Because these sequences are found in many different organisms and have a high degree of homology (the order of bases in the DNA sequence is very similar). These sequences are also highly conserved. This means that they are found in the DNA generation after generation. The thought is that if they were not present in the DNA then the organism would likely not survive to reproduce.

Specific Types of Non-coding Functional DNA

Protein production can be controlled at several steps. Two of these can be affected by non-coding DNA. As mentioned, some of the noncoding DNA sequences are regulatory sites that bind proteins and thereby control transcription. Others are transcribed into RNA and can control translation. One of these, microRNA, is predicted to control the translational activity of approximately 30% of all protein-coding genes in mammals. MicroRNA binds to transcripts (the product of transcription) and blocks their translation into proteins.

Introns are regions of DNA that are found within a gene. They are made into transcripts. However, they are usually spliced out of the transcript prior to translation. Sometimes, the spliced-out intron gets degraded, but other times it has a significant biological function. It has been proposed that some introns can regulate transfer RNA and ribosomal RNA activity and protein-coding gene expression.

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