Page 87 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

BIOCHEmISTRY ``BIOCHEMISTRY—MOlECUlAR BIOCHEmISTRY ``BIOCHEMISTRY—MOlECUlAR SECTION II 43

Introns vs exons Exons contain the actual genetic information Introns are intervening sequences and stay
coding for protein. in the nucleus, whereas exons exit and are
Introns do not code for protein, but are expressed.
important in regulation of gene expression.
Different exons are frequently combined by
alternative splicing to produce a larger number
of unique proteins.
Alternative splicing can produce a variety
of protein products from a single hnRNA
sequence (eg, transmembrane vs secreted Ig,
tropomyosin variants in muscle, dopamine
receptors in the brain).
Exon 1 Exon 2 Exon 3 Exon 4 Exon 5 Exon 6
5 3
DNA 3 5
Transcription

hnRNA 5 3
1 2 3 4 5 6
Splicing Alternative splicing

mRNA 5 3 5 3 5 3
1 2 4 5 6 1 3 5 6 1 3 4 5 6
Translation

Proteins 1 5 6 1 5 6 1 5 6
4 4
2 3 3

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