Appendix A: 

 Primer on Molecular 

 Genetics 



Genes 



Genes — the functional unit of genetic infonnation — encode the DNA sequences 

 required to make a protein. Genes also contain information that is used to regulate the 

 kind and amount of protein made in a particular type of cell. 



The human genome has 50.000 to 100.000 genes. A typical gene is 90% stuffer — 

 introns — whose function is unknown. A human gene may contain up to 30,000 base 

 pairs, but only about 10% of the base pairs are known, with certainty, to contain useful 

 information. This infonnation is read out in discontinuous blocks, called exons (Fig. 4). 

 Since three bases code for one amino acid (the building blocks of protein.s), the average 

 size of the protein coded by a gene will be 1000 amino acids. In addition to introns and 

 sequences that regulate the amount of protein made, special regions within the DNA 

 help organize it into chromosomes and control its replication. 



Fig. 4. Structure of human genes. 



When a gene is turned on by 

 signals at the regulatory region, the 

 entire gene — introns and exons — is 

 copied. Then the introns are spliced 

 out to make the shorter mRNA that 

 is translated into protein by the cell. 



3x10^ bp In the human genome 

 50.000 - 100.000 genes 

 30.000 base pairs per gene 



A gene is 10% information (exons) and 90% stuffer (introns) 



Portion of the 



chromosome Exon Exon Exon Exon 



containing a gene 4' ^ ^ ^ 



A noncoding region 

 including 

 regulatory region 



M 



leader 



Messenger RNA 

 (mRNA) 



Protein 



t 



Introns 



t t 



Introns Introns 



\ 



Noncoding 

 region 



Copying DNA and splicing out Introns 



processed gene 



taU 



Translation 



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