Read This! Introns are sections of pre mRNA that are noncoding That is, they don't provide useful information for the production of the pelypeptide being synthesized. There is evidence that suggests these low certain sections of DNA to code for different polypeptides when different sections are removed. The removal of specific sections is triggered by a signal response in the cell The portions of the pre mRNA chat remain are called exoas. The methyl cap Gometimes called the GTP cap or 5^4 cap) helps the mikNA molecule move through the nucleur pore and attach to a ribosome,its final destination, mRNA is short lived molecule. Once in the cytoplasm the mRN will be subject to exonucleases that immediately start removing individual nucleotides from the 3'' end of a nucleic acid. The individual mRNA nucleotides will then be free to be used again during the process of transcription. 16. The human genome contains about 25,000 genes and yet produces about 100,000 different polypeptides. Propose an explanation of how this is possible. 17. Using the information in the Read This box.develop a hypothesis to explain the advantage of the poly-A tail added to the 3' end of the mRNA.

16. The human genome contains about 25,000 genes and yet produces about 100,000 different polypeptides. This is possible due to the process of alternative splicing. During transcription, the pre-mRNA is synthesized from the DNA template, and it contains both coding regions (exons) and non-coding regions (introns). The introns are removed from the pre-mRNA during the process of splicing, and the exons are joined together to form the mature mRNA. However, different combinations of exons can be joined together during splicing, leading to the production of different polypeptides from the same gene. This process is known as alternative splicing, and it allows for the production of a large diversity of polypeptides from a relatively small number of genes.<br /><br />17. The poly-A tail is added to the 3' end of the mRNA during the process of transcription. The poly-A tail is a sequence of adenine nucleotides (A) that is added to the 3' end of the mRNA molecule. The length of the poly-A tail can vary, but it is typically between 50 and 250 nucleotides long. The poly-A tail serves several important functions in the cell. One of the main functions of the poly-A tail is to protect the mRNA from degradation by exonucleases. Exonucleases are enzymes that can remove individual nucleotides from the 3' end of a nucleic acid molecule. By adding a poly-A tail to the 3' end of the mRNA, the cell can prevent the exonucleases from degrading the mRNA, thereby protecting the mRNA from being broken down too quickly. This allows the mRNA to be transported out of the nucleus and into the cytoplasm, where it can be translated into a polypeptide by the ribosomes.