section9_ak - MIT Department of Biology 7.014 Introductory...

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MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 9 Answer Key March 7-8, 2005 Molecular Biology—Gene Regulation A. Gene regulation basics 1. What is a gene? A gene is a functional unit of heredity. It is a segment of DNA that contains all of the information to encode the sequence of a product and to regulate its expression. A gene encodes when, where, and what polypeptide or functional RNA should be made. 2. What is a protein? A protein is a polypeptide product of a gene that performs a particular function in the cell. 3. How is it possible that your liver cell and your skin cell can have identical DNA content, and yet look different and perform different functions? Although all cells in a given organism can trace their lineage to the original fertilized egg cell, cell division does not have to produce cells that behave in identical ways. Two cells that result from one division, and have the same genetic material can have different morphology and behavior due to differentiation— expressing a different set of genes to perform a different function in the organism. It is important to understand that differentiation usually involves the selective reading of a genome rather than a change in the sequence of the genome. 4. Why is there a need for gene regulation? In general terms, how is it accomplished? Not all genes need to be expressed at all times. Therefore, gene products are regulated in their timing and abundance. In general terms, gene expression is regulated at the level of production of the mRNA transcript. If no mRNA for a particular polypeptide is produced, no polypeptide is produced. If mRNA is allowed to be produced, than that mRNA can be translated into the polypeptide encoded by the gene. Levels of protein can also be regulated by abundance and stability of the mRNA transcript or by post-translational modifications. 5. What does a gene consist of? What is the role of each element? A gene that encodes a protein consists of a regulatory region, a promoter, a start codon, a stop codon, the intervening polypeptide encoding sequence and a transcriptional terminator.
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section9_ak - MIT Department of Biology 7.014 Introductory...

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