- You are studying a steroid hormone-binding protein in mice. Youhave isolated two proteins that have similar but not identicalamino acid sequences from a mixed tissue homogenate (prepared frombrain, muscle, liver, ovary, adrenal gland and kidney of a mixedpopulation of adult mice). There are at least three differentmolecular mechanisms that can give rise to similar butnon-identical proteins. List and explain two of these.
2. The differentiation of muscle cellsin the developing embryo is controlled by myogenin, ahelix-loop-helix (HLH) gene regulatory protein that functions as aheterodimer with another HLH protein. The activity of myogenin mustbe carefully controlled so it does not trigger premature expressionof muscle cell differentiation. The myogenin gene isturned on in advance of the time when it is needed, but myogenin isprevented from functioning by its tight binding to Id, an HLHprotein that lacks a DNA-binding domain, and by phosphorylation ofits DNA-binding domain. Explain how dimerization with Id andphosphorylation of the DNA-binding domain might act to keepmyogenin non-functional.
3. Imprinting occurs only in mammals,and why it should exist at all is a mystery. One gene that isimprinted in most mammalian species is Igf2 gene, whoseproduct � insulin-like growth factor-2 � is required for prenatalgrowth. Most mammalian females can mate with multiple males,generating multiple embryos with different fathers in each litter.If one father had an Igf2 allele that caused more rapidprenatal growth, embryos carrying his genes, it would prosper atthe expense of the other embryos. While this would be good for thefather�s genes (in an evolutionary sense), it would drain theresources of the mother, potentially putting her life at risk (notgood for her genes). Thus, it is in the mother�s interest tocounter these paternal effects with maternal changes that limit thegrowth of the embryo. Based on this scenario, decide whether theIgf2 gene is more likely to be imprinted in the male or inthe female.
- You are studying a steroid hormone-binding protein in mice. Youhave isolated two proteins that have similar but not identicalamino acid sequences from a mixed tissue homogenate (prepared frombrain, muscle, liver, ovary, adrenal gland and kidney of a mixedpopulation of adult mice). There are at least three differentmolecular mechanisms that can give rise to similar butnon-identical proteins. List and explain two of these.
2. The differentiation of muscle cellsin the developing embryo is controlled by myogenin, ahelix-loop-helix (HLH) gene regulatory protein that functions as aheterodimer with another HLH protein. The activity of myogenin mustbe carefully controlled so it does not trigger premature expressionof muscle cell differentiation. The myogenin gene isturned on in advance of the time when it is needed, but myogenin isprevented from functioning by its tight binding to Id, an HLHprotein that lacks a DNA-binding domain, and by phosphorylation ofits DNA-binding domain. Explain how dimerization with Id andphosphorylation of the DNA-binding domain might act to keepmyogenin non-functional.
3. Imprinting occurs only in mammals,and why it should exist at all is a mystery. One gene that isimprinted in most mammalian species is Igf2 gene, whoseproduct � insulin-like growth factor-2 � is required for prenatalgrowth. Most mammalian females can mate with multiple males,generating multiple embryos with different fathers in each litter.If one father had an Igf2 allele that caused more rapidprenatal growth, embryos carrying his genes, it would prosper atthe expense of the other embryos. While this would be good for thefather�s genes (in an evolutionary sense), it would drain theresources of the mother, potentially putting her life at risk (notgood for her genes). Thus, it is in the mother�s interest tocounter these paternal effects with maternal changes that limit thegrowth of the embryo. Based on this scenario, decide whether theIgf2 gene is more likely to be imprinted in the male or inthe female.
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