1. Peroxisomes are organelles surrounded by a single membrane. Soluble proteins that reside within peroxisomes are imported post-translationally, and they often contain the C-terminal tripeptide SKL (serine-lysine-leucine). a. How would you confirm that a C-terminal SKL tripeptide is a peroxisomal targeting signal? b. If cells were engineered to produce a hybrid protein consisting of a mitochondrial matrix protein (including its signal sequence) followed by a C-terminal SKL signal, where in the cell would you expect the hybrid protein to be found? Explain your reasoning. 2. Functional mitochondria can be isolated from cells. These isolated mitochondria are used to study oxidative phosphorylation and the import of proteins into the matrix. In an appropriate buffer, isolated mitochondria will rupture to generate “mitoplasts” in which the inner membrane remains intact but the outer membrane is lost. Would you expect mitoplasts to support oxidative phosphorylation? Would you expect mitoplasts to support import into the matrix? Explain. 3. Consider a transmembrane protein that spans the inner nuclear membrane. Suggest a pathway by which such a protein could reach its destination. In your scheme, describe how the proposed mechanism would ensure that specific proteins are stably localized to the inner nuclear membrane whereas others are not.
Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
1. Peroxisomes are organelles surrounded by a single membrane. Soluble proteins that reside within peroxisomes are imported post-translationally, and they often contain the C-terminal tripeptide SKL (serine-lysine-leucine).
a. How would you confirm that a C-terminal SKL tripeptide is a peroxisomal targeting signal?
b. If cells were engineered to produce a hybrid protein consisting of a mitochondrial matrix protein (including its signal sequence) followed by a C-terminal SKL signal, where in the cell would you expect the hybrid protein to be found? Explain your reasoning.
2. Functional mitochondria can be isolated from cells. These isolated mitochondria are used to study oxidative phosphorylation and the import of proteins into the matrix. In an appropriate buffer, isolated mitochondria will rupture to generate “mitoplasts” in which the inner membrane remains intact but the outer membrane is lost. Would you expect mitoplasts to support oxidative phosphorylation? Would you expect mitoplasts to support import into the matrix? Explain.
3. Consider a transmembrane protein that spans the inner nuclear membrane. Suggest a pathway by which such a protein could reach its destination. In your scheme, describe how the proposed mechanism would ensure that specific proteins are stably localized to the inner nuclear membrane whereas others are not.
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