What do budding yeast and human centromeres have in common? What are the functio
ID: 34298 • Letter: W
Question
What do budding yeast and human centromeres have in common? What are the functions of the centromere and the kinetochore during cell division? How do these fulfill this function? Why is DNA polymerase I unable to replicate the lagging strand fully during DNA replication? How does telomerase overcome this problem? How does the nuclear envelope reform around the nucleus after Mitosis? How would you describe the organization of the chromosomes in an interphase nucleus? Explain why the amount of heterochromatin varies in the nuclei of different cell types. What is the specialized structure that bridges the cytoplasm and nucleus? What unique types of proteins make up that structure? What domain of these proteins is critical to allow selective transport of soluble cytoplasmic macromolecules into the nucleus? How does an NILSallow import of a muclear protein? How does an NLS allow import of a nuclear protein? How does an NES allow a nuclear protein to escape? What family of proteins uses Ran as a sensor to determine whether a protein will be allowed into or out of the nucleus? How can the interaction of a protein respond to the two major classes of these proteins respond to RanGTP binding, and where will it go (nucleus or cytoplasm) depending on this binding?Explanation / Answer
The budding yeast centromere is an excellent model system for investigating the molecular mechanisms involved in chromosome segregation and genetic inheritance in other organisims too. For many years research group has studied the S. cerevisiae centromere, initially focusing on the CEN DNA, and later working to identify the proteins associated with the CEN DNA that assembles the kinetochore structure. In the early 1990's using a genetic assay based on a mutant CEN DNA, we identified a remarkable new protein, Cse4p, which is required to assemble centromere-specific nucleosomes and for accurate chromosome segregation during mitosis The Cse4p protein masquerades as an H3 histone protein and becomes incorporated into a nucleosome in place of H3. The specialized nucleosome with Cse4p forms only at the centromere. The genetically defined point centromeres of budding yeasts and the epigenetically specified regional centromeres of all other eukaryotes harbor a common epigenetic mark in the form of a non-standard nucleosome.
2.The centromere is the part of a chromosome that links sister chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore.Centromeres were first defined as genetic loci that direct the behavior of chromosomes.
Their physical role is to act as the site of assembly of the kinetochore - a highly complex multiprotein structure that is responsible for the actual events of chromosome segregation - i.e. binding microtubules and signalling to the cell cycle machinery when all chromosomes have adopted correct attachments to the spindle, so that it is safe for cell division to proceed to completion and for cells to enteranaphase.
3. Telomerase is also called telomere terminal transferase is a ribonucleoprotein that is an enzyme that adds DNA sequence repeats (the exact pattern is "TTAGGG" in all vertebrates including humans. In linear DNA (circular DNA does not have this problem), when the replication fork reaches the end of the helix, there is no place to produce the RNA primer needed to start the final Okazaki fragment on the lagging strand. Without the presence of telomerase, a section of single-stranded, or "unpaired", DNA of between 100
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