PCB3134 Exam 4 Review 1 Microtubules and intermediate filaments MT organization in cilia and flagella end associated with basal body MTOC end is distal to away from cell body Nuclear lamin basic structure and function Lamins are the most widespread Ifs they provide strength and support to the inner surface of the nuclear membrane Nuclear lamins form structural network underlying nuclear envelope o Building blocks of nuclear architecture Phosphorylation of lamins causes nuclear envelope breakdown during mitosis Assembly disassembly of lamins during the cell cycle Lamins in DNA metabolism replication and transcription Lamins interact with proteins located at the inner nuclear envelope Nucleolus structure and function sub nuclear organelle w o membrane association the ribosome producing factory Chromosome domains inside the nucleus n is the nucleolus and N is the nucleus The light staining whitish areas are euchromatin The dark staining areas are heterochromatin 2 Chromosome structure and function Chromosome chromatic nuclear figure DNA proteins that carries part or all of the hereditary information of an organism Chromatid each chromosome has replicated and comprises two chromatids each containing on of two identical DNA molecules The centromere where chromatids are attached at a constriction which is where the chromatids will separate during anaphase when the chromosomes are pulled apart and one chromatid goes to each side Define chromosome and chromatid what does chromosome painting refer to Chromosome painting Certain dyes selectively stain some regions of metaphase chromosomes more intensely than other regions producing characteristic banding patterns that are specific for individual chromosomes The regularity of chromosomal bands serve as useful visible landmarks along the length of each chromosome and can help to distinguish chromosomes of similar size and shape Useful markers for identifying specific chromosomes Define the nucleosome core particle 10nm beads on a string chromatin fiber composed of DNA and histones nucleosomes are about 10 nm in diameter and are the primary structural units of chromatin The core is an octamer containing 2 copies of each of histones H2A H2B H3 and H4 Higher order chromosome organization current model of chromosome structure a model for the folding of a nucleosomal chain at top into a zig zag ribbon of nucleosomes containing two strands In each strand the nucleosomes are aligned with each other like a stack of coins These 2 strands of nucleosomes are then wound into a left handed double helix called a two start helix loops and chromosome scaffolding Nonhistone proteins provide a structural scaffold for long chromatin loops molecules that contribute to higher order chromosome formation condensin multi protein complex which become phosphorylated as cells enter mitosis Phosphorylated condensin binds to DNA and winds it into super coils while unphosphorylated condensin does not wind the DNA into super coils Cohesin associate with chromosomes in late G1 The circular cohesin complexs link daughter chromosomes as they replicate in s phase If there is no cohesin complexs then the sister chromatids can associate properly Anaphase in mitosis is triggered by the cleavage of cohesin by APC anaphase promoting complex Three chromosome elements and their functions Origin of replication o the site where DNA synthesis is initiated Centromeres o primary constriction site on the chromosome where the kinetochore microturbules attach o where chromatids are attached at a constriction is required for their separation late in mitosis Telomeres o chromosome ends o special telomere sequences at the ends function in preventing chromosome shortening 3 Cell division cycle Mitosis how do kinetochores attach to the mitotic spindle the kinetochore assembles on the centromere and links the chromosome to MT polymers from the mitotic spindle during mitosis and meiosis core in A is the centrosome which is associated with the MTs at the end Dynamic instability purpose of it is for the MT to catch the kinetochore so that way it can become a kinetochore MT o This phenomenon only occurs at the plus end of the microtubule E now the kinetochore fibers leads the sister chromatid line up MT s are involved in long distance transport in neuron cells and forming spindles in replication o MT needs to connect to kinetochore so that the chromosome can be pulled apart the chromosome can be transported o If MT does not catch it tries to associate with it the kinetochore to grab the chromosome then this occurs if it reaches it it stabilizes o Allows MT to connect to kinetochore o Minus ends are anchored on the centrosome so they re very stable what triggers the separation of sister chromatids Landmark events in anaphase A and anaphase B Anaphase is triggered by the cleavage of cohesin APC C activated and cohesisns degraded Anaphase A movement is powered by MT shortening kinesin 13 proteins at the kinetochore and at the spindle pole involves the 2 sister chromatids separating from each other and being drawn to the respective pole This appears to occur quickly because the kinetochore MTs are under tension and as the cohesin attachments between chromosomes are released The chromosomes are free to move Anaphase B involved separation of the spindle poles sliding of antiparallel polar MTs powered by a Kinesin 5 end directed motor dynein dynactin located at the cell cortex pulling on astral MTs Four phases of the cell cycle and corresponding chromosome content in G1 phase for a diploid organism like us the genome content is 2n S phase duplicated DNA the genome number is 4n G2 has a genome number is 4n In M phase it goes from 4n 2n because chromosomes are split G0 cells are not undergoing replication Gap 0 G0 cells can be reactivated to enter G1 and replicate when in G0 phase they are quarescent experimental approaches that led to the discovery of cell cycle regulation what is a cdc mutant a mutation on a cell division cycle gene They are temperature sensitive They are yeast mutants that block the cell cycle Hartwell used budding yeast Nurse used Fission yeast Hunt identified cyclin Conservation of cell cycle regulation Cdc28 Cdc2 CdK1 what is MPF Cdc28 is a kinase o It is associated with a protein called a cyclin specifically a G1 cyclin o CDK means cyclin dependent kinase Cdc28 cdc2 CKD1 in humans they re homologs MPF maturation promoting factor o Mitosis promoting factor o Turns out to be the