lecture 6 Flashcards
cell cycle
- conserved in all eukaryotes
- sequences of events where contents of a cell are duplicated and divided into two
- cells do not divide at the same time
- they all follow the same steps tho
M phase
the nucleus and cytoplasm divide
- mitosis
- cytokinesis
interphase
period between cell divisions
- G1 phase
- S phase (synthesis)
- G2 phase
cell cycles in multicellular organisms
-any mature cells dont divide (nerve, muscle, red blood cells)
- some cells only divide when given an appropriate stimulus (when damaged liver cells replace tissue by dividing)
- some cells normally divide on an ongoing basis
cells in G0
- they do not divide
- metabolically active, carry out cell functions
cell control system
- delays later events until the earlier events are complete
major checkpoints
- start transition g1>s
-g2/m transition
- metaphase-to-anaphase transition
-problems in checkpoints can cause chromosome segregation defects
- controlled by molecular switches
mitosis
- process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division
interphase
g1
- centrosomes duplication initiated and completed by g2
s phase
- chromosomes replicated
prophase
- replicated chromosomees condence
- mitotoic spindle assembly starts and requires duplicated centrosomes
dynamic microtubules required for mitosis
non-dividing cell
- microtubules arranged in a radial pattern
- + ends radiating out
- - ends stabilized at MTOC
centrosome structure
- pair of centrioled in the centrosome, organized at right angles to each other, composed of nine fibrils of three microtubules each
-centrosomes matrix surrounds pair of centrioles, contains γ-tubulin ring complexes
centrosome duplication
- centrosome duplicated once per cell cycle during interphase
- pair of centrioles in centrosome
mititic spindle aassembly
- mitotic spindle assembly starts prophase (M phase)
- requires microtubule dynamics (dissasembly adn assembly)
- duplicated centrosomes seperate
nucelar envelope breakdown
- occurs at the boundary between prophase and prometaphase
nuclear lamina
- meshwork of interconnected nuclear lamin
- form a two dimensional lattice on the inner nuclear membrane
nuclear envelop breakdown
- phosphorylation of lamins and nuclear pore proteins trigger dissassembly of nucleat envelope into small membrane vesicles
prometaphase
- nuclear envelope is now disassembled
- mitonic spindle assembly can be completed
- kinetochore microtubules in the mitotoc spindle attatch to duplicated chromosomes
- chromosome move,ent begins
completion of the mitotic spindle assembly
- astral microtubules: help position the mitotic spindle
- non-kinetechore microtubules: cross-linked microtubules throughout the mitotic spindle
- kinetochore microtubules: attatch duplicated chromosomes to the spindle poles
kinetochore microtubules attatch to chromosomes
- kinetochores are located at the centremeres of chromosomes, one kinetochore for each sister chromatid
- microtubules from both spindle poles must attatch to the kinetochores of sistet chromatids, generates equal tension on both sides to line up chromosomes at equator
