Mitosis Flashcards
What are the different phases of the cell cycle before mitosis
G1: Metabolic changes, cell prepares for cell division
S: DNA replication, 2 sister chromatids
G2: Assembles for cytoplasmic materials necessary for mitosis and cytokinesis
M: nuclear division followed by cell division ( cytokinesis)
G1 is transformed into G0, if the cell has
no stimulus for division
What is the evolution the mitosis
Nuclear envelope may or may not breakdown
Some unicellular eukaryotes, spindle acts in nucleus = CLOSED MITOSIS
Animals and plants= OPEN MITOSIS
What are the features of mitotic phases
PROPHASE: chromosomes condense and visible
nuclear envelope breaks down
Spindle fibres emerge from centrosomes
PROMETAPHASE: kinetochores appear at centromere
spindle fibres attach to kinetochores
METAPHASE: Chromosomes lines at equator
Each sister chromatid attached to spindle fibre
ANAPHASE: Spindle pulls and centromeres split
sister chromatids (now called chromosomes)
pulled to opposite poles
Some spindle elongate cell
TELOPHASE: chromosomes decondense
Nuclear envelopes form
Spindle breaks down
CYTOKINESIS: Animal- cleavage furrow due to contractile actin
ring splits daughter cells
Plant- cell plate, precursor to new cell
wall separates daughter cells
What are the 3 types of spindle microtubules
astral, kinetochore and overlap
What are the functions of each spindle fibres
Overlap(polar): keeps chromosome in limited zone and supports spindle
Kinetochore: holds chromosomes
Astral: defines position of spindle in cell
difference between centromere and kinetochore
Centromere = region of chromosome that holds sister chromatids together ( constricted due to cohesisns and condesins)
Kinetochore= disc shaped protein complex allows spindle fibres to attach during cell division
How does microtubules become shorter or longer
MOTOR PROTEINS adds/removes tubulin subunits (elongation or shortening)
How do chromosomes move during anaphase
shortening of kinetochore fibres + elongation of polar (overlap) fibres)
What are the motor proteins for spindle assembly
Microtubule bound motors: promotes bipolar spindle
formation
Chromosome associated motors: allows proper kineto
orientation and chromosome movement to equator
What are some chromosome associated motors
Kinesisin 5= bipolarity established. Slides antiparallel microtubules apart with their minus ends so plus ends directed to spindle equator
Dyenin= moves microtubules to pole with “-“ ends. K fibres incorporates into spindle and spindle poles form
Kinetochore associated dyenin= transpoets chromosomes along astral microtubules toward spindle poles
Kinesisin 4+10= eject chromosome arms outward
Kinesisn 7= transports kinetchores toward ewquator along spindle microtubyukles
How is cytokinesis in animal cells
Contractile ring (actin and myosin filaments) enter cleavage furrow midway between 2 spindle poles
splits plams membrane of developing daughter cells
How is nuclear envelope broken down and reassembled
BREAKDOWN: End of G2, cyclin dependent kinases triggers start. Nuclear lamins phosphorylated so nuclear envelope breaksdown
REASSEMBLY: late anaphase, proteins ( SUN1 and LAP2) concentrated around chromosome.During telophase
they direct NE reassembly.
What are some strange mitosis in intracellular organisms
Endodyogeny: 2 daughter cells form while still in mother cell
TOXOPLASMA GONDII
Endopolyogeny: Many daughter cells form while in mother
PLASMODIUM
What are the main cell cycle checkpoints
G1- called restriction point, checks if cell big enough, has nutirents and growth factors
G2- checks if DNA is copied properly or damaged DNA
M- checks at metaphase before anaphase, checks if all chromosomes arranged properly at metaphase plate
How is mitosis controlled and what are exceptions
mediated by hormones/ growth factors
exceptions are early embryonic cells and cancer cells dont need permission
What are condesins and cohesins
Condesins: compact chromosomes during mitosis, produces loops
Cohesins: hold together 2 sister chromatids together. Produces loops, which organize genome during interphase
(cohesin mediated loops=TADS: organize DNA into compartments)
What is the action of cohesin
- embraces DNA within its coiled arms
- linkage between sister chromatids established during replication-forms loops during interphase
- During anaphase, cleavage of 1 subunit opens ring + release chromatids for separation
What is the action of condensins
*Create loops at each chromatid
- Gradual release of cohesisn + cooperative action of condensins lead to assembly of metaphase chromosome with 2 visible sister chromatids- condensation at metaphase
What is a cyclosome
Anaphase promoting complex
Activated if chromosomes well arranged at equator
They trigger transition from metaphase to anaphase by tagging specific proteins for degradation by UBIQUITIN
What enzyme does cyclosome release
SEPARASE
Breaks down last cohesins holding together sister chromatids
After cohesin breakdown, the kinetochore microtubules pull the chromosomes apart, to the opposite spindle poles.
Sister chromatids become separated chromosomes.
What are the proteins that direct the cell cycle
( G1, S, G2, M )
Cyclin dependent kinases and cyclins
What do the cyclin dependant kinases do for mitosis
Controls the stages of mitosis.
G1/s phase transition, DNa replication, chromosome condensation..
What is importance of satellites in chromosomes
(segment separated from rest of chrom by secondary constriction) helps formation of chromosome structures + heterochromatin
Open vs closed mitosis
open - segregation of chromosomes occurs after nuclear envelope breaks down
closed - segregation occurs with nuclear envelope still present
