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Biology lecture 6 Cellular Life 3 (Spindle Formation (Microtubule proteins…
Biology lecture 6 Cellular Life 3
Levels of replication
Double helix structure allows
DNA replication: whole genome unwinding and copying chrosomes
DNA Transcription: regulated unwinding of specific of specific genomes, creation of RNA copy
Nucleosomes-Chromatin and condensed structure-sister chromatids
Chromosomal Duplication
Centromere, chromosome arm chromosome duplication
Centrosome anchors chromatids, sister chromatids
separation of sister chromatids
Types of cell division
Bacteria binary fission
Mitosis
Have nuclei & multiple Chromosomes, no cell walls, nuclear envelope dissolves, chromosomes duplicates and separates, cell divides around this nuclear envelope re-forms
kinetochore microtubules
cytokinesis
: cytoplasmic events required to separate chromosomes and divide the cytoplasm
Role of spindle microtubules regulating division of cytoplasm
opposing centrosomes give polarity
Short "aster" microtubules give push in opposite direction away from centre
Before separation-Non kinechore microtubules play important role
Elongating the cytoplasm by extending in opposite directions
Cleavage, division of cytoplasm
Division without growth type of cleavage common in developing embryo
Formation of cleavage furrow
From which new membrane forms separating daughter cells
Contractile ring of microfilaents
Microfilament proteins important here(actin and myosin)
After separation of and migration of chromosomes
new microfilament bundles form along the equator
Push to counteract pull of spindle
invagination of membrane "cleavage"
The mitotic spindle
Spindle Formation
Microtubule proteins form from the centrosome & extend into the cytoplasm
more tubulin subunits added on- expansion of the microtubules
short microtubules = aster
longer microtbules = sindle microtubules
Targets: kinetchore proteins on the chromosomal centromere
microtubules which bind a protein kinetchore microtubules
Aster @ 1 end & microtubules @ kinetchore - Push/pull
Places torsion/stress on sister chromatids/chromosomes
Separation
Enzyme assisted separase- breaks down bonds between sister chromatids
sister chromatids migrate away
Moving along kinetchore microtubules towards centriole
moving along the network
Kinetchores shorten- depolymerisation, chroatids move on as they do
Stages of MItosis
Frequency of mitosis is tightly regulated and varies from cell type from tissue and from organism
Linked with growth and metabolism
need new nucleotides for DNA replication
New organelles, nutrients, increased cytoplasm and lipids
Mitosis is referred to as the M stage in the cell cycle
Non mitotic phase known as interphase
Divided into 3 different parts
G1, S (DNA synthesis), G2
Prophase,
Pro-metaphase,
metaphase
, anaphase
, telophase
Prophase: sister chromatids appear, early spindle fibre formation
pro-metaphase: nuclear membrane dissolves (but fragments remain) microtubules extend and connect to kinetchore
Metaphase: attached chromosomes align on metaphase plate, extension of spindle fibres forms symmetry & plate formation
Anaphase: seperation of sister chromatids, depolymerisation of microtubules and migration of chromatids
Telophase: reformation of nuclear membrane(from remnants of old envelope ) cytokinesis & cleavage, dissolution of spindle
Checkpoints for cell division
G1 checkpoint(before DNA replication, most important, no progression signal - cell cycle arrest G0 phase ) , G2 checkpoint, M checkpoint
Important to ensure enough metabolites available,
signals in external (& internal environment) control this - Growth factors
Too much proliferation bad CANCER
Sometimes a cell must die -Apotosis - programmed cell death
Escape From cell cycle control