Cell Cycle

Tissue Hemostasis

done through the regulation of cell count and size. Done by creating new cells, Growth arrest and cell loss.

mitogens

signaling molecules that stimulate cell replication

growth factors

cells that stimulate cell growth

survival factors

protect the cell against apoptosis.

G0 phase

normal state of the cell what it is not undergoing cell division. cells have to be driven to leave this stage

apoptosis

programed cell death. happens to cells lacking survival factors. plays an important role in regulating cells and removing unnecessary material, why we don’t have webbed hands.

caspase cascade

molecular mechanism of apoptosis. apoptosis signal triggers the initiator caspase. this activates the executioner caspases which destroy over 1k cell proteins which destroys the cell. one of the nucleases released chops up DNA

ECM and growth facors

the extra cellular matrix interacts with growth factors. when cells are suspended, they rarely leave g-phase, sometimes do when perched and frequently do when placed on a large patch. 

cell size control

mechanism is very much a mystery, but there is very large variation in cell size and shape across the body.

size control clues from yeast

in yeast cell division is normally regulated by the amount of nutrients present btu if you inhibit the m-Tor gene the cell will continue to divide in an environment without sufficient nutrients resulting in smaller and smaller cells.

cytoplasm to dna ratio

can be a regulator of cell size. if there is too much cytoplasm and not enough things to put in it the cell shrinks and vise versa.

growth factors and cell size

secreted growth factors can also control cell size. why inhibiting myostatin makes really muscular animals

Fluorescence activated Cell sorting

cells are given a fluorescent die indicating their amount of double stranded DNA, then the cell is dropped through a laser beam to check for fluorescence. After this the cell is given a charge based on whether or not it has fluorescence. After that the cells are sorted based off of charge. let’s researchers isolate cells at certain states in the cell cycle.

G1 checkpoint

gateway into the S phase, checks if the dna is intact and if the environment is favorable for replication.

G2 checkpoint

controls entrance into mitosis. ensures that all the dna is still intact and that it all has been replicated

frog egg division

frog eggs divide into smaller cells simultaneously every 30 or so minutes. experimental model showing cell replication regulation

maturation promoting factor

multi protein complex of m-cyclin and mdk. increased my-cylin presence increases mdk ativity which starts mitosis. m-cdk concentration is constant

cyclins cyclin dependent kinases and cell division checkpoints

when the two combine to form an active complex cell replication will pass the relevant checkpoint. This is deactivated when the complex is flagged with ubiquitin which flags the cyclin for digestion.

m-cdk and kinases

kinases can both activate and inactivate m-cdk regulated by positive feedback

cyclins for different steps

m-cyclin used for mitosis s-cyclin used for s-phase act as molecular switches for the different steps in the cell cycle

checkpoints and signaling

cell signaling helps the cell coordinate its cycle movement with internal and external factors

mitosis

the process of dividing the cell dna into two identical daughter cells.

cytokinesis

when the dividing cell splits the cytoplasm proteins and organelles between the two new cells.

prophase

first phase of mitosis. when the sister chromatids align and are condensed, the mitotic spindle starts to form and the nuclear envelope is still intact. 

kinetochore

molecular complex, allows spindle to attach to the chromatin. the microtubule enters the kinetochore then depolarizes causing it to fan out locking it in place.

condensin

molecular complex condenses compacts and configures dna ring strucure hinges around a strand of dna dna

cohesion

molecular complex holds sister chromatids together at the end of s-phase ring ring structure singes around two strands of dna.

mitotic spindle

long strands of microtubules centered at centrosomes. begin formation in prophase. grab chromatids during cell division and help the cell maintain its shape

prometaphase

second part of cell division. starts with the break down of the nuclear envelope. then the microtubules attach to the kinetochores.

role of the cytoskeleton in cell division

the cytoskeleton segregates sister chromosomes and aligns the microtubules.

metaphase

third part of mitosis, mitotic spindle aligns the sister chromatids in the center of the cell. done by kinesin proteins on the microtubules.

anaphase

fourth part of mitosis, starts when the sister chromatids separate happens because of motor proteins pulling the spindle apart. 

Anaphase A

shortening of the kinetochore microtubules. force is mainly generated at the kinetochores.

Anaphase B

microtubules expand, sliding force at the overlap is used to push the poles apart.

telophase

last part of mitosis. the daughter chromatids assemble at the respective poles and the nuclear envelope beings to re-form. the contractile ring also assembles and begins to contract.

nuclear Lamins

form a network of proteins under the inner membrane of the nuclear envelope which provides support to the nucleus. in prophase they are phosphorylated leading to the degradation of the nuclear envelope but in telophase they are dephosphorylated letting the envelope re-form.

nuclear vesicles

vesicles containing important parts of the nuclear membrane which assemble around chromatins in telophase

actomyosin contractile ring

during cytokinesis it circles the parent cell and constricts separating it into two daughter cells.

sister chromatins

bound together identical copies of chromosomes.

advantages of sexual reproduction

production of gametes, recombination, and the resulting mix of parental dna

meiosis

cellular division which forms haploid cells that are genetically distinct.

haploid cells

cells that only have one set of chromosomes

s-phase 

part of the cell cycle where dna is replicated