cell cycle :/

cell theory

all organisms consist of cells and arise from pre-existing cells

cell devision

2 cells produced a cycle, daughter cells have all genetic material of parent cell, most times daughter cells are genetically identical to parent cell

why do cells engage in mitosis

cells replicate for growth, replacement, and repair (fibroblasts divide and secrete collagen at site of wound to make scar tissue)

phases of cell cycle

mitotic phase (10% of cell cycle) and interphase (90% of cell cylce)

interphase

G1 phase centered on growth, S phase when chromosomes are replicated, G2 phase where the cell completes preparations for cell division

mitosis

actual nuclear division (replication, alignment, and separation)

synthesis phase

each chromosome has a pair of sister chromatids connected by a kinetochore

what happens to chromosomes in mitosis

each chromosome is replicated and then divides

phases of mitosis

prophase, prometaphase, metaphase, anaphase, and telophase

prophase

chromosomes condense, centrosomes migrate to the poles while producing spindle fibers, nuclear membrane fragments

prometaphase

nuclear envelope fragments and microtubules from the spindle fibers connect to the kinetochores in the centromere

metaphase

chromosomes are moved by growing spindle fibers to the equator of the cell (metaphase plate), centrosomes are at the poles, no nuclear membrane

anaphase

kinetochore splits in two, spindle fibers shorten from kinetochore end separating sister chromatids and pulling them towards the poles

telophase

nuclear membrane reforms around each region of chromosomes, nucleolus reforms, cytokinesis may occur

cytokinesis

division of the cytoplasm

cytokinesis in plants

a cell plate made up of cell wall components gradually forms in the middle of the cell

cell cycle regulation

cell cycle events are triggered by cell-cycle control system, affected by internal and external controls

checkpoints

G1, G2, and M phases, G1 is most critical, cells may go into G0 to never divide again

G0

non-dividing state, most cells in the human body will not divide like mature nerve cells and mature muscle cells

cyclin

cytoplasmic protein that fluctuates in concentration

cyclin-dependent proteins

activate other proteins in the cell by phosphorylation (cyclin dependent kinase)

cyclin-dependent kinase

activity fluctuates during the cell cycle because it is controlled by cyclins, whose concentration varies

MPF

maturation-promoting factor, a cyclin-dependent kinase complex that triggers a cell’s passage past the G2 checkpoint into mitosis

internal factor

M checkpoint does not proceed until signal is received that all kinetochores are attached to a spindle

external factor

cycle will not proceed if requirements are not met, density dependent inhibition, anchorage dependence

growth factor

platelet derived growth factor (PDGF) stimulates the growth of blood vessels

density dependent inhibition

under crowded conditions, cells will not divide

anchorage dependence

cells must be attached to a substrate in order to divide

cancer cells do not exhibit…

density dependent or anchorage dependence, they’ll just keep dividing

apoptosis

programmed cell death (blebbing, partition of cytoplasm and apoptotic bodies, phagocytosis) important in embryonic development and flower parts

cancer cells

do not respond normally to the body’s control mechanisms, may make their own growth factor, convey growth factor’s signal without growth factor, or have an abnormal cell cycle control system

transformation

normal cells are converted to cancerous cells, if they remain only at original site they are benign, if they travel (metastasize) it is malignant