bio ch 12

continuity of life

based on the reproduction of cells and cell division

unicellular organisms

division of one cell reproduces the entire organism

multicellular organisms depend on cell division

development from a fertilized egg, growth and repair

cell cycle

the life of a cell from its formation to division

genome

all the DNA in a cell

chromosomes

DNA molecules in a cell are packed into it

somatic cells

(nonreproductive cells) have two sets of chromosomes

Gametes (sperm and egg)

have only one set of chromosomes - half as many as somatic

sister chromatids

each duplicated cell has two of them, joined copies of the original chromosome, attached along their lengths by cohesins

centromere

“narrow waist” of the duplicated chromosomes where two chromatids are most likely attached

sister chromatids during cell division

separate and move into two nuclei - then called chromosomes

eukaryotic cell division consists of

mitosis and cytokinesis

mitosis

division of the genetic material in the nucleus

cytokinesis

division of the cytoplasm

cell cycle consists of

mitotic M phase (mitosis and cytokinesis), interphase i

interphase

cell growth and copying of chromosomes in preparation for cell division

interphase divided into three parts (abt 90% of cycle)

G1 S G2 - cells grow during all phases but chromosomes are duplicated only during s phase

G1

“first gap” preparation for nuclear division

S

“Synthesis” DNA synthesis

G2

“second gap” separation of nucleic acid

prophase

chromatins condense into chromosomes and mitotic spindles begin to form

prometaphase

kinetochore attaches to sister chromatids and nonkinetochore fibers and nuclear envelope breaks down

metaphase

chromosomes align in the center at the metaphase plate

anaphase

motor protein walks chromosomes to centrosomes opposite poles so they each get copies

telophase and cytokinesis

nuclear envelopes start to reform around genome and spindle falls apart cleavage furrow

mitotic spindle

structure made of microtubles that control chromosome movement during mitosis

microtuble organizing center

assembly of spindle microtubles begins in the centrosome

kinetochores

protein complexes associated with centrosomes

metaphase plate

plane midway between the spindles two poles

cleavage furrow

cytokinesis occurs by a process known as cleavage in animal cells

cell plate

forms during cytokinesis in plant cells - deposition of cellulose

binary fission

prokaryotes are reproduced by this type of cell division - chromosomes replicate at origin of replication and the two daughter cells move apart

cell cycle is driven by

specific chemical signals present in the cytoplasm

cell cycle control system

sequential events of the cell cycle are directed by it - regulated by both internal and external controls - specific checkpoints

cyclins and cyclin dependent kinases (cdks)

two types of regulatory proteins involved in the cell cycle control

MPF (maturation - promoting factor )

cyclin complex that triggers a cells passage past the G2 checkpoint into the M phase

checkpoints

G1 Most important , G2 and M

G0 phase

if cell does not pass G1 checkpoint it will exit the cycle switching to a nondividing state

external factors that influence cell division

growth factors are released by certain cells and stimulate other cells to divide

in density dependent inhibition

crowded cells will stop dividing

anchorage dependence

most cells exhibit this to divide they must be attached to a substratum

transformation

cells that acquire the ability to divide indefinitely undergo this

tumors

cancer cells that are not eliminated by the immune system - masses of abnormal cells within normal tissue - if they remain only at original site they become a benign tumor

malignant tumors

invade surrounding tissues that can undergo metastasis - the spread of the cancer cells to other parts