cell division and differentiation

hyperplasia

cell division

hypertrophy

making a cell bigger

the chromosomal cycle

DNA replication and segregation

(mitosis)

cytoplasmic cycle

organelle replication and physical division

(cytokinesis)

centrosome cycle

replication of the mitotic spindle

G1 phase

• start point

• phase of normal activity eg biosynthesis

• often longest phase

S phase

• synthesis, cell contents double

  • DNA and cytoplasm

• time can vary depending on DNA content

• chromosomes duplicate to form sister chromatids

• long in species that have lots of DNA

G2 phase

• second gap phase

• normal biosynthessi occurs

• only occurs when all DNA is replicated

M phase

• mitosis

• very short

• involves bost mitosis and cytokinesis

• 6 stages

G0 phase

can be transient or permanent

G2/M checkpoint

• cell size

• DNA replication

spindle assembly checkpoint

chromosomal attachment to spindle

G1 checkpoint

• cell size

• nutrient

• DNA damage

• growth factor

intra s phase checkpoint

DNA damage

DNA replication

what molecules drive the cell cycle?

cyclins and CDK

what are the 2 cytokeletal machines

• mitotic spindle- microtubules

• contractile ring- actin and myosin

what does the spindle contain

formed by the centrosome

contains a pair of cylindrical centrioles

how do microtubules grow out

• like points of a star

• 1 centrosome is 1 pole of spindle

• duplication occurs in the S phase

how does the contractile ring form

• forms under plasma membrane at the equator of the cell

• contracts to divide into two

what happens in prometaphase

• nuclear membrane breaks down

• spindle and chromosoes now meet

• attachment is via kinetochores

• spindle begins to move to the poles of the cell

how do chromosomes physically separate in anaphase

• spindle poles move outward

• microtubules shorten

• chromosomes slides along microtubule

how does cytokinesis work

• starts in anaphase, ends in telophase

• actinomyosin ring assembles under the cell membrane

• contraction of this ring pinches cell into two at the cleavage furrow

• requires membrane manufacture

• each cell has one full set of chromosomes, a centrosome and about half a cytoplasm

feature of differentiated cells

• are often post mitotic- cannot undergo further cell division and are in G0

• some differentiated cells can be slowly dividing

• they express specific sets of genes that are characteristic of that particular cell type so they will have a specific set of proteins

• generally signals from other cells the ecm and hromones direct a cell to begin differentiation

what are the 2 steps in differentiation

• specification- capable of autonomous differentiation in isolation but can be reversed. not fate commited.

• determination- when the cell differenitates into a specific cell type even when it is placed among cells of a different type. this is irreversible and fate committed.

can a cell change its differentiated state

• it can sometimes

• during regeneration

• eg newt limb where injury promotes muscle cells to de differentate and then re differentiate into cartilage

• cloning

early prophase

late prophase

prometaphase

metaphase

early anaphase

late anaphase

late telophase