IB biology HL - cell division

needs for division

• repair

• growth

• reproduction

cell theory

• all living organisms are made of cells

• cells are the basic units of life

• all cells are made from pre-existing cells

cytokinesis

end part of mitosis -

separation of two cells from each other

caused by contraction of actin and myosin - the cleavage furrow is created, pinching apart cells

in plant cells, the vesicles assemble sections of the membrane and of cell walls to achieve splitting. because of need to form a cell wall

mitosis for prokaryotes

called binary fussion as no nucleus

unusual cytokinesis

• when two daughter cells are not the same

• one smaller and one larger

ovogenesis

• female egg cells always have some which will be never mature

• one primary ovocyte results in 3 polar bodies and one mature ovum

budding yeast

• nucleus gets split off in one smaller and one larger

what needs to happen before mitosis

DNA replication must occur, as exact copies

chromosome

one chromatid

centromere

pinching at middle of the chromatid

chromosomes with two sister chromatics

at the end of interfase, double pairs of chromatids which are the same.

steps of cell cycle - to fill up

interphase → duplication of dna

mitosis → mitosis

cytokinesis → cells spilling

condensation of chromosomes

uses histone proteins to supercoil DNA

Microtubules and microtubule motors to move DNA

phases of mitosis

PMATI -

prophase

metaphase

anaphase

telophase

interfase

Prophase

• condensation/ supercoiling of DNA using histone proteins/ condensation of chromatin into visible chromosomes

• dissolving of nucleolus

• duplication of centrioles

• nuclear envelope also goes

metaphase

• centrioles migrate to opposite sides of cell, along equator

• spindle fibers form between the two centrioles

anaphase

• centromeres will get pulled apart, and sister chromatids migrate to opposite side of the cell

• sister chromatids are pulled apart

telophase

spindle fibers disintegrate

nuclear envelope reforms around the groups of chromosomes

cytokinesis

the cell cycle

• interphase ( G1, S, G2 )

• division of the nucleus by mitosis

• division of the cytoplasm and whole cell by cytokinesis

interphase, G1

cytoplasm active, new organelles formed, intense biochemical activity. main living/function occurs

interphase, S

chromosomes are replicated → 2 chromatids for each chromosome. not visible as not supercoiled are now chromatin

interphase, G2

more growth of cell and preparation for mitosis

when does cell proliferation normally occur ?

• growth

• replacement

• repair

meristems

Zones in plants where undifferentiated cell divide rapidly.

2 types of meristems

• apical meristematic tissue : the tip of branches and root tips

• lateral meristematic tissue - in stems, allow plants to thicken

where do you find stem cells animals

found in embryos, but soon, embryonic cells specialise

• bone marrow

• skin

• stomach lining

• nails

cell cycle checkpoints

G1, before S phase

G2, before Mitosis.

if the cells fail the check, they undergo apoptosis. kinases control that

Kinases

kinases are enzymes that either activate or inactivate certain proteins

they can get activated by other specific proteins: they are referred to as cyclin-dependent kinases (CDK). they are the main controllers of the cell cycle. usually, they are inactive

As concentration of cyclins increases, during G1 they combine with CDK molecules. This activates it, and turns it into a complex that functions as a mitosis promoting factor. There is a threshold of how many cyclins are needed

As it accumulates, it triggers chromosome condensation, fragmentation of the nuclear membrane, and finally, spindle formation: mitosis is switched on.

by anaphase of mitosis, destruction of cyclins commences ( but CDK persists in the cytoplasm)

benign tumour

tends to grow slowly and doesn’t spread to other parts of the body

malignant tumour

grows rapidly, invades and destroys nearby tissues, and spreads throughout the body. secretes signals triggering growth of blood and lymph vessels to serve the tumour cell.

primary tumour

a cancer growing at the site where the abnormal growth first occured

secondary tumour

formed when cancerous cells detach from a primary tumour, penetrate walls of blood or lympth vessels, and circulate throughout body and reattach somewhere else