Cell Division

Cell Division

Nuclear division followed by cytokinesis

DNA organization

Dna is tored in the form of chromatin and during cell division and becomes more condensed during cell division

Chromosome

Dense packaging of chromatin existing during mitosis and meiosis

Chromatid

one half of a duplicated chromosome

Haploid

1 set of chromosomes (n)

Diploid

2 sets of chromosomes (2n)

Homologous chromsomes

Two sets of every chromomsme forming a pair

similar in legth gene position and centromere position

Microtubules organizing centers

in animals centrosomes

plants have microtubule organizign centers

centrosomes

composed of 2 centrioles

spindle fibers

tbe microtubules that emerge from the centromere are called spible fibers

spindle fibers allow for the chromosome and chromatid to be seperated during cell division

kinetochore

during cell divsiio spindle fibers attach to kinetochore

located on teh centromere region

serve as an anchor point

Mitosis

occurs in somatic and germ cells

Meiosis

Occurs in germ gamete producing cells

Mitosis phases

prophase

prometaphase

metaphase

anaphase

telophase and cytokinesis

Prophase

chromatin condenses into chromosomes

nucleolus disapears

mitotic spindle begin to form

centrosomes begin to move toward oppostie ends of cell

prometaphase

nucleus disassembles

chromosome condense even further

chromatid is attached to kinetochore

mitotic spindle further develops

spindle fibers begin to attach to kinetochores of chromosomes

metaphase

chromosomes are lined up across the center of cell

metaphase plate

centrosomes have reach oppostie ends of cell

mitotic spindle is fully developed

all chromosomes are attach to spindle fibers

kartotyping performed here

anaphase

microtubles shorten

chromatids are pulled apart

each sister chromatied is an individual chromosome

telophase

nucleoi reappear

two nuclear envelopes develop

chromosomes deconde back into chromatin

spindle fiber diaspear

cytokinesis

physical division of two cells

animal cells cytokinesis

cleavage furrow

contracticle ring formed by actin and myosin

plant cell cytokinesis

cell plate

end of mitosis

parent cell becomes two daughter cell

the dna of each daughter cell is identical of the paretn cell

amount of DNA in each daughter cell is identifcal to the parent

karotyping

a complete set of chromosomes found during metaphase

identify genetic disorder

Meiosis

comprised of two stages

this process produce haploid cells

meioisis 1

seperation of homologus chromosomes

genetic recombination occurs here

meisosis 2

seperation of sister chromatids

Prophase 1

nucleolus and nucleus disappear

chromatin condense into chromosomes

meiotic spindle begins to form

centrosomes begin to move toward oppostie ends of the cell

CROSSING OVER

microtubles begin to attach

Crossing Over

process of genetic recombination producing chromosomes that are unique at the genetic level

attach at the chiasmata

Chiasmata

region when crossing over occurs creating genetic diversity

Tetrad

synapsis when homlogous chromosme pair up into tetrad

term used to described pari homologous chromosomes m

metaphase 1

homologous pairs are lined up across metaphase plate

microtubules are attached to kinetochores

Anaphase 1

meitoic spindle shortens

homologus pairs uncouple and are pulled to opposite poles

process called disjunction

telophase 1

nuclear envelope re devlop

chromosmes begin to decondense

each enw daughter cell has a new nucleus with half the number of chromosomes

chromosomes are not genetically identical to parent cell due to recombination

how many chromosomes does meiosis 1 create

2 haploids

Meiosis 2

seperate sister chromatids to opposite ends of the cel

Prophase 2

nucleus and nucleolus disapear

chromosomnes condense

meiotic spindle develop and begin to attach to chromosomes

centrosomes move toward oppostie ends of cell

metaphase 2

chromosomes line up on metaphase plate

meitoic spindle fully formed and attach to each chromosome by kinetochores sis

anaphase 2

microtubules shorten

chromatids are pulled apart

each sister chromatid is now considered an indivudla chromsome

telophase 2

nucleolus reform

nucleus redevlip

spindle fiber disapear

chromomoseos disapear

end of meiosis

four daughter cells

each daughter cell is haploid

daughter cell is different from parent

Genetic Varaition

genetic recombination occur during three events

• crossing over

• independent assortmnet

  • random joining of gametes

Cell Cycle

sequence of events that occur before and during the process of cell division

cell division phase

mitosis - physical division and seperation of phase

Interphase

sequence of events that occur before the cell undergoes cell division

what phase do cells spend most time in

interphase

G1 Gap Phase

Cell growth

cell increase in size

protein synthesis begins in preparation

S Phase

Synthesis Phase

DNA replication

• all dna replicated in S phase before mitosis

• this is where sister chromatidds are formed

  • centrosomes replicate

G2 phase

Final preparartion for mitosis

organelles replicate

cell continunes to grow

cells check that everything is ready to proceed with mitosis

G0 phase

state of a cell that is not dividing

cell will re enter cell cycle at g1 based on different enviroment cues

Surface to Volume Ratio

Larger cells are bad because hard to transfer things around cell

Large S:V is good because celliuar exchange good

Small S:V is bad

Genome to Volume Ratio

genome size remains constant throughout life

when G:V decreases cell exceed ability of its genome to produce enough amounts of regulation for cell activites

Small G:V is bad

skeletal muscle dilemma

skeletal muscle cells are not capable of dividing but are caplable of growing much larger

get big by hypertrophy

Cell Cycle Specific Regulation

Checkponints

density dependent inhibition

anchorage dependence

Cell Cycle Checkpoints

End of G1

Cell growth is assessed and ready to reproduce

sufficnet nutrietns

cell products

healthy DNA

adequate cell size

G2 Phase chekcpoint

Make sure the DNA has been replicated error free and no mutations

M Phase or spindle checkpoint

cell evlautes if all sister chromatid are attached to a spindle fiber

mitosis stops if spindle fibers are not attached ot both sides

Density dependent inhibiion

cells stop dividing when the surrounding of cell density reaches a maximum

Anchorage dependence

cells will only divide when attached to an external surface

prevent cells from multiplying while floating

Cancer

Cancer cells defy regulations of cell division

cancer steps

a normal cell divides only when new cells are needed

mutations call divide uncontrollably

the mutataed cells continuen to increase

so many cells created masses called tumors

Metatsis

maligant cells break loose and travel to other tissues and organs

p53 gene activelty suppresses tumors

mutation of the gene causing the cell to continue dividing in an uncontrolled amnner leading to tumor grwoth

c

cancer drugs

can inhibit mitosis and stop growth

lablle cells

continuously dividing

quiescent cells

do not divide but can be stimulated to as needed

fixed

cell have little to no cpacity for cell division