cell division

copy the DNA

replication

split the cell in two to form daughter cells

binary fission

hereditary

the - information a prokaryote is stored in DNA

circle

the prokaryotics chromosome is a single- of DNA

origin of replication

DNA replication begins with the unzipping of the double stranded DNA at a point

complementary

a new double helix is formed by adding - nucleotides to the exposed DNA strands that have been unizpped

identical copies

the end result of replication is that the cell possesses two- of the hereditary information

more DNA

eukaryotic cells contain- than prokaryotic cells and the DNA is also packaged differently

• cell division in eukaryotic cells is more complex

DNA, linear

is eukaryotic cells is- and packaged into a compact chromosomes

• there is more than one chromosome is a eukaryotic cell

mitosis

is a cell division mechanism that occurs in non reproductive cells

• somatic cells

meiosis

is a cell division mechanisms that occurs in cells that participate in sexual reproduction

• germ cells

interphase

G1 phase- the primary growth phase of the cell following division

• most cells spend the majority of their lifespan in this phase

s phase

DNA replication occurs in preparation for cell division

G2 phase

further preparation for cell division, including replication of mitochondria and synthetics

Mitosis ( m phase)

a micro tubular apparatus binds to the chromosomes and moves them apart

cytokinessis ( c phase)

the cytoplasm divides, creating two daughter cells

chromsome

number varies among organisms

• most eukaryotes have between 10 and 50 chromosomes in their somatic cells

homologous chromosomes

homologues contain information about the same traits but the information may vary

diploid cells

cells that have two of each type of chromosome are called

• one chromosome of each pair is inherited from the mother and other is inherited from the father

sister chromatids

prior to cell division, each of the homologous chromosomes replicates, forming two identical copies

centromere

the sister chromatids are joined together by a structure

• humans have 23 pairs of homologous chromosomes

• when each chromosome in the pair is replicated, this makes for a total of 92 chromatids

kinetochore

proteins are overlaid

karyotype

a- is an arrangment of metaphase chromosomes

• chromosomes can be compared based on size, shape, and centromere location

• the karytotype on the right shows the 23 pairs of human chromsomes arranged from long to short and numbered accordingly

chromatin

chromosomes are comprised of- a complex of DNA and protein interphase DNA is chromatin

• there also is some RNA associated with chromosomes

• the DNA is a chromosome is one very long double stranded fiber that extends unbroken for the length of the chromosomes

coiled

the DNA is- in order to allow it to fit into a small space despite being very long

histones

the- have positive charges to counteract the negative charge associated with the phosphate groups the DNA

nucleosome

the DNA coils around a core of eight histone proteins to form a complex called a

• the nucleosomes in turn can be coiled together further to form a compact chromosome

beads on a string

histones are on interphase DNA like

solenoid

they get flipped to save space and stacked into a 30nm fiber structure

• solenoids are then bound by scaffold proteins at designated positions to form the ends of loops

• loop associations and further packaging result in metaphase chromosomes

condensation

although not visible chromsomes begin to wind up tightly in a process called

• the cell division that follows interpahse is division of the nuclear contents called mitosis

distinct stages

mitosis is a continuous process but it is divided by observation, for ease of study into

• prophase

• metaphase

• anaphase

• telophase

prophase

the condensed chromosomes first become visible with a light microscope

disintegrate

the nuclear envelope begins to

spindle

centrosomes ( centrioles in animal cells) begin to assemble a network of protein cables

microtublues

each cable in the spindle is made of

• some of the microtubles attach to the chromosomes

• when the process is complete the, sister chromatids of a chromsome are attached by microtubles to opposite poles of the cell

anaphase

centromeres cleaved after spindle checkpoint satisafied

• sister chromatids separated dunamic tension of MTs and dynein motors anchored to PM

• the microtubules of the spindle are dismantled starting at the poles

• this pulls the chromatids toward the poles

telophase

a nuclear envelope forms around the set of chromosomes at each pole

• the chromsomes being to decondense

• thenucleolus reappears

cytokinesis

occurs at the end of mitosis, almost indistingusihable in timing from karyokinesis and is a division of the cytoplasm into rougly equal halves

• in animals cytokinesis occurs by actin filaments contracting and pinching the cell in two

cleavage furrow

this action is evident as a- that appears between the daughter cells. exactly on same plane where chromsomes aligned during metaphase

• in plants, a new cell wall is laid down to divide the two daughter cells

cell plate

the cell wall grows at right angles to the mitotic spindle and is called

cell death

cells are programmed to undergo division only so many times and then die

• human cells divide about 50 times

• others reach a terminal differentiation, serve their purpose and die

• cancer cells divide by losing normal control mechanisms and is therefore said to be uncontrolled

• cell death is programmed normally

three checkpoints

checkpoint assesses cell growth to determine if a cell will divide, delay division or enter the resting stage

checkpoint assesses replication which occurred during s

M checkpoints

• assesses the progression of mitosis of at metaphase spindle assembly before continuing metaphase

• assesses the progression of mitosis in late anaphase chromosome separation before continuing to telophase

growth factors

over 50 different proteins serve as- which trigger the cell cycle

platelet derived growth factor is present in blood and triggers neighboring cell to divide to heal a wound

• the cell proliferation signaling pathway binds a growth factor with a specific cell surface receptor, triggers and intracellular signaling pathway, and activates proteins which initiate cell division

G0 phase

• cells are not growing

• cells are not replicating chromosomes

• cells are not dividing

telomeres

• chromosomes have an extra length of DNA on the ends called telomeres, created by the enzyme telomerase

• each time the cell divides, its chromosomes get shorter

• after about 50 cell cycles, the telomere is gone and the cell enters senescence

• limiting the number of cell divisions lessens the risk of cancer

cancer

is a growth disorder of cells

beings when apparently normal cells grow uncontrollably

result is a growing cluster of cells called a tumor

malignant tumors are invasive

metasitasize

cells from malignant tumors can- leaving and spreading to different areas of the body to form new tumors

mutations

cancer is caused by damage- to genes that encode growth factors or gene regulatory sequences

may result from chemical or environmental exposure such as UV rays

viral exposure may also alter DNA

proto-oncogenes

these genes encode proteins that stimulate cell division

when mutated, these genes become oncogenes and can cause cells to divide excessively

tumor suppressor genes

• these genes normally turn off cell division in healthy cells

• when mutated, these genes allow uncontrolled cell division

cell cycle

in about 50 of cancers, the p53 gene malfunctions because of chemical or radiation damage so the protein the gene encodes does not prevent tumor growth

• another common cause of cancer is a mutated MDM2 gene becomes overactive and its protein produce suppresses