cell division/ mitosis Flashcards
Prokaryotes don’t have— in cell division so can’t perform certain tasks
No nucleus so no mitosis
No microtubules or motor proteins to move chromosome.
Divide by Prokaryotic fission
How do prokaryotes divide
Divide by Prokaryotic fission
Prokaryotic fission
single circular chromosome binds to cell membrane
DNA replication in both directions around circle
Cell divides by adding to cell membrane
Eukaryotic cells have (blank) And (blank) is needed for cell division which is divided into (blank) parts
DNA contained in nuclear membrane DNA replicated prior to nuclear division ( in interphase) Microtubules and microfilaments needed Motor proteins and ATP required Cell division divided into two parts
what are the two parts to eukaryotic cell division
mitosis = division of nucleus cytokinesis = division of cytoplasm
Mitosis
produces clones (daughter cells) divides nucleus
mitosis in unicellular organisms
reproduction
mitosis in multicellular organisms
asexual reproduction (budding)
growth
replacement
repair
Meiosis
produces haploid cells (chromosome number cut in ½ non-identical cells gametes) only done for sexual reproduction
somatic cell
Somatic cell –
normal diploid body cell
diploid cell
Diploid cell –
has 2 copies of each chromosome
haploid cell
Haploid cell –
has 1 copy of each chromosome
chromosome
Chromosome –
naturally occurring segment of DNA and associated proteins
chromatin
DNA wrapped around histones
no supercoiling
Most DNA available for transcription
not visible under microscope
chromatid
nucleosomes supercoiled into compact ‘arms’
DNA packaged for transport not use
condensed chromosomes visible
centromere
constriction in center of chromatids, a region of DNA that binds to cohesin proteins that function to hold sister chromatids together
cohesins
hold sister chromatids together more loosely along their lengths
sister chromatids
Identical
Formed by semi-conservative replication
While joined at centromere = 1 chromosome
semiconservative replication
parent strand splits into two new molecules. each new one contains one parent strand and one new complimentary strand
unduplicated
One chromosome
One chromatid
One double helix
duplicated
One chromosome
(one centromere)
Two chromatids
Two double helixes
genome
all of a cells DNA
All eukaryotes have set # Chromosome in their genome
how many genomes do humans have
46 two of each type, 23 different types
Mitotic Spindle formation
Tubulin subunits in centrosome begin to assemble into microtubules
microtubules grow toward the center to form spindle fibers
short microtubules form a radial array called an aster
centrioles present in animals but not needed
what is an aster
short microtubules that form a radial array
kinetochore
proteins located at centromere
Attachment site for some microtubules of spindle
Polar microtubules overlap with microtubules from opposite pole at center of cell
prophase
Centrosomes begin producing microtubules & moving toward opposite poles
Chromosomes condense into… chromatids
Nucleoli disappear.
pro metaphase
Nuclear envelope breaks down
Microtubules attach to …kinetochores
Polar microtubules overlap at equator
metaphase
Chromosomes lined up at equator Pulled by kinetochore microtubules C line up single file, One sister chromatid on each side Centrosomes reach poles
anaphase
Cohesin proteins cleaved by Separase enzymes
Separated sister chromatids move toward opposite poles
Kinetochore microtubules shrink as they depolymerize at centrosome
Motor proteins drag chromatids along shrinking microtubules toward poles
Cell elongates as motor proteins push polar microtubules past each other
telophase
Begins when chromatids reach poles Microtubules disassemble Nuclear envelope reforms Chromosomes de-condense into chromatin
When does cytokinesis start, is it different for animals and plants and does it always happen?
Cytokinesis begins before mitosis is complete
Different in plants and animals
Does not always take place
Animal cell cytokinesis
Contractile Ring Mechanism
1) a band of microfilaments of the cell cortex contracts
2) indentation forms : cleavage furrow
3) ring contracts until cell membrane is pinched in 2
myosin motor proteins
Move actin filaments
Past each other to tighten ring
Plant Cytokinesis
Cell Plate Formation
Vesicles containing cell wall components move
from golgi to equator
Merging vesicle membranes form new cell membrane
Cell wall components assembled in center of merging vesicles form new primary cell wall
primary cell wall
flexible stretchy allows growth
secondary cell wall
deposited inside primary wall
solid, inflexible, support wall
Cell Cycle – Pattern of stages in cell life
Interphase – time spent between cell divisions
(90% of cell cycle)
Mitosis – nuclear division
Cytokinesis – cytoplasmic division
interphase three sub phases
G1-gap one
S- synthesis
G2- gap 2
interphase gap one
gap 1- cell grows ( max size based on..SA:V ratio)
cell performs its function for the body
cell may never leave G1 (ex nerve cells = G0)
interphase synthesis
synthesis :entire genome is synthesized
by semi-conservative replication
Growth and cell function continue
interphase gap two
cell grows & prepares to divide duplicates centrosomes & centrioles (not required: present in animals)
G0
some cells that almost never divide are said to be stuck in G0
time for interphase and sub phases
Usually, cells will take interphase 18 -20 hours.
G1 – highly variable
some cells are in G1 only long enough to grow
some almost never divide and are said to enter G0
S phase 5 -6 hours
G2 3 -4 hours in most cells.
Mitosis, & cytokinesis only takes about 2 hours
cell cycle is controlled by
checkpoints
checkpoints
places where the cell cycle stops
Cell cycle only resumes if certain criteria are met
how does cell signal criteria has been met
by making checkpoint proteins called cyclins.
Cyclins activate
Cyclin Dependent Kinases (CDKs)
Cyclin Dependent Kinases (CDKs)
act to signal the cell to move on to the next step in the cell cycle.
a type of Kinase that only functions when bound to cyclin.
what is activated when all criteria for a checkpoint are met
the check point gene for that checkpoint is activated
checkpoint gene
contains the instructions for making one specific checkpoint protein (cyclin).
checkpoint protein is also known as
cyclin
what is the chain reaction with cyclin
Production of that particular cyclin for the checkpoint gene activates a specific CDK which sets of a chain of reactions that lets the cell cycle pass that checkpoint and continue the cell cycle.
what happens after cyclin is used
it breaks down after one use and the levels of that type of cyclin drop
do CDK levels remain constant or change
remain constant, they stay the same but cyclin is the one broken down and rebuilt
the cell cycle is controlled by changing levels of
cyclin
kinase
group of enzymes that phosphorylate proteins (activate them)
what do activated CDKs do
phosphorylates a protein.
what does phosphorylating a protein does
Activating (phosphorylating) that proteins sets off a transduction cascade that transduces the signal to proceed to the next checkpoint
Animal cells stay in G1 or G0 unless signaled by
growth factors
checkpoints are regulated by
CDKs
G1 checkpoint
cycle initiation
a) controlled by cell size
b) growth factors
c) environment
G2 checkpoint
transition to M
a) DNA replication complete b) DNA damage/mutations
M spindle checkpoint
spindle attachment
growth factors
are Signal molecules
released by cells to signal nearby cells to divide
Process of growth factors
They diffuse through intracellular fluids
bind to membrane receptors on target cell
transduction of signal causes cyclin production
cyclins activate CDK CDK phosphorylates first protein of cascade that moves cell past G1 checkpoint
what are an example of cell to cell communication
growth factors
example of growth factor
Platelet-derived Growth Factor
PDGF released by platelets cause
Fibroblast(wound repair) cells to divide
PDGF process
PDGF binds to receptor on Fibroblast
signal transduction pathway initiated
cell passes G1 checkpoint and starts to divide
Cyclin-CKD example
MPF
M-phase Promoting Factor, CDK cyclin complex
MPF steps
checkpoint gene for MPF cyclin is activated
MPF cyclin levels build up & build MPF levels
High enough concentration of MPF allows Cell to move from G2 into M phase
MPF concentration reduced in Anaphase by breakdown of cyclin causing MPF to revert to inactive CDK
CKI
Cyclin Dependent Kinase Inhibitors
stop the CDK enzymes from working
CKI example
CKI p21 stops CDK2 from working…thus
Stopping the transition from G1 – S phase
The CKI inhibitor molecule p21 is only active when
tumor suppressor gene p53 is transcribed (copied)
normal Cell Division limited by
Density-dependent Inhibition: cells that are crowded stop dividing
Anchorage dependency: cell must be anchored to extra-cellular matrix of a tissue to divide
Cell Division in Cancer Cells (the do nots)
Cancer Cells NOT inhibited by density or anchorage
CC do NOT stop dividing when out of Growth Factor
CC do not follow signals of check point genes
CC do not self-destruct by apoptosis
origin of cancer cells
Cancer cells avoid —
1 cell undergoes transformation (damage to DNA) Transformed cell avoids immune system avoids apoptosis ignores regular cell cycle signals uncontrolled cell division
Benign tumor
cells stay anchored
Malignant tumor
cells spread = cancer
Metastasis
spread of cancer cells
Uncontrolled cell division
Results from the failure of more than one checkpoint gene
Which causes non-functional checkpoint proteins
Causes tumor development
May cause cancer
Cancer Cell Changes
Mutation of Check Point Genes
Change in chromosome number/structure
Abnormal/irregular cell membrane lacks attachment proteins damaged signal/receptor proteins
Secrete signal molecules that encourage blood vessel growth
Cancer Treatment
radiation or chemotherapy
radiation
for localized tumor
chemotherapy
poisons most damaging to dividng cells
