Cell Division Flashcards
what is a genome?
a cell’s total DNA
how many genes is a genome made up of?
~20,000 genes
where is prokaryote DNA found?
in a single circle called the nucleoid
small circles called plasmids
eukaryote DNA
several DNA double helices packaged into chromosomes
what form is a cell’s DNA during interphase?
is in loose form called chromatin
what happens to DNA during prophase?
condenses from chromatin to tightly coiled structure called chromosomes
what is another term for body cell?
somatic cell
how many chromosomes do human somatic cells have?
46 chromosomes
how many chromosomes do you have in a liver cell? skin cell? eye cell?
all cells in the body contain 46 chromosomes
cell division enable the genome of one somatic cell to be passed onto what?
two daughter cells
what happens during Mitosis (M phase) ?
divides the nucleus and sister chromatids and is immediately followed by cytokinesis
what happens during cytokinesis?
divides entire cell/cytoplasm
what does mitosis consist of?
prophase, metaphase, anaphase, telophase
what does mitosis and cytokinesis enable organisms to do? (2)
grow and develop
allows for tissue renewal
what happens when a unicellular organism undergoes mitosis/cytokinesis?
an entire new organism is created
what happens to the number of chromosomes during cell cycle?
chromosomes in somatic cells first make copies of themselves, so 46 becomes 92 during S phase. then it goes back to 46 per cell when the cell divided into 2 new daughter cells in the M phase
what happens during S phase?
DNA replication - helicase, polymerase, ligase etc all work
what does the cell cycle describe?
the sequence of events that occur during each phase of a cell’s life
in what phase do cells spend most of their lives in?
interphase
what is interphase made up of?
G1 (1st gap)
S (Synthesis of DNA)
G2 (2nd gap)
what happens to cells during G1 phase? (2)
grows
make proteins and organelles
what happens to cells during S phase? (3)
grow
make proteins and organelles
copy their DNA (2 sister chromatids)
what happens to cells during G2 phase? (3)
grow
make proteins and organelles
make sure the cell is ready to enter into the M phase
what happens to a cell after the M phase?
cell cycle either repeat or cell can become dormant (G0)
characteristics of Early Prophase? (3)
chromatin condenses into 2 identical sister chromatids
nucleolus disappears
spindle apparatus starts to form that extend from the asters and centrioles
what is the spindle apparatus made of?
microtubules - tubulin
what do the asters and centrioles together make up?
centrosomes
characteristics of Late Prophase/Prometaphase (3)
nuclear envelope breaks down
microtubules attach to kinetochores
Nonkinetochore microtubules form
what are kinetochores?
protein structure on the outside of each sister chromatids
metaphase characteristics (3)
spindle apparatus is complete
sister chromatids line up at the metaphase plate
nonkinetochore microtubules overlap
what is the metaphase plate?
equator of the cell
anaphase characteristics (2)
sister chromatids split and are now considered as chromosomes
chromosomes move toward opposite poles
telophase characteristics (4)
cell elongates and begins to pinch inwards (cytokinesis)
nuclear envelope reforms
nucleolus reappears
chromosome start to loosen back into chromatin
what does the spindle apparatus include? (4)
centrosomes
non-kinetochore microtubules
kinetochore microtubules
centrioles
what are centrosomes made up of?
centriole pair at a right angle and aster
what are asters?
microtubules in a star shape
how can aster microtubules elongate?
adding more protein tubulin
what do non kinetochore microtubules do? (2)
never attach to kinetochore of sister chromatids
enable entire cell to lengthen
what do kinetochore microtubules do? (2)
attach to the kinetochore of sister chromatids during late prophase/prometaphase
pull sisters apart and shorten as they get near the pole
where are centrioles found?
animal cells only
when are centrioles replicated?
interphase
as chromosomes move toward their respective poled, what happens to the microtubules?
they shorten on the side attached to the chromosomes - piece of the microtubule break off into small tubulin subunits
cytokinesis in plants
plant cells build a cell plate formed from vesicles
cytokinesis in animals
occurs by forming a cleavage furrow
what is a cleavage furrow?
a groove in the cell near the old metaphase plate created by microfilaments
unicellular organism cell division differences
nuclear membrane does not break down even though spindle apparatus forms
what does the difference in cell division between unicellular and multicellular organisms serves as?
a possible indication that this is an intermediate stage to the evolution to mitosis
who do mitosis?
eukaryotes
what do bacteria/prokaryotes do for cell division?
binary fission
what happens during binary fission?
bacteria copy their DNA and attach it to the cell membrane, the cell lengthen, and then the cell divides into two
what are needed to regulate the cell cycle?
chemical checkpoints
what do chemical checkpoints act as?
gate keepers that tell the cell to go or stop dividing
which cells divide frequently?
skin and sperm cells
which do not divide in an adult?
liver and muscle (unless injured)
most neurons (some can regenerate)
how many major checkpoints are in the cell cyle?
3 - can be found in G1, G2, and M phases
G1 checkpoint
most important in terms of energy consumption - determines if a cell will get the “go signal” or be switched to an inactive/G0 state
what is Cdk?
cyclin dependent kinases
what are cdks?
enzymes that carry phosphates from ATP
does Cdk get used up?
no - it’s an enzyme so it gets reused
how does Cdk work?
it has an active site where a specific molecule can bind
needs to bind to a protein called cyclin to be “active”
derivation of the name cyclin
it cycles/fluctuates its concentrations/gets brown down after G2
what happens to cdk at G1
Cdk + ATP –> Cdk (w/ 2 organic phosphates) + AMP
cdk at G2
cyclin attached to cdk with 2 organic phosphates
when cdk comes together with cyclin, what is thus complex called?
MPF- M phase Promoting Factor
what does MPF activate?
the passage from the G2 checkpoint into the M phase
what happens to MPF in mitosis?
the 2 phosphates break off and are used to phosphorylate other reactions in mitosis like breaking up nuclear envelope
cyclin breaks down and Cdk can be used again
what is the M checkpoint important for?
to make sure that daughter cells each end up with 1 copy of each chromosome
where in mitosis does the M-phase checkpoint occur?
end of metaphase/before anaphase
what are internal factors that influence cell division?
checkpoints in the somatic cell cycle
example of external factor that influence cell division
growth factor - protein that some cells secrete externally to trigger neighboring cells to divide
PDGF
Platelet derived growth factor - released from platelets and it causes connective tissue to divide and allow wounds to heal
under what cases do cells exhibit density-dependent inhibition?
normal
what is density dependent inhibition in cells?
when cells get crowded, they stop dividing
what other characteristic do normal cells have?
anchorage - in order to divide, the cell must be attached to something`
what is cancer
uncontrolled cell division (no density dependent inhibition) and has no anchorage
what do cancer cells do to other cells?
divide uncontrollably and invade other tissues
at what points do cancerous cells stop dividing (if they even do)?
often at abnormal points in the cell cycle- not G0
in a lab situation, what can cancer cells become?
immortal
what are HeLa cells?
one cancerous cell line that has been dividing in a lab since 1951
named after Henriette Lacks who died of cervical cancer as a result of HPV
normal cell lifespan
normal cells divide between 20-50 times before they stop dividing, age, and die (apoptosis)
tumor
mass of abnormal cells
benign tumor (2)
slow dividing and localized at original site
malignant tumor (2)
rapidly dividing and impairs the function of one or more organs near by
metastasis
cancer spreads beyond original site by blood or lymph vessels (lymphatic system- immune)
available treatments for cancer (4)
- cut - biopsy + surgery
- burn - radiotherapy
- poison - chemotherapy
- immunotherapy - mixture of three, try to train immune system to kill cancer rather than destroying cancer cells directly
