Lecture 17-19: Cell Division Flashcards
three reasons why cells divide:
reproduction
growth of an organism
repair/replacement of lost cells
the three broad categories cells can be grouped into based on their involvement in the cell cycle:
- Cells that do not cycle, but stay in a resting state (G0)
- Cells that normally do not divide, but can be induced to if needed
- Cells that divide regularly
what is a cell’s genetic information called?
genome
what is DNA packaged into?
chromosomes
chromatin (what makes up chromosomes) is composed of what two things:
1 DNA molecule and associated proteins (histones)
______ contain several hundred to thousand genes:
chromosomes
what is the actively expressed part of the chromosome? (i.e when cell is not dividing)
euchromatin
what are somatic cells?
cells that aren’t gametes
how many chromosomes are in human somatic cells?
46 chromosomes (2 sets of 23)
cell division results in genetically identical ________
daughter cells
a chromosome has a constriction called the _____
centromere
what is the centromere composed of?
repetitive sequences in the DNA
how are sister chromatids held together?
by cohesion proteins
______ separates the sister chromatids into 2 chromosomes and distributes one to each daughter cell
mitosis
what separates the cytoplasm?
cytokinesis
cell cycle = ?
time it takes from one cell division event to the next
the five stages of mitosis:
prophase
prometaphase
metaphase
anaphase
telophase
cytokinesis
actin microfilaments and mysoin are used in animal cells for what?
cytokinesis: they form a ring in the cytoplasm, which contracts using ATP -> making a cleavage furrow (like a drawstring bag!)
do plant cells have a cleavage furrow?
No!
what do plant cells use instead of a cleavage furrow?
form a cell plate (using vesicles to deliver materials) in between cell walls (made of carbohydrates/cellulose) which then cuts the cell in half and separates the cells
what is binary fission?
a form of asexual reproduction in prokaryotes
how is the DNA replicated using binary fission in prokaryotes?
begins replicating DNA from a single point in the circular DNA
what is the origin of replication?
the original point where DNA is replicated in prokaryotes using binary fission
is mitosis possible without cytokinesis?
yes! results in one huge cell
can cells divide at different rates within the organism?
yes! it all depends on cell function and location (ex. skin cells divide all the time, liver cells cand divide but only when needed)
three main checkpoints in the cell cycle control system:
G1, G2, M
why do we have checkpoints in the cell cycle?
to make sure everything passes certain conditions before the cycle continues! (i.e to catch mistakes!)
the cell cycle control system is regulated by ____ and ________
cyclins and cyclin-dependant kinases
what are cyclins?
proteins with fluctuating concentrations within the cytoplasm
when do cyclins attach to cyclin-dependant kinases to form complexes?
if the concentration of cyclin is high enough
why do cyclins attach to cyclin-dependant kinases to form complexes?
the kinase activates other proteins, causing the cell to proceed in the cycle!
when is cyclin degraded (inactivating the kinase)?
at the end of the cycle
what are the three parts of the maturation-promoting factor (MPF)?
a kinase, cyclin and a phosphate group
when does the G1 checkpoint occur?
before the S phase
which cells don’t pass the G1 checkpoint?
neurons and non-dividing cells
when does the G2 checkpoint occur?
before mitosis
which checkpoint interacts with MPF?
G2 checkpoint
when does the M checkpoint occur?
during metaphase
what is aneuploidy?
incorrect number of chromosomes
what causes cancer?
when a group of cells uncontrollably divide
what does it mean when a tumor is benign?
when abnormal cells cant spread, easily removable by surgery
what does it mean when cells are malignant?
the cells have enough mutations that they can spread throughout the body, resulting in cancer
basic explanation of the Hershey and Chase experiment:
showed that the phage T2 DNA was the mechanism for the virus to reprogram host cells, they saw that the DNA entered the cell but the protein remained external
DNA has _______ bases
nitrogenous
what are the two purine bases?
adenosine (A) and guanine (G)
what are the two pyrmidine bases?
thymine (T) and cytosine (C)
what kind of bonds hold DNA strands together?
hydrogen bonds
each DNA strand serves as a template to make _____ new complementary strands
two
prokaryotes have ______ DNA
circular
where does replication begin in prokaryotes?
origins of replication (ORI’s), a specific sequence of DNA nucleotides
_______ is the main enzyme that catalyses the DNA synthesis
DNA polymerase III
DAN synthesis is only completed in what direction?
5’ to 3’
when the lagging strand is sythesised, it creates fragments called…?
okazaki fragments
what is the solution for staggered ends in DAN replication?
telomeres!
what is a telomere?
a short, repeated DNA sequences and specific proetins that protect the ends of chromosomes
germline cells that produce gametes make an enzyme called ______ which extends the telomeres to 100% length
telomerase
What happens when incorrect nucleotides are missed in DNA replication?
mismatch repair
can errors happen after replication?
yes! examples include UV radiation, cigarette smoke and other chemicals
what are histones?
positively charged proteins that initially pack the chromatin
four forms of chromatin during cell division:
chromatin -> heterochromatin -> euchromatin -> chromosomes
