cell cycle and mitosis Flashcards
why do cells divide?
growth, repair, reproduce
prokaryotic cell division
cell division occurs through binary fission
dont require any signal
as long as there are nutrients in the environment they will divide
divide very rapidly, every 30 minutes
DNA in prokaryotes is usually a single chromosome that takes the form of a closed circle, so it must be extremely tightly folded
how do prokaryotes divide?
origin of replication (ori) is where replication starts
as replication starts there will be two copies of the origin of replication
these two origins will move away from each other and become tethered to the plasma membrane of the cell
origins will be pulled apart from one another in opposite directions
movement of origins of replication moving apart results in the one bacterial cell pinching in the middle to form two cells
fission results in two daughter cells
how is eukaryotic and prokaryotic division different
eukaryotes are larger and more complex with large numbers of chromosomes, many organelles, an endomembrane system, and a cytoskeleton that must be properly replicated and distributed equally to the daughter cells
cell division is rarely continuous and is regulated
need a signal to divide
why is it important to regulate cell division in multicellular organisms?
if you divide uncontrollably you can generate extra tissue or tumors
genome
collection of all dna blueprints of organism
how do we package 2m worth of DNA into a cell
package dna into chromosomes
chromosomes
linear DNA molecules with many proteins
contain hundreds to thousands of genes
humans have 46 chromosomes/ 23 pairs of them
somatic cells are diploid
somatic cells
all cells but sexual cells (gametes—> eggs/sperms)
having diploid chromosomes means what
we have two copies of each gene
one from male and one from female
centromere
waist that connects the chromatids of a paired chromatids
repetitive sequences of DNA bound by centromeric proteins
loci
specific location of a gene on a chromosome
alleles
versions of genes
same loci on a chromosome
difference in alleles changes the type of protein produced by the blueprint
what is constituted as a chromosome
I I is two chromosomes X is one chromosome
diploid
when you have two of the same version of chromosome
haploid
when u only have one subset of a pair of homologous chromosomes
cohesin
proteins that attach along the entire length of chromosomes to keep paired chromatids together
because we have very large genomes, packing them has to be a very precise, controlled process
thus we use
histones
histones charge
mostly positively charged in the point of contact with dna
important because dna is negatively charged due to its negatively charged phosphates
what connects histone clusters
linker dna
histone clusters are called
nucleosomes
what does the distance between nucleosomes change
how accessible the dna is gonna be for transcription (more or less)
chromatin
dna-histone complex
come as either heterochromatin(tightly packed nucleosome complex) or euchromatin (relaxed fit of nucleeosomes)
example of heterochromatin
chromosomes
tightly packed
karyotype
the number and size and shape of chromosomes
chromosome duplication
process called mitosis
chromosome replicates, creating two copies of each of its genes —> results in paired chromatids connected by cohesin proteins
mitosis separates the two paired chromatids from one another into two chromosomes in different daughter cells
results in two daughter cells that are genetically identical copies of the original cell
no genetic variation between daughter cells and parent cell
eukaryotic cell cycle
4 phases
G1 phase
S phase
G2 phase
m phase
interphase
every phase other than m phase
m phase general descriotion
mitosis
division of DNA inside the cell (division of nucelus)
cytokinesis also occurs (division of daughter cells)
G1 phase
gap 1
period between M phase and S phase
phase where cell carries out its function until something signals it to divide
S phase
dna synthesis phase
replication occurs – > replicated chromosomes
replicated DNA
G2 phase
replicate everything other than DNA
- ER, organelles, cytoskeleton, etc
how is the cell cycle regulated
checkpoints
G1, G2 M checkpoints
G1 checkpoint
after signal is received to replicate, the cell ensures it is in the right shape to do so
ensure that all the genes are in the right place and shape —> so that they are functional
G2 checkpoint
ensure copies are correct and everything has been replicated
M checkpoint
ensure dna is going to be properly divided
experiment where cells in one phase of cell cycle are fused with a cell in a different phase
fusing cells allows the cells to move to a different phase of cell cycle (dependent on what phase the other cell was in)
Sharing cytoplasm allowed for this change in phase, due to CDKs presence
kinases
a protein that adds a phosphate group to a protein (phosphorylate)
Cyclin dependent kinases
a kinase that requires cyclin to work
CDK will phosphorylate many proteins and activate or inhibit their activity
Covalently add phosphate to proteins and regulate how they work
CDK is always there but its active site is not always exposed
Cyclin is made when the cell must move to the next phase/ when it is required
Cyclin binding to cdk changes its conformation, exposing its active site
A protein substrate and ATP bind to cdk and protein is phosphorylated
How cdk governs the cell cycle
Many pairs of cyclin and cdk
Work as checkpoint of cell cycle
example of cdk
Maturation promoting factor (MPF)
Exists between G2 and M phase at a checkpoint
Allows for cell to go into mitosis
Cyclin concentration goes down after M phase, so MPF activity also goes down
Checkpoint triggers
G1
Dna damage
S
Incomplete replication or DNA damage
G2
Dna damage
M
Chromosome unattached to spindle
Mitosis
Goal:
Separate duplicated DNA in the chromosome to the 2 daughter cells
The daughter cells are genetically identical
5 phases of mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
mitosis interphase
Pre-mitosis stages
Nuclear envelope encloses nucleus
Nucleus still maintains nucleolus
Two centrosomes(make spindle fibers) have formed by duplication
Chromosomes are duplicated during S-phase but have yet to condense
mitosis prophase
Chromatin fibers become tightly coiled and condense into discrete chromosomes
Nucleoli disappear ( nucleolus)
Each duplicated chromosome appears as two identical paired chromatids joined at the centromere
Mitotic spindle begins to form
Centromeres move away from one another (waist of chromosomes)
Want to center in the cell
mitosis prometaphase
Nuclear envelope fragments
Microtubules extend from each centrosome, invading ex-nuclear space
Kinetochores. A specialized protein structure, forms at the centromere of each chromatid
metaphase
Centrosomes(type of mtoc) are now at opposite poles of the cell
Chromosomes have arrived at metaphase plate (center of ell)
Plane that is equidistant between spindles two poles
The kinetochores of paired chromatids attach to kinetochore microtubules coming from each pole
Mitotic spindle
assembly of microtubules and their associated proteins that move chromatids around
Kinetochore microtubules attach to chromatids at their centromeres
Polar microtubules
Microtubules that don’t attach to kinetochores but serve to center the spindle
Aster
Serve to center spindle in the cell
anaphase mitosis
Cohesin protein degrades, allowing sister chromatids to part
Each chromatid is now an independent chromosome
Daughter chromosomes move towards opposite ends of cell as kinetochore microtubules shorten
Polar microtubules extend, pushing cell apart
mitosis telophase
Two daughter nuc;lei form in the cell, nuclear envelope arise from fragments of parent cell’s nucleus
Nucleoli reappear
Chromosomes decondense
Spindle microtubules depolymerase
Cytokinesis
Break two cells apart
In animals
You develop a contractual ring of microfilaments (pinch)
In plant cells
Vesicles form cell plate creating a new cell wall/cell plate
