Cell Cycle

CSF Exam 3

variation of the cell cycle

different organisms and different cell types within an organism spend different amounts of time in these phases

G1 major function

cell growth

G1 activities

perform regular cellular functions (different in specialized cells)
make proteins and organelles

G1 checkpoint

adjust if something has gone wrong
point where the cell commits to entering cell cycle OR a quiscent state (check internal/external conditions)

reasons to go dormant

DNA damage
size check
nutrient check
function

G0

pause
no longer actively dividing but they maintain metabolic activity
not "dormant" but functional
temporary or permanent

differentiated neurons

stem cells differentiate into neurons and also have self proliferation

its best that not all neurons actively divide

to protect the complex
lack necessary organelles for cell division

reasons for differentiated neurons

dividing neurons could disrupt neural network
loss of learning and memory
what if they don't pass a checkpoint and enter apoptosis

stem cell DO enter G0

quiescent stem cells

mtor

a protein kinase that acts as regulator of cell growth, proliferation, and metabolism by responding to environmental cues (nutrients and growth factors

overactivation of certain pathways can lead to cell death (apoptosis) rather than repair (autophagy)

mtor

quiscent stem cell may differentiate into the wrong type of cells

make lots of glial cells and not mature neurons

S phase - synthesis major function

prepare for cell division

S phase synthesis activities

DNA replication
centrosome replication (begins)

centrosome organelle

microtubule organizing centers that form spindles during cell division
two perpendicular centrioles

DNA replication - major activity in synthesis

enzyme: DNA polymerase
function: synthesize DNA

steps: intiation, elongation, termination

DNA replication initiation

unwind DNA (helicase)
prevent supercoiling using topoisomerase
prevent re-annealing/back together (SSBP)

DNA replication elongation

make short RNA primers (primase)
synthesize new strands off the primers (DNA polymerase)

leading strand

cont 5' to 3'

lagging strand

discontinuous okazaki fragments

DNA replication termination

reach the end of chromosome synthesis
primers removed and new pieces synthesized by polymerase
fragments joined by DNA ligase
(don't have full okazaki fragments)synthetic DNA replication

synthetic DNA replication

polymerase chain reaction PCR - copying DNA in vitro

in vivo cloning

method uses living organisms (bacteria) to replicate gene of interest
1. restriction enzyme cut desired gene from chr and to open circular DNA molecule called vector (plasmid)
2. gene of interest and vector joined together by ligase creating recombinant DNA molecule
3. recombinant DNA is then introduced into bacterial cells
4. as bacteria reproduce, they replicate the recombinant DNA, creating a large number of identical copies of the gene of interest within a clone of bacterial cells

in vitro PCR

amplifies DNA in a test tube w out living cels
1. dsDNA with gene of interest heated to separate strands
2. primers (short DNA seq) bind to ends of gene of interest
3. DNA polymerase syntheizes new complementary DNA strands doubling the amount of DNA
4. repeated in thermal cycler and end up with lots of copies

steps of PCR

1. denature - high heat unwind DNA
2. annealing - specific primers low temp
3. extension - middle temp polymerase adds nucleotides (dNTPs)

when do you have a higher denaturing temp

when you have more GC pairs

longer fragment annealing/denaturation

need longer annealing and denaturation to ensure complete strand separation and efficient primer binding

PCR components

template (thing to be copied)
primers (designed for specific piece)
polymerase (to build the strand)
dNTPs (building blocks)
buffer (keep everyone happy)

G2 major function

grow and make more stuff
prepare for mitosis

G2 activities

make new proteins and organelles
newly duplicated centrosome matures

G2 checkpoint

check for
DNA damage
size check
proper replication

mitosis phase general

mitosis + cytokinesis

mitosis goal

make an identical cell
want a full sel of maternal and paternal chr

chromatid

one of two identical halves of a chromosome

chromosomes are duplicated in S phase

sister chromatids stay paired until separation in mitosis

prophase

condensing the cells
breakdown of nuclear membrane starts (no longer cont)
chr are visible and being to form in nucleus

metaphase

sister chromatids line up along the metaphase plate
nuclear membrane is gone

anaphase

sister chromatids move to opposite poles
early and late anaphases

telophase

nuclear envelope/nucleolus reforms
chromosomes decondense

major players in PMAT

microtubules and centrosomes

prophase major role

centrosomes move to opposite poles and spindle formation begins

prometaphase

spindles attach to chromosomes at the kinetochore

metaphase major role

mitotic spindles are attached and help with orientation/alignment at the metaphase plate

anaphase major role

mitotic spindles help pull chr apart

telophase major role

mitotic spindles have finished their job and are broken down

cytokinesis major function

make two cells
cytoskeleton is the star of the show!

cytokinesis activities

material will split bt cells and a new membrane gets created resulting in two daughter cells

mechanism of cytokinesis

1. microtubules which form the spindle fibers -- signal where the cell will divide (cleavage site)
2. actomyosin ring formed by actin filaments and myosin motor proteins -- contracts to pinch cell in half

failure to enter/stay in G0

this can lead to apoptosis

you cannot make mitochondria from scratch

mitochon made from mitochon
made from mitochondrial fission and fusion

rest of the cell made from golgi (and previosuly mito)

g1: functioning normaly
S/g2: double in size, dissociate from centrosome
g2/prophase: fragments from ribbon structure to small clusters that form stacks —> formation of stacks is g2 checkpoint
metaphase: fragment further into golgi haze
anaphase: disperse
telophase: reassemble

more of the rest of the cell in ER

g1: functioning normaly
s: expansion
g2: lots of grwoth anf function (prep for division)
mitosis
- nuc envelope breaks down and fuses w ER
- structural rearrangement occurs to mostly tubular structure but it stays unified through mitosis
- telophase forms new nuc envelopes and goes back to original form

meiosis is a special type of cell division that takes place in gametes

gaol is to facilitate recombination and sometimes produce different types of cells

what facilitates recombination

the synaptonemal complex
zipper like bridge bt homo chr during prophase 1 holding them together for genetic exchange

male meiosis

four functional sperm cells made by equal division

female meiosis

meiosis 1 assymetrical cell division -- one occyte and 3 polar bodies

selfish genetic elements

increase their own transmission to the next generation even if it harms the organism
female meiosis is a great place to be selfish
want to be in oocyte not polar body