Chapter 12 - C+G Biology

cell division

reproduction of cells

parent cell —> gets bigger (double DNA) —> separates DNA (through mitosis) = 2 daughter cells

• it takes longer for multicellular organisms to reproduce that unicellular organisms 

reproduction for bacteria

binary fission - cell doubles its DNA, gets a little bigger, then splits right down the middle. bacteria can divide really fast 

mulitcellular eukaryotes (organisms) go…

from one cell —> two cells

• reproduce

• GROW

• HEAL

constantly turning over, seen most in puberty but e are always turning over. Cells can get older (that’s why we see more mutations with age)

genome

genetic material of a cell (DNA)

everything that’s living/has cells is a DNA based genome

• viruses have an RNA based genome (non living) 

chromosomes

distinct piece of DNA (with a beginning and an end)

humans have…

46 chromosomes (23 w/ a copy)

every somatic cell has…

46 chromosomes

haploid

(n)

if an organism only has 1 set of chromosomes 

diploid

2 sets of chromosomes (23 from mom, 23 from dad = 46 (you))

this is most human cells 

somatic cells

diploid cells - cells in body that are not reproductive (make up most tissues and organs: heart, brain, liver, lung, etc…) 

any cell that is not sperm/egg depending on your gender 

gametes

haploid cells 

sperm cells for biological man

egg cells for biological female

chromatin

unwound/loose form of DNA

euchromatin

DNA, really unwound form, genes are ON

heterochromatin

DNA, a little less unwound/little more condensed , genes are OFF

sister chromatids

identical copies of a single chromosome that are joined together at a centromere after DNA replication.

the location of centromere classifies the sister chromatid 

if centromere is in the dead middle 

metacentric chromosome 

if centromere is “far” further way from middle/closer to ends

acrocentric

if centromere is off-center (a little bit below, further away)

submetacentric

if centromere is all the way at the end 

telocentric 

acrocentric sister chromatids have

the longest q-arm and shortest p-arm

metacentric chromosomes have

the longest p-arm and shortest q-arm

there are 2 sides of sister chromatin, p-arm and q-arm…

p-arm = the shorter side

q-arm = longer arm 

why does the cell cycle happen

we want to be able to divide our cells (proliferation) = grow, repair, and reproduce

Interphase

largest phase

90% to complete interphase 

G1, S, G2

~ 22 hours to complete out of ~24 hours 

M Phase

10%

~ 2 hours of the ~24 hours 

the cell cycle produces…

2 cells! these can either keep going back and getting divided further or they can come out

G0 phase

cell comes out of cell cycle

these can be either differentiated, senescence, or quiescent cells 

what does “G” stand for 

growth 

what does “S” stand for

synthesis (making DNA)

stem cells

special cells that can both self-renew and develop into other kinds of cells (divide many times, then become specialized) 

differentiated and senescence cells…

once they come out of the cell cycle they will not go back in

differentiated cells

cells that are doing their function (heart, skin, liver cells etc…) doing the function of whatever the tissue requires. they have a role/identity and they look like it. (they are the majority of your cells) 

senescence cells 

STEM cells that have done the cell cycle a lot (40-60 times) before they become senescence. They start to get tired so they don’t go into the cell cycle anymore (don’t divide) but they also don’t due (apoptosis) so they build up in the cell and cause cause diseases (especially in a lot of old folks)

quiescent cells 

cells that have failed a check point (did not exit at the proper time) did not make it to the exit,  stopped at the side of the road 

• can re-enter if issue is fixed, otherwise it will die it issue doesn’t get fixed after ~24 hours (commit apoptosis)

cell cycle will not happen without 

growth factors (which is a type of signaling molecule (usually a protien) that tells cells to grow, survive, or divide)).

cyclins and CDK1 =

cell cycle able to keep happening

CDKI =

no cell cycle

importance of cell cycle regulation

has to be highly regulated - if we don’t regulate our cells and cells are constantly going into cell cycle this leads to cancer — proliferates uncontrollably because it has removed all of the check points. 

G1 checkpoint

also called “R Point” or “restriction point”

checking to see if we got enough growth factors—if we’re receiving signals that we need to divide (go into cell cycle)

go/no go point 

Rb is the protein that is involved in this, usually noted pRb to indicate it is the protein and not the retina blastoma disease)

are there enough growth factors? becomes quiescent if we fail (apoptosis if can’t fix itself)

G2 checkpoint

checking to see if we made DNA correctly 

how we push through G2:

we need a lot of cyclin A, specifically cyclin A (A comes first) bound to CDK1 (Maturation promoting factor) + lot of phosphorylation happening meaning DNA was correct and will pass the G2 check point

if G2 checkpoint is failed it means there was an issue in DNA in the s-phase. apoptosis will happen if it doesn’t pass G2.

regulation

cyclins and cyclin dependent kinases are how G2 and other check points are controlled

cyclin

type of regulatory protein that continues the cell cycle

cyclin dependent kinase

2 proteins come together to form a quaternary complex of cyclins

cyclin dependent kinases can only phosphorylate if they are bound to a cyclin

• they bind to a specific cyclin ad can phosphorylate serine and tyrosine residues 

M checkpoint

controlled by cyclin B (b comes second) and CDK1

cyclin-dependent kinase inhibitors

inhibit CDK1//CDKI

• p21 is a classic example (phosphatases, remove phosphate groups/block activity)

pRb’s job is…

to bind and sequester (block/inhibit/pull away) E2F - if E2F is released this will push is into S phase

if Rb is phosphorylated —> conformational change = release of E2F (passes check point bc/ there were enough growth factors to cause phosphorylation cascade)

pRb bound to E2F = fail check point (needs to be phosphorylated/released in order to pass

hypophosphorylation

1st complex

cyclin D + CDK 4/6

1 phosphate 

hyperphosphorylation

2nd complex

cyclin E + CDK 2

lots pf phosphate groups (causes shape change) 

mitosis 

separate DNA in half 

if we fail mitosis/checkpoints = cancer

human cells are typically diploid (46 chromosomes in diploid cells)

G2 phase

metabolic activity, growth prep for cell division (getting ready for M phase)

2 centrosomes form (composed of 2 centrioles each) moves to either end of the cell

• DNA = chromatin but duplicated 

prophase 

1st phase of mitosis 

• DNA = chromosomes form, each joined to sister chromatid

• nucleoli disappear, nuclear envelope phosphorylated 

• mitotic spindle forms (made of microtubules): move and separate DNA (moved to either end) 

centrosomes move away from each other 

pro-metaphase

2nd phase of mitosis - transitionary phase 

• nuclear envelope is completely gone (fragments) —> in process of moving it to the middle

• microtubules attach at kinetochore (site) on centromere of chromatids (these are called kinetochore microtubules) 

• non-kinetochore microtubules (do not bind to kinetochore) — lengthen the cell 

DNA = sister chromatids fused

metaphase

3rd phase - “middle”

• chromosomes will arrive at metaphase plate (single line of 46 chromosomes for humans)

• DNA = sister chromatids fused 

• M checkpoint = all checkpoints attached to microtubules Question: have we fused the microtubules to the kinetochore (so that DNA will be equally separated) 

• M checkpoint: regulated by cyclin B and CDK1 — if we FAIL this, cel will become quiescent (standby cell waiting to be fixed to enter cycle or die by committing apoptosis)

anaphase

if we pass M check point

• sister chromatids are pulled apart from each other

• DNA = chromosomes, no sister 

telophase

opposite of prophase

end of mitosis 

• 2 nuclei begin to form

• nucleoli reappear

• mitotic spindle breaks down 

cytokinesis

equal divide of cell in half

actin based microfilament (squeezing cell by actin ring) squeeze to pinch into 2 cells 

actin = protein that forms microfilaments

microfilaments = long thin fibers made of the protein actin that help the cell maintain its shape, move, and divide 

• cleavage furrow -  The cleavage furrow is a shallow indentation or pinching that forms on the cell’s surface during cytokinesis (the last step of mitosis).
  It marks the site where the cell membrane will divide to create two daughter cells.

• inhibiting action doesn’t allow cytokinesis 

carcinoma

epithelial tissue (lining tissue) lung/skin

• adenocarcinoma - secretary epithelial (something that secretes)

how is the type of cancer determined?

which cell became the tumor

sarcoma

connective tissue (bones)

lymphoma

blood cells (hematopoietic - fancy scientific names for blood cells)

lukemia

sub type of lukemia = derived T-cells or B-cells (childhood cancers)

neuroectodermal

nervous system

teraromas 

freaky cancel cells w/ teeth and hair (demon babies) 

risk factors of cancer

• hereditary

• UV radiation

• chemicals

• viruses

• smoking

• cells dividing