Mitosis and Meiosis

Roles of Cell Division in a cell

Roles of Cell Division in a cell

Growth of an organism, repair of worn out cells, Asexual reproduction

Genome

All the DNA (usually packaged into chromosomes) in a cell

Chromosomes

an organized form of DNA (in the form of chromatin) that is packaged up in preperation for cell division

Somatic cells

non-reproductive cells w/ two sets of chromosomes (2n)

ex: human cells w/ 46 (23 in each set)

Gamete Cells

reproductive cells with one set of chromosomes (n)

ex: sperm and egg with 23

chromatin

the unraveled “messy” version of chromosomes, found in the cell almost always until it turns into chromosomes before cell division

chromatid

a copy of a chromosome joined to another sister chromatid along their lengths (via cohesions)

centromere

the narrow waist of the chromosome where two chromatids are closely attatched

Phases of the cell cycle

Interphase : Cell growth (G1), DNA replication (S), mitosis preperation (G2)

Mitosis (Cell division): Prophase, Prometaphase, metaphase, anaphase, telophase, cytokinisis

Characteristics of prophase

• nucleolus dissapears

• chromatin fibers begin to coil and condense into chromosomes (2 sister chromatids)

• mitotic spindle begins to form

• Centrosomes begin to move away from eachother

Characteristics of prometaphase

• nuclear envelope breaks

• microtubules, both kinetechore and not, from centrosome begin to move chromosomes or lengthen cell

• chromosomes are more condensed

• kinetochore formed at each sister chromatid

Characteristics of metaphase

• centrosomes are now at cell poles

• chromosomes align at metaphase plate after being pushed by microtubules

• kinetochores of each chromatid are attached to the kinetochore-microtubule

Characteristics of anaphase

• shortest stage

• cohesion proteins keeping together sister chromatids are cleaved and they can part to become their own chromosomes

• 2 new daughter chromosomes for each original move towards cell pole

• kinetechore microtubules shorten to pull them

• nonkinetochore microtubules lengthen the cell by overlapping and pushing against each other

Characteristics of telophase

• two daughter nuceli reform

• nuclear envelopes reform from the fragments

• nucleoli reform

• chromosomes begin to uncondense

• spindle microtubules dissapear

cytokinesis

• two daughter cells form

• cleavege furrow formed in animal cellls

• new cell wall formed in animal cells

mitotic spindle

a structure made of microtubules that controls chromosome movement during mitosis. consists of centrosome pairs, spindle microtubules, and asters (array of short microtubules extending from censtrosome)

kinetochore

protein complex associated w centromeres and attatched to each sister chromatin. attatches to kinetochore microtubules

metaphase plate

imaginary line down the middle of the cell where chromosomes align during metaphase

kinetechore microtubules

extend from the centrosomes and attactch to kinetichores on each chromatid pair. pulls them to the middle and eventually apart

non kinetochore microtubules

overlap and push up against eachother to elongate the cell

binary fission

how prokaryotes such as bacteria duplicate. chromosomes rpelicate at origin of replication, move apart, and the plasma membrane pinches in two

cell cycle control system

internal and external controls that regulate the cell cycle, characterized by checkpoints

cyclins

a regulatory protein involved in cell cycle control named for cyclically fluctuating conc. in cell

cyclin dependent kinases (cdks)

must be attached to cyclin to be active, activity rises and falls along w cyclin conc.

MPF(Maturating promoting factor)

a cyclin cdk complex that triggers a cells passage past the g2 phase into the mitotic phase

g1 checkpoint

at this point, if it recieves a check the cell usually goes through all other phases and divides normally. if it doesnt, the cell will switch to the nondividing g0 phase

growth factors

factors released by other cells that stimulate others to divide

density dependent inhibition

cells stop dividing once they reach a certain density

anchorage dependence

to divide, a cell must be attatched to a substratum

benign tumors

cancerous cells remain at the original site and do not spread

malignant tumors

cancerous cells invade surrounding tissue and undergo metastasis

metastasis

the spread of cancer cells to other parts of the body

Heredity

The transmission of traits from one generation to the next

Gene

are the units of heredity and are made up of segments of DNA

locus

A gene’s specific position along a chromosome

asexual reproduction

a single individual passes all of its genes to its offspring without the fusion of gametes & makes clones (exact copies)

sexual reproduction

2 parents give rise to offspring that have unique combinations of genes inherited from the 2 parents

life cycle

the generation-to-generation sequence of stages in the reproductive history of an organism

karyotype

an ordered display of the pairs of chromosomes from a cell (homologous pairs)

homologs/homologous chromosomes

the chromosomes that make up a homologous pair

sex chromosomes

determine the sex of the individual (X and Y, XX = girl XY = boy)

diploid vs haploid chromosome number

diploid = 2n (ex: 46), haploid = n (ex: 23)

fertilization

the union of gametes (the sperm and the egg)

zygote

The fertilized egg with one set of chromosomes from each parent

meiosis 1

homologous chromosomes are seperated into two haploid cell each w 23 chromosomes in humans (meiosis isnt done yet, because each chromosome still has a pair of sister chromatids)

meiosis 2

the haploid cells from meiosis 1 each seperate again into 2 more haploid cells each w 23 chromosomes in humans (no more pairs of sister chromatids, just chromatin now)

events/traits unique to meiosis

in both meiosis 1 and 2, the same steps as mitosis happen except:

1. Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information (switching it up to give variety)

2. Alignment of homologous pairs at the metaphase plate (instead of seperate chromosomes, they align in pairs)

3. Separation of homologs during anaphase I (instead of sister chromatid sepertaion, just the homologs seperate for now)

4. Starting meiosis 2 with haploid cells instead of diploid ones (half the num of chromosomes as usual)

mitosis vs meiosis (productwise)

mitosis produces 2 diploid cells that are identical clones. meiosis produces 4 haploid cells that all vary due to chromosomes being switched around between father and mother genes

recombinant chromosomes

chromosomes with combined DNA from both parents. a product of chromosomes crossing over during meiosis.

random fertilization

it adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)