Cell division

what is cell division

is the process by which cells replicate most eukaryotic cell division starts with nuclear division (karyokinesis) followed by cytoplasmic division (cytokinesis)

what is chromatin

is a condensed form of DNA that is wrapped around histones DNA is stored as chromatin but during cell division it condenses even more into chromosomes

what is chromosomes

dense packaging of chromatin existing during mitosis and meiosis

• chromosomes can be in duplicated or unduplicated forms

what is chromatid

one half of a duplicated chromosome

what is sister chromatids

two identical duplicated chromatids connected at the centromere

what is centromere

region that connects two sister chromatids where kinetochores attach

Haploid vs diploid cell

• n = number of chromosomes in a set

• haploid cell (n) have 1 set of chromosomes

  • diploid cell (2n) have 2 sets of chromosomes; one from the mother and one form the farther

most human cells are what cell

diploid cell

• human cells; n = 23, 2n = 46

what is homologous chromosomes

pairs of chromosomes (one from each parent) found in diploid cells that are similar in length gene position and centromere position both chromosomes carry genes fro the same traits but are non identical

in humans how many homologous pairs does female and male have

1) females have 23 homologous pairs

2) males have 22 homologous pairs ( the X and Y sex chromosomes are non homologous)

what is centrosomes

are the microtubule organizing centers (MTOCs) of animal cells

what is spindle fibers

microtubules that emerge from the centrosome and allow chromosomes and chromatids to be separated during cell division

where does the spindle fibers attach and not attach

spindle fibers do not attach directly to chromosomes, they attach to kinetochores ( proteins that adhere to the chromosome centromere region)

does plant cells have centrosomes

no it does not

what is mitosis

nuclear division that creates a pair of diploid cells that are genetically identical to the original cell

where does mitosis occurs

in somatic cells ( cells not directly involved in producing gametes)

mitosis overview

1) prophase

2) pro-metaphase

3) metaphase

4) telophase

5) cytokinesis

prophase

• Chromatin condenses into chromosomes.

• Nucleolus disappears.

• Mitotic spindle begins to form.

• Centrosomes begin to move towards opposite ends of the cell.

pro metaphase

• Nucleus disassembles.

• Chromosomes condense even further.

• Each chromatid is attached to a kinetochore.

• Mitotic spindle further develops.

  • Spindle fibers attach to kinetochores on chromosomes.

metaphase

• Chromosomes line up at the center of the cell (metaphase plate).

• Centrosomes are at opposite ends of the cell.

• Mitotic spindle is fully developed.

• Microtubules are attached to kinetochores.

• Karyotyping is preformed during metaphase.

what is karyotyping

visualizing a cell’s chromosomes using a microscope

what does the karyotyping used to

identify chromosomal abnormalities

anaphase

• Microtubules shorten.

• Sister chromatids are pulled apart.

• Chromosomes are pulled to opposite ends of the cell.

once sister chromatids are pull apart in the anaphase what does it count as

considered a chromosome

telophase

• Nucleoli redevelop

• Two nuclear envelopes develop (nuclei re-form).

• Chromosomes decondense back into chromatin.

• Spindle fibers disappear.

• Cytokinesis occurs during telophase.

cytokinesis

division to form two cells this is not part of mitosis (mitosis refers to nuclear division) but is required for cell division

what is cytokinesis in animal cells

form a cleavage furrow - actin and myosin ring contracts separating the cell into two daughter cells

what is cytokinesis in plant cells

form a cell plate - cell wall forms between the two nuclei fusing with the existing cell wall and separating the cell into two daughter cells

For dat when the question states that a cell has undergone mitosis/meiosis it is usually to assume that

cytokinesis has also occurred

final result of mitosis

two genetically identical diploid daughter cells which have the same amount DNA as the parent cell

what is meiosis (reductive division)

nuclear division that produces four haploid gametes that are not genetically identical to the original cell

what is gametes

an organism’s reproductive cells (sperm in males and eggs in females)

where does meiosis occurs

in germ cells ( specialized cells that produce gametes)

meiosis is comprised of two stages

1) meiosis I

2) meiosis II

meiosis I

genetic recombination occurs and the cell separates homologous chromosomes

meiosis II

sister chromatids separate to form gametes

meiosis I overview

1) prophase I

2) metaphase I

3) anaphase I

4) telophase I and cytokinesis

prophase I

• Nucleolus and nucleus disappear.

• Chromatin condenses into chromosomes.

• Meiotic spindle begin to form.

• Centrosomes begin to move towards opposite ends of the cell.

• Homologous chromosomes undergo synapsis and crossing over.

synapsis (prophase I)

process by which homologous chromosomes pair up forming tetrads

what is tetrad (prophase I)

structure formed from paired homologous chromosomes must be present for genetic recombination to occur

what is crossing over (prophase I)

exchange of chromosome segments between paired up chromosomes ( genetic recombination) produces genetic variation in gametes

• plays the most significant role in increasing genetic diversity

what is chiasmata (prophase I)

locations where homologous chromosomes meet to swap segments

where does the spindle fibers attach to (prophase I)

kinetochores of homologous chromosomes

metaphase I

• Homologous pairs are lined up across the metaphase plate.

• Microtubules are attached to kinetochores.

• Meiotic spindle is fully developed.

anaphase I

• Microtubules shorten.

• Homologous pairs uncouple and are pulled to opposite poles (disjunction).

telophase I and cytokinesis

• Two nuclear envelopes develop (nuclei re-form).

• Chromosomes decondense back into chromatin.

• Spindle fibers disappear.

• Cytokinesis splits the cell into two daughter cells.

final result of meiosis I

two daughter cells with half the number of chromosomes as the parent (2n parent cell to n daughter cells)

meiosis II

further separates two cells (the products of meiosis I) into four gametes

are the chromosomes identical to the parent cell at the end of meiosis I

are not genetically identical to the parent cell due to crossing over

what is type of cells will meiosis start and finishes with

haploid cells

meiosis II overview

1) prophase II

2) metaphase II

3) anaphase II

4) telophase II and cytokinesis

prophase II

• Nucleus disassembles.

• Chromatin condenses into chromosomes.

• Meiotic spindle begins to form.

• Microtubules attach to kinetochores.

where does crossing over occurs

in prophase I

metaphase II

• Chromosomes are lined up at the metaphase plate.

• Microtubules are attached to kinetochores on chromosomes.

anaphase II

• Microtubules shorten.

• Sister chromatids are pulled to opposite ends.

what does each sister chromatid considered after anaphase II

individual chromosome

telophase II and cytokinesis

• Nucleoli redevelop.

• Two nuclear envelopes develop (nuclei re-form).

• Chromosomes decondense back into chromatin.

• Spindle fibers disappear.

• Cytokinesis splits the cell into two daughter cells.

final result of meiosis

four haploid daughter cells each with half the amount of DNA as the parent cell

are the DNA of daughter cells identical to the parent cell

not identical to the parent cell due to genetic recombination in prophase I

3 events contribute to the genetic diversity in offspring

1) crossing over

2) independent assortment

3) random joining of gametes

what is independent assortment

each homologous chromosome or sister chromatid is randomly distributed into either daughter cell r

what is random joining of gametes

different sperm can fertilize different eggs during fertilization

what is cell cycle

a sequence of events that cells undergo to grow and divide

what is interphase

stage of the cell cycle during which cells grow and prepare for cell division but are not actively dividing

what does the interphase do

1) ensures each daughter cell will have enough resources to survive

2) cells spend most of the cell cycle in interphase

the phases of interphase include

1) G1 phase

2) S phase

3) G2 phase

4) G0 phase

what is G1 phase

cell grows and synthesizes proteins needed for cell division

• usually the longest phase of the cell cycle

what is S phase

DNA and centrosomes are replicated sister chromatids are formed

• DNA replication occurs before mitosis

what is G2 phase

cell continues to grow and organelles replicate cell checks that everything is ready (chromosomes are replicated) to proceed with mitosis

what is G0 phase

resting phase cells are active but do not divide or prepare to divide

senescent cells

enter G0 permanently (nerve and muscle)

quiescent cells

enter G0 temporarily and then re enter the cell cycle (memory t cells)

• do not usually divide but can be stimulated to divide (liver cells)

M phase

mitosis and cytokinesis outside of interphase

cells must divide

bc of functional limitations

what are some functional limitations for cells

1) surface to volume ratio (S:V ratio)

2) genome to volume ratio (G:V ratio)

what is S:V ratio for cells to must divide

as a cell grows its volume grows faster than its surface area a large cell must exchange more resources with the environment but has proportionately less surface area to do so

small and large S:V ratio of a cell

1) large S:V = efficient cellular exchange

2) small S:V = inefficient cellular exchange

what is G:V ratio for cells to must divide

as a cell grows its volume increase but its genome size (amount of DNA) remains constant as G:V ratio decreases. A large cell must transcribe more gene products to support its cellular activity but has access to a limited number of genes

small G:V ratio

cellular activity exceeds the production capacity of its genome

what is the reason why skeletal muscles cells are senescent (non dividing) but still grow in response to exercise

to overcome limitations of large cells skeletal muscle cell are multi-nucleated (increase G:V) and long/cylindrical (increase S:V)

regulation of the cell cycle

1) cell cycle checkpoints

2) density dependent inhibition

3) anchorage dependence

what is cell cycle check points

ensure the cell is prepared to progress to the next stage of the cell cycle

types of cell cycle checkpoints

1) restriction checkpoint (end of G1)

2) DNA damage checkpoint (end of G2)

3) M/spindle checkpoint (during metaphase)

what is restriction checkpoint

end of G1 ensures appropriate cell growth and intracellular conditions if conditions are suitable cell enters S phase

what is DNA damage checkpoint

end of G2 ensures accurate and complete DNA replication if DNA is replicated and undamaged cell enter M phase

what is M/spindle checkpoint

during metaphase ensures sister chromatids are attached to spindle fibers if spindle fibers are not attached to each sister chromatid mitosis stops

if a cell fails a cell cycle checkpoint what happens

it enters G0 or dies (apoptosis)

what is density dependent inhibition

cells stop dividing when the surrounding cell density reaches a maximum prevents overcrowded cells from dividing

what is anchorage dependence

cells will only divide when attached to an external surface prevents cells from multiplying while floating freely through the body

what is cancer mutated cells

that Mutated cells that divide uncontrollably, bypassing the normal regulation of cell division and forming cell masses called tumors.

what is a tumor

malignant when its cells break loose and travel to other tissues and organs (a process called metastasis)

what does many cancer drugs do

work by inhibiting mitosis (inhibit microtubules from breaking down or separating from chromosomes) which kills cancer cells quicker than healthy cells

frequency of cell division

1) labile cells

2) quiescent/stable

3) fixed/permanent

what is labile cells

continuously divide (skin cells)

what is fixed/permanent cells

little to no capacity for cell division ( cardiac muscle cells)

counting chromosomes (mitosis) for cells where X = diploid number

mitosis number of chromosomes

1) prophase - X

2) metaphase - X

3) anaphase - 2X

4) telophase - 2X

end of mitosis (separated cells) - X

mitosis number of chromatids

1) prophase - 2X

2) metaphase - 2X

3) anaphase - 2X

4) telophase - 2X

end of mitosis (separated cells) - X

in humans the diploid number is

46 (23 maternal and 23 paternal chromosomes)

counting chromosomes (meiosis I) for cells where X = diploid number

meiosis I number of chromosomes

1) prophase - X

2) metaphase - X

3) anaphase - X

4) telophase - X

end of meiosis I (separated cells) - ½X

meiosis I number of chromatids

1) prophase - 2X

2) metaphase - 2X

3) anaphase - 2X

4) telophase - 2X

end of meiosis I (separated cells) - X

counting chromosomes (meiosis II) for cells where X = diploid number

meiosis II number of chromosomes

1) prophase - ½X

2) metaphase - ½X

3) anaphase - X

4) telophase - X

end of meiosis I (separated cells) - ½X

meiosis II number of chromatids

1) prophase - X

2) metaphase - X

3) anaphase - X

4) telophase - X

end of meiosis II (separated cells) - ½X