Chapter 5: Cell Division

Question 1

cell division

Answer 1

nuclear division (karyokinesis) followed by cytokinesis

1. diploid cells= two copies of every chromosome, forming pairs (homologous chromosome)
2. Humans have 46 chromosomes, 23 homologous pair, a total of 92 chromatids (depends on stage)

Question 2

microtubule organizing centers (MTOCs)

Answer 2

aka centrosomes

1. pair of these lay outside of nucleus
2. in animal cells, each MTOC contains pair of centrioles.
   * ** plants do have MTOCs called centrosomes, but they aren’t composed of centrioles

Question 3

Mitosis

Answer 3

prophase, metaphasem anaphase, telophase, cytokinesis

1. occurs in somatic cells
2. occurs in asexual reproduction such as in plants and singled celled organisms

Question 4

prophase

Answer 4

1. nucleus diassembles: nucleolus disappear, chromatin condenses into chromosomes, and nuclear envelope breaks down
2. mitotic spindle is formed and microtubules (composed of tubulin) begin connection to kinetochores

Question 5

metaphase

Answer 5

1. chromosomes line up single file at center, each chromatid is complete with a centromere and a kinetochore, once separated, it is a chromosome ***to keep track of total=count the centromeres
2. centrosomes at opposite ends of cell *** (note: once separated that’s the end of metaphase, so to be precise the chromosomes # doubles at anaphase.
3. karyotyping performed here

Question 6

anaphase

Answer 6

1. microtubules shorten, each chromosome is pulled apart into two chromatids (once separated it is a chromosome; chromosome # doubles)
2. pulls the chromosome to opposite poles (disjuction)
3. at end of this phase, each pole has a complete set of chromosomes, same as original cell before replication

Question 7

telophase

Answer 7

1. nuclear division, nuclear envelope develops, chromosomes=> chromatin, nucleoli reappear

Question 8

cytokinesis

Answer 8

1. actually begins during the later stages of mitosis (most sources indicate it begins toward the end of anaphase)
2. division of cytoplasm to from 2 cells

Question 9

cleavage furrow

Answer 9

actin and myosin microfilaments shorten, pull plasma membrane into center (animal cells)

Question 10

cell plate

Answer 10

1. vesicles from the golgi bodies migrate and fuse to form cell plate, out growth and merge with plasma membrane separating the two new cells (plants).
2. cells don’t actually separate from each other, middle lamella cements adjacent cells together

Question 11

interphase

Answer 11

begins after mitosis and cytokinesis are complete, and consists of G1, S, G2

1. cell cycle= M, G1, S, G2 phases
2. G1=cell increases in size, and the G1 checkpoint ensures everything is ready for DNA synthesis
3. S phase= second molecule of DNA replicated from the first, provides sister chromatids–DNA synthesis
4. G2=rapid cell growth, preparation for of genetic material for cellular division
5. more time spent in interphase than mitosis (>90%). Growth occurs in ALL 3 PHASES, not just the G’s
6. There are checkpoints in these cycles to make sure things are going as planned
   - —End of G1(restriction point** most important one)=cell growth assessed and favorable conditions checked. If fails, cell enter G0 (checks extracellular environment)
   * ** nerve and muscle cells remain here, rarely divide after maturing!!
   - —end of G2=checks for sufficient mitosis promoting factor (MPF) levels to proceed… check if DNA is duplicated properly
   - —-M checkpoint (metaphase checkpoint) during mitosis that triggers start of G1??… make sure chromosomes are attached .. make sure mitotic spindle is grabbing the kinetochore properly

Question 12

meiosis 1

Answer 12

meiosis 1 is reduction division

1. homologous chromosomes pair at plate, migrate to opposite poles (no separation of sister chromatids)
2. occurs in germ cells (egg, sperm, pollen)
3. fertilization/syngamy=fusion of two haploid gametes=diploid zygote
4. ends with 4 haploid daughter cells, with half the number of chromosomes (one chromosomes from each homologous pair … get either moms or dads)

Question 13

prophase 1

Answer 13

1. nucleus disassembles: nucleolus disappears and nuclear envelope breaks down, chromatin condenses, spindle develps. 2. MT’s begin attaching kinetochores
2. crossing over meansn
   genetic recombination
   —synapsis= homologous chromosomes pair up. these pairs are referred to as tetrads (group of 4 chromatids) or bivalents
   — chiasmata: region where crossing over occur of non-sister chromatids
   —-synaptonemal complex: protein structure that temporarily forms between homolgous chromosomes: gives rise to the tetrad w/ chiasmata and crossing over

Question 14

metaphase 1

Answer 14

1. homologous pairs are spread across metaphase plate
2. microtubules attached to kinetochores of one member of each homolgous pair
3. microtubules from other site attach to 2nd member of pair

Question 15

anaphase 1

Answer 15

1. homologues within tetrads uncouple and pulled to opposite sides (disjuction)

Question 16

telophase 1

Answer 16

1. nuclear membrane develops
2. each pole forms a new nucleus that has half number of chromosomes (from homolgous pair to each chromosome =chr 2 sister chromatids)
3. chromosome reduction phase to haploid
   - — interphase may occurs in between here

Question 17

meiosis 2

Answer 17

chromosomes spread across metaphase plate and sister chromatids separate and migrate to opposite poles. It is similar to mitosis

Question 18

prophase 2

Answer 18

nuclear envelope disappears and spindle develops etc, no chiasmata and no crossing over

Question 19

metaphase 2

Answer 19

chromosomes align on plate like in mitosis but now with half number of chromosomes (no extra copy)

Question 20

anaphase 2

Answer 20

each chromosome is pulled into 2 separate chromatids and migrate to opposite poles of cell

Question 21

telophase 2

Answer 21

nuclear envelope reappears and cytokinesis occurs=> 4 haploid cells (each chromosome=1 chromatid)

Question 22

zygote))

Answer 22

forms after fertilization

1. singled celled and then divides by mitosis to produce a multicellular organism
2. Note that one copy of each chromosome in the zygote originates from one parent, and the second copy from the other parent
3. Thus, a pair of homolgous chromosomes in the diploid zygote represents both maternal and paternal heritage

Question 23

alternation of generations: plant life cycle

Answer 23

1. meiosis in sporangia produces spores (haploid)
2. spores undergo mitosis to become multicellular (gametophyte) which is haploid (n) since spores are already haploid
3. the gametes fuse and produce a diploid cell (zygote 2N) that grows by mitosis to become sporophyte. Cells in sporophyte (sporangia) undergoes meiosis to produce haploid spores which germinate and repeat life cycle
   * ** alternation of generations refers to the diploid and haploid stages

Question 24

3 components of genetic variation

Answer 24

genetic recombination during meiosis and sexual reproduction originates from three events:

1. crossing over during prophase 1 of non-sister of homologous chromosomes
2. independent assortment of homologues during metaphase 1 (which chromosomes goes into which cell)
3. random joining of gametes aka germ cells (which sperm fertilizes which egg–genetic composition of gamete affects this)

Question 25

regulation of cell cycle

Answer 25

functional limitations

Question 26

1. surface to volume ration (S/V)

Answer 26

1. as volume gets much larger when cell grows (x^3) vs SA (x^2)
2. when S/V is large (such as 4:8) … exchange becomes easier
3. when S/V is small ( such as 4:512).. exchange is hard, leads to cell death or cell division to increase

Question 27

2. genome - volume-ratio (G/V)

Answer 27

1. genome size remains constant; as cell grows, only volume increase.
2. G/V will be small and this exceed the ability of its genome to produce sufficient amounts of regulatory activities
3. some large cells (parmecium, human skeletal muscle) are multinucleated to deal with this

Question 28

A.checkpoints

Answer 28

cell specific regulations

Question 29

1.G1 checkpoints

Answer 29

1. aka restriction point, the most important one
2. at the end of G1 phase, if the cell is not ready to divide it may arrest here (G0 phase- nerve and muscle cells remain here, rarely divide after maturing) and never proceed or wait until it is ready

Question 30

2. G2 checkpoint

Answer 30

1. end of G2 phase, evaluates accuracy of DNA replication and signal whether to begin mitosis

Question 31

3. M checkpoint

Answer 31

1. during metaphase, ensures microtubules are properly attached to all kinetochores.. prevents anaphase if not

Question 32

B. cyclin-dependent kinases (Cdk’s)

Answer 32

1. Cdk enzyme activates proteins that regulate cell cycle by phosphorylation; Cdk’s are activated by protein cyclin

Question 33

C. growth facotrs

Answer 33

plasma membrane has receptors for growth factors that stimulate cell for division (such as damaged cell)

Question 34

D. density-dependent inhibition

Answer 34

cell stop dividing when surrounding cell density reaches maximum

Question 35

E. anchorage dependence

Answer 35

most cells only divide when attached to an external surface such as neighboring cells or side of culture dis

Question 36

cancer

Answer 36

defy all of the 5 conditions above (called transformed cells)