Ch 11: Cell cycle and cell division

Question 1

Steps of DNA condensation

Answer 1

o 1) wrapping of DNA about 2 rimes around a protein complex called a NUCLEOSOME
• made up protein histones
 H2A, H2B, H3, H4
• Each nucleosome has to copies
o 2) nucleosomes coil around each other to form the “30nM fiber” which requires a third histone H1
o 3) 30nM fiber is condensed further into chromatin

Question 2

greatest amount of condensation occurs in

Answer 2

prophase

Question 3

after DNA synthesis, two identical chromosomes are called

Answer 3

sister chromatids that are held together by cohesion protein

o Centromere forms where the two legs cross

Question 4

humans have

Answer 4

46 chromosomes

Question 5

how long does the eukaryotic cell cycle take

Answer 5

from 30 min to 24 hrs

Question 6

G1 phase

Answer 6

• Takes 11 hours
• Cells prepare for DNA synthesis
• Cellular metabolism occurs to increase cell mass

Question 7

S phase

Answer 7

• Synthesis
• Takes 8 hours
• DNA synthesis occurs

Question 8

G2 phase

Answer 8

• 4 hrs

* cell prepares for the final M phase and cell division

Question 9

M phase

Answer 9

• Mitosis

* 1 hr

Question 10

G1 checkpoint

Answer 10

• Cell decides whether its DNA is fit to be replicated
• RB protein
 Has a negative effect
 Prevents cell from enetering S phase
 Must be inactivated for cell to proceed into s phase

Question 11

what happens if cell can’t continue in cell cycle

Answer 11

o Due to uv radiation
o RB protein stays active
o Cell cycle stays blocked in G1 until DNA damage induced by UV light has been removed
o Aka DNA repair

Question 12

Cell can go thru a checkpoint only when what becomes active

Answer 12

when a cdk becomes active

o CDK adds a phosphate to a large molecule (amino acid of the surface of a protein)
o Cdk is an inactive kindase
• Only becomes active when it interacts with another protein called a cyclin
• THAT’S WHY IT’S CALLED A CYCLIN DEPENDENT KINASE
o When the cell can go thru the duplication, a cyclin interacts with a cdk and together they signal the cell to proceed thru the G1 checkpoint
• Begins when the active cdk/cyclin complex puts a phosphate onto the RB protein→inactivating RB and allowing DNA to move into S phase to duplicate DNA

Question 13

Mitosis

Answer 13

• Cell divides
• M phase has two parts
o Mitosis: nuclear division
o Cytokinesis: actual cell division

Question 14

Interphase

Answer 14

G1, G2, S

Question 15

Prophase

Answer 15

• Chromosomes become maximally condensed

* Shaped like an X with centromere at crossing point

Question 16

prometaphase

Answer 16

• Tubulin protein forms into microtubules which stretch across the nucleus to form 46 spindle fibers
 Looks like an arc
• All 46 spindle fiber arcs meet on each side of the cell at a structure called a pole
• 46 chromatids (chromosome pairs) use their centromeres to attach to the spindle fibers
• nuclear membrane disappears

Question 17

metaphase

Answer 17

• 46 chromatids align at the midcell

Question 18

anaphase

Answer 18

• Cohesion protein is degraded
• Sister chromatids separate and each sister chromosome moves to a pole
• 46 sister chromosomes are clustered around two poles on either side of the cell

Question 19

telophase

Answer 19

• Around each cluster of chromosomes, the nuclear membrane reforms
• Spindle fibers disappear
• Cell divides (cytokinesis) via a pinching process, which involves mainly actin and myosin

Question 20

cytokinesis

Answer 20

• After nuclear division is complete, the cell divides, which requires actin/myosin to pinch off the middle of the cell turning it into two cells

Question 21

Somatic vs gamete

Answer 21

• Majority of cells in body are somatic
o Divide by mitosis
o 46 chromosomes and 23 pairs (1 from mom and 1 from dad
o 2n chromosomes
o diploid
• minority of cells in the sex organs are called gametes
o sperm and egg cells
o 1n: one copy of each of the 23 chromosomes
o haploid cells
• arise from special diploid cells in the sex organs via meiosis

Question 22

meiosis vs mitosis

Answer 22

• Mitosis requires 1 round of DNA replication and one cell division
o One cell becomes two cells
• Meiosis requires 1 round of DNA replication followed by two cell divisions aka M1 and M2
o 1 cell becomes four cells

Question 23

meiosis 1

Answer 23

• Only 23 spindle fibers form and each pair of sister chromatids attaches side by side on a single spindle fiber
• During anaphase of meiosis 1, cohesion is NOT DEGRADED and 1m sister chromatids move together as a unit toward one pole and 1f sister chromatids move together as a unit to the other pole
• After meiosis I, there has been 1 round of DNA replication and cell division, so both new cells have 2n chromosomes

Question 24

meiosis ii

Answer 24

• Second cell division
• No DNA replication
• Only 23 spindle fibers form and each pair of sister chromatids attaches to one spindle fiber
• During anaphase, cohesion IS DEGRADED and the two sister chromatids of each pair separate and move toward opposite poles
• When cell division occurs, each cell is now haploid and contains only a 1n complement of chromosomes, meaning that each cell has only copy of chromosome 1, one copy of chromosome 2, etc

Question 25

meiosis generates genetic diversity in two ways

Answer 25

• No cellular mechanism distinguishes between the mother’s ves the father’s verion of a chromosome in terms of movement toward the poles during meiosis I
• During prophase I a region on the 1m chromatid can be exchanged with the identical region on the 1f chromatid in a process called chiasma which occurs by recombination

Question 26

the replacement of cells that die

Answer 26

• To maintain cell number stais, cell division must only occur when a cell dies and must be replaced
• Goes thru stem cell division
o Asymmetric
o One of the daughter cells remains a stem cell while the other cell replaces the cell that died

Question 27

cell death

Answer 27

apoptosis