Eukaryotic Cell Reproduction

Question 1

somatic cell

Answer 1

body cell, any cell with 46 chromosomes

Question 2

cell cycle

Answer 2

the time from a generation event (the division of one cell into two daughter cells) until the new cell divides

Question 3

interphase

Answer 3

the phase between cell divisions

• the cell is metabolically active and carries out its specific functions
• constitutes ~90% of the cell cycle
• can be further subdivided into G1, S and G2

Question 4

g1 phase

Answer 4

first phase of interphase
cells are growing and carrying out normal function
-may receive signals to begin preparation for division, or may also receive signals to stay in G0 and continue carrying out functions

Question 5

s phase

Answer 5

second phase of interphase
cell is still growing and is still metabolically active, but has committed to dividing
-DNA is replicated in preparation for division

Question 6

g2 phase

Answer 6

third phase of interphase

• cell grows in preparation for cytokinesis
• centrosome copies itself
  note: the nuclear envelope is still intact, and the chromatin is still fully uncondensed (not seen as chromosomes yet)

Question 7

mitosis

Answer 7

division of the nuclear contents (DNA)

proceeds in 5 steps (prophase, prometaphase, metaphase, anaphase, telophase)

Question 8

cytokinesis

Answer 8

division of the cytoplasmic contents

initiated during anaphase or telophase

Question 9

chromatin

Answer 9

complex of DNA, histones and scaffold proteins that condense the DNA so that it will fit into the nucleus

Question 10

chromatid

Answer 10

A single (double-stranded) copy of a chromosome 
-may be found in isolation or attached to the duplicate copy

Question 11

sister chromatids

Answer 11

the two matching copies of a chromosome that are attached at the centromere from the time of DNA replication (in S phase) to their separation (in anaphase)

Question 12

centromere

Answer 12

region of the DNA where duplicated chromosomes are attached until they are separated during anaphase

Question 13

centrosome

Answer 13

microtubule organizing centre (MTOC) in animal cells from which all microtubules grow
-composed of two orthogonal centrioles

Question 14

centriole

Answer 14

structure that makes up the centrosomes; composed of 9 triplet microtubules arranged in a ring

Question 15

kinetochore

Answer 15

point on the sister chromatids where the kinetochore microtubules attach during prometaphase
-attachment protein structure at the centromere

Question 16

metaphase plate

Answer 16

imaginary line halfway between the two cell poles where the sister chromatids line up during metaphase

Question 17

checkpoint

Answer 17

control point in the cell cycle in which the cell ‘stops’ and ‘goes’ in response to cellular and environmental signals

• three major are G1, G2 and M
• protects against cancer

Question 18

prophase

Answer 18

• chromatin begins to condense; sister chromatids become visible and are joined by cohesion points at the centromere (note: nuclear envelope still in place)
• centrosomes begin to move towards opposite poles of the cell
• normal cellular microtubules begin to disassemble and are repolymerized into the forming mitotic spindle

Question 19

prometaphase

Answer 19

• nuclear envelope breaks apart, the now fully condensed DNA disperses throughout the cell
• mitotic spindle is completed
• kinetochore MTs are attached to sister chromatids
• polar MTs overlap
• aster attaches to the PM

Question 20

metaphase

Answer 20

tug-of-war between kinetochore MTs aligns sister chromatids on the metaphase plate

Question 21

anaphase

Answer 21

• kinetochore MTs pull sister chromatids apart (centromeres cleaved?)
• polar MTs cause the cell to elongate, increasing the distance btw the 2 poles
• each end of the cell has an identical, complete set of chromosomes

Question 22

telophase

Answer 22

• mitotic spindle disassembles and one centrosome is left for each daughter cell
• new nuclear envelops form around the DNA from fragments of the parent cell’s nuclear envelope
• chromosomes begin to decondense
• cytokinesis occurs

Question 23

mitotic spindle

Answer 23

• grows out of the centrosome (in animal cells) by adding more tubulin monomers
• primary functions are to move DNA to opposite ends of the cell and elongate the cell to prepare for cytokinesis
• consists of 3 microtubule subunits (kinetochore, polar and aster)

Question 24

kinetochore microtubules

Answer 24

attach to the kinetochore on sister chromatids during prometaphase and pull the chromatids apart in anaphase
-motor protein kinesis (powered by ATP synthesis) pulls the chromatid along the shortening kinetochore microtubules

Question 25

polar microtubules

Answer 25

primary function is to push the poles apart to elongate the cell

• starting in prophase, they overlap with another polar MT from the other pole of the cell, attached at the centre by kinesin motor proteins
• in anaphase, the kinesins (powered by ATP hydrolysis) walk towards each other, pushing apart the polar MTs (and by extension the centrosomes) causing the cell to elongate

Question 26

aster microtubules

Answer 26

primary function is to anchor the centrosomes at opposite poles of the cell
-during prometaphase, aster MTs attach themselves to the PM so that when anaphase begins, the centrosome is not pulled towards the middle of the cell

Question 27

cleavage furrow

Answer 27

shallow groove on cell surface at metaphase plate

• made of contractile ring of actin microfilaments and myosin motor protein
• ring contracts (using ATP hydrolysis), pinching the cell in two

Question 28

G1 Checkpoint

Answer 28

controls the decision to divide and enter S phase

• once past this checkpoint, the cell is committed to division
• if cell doesn’t pass checkpoint, it switches to a non-dividing state called G0 phase
• regulated by growth factors, cell density and anchorage

Question 29

G2 checkpoint

Answer 29

controls entry into mitosis

-ensures all the DNA has been copied and that the cell is big enough

Question 30

M checkpoint

Answer 30

happens at the end of metaphase and controls entry into anaphase
-checks that both kinetochores of a centromere are attached to a kinetochore MT to ensure both daughters receive a copy of each chromosome