Cell cycle and mitosis

Question 1

interphase

Answer 1

the cell grows; in preparation for cell division the chromosomes are duplicated with the genetic material (DNA) copied precisely

Question 2

G1 phase

Answer 2

growth

Question 3

S phase

Answer 3

continuation of growth and copying chromosomes

Question 4

G2 phase

Answer 4

more growth and completion of preparation for division

• nuclear envelope encloses nucleus
• two centrosomes have formed
• chromosomes cannot be seen individually because they have not yet condensed

Question 5

mitosis

Answer 5

distribution of chromosomes into 2 daughter nuclei

Question 6

cytokinesis

Answer 6

division of cytoplasm, the cell divides into 2 daughter cells, genetically identical to each other and parent cell

• occurs by cleavage
• cleavage furrow appears
• contractile ring of actin microfilaments (myosin) appears
• ring contracts
• parent cell is pinched in two

Question 7

checkpoint

Answer 7

is where stop and go-ahead signals can regulate the cycle

Question 8

cyclins and CDKs

Answer 8

regulatory molecules (proteins) - protein kinases and cyclins, they are inactive much of the time, to be active, kinase must be attached to a cyclin - Cyclin Dependent Kinases

• cyclin level rises during S and G2 phases and falls during M phase
• MPF - maturation promoting factor (m-phase promoting factor) triggers the cell’s passage into the mitotic phase

Question 9

prophase

Answer 9

• chromatin fibers become more tightly coiled
• nucleoli disappear
• each duplicated chromosome appears as 2 identical sister chromatids joined at the centromeres
• mitotic spindle begins to form (composed of centrosomes ad microtubules extending from them)
• centrosomes move away from each other, propelled partly by the microtubules

Question 10

prometaphase

Answer 10

• nuclear envelope fragments
• microtubules can invade the nuclear area
• chromosomes have become even more condensed
• kinetochore has formed
• some microtubules are now kinetochore microtubules
• nonkinetochore microtubules interact with those from opposite sides of the spindle, lengthening the cell

Question 11

metaphase

Answer 11

• centrosomes are at opposite poles of the cell
• chromosomes all arrived at the metaphase plate (equidistant between poles)
• for each chromosome, kinetochores of sister chromatids are attached to kinetochore microtubules coming from opposite poles

Question 12

anaphase

Answer 12

• shortest stage of mitosis
• begins when cohesin proteins are cleared
• each chromatid becomes an independent chromosome
• two new daughter chromosomes begin moving towards opposite end of the cell - kinetochore microtubules shorten
• cell elongates as the nonkinetochore microtubules lengthen
• by the end of anaphase, two ends of the cell have identical and complete collections of chromosomes

Question 13

telophase

Answer 13

• two daughter nuclei form in the cell
• nuclear envelopes arise
• nucleoli reappear
• chromosomes become less condensed
• any remaining spindle microtubules are depolymerized

Question 14

centrosomes

Answer 14

structures made from two centrioles (centrioles are microtubule rings); the main purpose of a centrosome isto organize microtubules and provide structure for the cell, as well as work to pull chromatids apart during cell division

Question 15

sister chromatids

Answer 15

the identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere

Question 16

kinetochore

Answer 16

a large protein complex that assembles on a specialized region of the chromosome called the centrome

Question 17

centromere

Answer 17

a constricted region of a chromosome

Question 18

DNA synthesis

Answer 18

at each end of a replication bubble is a replication fork; Y-shaped region where the parental strands of DNA unwind

Question 19

helicases

Answer 19

enzymes that untwist the double helix, separating the 2 parental strands and making them available as template strands

Question 20

single-strand binding proteins

Answer 20

bind to the unpaired DNA strands, keeping them from re-pairing

Question 21

leading strand

Answer 21

DNA polymerase III remains in the replication fork on template strand and adds nucleotides to new complementary strand as the fork progresses; 1 primer is required

Question 22

lagging strand

Answer 22

DNA polymerase III must work along the other template strand in the direction away from the replication fork; it synthesizes discontinously, as segments - Okazaki fragments

Question 23

DNA ligase

Answer 23

joins the sugar-phosphate backbones of all the Okazaki fragments into a continuous DNA strand

Question 24

topoisomerase

Answer 24

relieves overwinding strain ahead of replication forks by breaking, swiveling and rejoining DNA strands

Question 25

primase

Answer 25

synthesizes an RNA primer at 5’ end of the leading strand and 5’ end of each Okazaki fragment of the lagging strand

Question 26

DNA polymerase III

Answer 26

using parental DNA as a template, synthesizes new DNA strand

Question 27

DNA polymerase I

Answer 27

removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added to 3’ end of adjacent fragment