Chapter 5- The cell cycle

Question 1

Interphase

Answer 1

1. Gap phase 1 (G1 ) - cell grows in preparation for cell division. Also checks for favorable conditions. If favorable, cell will enter S phase.
   If unfavorable, cell will enter G0 phase.
   a. G0 phase - cells still carry out their functions but halt in the cell cycle. Cells that do not divide are stuck here.
2. Synthesis phase (S) - cell replicates its genome here and moves to G2 phase when completed.
   Centrosome duplicates.
3. Gap phase 2 (G2 ) - cell continues to grow and prepare for cell division by checking DNA for any errors after replication. Also checks for
   mitosis promoting factor (MPF), which needs to be present in adequate amounts for cell cycle continuation. Organelles are replicated here.

Question 2

Microtubule Organizing Centers (MTOCs)

Answer 2

-they organize extension of microtubules, which are made of the protein tubulin.
-MTOCs are responsible for forming the spindle apparatus, which guides chromosomes
during karyokinesis.

Question 3

Centrosomes

Answer 3

• contain centrioles oriented at 90 degrees angle to each other.
• Act as MTOCs
• located near the nucleus
• they replicate during the S phase so each daughter cell has 1 centrosome

Question 4

Microtubules in the spindle apparatus:

Answer 4

1. Kinetochore microtubules - extend from centrosomes and attach to kinetochores on chromosomes.
2. Astral microtubules - extend from
   centrosomes to the cell membrane to orient the spindle apparatus.
3. Polar microtubules - extend from the two
   centrosomes and connect with each other. They push centrosomes to opposite ends of
   the cell.

Question 5

Centrioles

Answer 5

-hollow cylinders made of nine triples of microtubules (9x3 array)

Question 6

Pericentriolar material

Answer 6

• surrounds the centrioles

- responsible for microtubule nucleation.

Question 7

Cilia and flagella

Answer 7

• nine doublets of microtubules with 2 singlets in center (9+2 array)
• produced by basal body which is formed by the mother centriole attaching itself to the cell membrane

Question 8

Mitosis (M phase)

Answer 8

-stage where karyokinesis and cytokinesis occurs
-Karyokinesis is just the nuclear division that involves a diploid parent cell dividing into two diploid daughter cells
Four phases of mitosis:
1. Prophase - chromatin condenses into
chromosomes (X-shaped dyads). The
nucleolus and nuclear envelope disappear.
Spindle apparatus forms.
2. Metaphase - the spindle apparatus guides the chromosomes to the metaphase plate
(midpoint of cell) in a single file.
3. Anaphase- kinetochore microtubules shorten to pull sister chromatids apart. Now, the sister chromatids are considered separate
chromosomes. Chromosome number
doubles.
4. Telophase - chromosomes have segregated
and nuclear membranes reform. In addition,
nucleoli reappear and chromosomes
decondense into chromatin.
-Cytokinesis- the physical separation of the cytoplasm and cell membrane into 2 daughter cells.

Question 9

Cytokinesis

Answer 9

-the physical separation of the cytoplasm and cell membrane into 2 daughter cells.
-In animal cells, cytokinesis begins in late anaphase
with the formation of a cleavage furrow. The
cleavage furrow is a contractile ring of actin
microfilaments and myosin motors that pinches the
cell into two.
-In plant cells, cytokinesis begins in telophase with the formation of a cell plate. The cell plate is
created by vesicles from the Golgi apparatus and ends up producing the middle lamella (cements plant cells together).