cell division DAT

Microtubule organizing centers (MTOCs)

are

present in eukaryotic cells; 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.

Centrosomes

are organelles found in animal cells

that contain a pair of centrioles. They act as

microtubule organizing centers (MTOCs).

Centrioles

are hollow cylinders made of microtubules.

Centrosomes

centrioles oriented at 90

degree angles to one another. They replicate during

the S phase of the cell cycle so that each daughter cell

after cell division has one centrosome.

Karyokinesis

The nucleus divides (the DNA gets separated into two groups).

What makes plant cytokinesis unique from animal cytokinesis?

The main difference is that plant cells form a cell plate, while animal cells divide by pinching inward.

Which stage does a cell spend most of its time within the cell cycle?

interphase

• in between each cell cycle is an interphase stage. This is the where the cell prepares for cell division, and this “in between” or “prep” stage where cell spends 90% of time

Gap phase 1 (G₁):

• The cell grows in preparation for cell division. The cell also checks for favorable conditions. If favorable, the cell will enter the S phase. If unfavorable, the cell will enter the G₀ phase.

G₀

cells that do not divide are found in this phase

S

centrosome is replicated

G₂

During G₂, a cell will continue to grow and prepare for cell division by checking DNA for any errors after replication. The cell will also check for mitosis promoting factor (MPF). Lastly, the cell's organelles are replicated. 

Kinetochore microtubules:

Extend from centrosomes and attach to kinetochores on chromosomes. These are the microtubules that pull chromosomes apart during anaphase.

Astral microtubules

Extend from centrosomes to the cell membrane to orient the spindle apparatus. 

If 2n=46, how many chromosomes would be expected in anaphase?

92

Which of the following is a characteristic of meiosis but NOT mitosis?

homologous chromsomes pair up

Cleavage furrow formation

• During cytokinesis in animal cells, a cleavage furrow pinches the cell into two.

• This furrow is formed by a contractile ring of actin microfilaments and myosin, not microtubules.

• Therefore, if microtubule polymerization is inhibited, the cleavage furrow can still form normally.

• So this is the EXCEPTION – it is not directly affected by microtubule inhibition.

microtubules

• Microtubules attach to chromosomes and direct the chromosomes' movements to opposite sides of the cell during the M phase.

• 
  

If 2n=20, how many tetrads are present during prophase I?

10

binary fission

begins as one parent chromosome within a cell replicates into two daughter chromosomes. The chromosomes then move to opposite ends of the cell.

A septum forms between the two chromosomes, splitting the parent cell into two separate daughter cells.

How many autosomes are present in the nucleus of a human cell?

44

Synapsis 

process where homologous chromosomes pair up and align, setting the stage for genetic recombination. The chiasma is the specific site where homologous chromosomes exchange genetic material, visibly marking the point of recombination. Crossing over increases genetic variation in daughter cells. (prophase 1)