Cell Cycle & Division

Question 1

why do cells divide

Answer 1

• Cells divide to replace old, dead, or damaged cells
• Cells divide so that living things can GROW.
• Organisms GROW because of CELL DIVISION.

Question 2

what are the two main phases of the cell cycle

Answer 2

Interphase:
Growth, normal activities & DNA replication – 90% of the cell cycle!
Consists of G1, S, G2 phases

Cell Division:
Mitosis = division of the nucleus
Cytokinesis= division of the cytoplasm

Question 3

which cells divide

Answer 3

most cells:
Somatic Cells: any cells in the body, except sperm and egg cells. “soma” = body. Somatic cells are diploid cells.

Diploid (2n): cells that have 2 complete sets of chromosomes - one set from each biological parent.

Question 4

what are daughter cells

Answer 4

Exact Replicas of the parent cell with the SAME number of chromosomes.

Question 5

what are the 2 forms of DNA

Answer 5

Chromatin:
Long, tangled strands of DNA found in the nucleus during most of the cell cycle. (uncondensed DNA)

Chromosomes:
Bundled structures of DNA & proteins that contain the cell’s genetic information. (condensed DNA)

chromatin condenses into chromosomes

Question 6

what does cell devision require

Answer 6

Cell division requires the separation of identical genetic material-DNA - between two daughter cells.

A dividing cell duplicates its DNA, and splits the sets between two daughter cells.

Question 7

Prophase

Answer 7

• Replicated DNA condenses into chromosomes.
• Nucleolus disappears
• Nuclear envelope disappears
• Mitotic spindles begin to form and push centrioles towards the poles of the cell.

Question 8

Prometaphase

Answer 8

• Chromosomes continue to condense
• Kinetochores (proteins associated with the centromere) appear
• Mitotic spindle microtubules begin to attach to the kinetochore at the centromere of the chromosomes

Question 9

Metaphase

Answer 9

Spindle fibers push chromosomes to the equator of the cell with the centrioles at the poles

Question 10

Anaphase

Answer 10

• Spindles shorten
• Sister chromatids are split apart and pulled towards opposite poles of the cell.

Question 11

Telophase

Answer 11

• Nuclear envelope begins to form.
• Chromosomes relax and return to chromatin form.
• Spindle fibers disappear.
• Nucleolus reforms.
• Cell membrane begins to pinch.

Question 12

Cytokenesis

Answer 12

Cytokinesis = division of cytoplasm!
Animal Cells: Cell membrane completely pinches together (animal cells)
Plant cells: cell wall forms
= TWO identical daughter cells!
- not mart of mitosis

Question 13

what is the cell control system

Answer 13

a cycling set of molecules in the cell that triggers and coordinates key events in the cell cycle.

Checkpoints in the cell cycle can
- stop an event or
- signal an event to proceed.

Question 14

what are the 3 major checkpoints in the cell cycle

Answer 14

• G1 checkpoint: allows entry into the S phase or causes the cell to leave the cycle, entering a non-dividing G0 phase.
• G2 checkpoint
• M checkpoint

Question 15

what happens if a checkpoint fails

Answer 15

cell will proceed to apoptosis
Apoptosis = programmed cell death
Prevention of any errors proceeding

Question 16

how do prokaryotes divide

Answer 16

Prokaryotes (bacteria & archaea) divide by binary fission = dividing in half.
The circular DNA (chromosome) of a bacteria is copied and split between two cells.
Remember: this is much smaller than eukaryotes