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Section 2 Cell Division
Cell Division: The process by which cells produce
offspring cells.
All cells come from preexisting cells.
Cell division differs in prokaryotes and eukaryotes.
Cell reproduction: 1 cell makes 2 cells.
25 million cells per second are produces by an
adult human.
Cell Division in Prokaryotes
Cell division in prokaryotes is called Binary
Fission.
Binary Fission one cell makes two cells.
Example: Bacteria
Process:
Cell Division in Prokaryotes
Cell Division in Eukaryotes
Both the cytoplasm and the nucleus divide.
Mitosis: Cell division that results in cells with
identical genetic material as the original cell.
The cell Cycle: The repeating set of events in the
life of the cell.
Steps in the cell cycle
Interphase: Time between cell divisions. Cells are
growing in size.
Mitosis: The nucleus of the cell divides.
Cytokinesis: The division of the cell’s cytoplasm.
Interphase
G1 Cell Growth
S –DNA is copied
G2 Cell grows and prepares for cell division.
G 0 Exit the cell cycle and do not copy their DNA.
Steps of the cell cycle
Mitosis: Division of the nucleus.
Divided into four phases.
Prophase, Metaphase, Anaphase and
Telephase.
Prophase (Step 1)
First stage of mitosis.
Shortening and tight coiling of DNA into rodshaped chromosomes.
Centrosomes appear and separate.
Spindle fibers radiate from the centrosomes.
Metaphase(Step 2)
Second stage
Kinetochore fibers move the chromosomes to the
center of the cell.
Anaphase(Step 3)
3rd stage
Chromatids of each chromosome separate at the
centromere and move toward opposite poles of the
dividing cell.
Telophase
th
(4
step)
4th stage
Spindle fibers disassemble
Chromosomes become less tightly coiled
Chromatin state
Nuclear envelope forms.
Cytokinesis
Cells start to divide.
Cell membrane pinches in and separate the cell
into TWO cells.
Cytokinesis in plants form a cell plate.
Cell plate becomes the cell wall.
Control of cell division
Cell growth(G1) check point: If the cell is healthy it will go
to DNA synthesis.
If the cell is not big enough or unhealthy it will stay in G0
phase.
DNA synthesis((G2) Checkpoint: If the cell is copied
correctly it will go to the next step. If not it will stop.
Mitosis checkpoint: Checks to make sure the cell divides
correctly.
Control is lost: Cancer
If mutation occurs the cell will not grow or divide
properly. This will lead to cancer.
Cancer cells do not respond to the body’s control
mechanisms.
Results in overproduction of damaged cells.