Cell Cycle, Mitosis & Meiosis Review Spring 2015 (Not all-inclusive, but a good overview)
Cell Cycle – the “life cycle” of a cell. Most of the cell’s life it is just hanging out doing its job. It is NOT reproducing, just like humans. (See page 281 in text) Here is a general overview:
1.
Interphase – just hanging out, doing its job a.
G1 – growth: cell was just “born” so it needs to get a little bigger and make its organelles, etc.
Note: It doesn’t want to get TOO big because it won’t have enough surface area to take in nutrients and get rid of waste if the cytoplasm is huge. (Surface Area:
Volume) b.
S – synthesis: DNA copies itself so the new cell will have its own DNA c.
G2 – more growth: makes what it needs to divide
2.
Cell Division/M Phase – prepares to divide. a.
Mitosis – division of nucleus so both new cells get correct amount of DNA b.
Cytokinesis – cell membrane divides and 2 cells are produced
Each step of the way PROTEINS check to make sure everything was done correctly before the cell moves to the next step. These proteins are collectively called: CYCLINS. (These are internal regulators of the cycle. External regulators of the cell cycle are OUTSIDE the cell. Ex. If a cell hits a wall or another cell it will stop dividing.)
Mitosis – (page 282 of text) Tricky word … when used in the cell cycle it refers to the division of the nucleus. When used in general terms it means the process to create identical daughter
cells. So one diploid cell divides to become 2 diploid cells identical to the original. Steps for this to happen:
1.
Prophase – a.
Chromatin condenses into chromosomes (with 2 sister chromatids connected at centromere) b.
Nuclear envelope disappears c.
Centrioles form spindles
2.
Metaphase – Chromosomes line up in the middle of the cell and attach to spindles
3.
Anaphase – Sister chromatids are pulled apart by centrioles and go to opposite ends of the cell
4.
Telophase – a.
Chromosomes decondense back into chromatin b.
Nuclear envelopes form around each mass of chromatin

Then …cytokinesis and you have two daughter cells identical to the original cell.
Cancer is a disease where the cell cycle is out of control. There is too much mitosis, producing too many cells – a tumor.
Meiosis is SIMILAR but there are some major differences.
Meiosis – (page 324 of text) the process to create gametes (also called sex cells or specifically
eggs, sperm and pollen). Since gametes have HALF the number of chromosomes as the original cell the cell needs to divide TWICE. So one diploid cell produces FOUR HAPLOID cells.
Steps for Meiosis I to happen:
1.
Prophase I – a.
Chromatin condenses into chromosomes (with 2 sister chromatids connected at centromere) b.
Nuclear envelope disappears c.
Centrioles form spindles d.
Homologous chromosomes pair up e.
Crossing over happens and genetic material is swapped between homologous chromosomes.
2.
Metaphase I – Chromosomes line up in the middle of the cell and attach to spindles
3.
AnaphaseI – Sister chromatids are pulled apart by centrioles and go to opposite ends of the cell
4.
Telophase I – f.
Chromosomes decondense back into chromatin g.
Nuclear envelopes form around each mass of chromatin
Then …cytokinesis and you have two daughter cells. But they still have too much DNA so …
Steps for Meiosis II to happen:
5.
Prophase II – a.
Chromatin condenses into chromosomes (with 2 sister chromatids connected at centromere) b.
Nuclear envelope disappears c.
Centrioles form spindles
6.
Metaphase II – Chromosomes line up in the middle of the cell and attach to spindles

7.
AnaphaseII – Sister chromatids are pulled apart by centrioles and go to opposite ends of the cell
8.
Telophase II – a.
Chromosomes decondense back into chromatin b.
Nuclear envelopes form around each mass of chromatin
Then …cytokinesis II and you have four genetically diverse daughter cells. (Actually, you would have 4 sperm and 4 pollen but eggs are special. You get ONE egg with all the good stuff and 3 tiny polar bodies that dissolve.)
Purpose
Type of cells made
Number of division
Crossing over?
Tetrads form?
Mitosis
Repair/healing, Growth, maintenance
Genetically identical to parent cell
Number of daughter cells 2
Sets of chromosomes
(original -> daughter cells)
2N -> 2N
1
No
No
Meiosis
Produce gametes (also called sex cells) specifically: egg, sperm or pollen
Genetically diverse from parent cell
4
2N -> N
2
Yes – in prophase 1
Yes – of homologous chromosomes
Diagram: