1. The Cell Cycle: Creating Somatic Cells

2. Why do cells divide? Allow an organism to grow
So organisms can replace and repair worn out, damaged, or old cells
Some cells can divide every 20 minutes (bacteria) human cells can take up to a day to divide
Cell Theory- all cells come from other cells
To reproduce (unicellular organisms)

3. Chromosomes Chromosomes- carry genetic information
Somatic Cells- (body cells) have 2 copies of genetic information stored in the nucleus
(1 copy from each parent)
Diploid- (2n)
Humans have 46 chromosomes in each somatic cell
Gametes (sex cells) have 1 copy of genetic information
Haploid (n)
Humans have 23 chromosomes in each gamete

4. Chromosomes Chromatid- ½ a chromosome
Sister
Chromosomes
Chromatid- ½ a chromosome
Sister chromatid- 2 identical DNA molecules attached at a centromere
Centromere- holds sister chromatids together

5. The Cell Cycle 3 Main Steps
Interphase- cells work, grow, and prepare to make new cells in this phase
Mitosis- cells divide
Cytokinesis-cytoplasm splits after a cell divides and 2 new cells are made

6. Step 1: Interphase
Interphase- the cell spends 90% of its time in this phase
3 parts (G1, S, G2)
G1- Cell grows, makes new organelles
S- (Synthesis Phase)
Chromatin (unwound DNA) is copied in the nucleus
DNA Replication
G2- cell grows, works, prepares to divide

7. Step 2: Mitosis Mitosis- cell divides into 2 identical daughter cells
Also called asexual reproduction
4 steps of Mitosis
Prophase
Metaphase
Anaphase
Telophase

8. Prophase Prophase- chromatin condenses into chromosomes
Centrioles move to opposite ends of cells
Centrioles- special organelles involved in cell division, makes spindle fibers
Nuclear membrane disappears

9. Metaphase Chromosomes line up in the middle of the cell
Spindle Fibers attach to centromeres

10. Anaphase
Spindle Fibers separate sister chromatids and move them to opposite ends of the cell

11. Telophase Chromosomes decondense (loosen) into chromatin
Nuclear membrane reforms
Cleavage furrow forms

12. Step 3: Cytokinesis Cytoplasm divides
Cell pinches in half to form 2 new, identical daughter cells
In plant cells, a cell plate forms

13. The Cell Cycle: Creating Sex Cells

14. Review: Mitosis What types of cells do mitosis?
How many cells does mitosis make?
Are they the same or different?
How many chromosomes are in each cell?
Is this haploid or diploid?

15. Haploid vs. Diploid Somatic Cells are diploid
Human somatic cells have 46 chromosomes; 23 from mom and 23 from dad
Homologous Chromosomes- a chromosome PAIR, one inherited from the mother and one from the father, containing genes for the same trait

16. Karyotype In humans there are 23 pairs of homologous chromosomes
-A picture of all the chromosomes a person has in their cells
In humans there are 23 pairs of homologous chromosomes
The first 22 pairs are called autosomes
The 23rd pair, the sex chromosome, differs between males and females.
Females have 2 X chromosomes and males have one X and one Y chromosome

17. Female Reproductive System

18. Male Reproductive System

19. Cell Cycle: Creating Gametes
Interphase, Meiosis, Cytokinesis
Meiosis- makes 4 daughter cells that are not genetically identical
Used to make gametes (sex cells)

20. Meiosis I: PMAT 1 Prophase I, Metaphase I, Anaphase I, Telophase I
A single cell divides into 2 daughter cells that are not genetically identical
The homologous chromosomes come together and swap parts of themselves with each other (called crossing over)
Crossing Over ensures that the daughter cells produced after the first cytokinesis are not genetically identical

21. Meiosis II: PMAT 2
Two diploid cells divide to form 4 haploid daughter cells

22. Independent Assortment
Independent Assortment- each homologous chromosome is randomly assorted into different gametes
Result: 4 daughter cells that are genetically different and haploid

23. Controlling Cell Division
Check points- act as stop signs that ensure only healthy cells move forward
In G1, S, G2
Regulatory Proteins control information in DNA
Contact Inhibition- cells stop growing and dividing when they get too crowded

24. Uncontrolled Cell Growth
Mutant genes prevent cells from being stopped at check points or provide a false positive that allows them to slip through
Disrupt normal controls
Can cause tumors and cancer to form
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25. Prokaryotes’ Cell Division
Most bacterial genes are located on a single chromosome made up of a circle of DNA and proteins
Bacteria do not have as many genes or DNA molecules as long as eukaryotes
Prokaryotes reproduce by binary fission, not mitosis
In binary fission, chromosome replication begins at one point in the circular chromosome, the origin of replication