1. Chapter 8
The Cell Cycle

2. 8.1 Cell Division in Eukaryotes
Prokaryotes – divide in two
Eukaryotes – a more complex process to be able to divide in two = cell cycle

3. 8.1 Cell Division in Eukaryotes
Multicellular Organisms’ Development
Multicellular organisms develop from a single fertilized egg cell. The many cell types these organisms are made of go through many cell cycles that began with that fertilized egg.

4. 8.1 Cell Division in Eukaryotes
Purposes of cells division
By dividing into many cells, surface area keeps up with the cell’s growing volume (helps for diffusion of materials into cell).
Replaces cells that are damaged, worn out, or dead (ex: skin cells).

5. 8.1 Cell Division in Eukaryotes
In Plants:
Specialized regions at tips of roots & stems that repeatedly divide  will turn into mature tissues (stems, leaves, roots, etc).
In Animals:
Cell division produce many types of cells (nerve, skin, blood, etc.) that coordinate organs & organ systems.

6. 8.1 Cell Division in Eukaryotes
Timing of Cell Divisions
Cells divide at different rates & times so that the development is coordinated with neighboring cells to produce organs/organ systems

7. 8.1 Cell Division in Eukaryotes
Eukaryotic Cell Division Requirements
- Accurate replication & equal division of the cell’s DNA
- Each daughter cell should receive identical set of chromosomes

8. 8.1 Cell Division in Eukaryotes
Consequences of errors
Error in DNA replication  birth defects, cancer, serious diseases, or death
Picture of a child with Down Syndrome, which is caused when the fertilized egg cell receives an extra copy of the 21st chromosome.

9. 8.2 The Phases of the Cell Cycle

10. 8.2 The Phases of the Cell Cycle
Starting & Ending “Products”
Starts once a new cell is formed.
Ends as soon as that cell divides into 2 IDENTICAL cells.
Mitosis – process of dividing nuclear material
Interphase – “resting” period between divisions

11. 8.2 The Phases of the Cell Cycle
INTERPHASE
Individual chromosomes are NOT visible during interphase.
3 stages of interphase:
G1: Gap 1 or prereplication
S: Synthesis ( or DNA replication)
G2: Gap 2 or premitosis

12. 8.2 The Phases of the Cell Cycle
INTERPHASE
Gap (G) Phases
Cells grow
Synthesize RNA, proteins, & other molecules to prepare for mitosis. G0
- A stopping point in G1: non-division stage
- Cells are metabolically active but non-dividing

13. 8.2 The Phases of the Cell Cycle
INTERPHASE
Restriction Point
- “point of no return”
- the point at which a cell commits itself to complete the cell cycle
Synthesis (S) Phase
- DNA of each chromosome replicates to form an identical set
- Doubles the # of genes in the nucleus

14. 8.2 The Phases of the Cell Cycle
INTERPHASE
Specific events of G2
- The specific molecules for mitosis are made

15. 8.2 The Phases of the Cell Cycle
MITOSIS
(Nuclear division)
Each new daughter cell receives one copy of each chromosome
Nucleus divides into 2 nuclei with identical chromosomes

16. 8.2 The Phases of the Cell Cycle
CYTOKINESIS
Division of the whole cell; splitting of the cytoplasm
Each cell enters G1 to start the cycle over again.

17. 8.6 Mitosis & Cell Division Chromosome Structure
Sister chromatids – the two copies of each chromosome made during the S phase
Entering mitosis, a chromosome looks like:

18. 8.6 Mitosis & Cell Division
Chromosome Structure
Centromere – a narrow point near the center of the chromosome attached by proteins that connects the sister chromatids
Kinetochore – within the centromere; a protein complex responsible for moving the chromatids during division

19. 8.6 Mitosis & Cell Division
Chromosome segregation – the separation of sister chromatids
Results in each nucleus receiving one copy of each chromosome
Anueploid – cell with an abnormal number of chromosomes (caused by a mistake during cell division)

20. 8.6 Mitosis & Cell Division
Mitosis is continuous, but we consider it to have 4 distinct steps: prophase, metaphase, anaphase, & telophase.

21. 8.6 Mitosis & Cell Division
Prophase
- Nuclear membrane
breaks down.
- Chromosomes
condense.
- Spindle fibers form
& anchor to the centrioles
and the kinetochore of
each chromosome.

22. 8.6 Mitosis & Cell Division
Metaphase
- Metaphase plate forms:
the line of chromosomes
down the middle of cell that
is perpendicular to the
spindle

23. 8.6 Mitosis & Cell Division
Anaphase
- Enzymes break down the
proteins holding the chromatids
together.
- Sister chromatids are pulled
along the spindle towards the
spindle poles by their
kinetochores
- Chromatids can now be called
chromosomes.

24. 8.6 Mitosis & Cell Division
Telophase
Chromosomes expand &
nuclear envelope reforms around
them.
- 2 new nuclei are formed.

25. 8.6 Mitosis & Cell Division
Cytokinesis
Division of the cytoplasm.
Cell is divided in 2 as plasma membrane pinches between the 2 cells.
Both daughter cells now enter the G1 phase of interphase.

26. 8.7 Differences in Mitosis
Plant Cells
Vesicles containing cellulose collect between the 2 nuclei.
Vesicles fuse – creating the plasma membrane & cellulose is released in between the 2 cells forming the cell wall.
Animal Cells
Cytokinesis begins around anaphase.
No cell wall to have to divide between the cells.