1. Cell Growth & Division
Biology  Pearland ISD

2. Cell Division There are 2 main reasons cell divides:
The cell has more trouble trying to move nutrients and wastes across the cell membrane.
The larger a cell becomes, the greater the demand it puts on its DNA.
Bottom line – cells need to be replaced

3. Cell Cycle The sequence of growth and division of a cell
An average cycle may be 22 hours
Three general periods:
resting phase
growth phase
division phase

4. G0 (Resting phase) Non-dividing, differentiated state.
Most human cells are in G0 phase.
Liver cells:
Generally in G0, but can be “called back” to cell cycle by external cues.
Nerve & muscle cells:
Highly specialized.
Arrested in G0 & can never divide.

5. Interphase (Growth phase)
Most of the cell’s life is spent in interphase
Longest phase –(90% of cell’s growth)
Centrioles – help to organize cell division Chromatin – DNA bound protein within the nucleus

6. Interphase (Growth phase)
New DNA is formed during 3 phases:
G1 – 1st period of growth
1. Increase in size.
2. Makes new proteins and
organelles.
S – DNA is synthesized or replicated
1. Chromosomes are replicated.
2. New DNA molecules are made.
G2 – final cell growth
1. Shortest phase
2. Prepares cell for mitosis

7. S-Phase of the Cell Cycle
Synthesis

8. DNA Genetic information = genome. Packaged into chromosomes.
During the S phase, the chromosomes enter a relaxed state that allows the enzyme DNA polymerase to access the DNA double helix inside each chromosome.
50 µm

9. Copying & Packaging DNA
When cell is ready to divide…
Copy DNA first, then…
Coil up doubled chromosomes like thread on a spool…
Now move DNA around cell without having it tangle & break.
Copying DNA
Coil DNA into compact chromosomes

10. DNA & Chromosomes
The DNA in a eukaryotic cell is organized into several linear chromosomes, whose organization is much more complex than the single, circular DNA molecule in a prokaryotic cell.
All eukaryotic cells store genetic information in chromosomes.
Most eukaryotes have between 10 and 50 chromosomes in their body cells.
Human cells have 46 chromosomes.
23 nearly-identical pairs

11. Chromosomes
A structure inside the cell’s nucleus containing long, tightly-coiled strands of DNA wrapped around proteins.

12. Structure of Chromosomes
Chromosomes are composed of a complex of DNA and protein called chromatin that condenses during cell division.
DNA exists as a single, long, double-stranded fiber extending chromosome’s entire length.
Each unduplicated chromosome contains one DNA molecule, which may be several inches long.

13. Chromosomes Maternal set of chromosomes (n = 3) Two sister chromatids
Paternal set of
2n = 6
Two sister chromatids
of one replicated
chromosome
Two non-sister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
Centromere

14. Pair of sister chromatids
Chromosomes
Pair of sister chromatids
Kinetochore
proteins
Centromere
(DNA that is
hidden beneath
the kinetochore
proteins)
One
chromatid
(dark blue)
(light blue)
The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores.

15. Chromosomes In a diploid cell, the chromosomes occur in pairs.
The 2 members of each pair are called homologous chromosomes or homologues.
In a cell in which DNA synthesis has occurred all the chromosomes are duplicated and thus each consists of two identical sister chromatids.

16. Chromosomes Non-homologous chromosomes: Sex chromosomes:
Look different.
Control different traits.
Sex chromosomes:
Are distinct from each other in their characteristics.
Are represented as X and Y.
Determine the sex of the individual, XX being female, XY being male.

17. Chromosome Duplication
In preparation for cell division, DNA is replicated and the chromosomes condense.
Each duplicated chromosome has two sister chromatids, which separate during cell division.

18. 0.5 µm
Chromosome duplication (including DNA synthesis)
Centromere
Separation of sister chromatids
Sister chromatids
Centrometers
A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule.
Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule.
Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.

19. Chromosome Duplication
Because of duplication, each condensed chromosome consists of 2 identical chromatids joined by a centromere.
Each duplicated chromosome contains 2 identical DNA molecules (unless a mutation occurred), one in each chromatid.
Homologous chromosomes are made up of sister chromatids joined at the centromere.
Two Unduplicated
Chromosomes
Centromere
Sister
chromatids
Duplication
Non-sister chromatids
Two Duplicated Chromosomes

20. Terms to know
Chromosome – contains genetic information (DNA) passed from one generation to the next
Spindle – microtubule that helps separate chromosomes
A – centromere: center of chromosome B – chromatids: two identical “sister” parts of the chromosome

21. Takes place within the nucleus of the cell.
Mitosis
Takes place within the nucleus of the cell.

22. Mitosis (Division phase)
4 Phases:
(PMAT)
Prophase
Metaphase
Anaphase
Telophase

23. 4 phases that blend from one to another

24. Prophase 1st and longest phase of mitosis Chromatin become chromosomes
Chromatids are joined by centromere
Nucleus disappears
Centrioles migrate to poles
Spindles are formed

25. Metaphase 2nd phase of mitosis Chromosomes meet in the middle of cell
Pulled by spindles
Each chromosome is attached to top of spindle

26. Anaphase 3rd phase of mitosis Centromeres are split apart
Chromatids are pulled apart and begin to drift to opposite poles

27. Telophase Final phase of mitosis Begins when chromatids reach poles
New nucleus starts to form
Chromosomes start to unwind
Spindles disappear
Cytoplasm begins to divide

28. Cytokinesis Cytoplasm pinches in half
Each daughter cell has an identical set of chromosomes

31. Cancer Cancer is a disorder where the cell has uncontrolled growth.
Cancer cells do NOT respond to regulators.
This causes the cells to form masses called tumors, which can damage surrounding tissues.

34. Cancer Development
Cancer develops only after a cell experiences ~6 key mutations (“hits”).
Unlimited growth
Turn ON growth promoter genes.
Ignore checkpoints
Turn OFF tumor suppressor genes.
Escape apoptosis
Turn OFF suicide genes.
Immortality = unlimited divisions
Turn ON chromosome maintenance genes.
Promotes blood vessel growth
Turn ON blood vessel growth genes.
Overcome anchor & density dependence
Turn OFF touch-sensor gene.

35. Cancer Triggers Mutations in cells can be triggered by: UV radiation
Chemical exposure
Radiation exposure
Heat
Cigarette smoke
Pollution
Age
Genetics

37. Growing out of control, cancer cells produce malignant tumors
Cancer cells do not respond normally to the cell cycle control system
Divide excessively.
Can invade other tissues.
May kill the organism.

38. If an abnormal cell avoids destruction by the immune system, it may form a tumor
Benign: abnormal cells remain at original site
Malignant: abnormal cells can spread to other tissues and parts of the body
Metastasis: spread of cancer cells through the circulatory system

39. Cancers are named according to location of origin:
Carcinoma: external or internal body coverings
Sarcoma: tissues that support the body
Leukemia and lymphoma: blood-forming tissues
Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division