Cell Reproduction Unit
Chromosome Structure
- chromosome = a long continuous thread of DNA that consists of numerous genes with regulatory
information coiled around proteins in compact structures
- DNA wraps around proteins (called histones) to become compact
Cell Cycle
= the regular pattern of growth, DNA duplication, and cell division that occurs in cells
- results in two cells (daughter cells) identical to one another
- made up of 5 Phases
1) G1 Phase
- cell grows in size (cell growth)
Interphase
2) S Phase
- makes a copy of its DNA (DNA is copied)
3) G2 Phase
- cell prepares for cell division
**G1, S, and G2 Phase collectively are called Interphase**
4) M Phase (Mitosis)
- nucleus divides
5) C Phase (Cytokinesis)
- cytoplasm divides
Phases of Mitosis
- discovered by Walther Flemming in 1882
- makes body cells (skin, blood, organs, etc)
1) Prophase
- DNA coils to become chromosomes
- nuclear membrane disappears
- microtubules called spindle fibers grow from centrioles to center of cell
2) Metaphase
- chromosomes line up in the center
3) Anaphase
- chromosomes pull apart and move to opposite ends of cell
4) Telophase
- chromosomes uncoil
- nuclear membrane reforms
Cytokinesis
- cell membrane forms a cleavage furrow and cytoplasm divides
- in plants, a cell plate forms between each cell
Regulation of Cell Division
- controlled by external and internal factors
- External Factors
1) cell to cell contact
2) growth factors = group of proteins that stimulate cell division
- most cells controlled by a combination of growth factors
- Internal Factors
- enzymes and proteins released by the cell
ex)
1) kinases = enzymes that increase the energy to a cell
2) cyclins = proteins that control the cell cycle
- apoptosis = programmed cell death
Cancer
= common name for a class of diseases characterized by uncontrolled cell division
- benign tumor = cancer cells typically remain clustered together
- malignant tumor = some of the cancer cells can break away (metastasize) from the tumor
- can form tumors in other parts of the body
- why are tumors harmful?
- use energy from the body but do nothing for the body
- exert pressure on surrounding organs
- carcinogens = substances known to produce or promote the development of cancer
- treatment includes radiation and chemotherapy
Asexual vs. Sexual Reproduction
- Asexual reproduction = reproduction of offspring from one parent
- offspring are genetically identical to the parent….this is a BAD thing
- Sexual reproduction = reproduction of offspring from two parents (egg and sperm = gametes)
- offspring are genetically different from the parents ….this is a GOOD thing
- Asexual reproduction is more efficient that sexual reproduction
- Some eukaryotic cells divide by mitosis: plant cuttings, budding yeast, flatworms and sea stars can
grow from pieces of original
- some organisms can reproduce by asexual or sexual reproduction (depends on conditions)