Unit 2 DB: Cancer Risk Factors (Biology)
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Post_BIO120-Unit2B.pdf
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
BIO120 Concepts of Biology
Unit 2 Lecture Part Two: Cell Division
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
The ultimate purpose of cell division is to transmit genetic material to the next generation of cells. The sum of all genes or genetic material of an organism is called the genome.
• In prokaryotes, the genome is single circular piece of DNA
• In eukaryote, the genome consists of multiple, linear chromosomes (23 pairs in humans)
Eukaryote cells can have more than one copy of each chromosome, a condition called diploidy. Haploid cells have one copy; diploid cells have two. For example, human gametes (sperm and eggs) are haploid with 23 chromosomes. The rest of the cells of the body (somatic cell) are diploid with 23 pairs of chromosomes. Each pair of matched chromosomes are homologous chromosomes (e.g. the chromosomes 1 from your dad and from you mom are homologous chromosomes). Different species have different number of chromosomes, which provides a reproductive barrier between species.
Genome
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Prokaryotes reproduce asexually in which the daughter cells are clones of the original cell. The most common form of asexual reproduction in prokaryotes is binary fission. During binary fission, DNA starts to replicate at a specific site on the DNA: the origin of replication. After DNA replication, the chromosome attach to opposite sides of the cell. A protein called Ftsz then forms a ring between the genomes. A septum (a partition) then forms between the cells causing them to pinch off from each other.
Prokaryotes: Binary Fission
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Eukaryote cells have two forms of cell division: mitosis and meiosis. Cells divide by mitosis to create two daughter cells that have same genetic material. Mitosis allows multicellular organisms to grow and differentiate. Cells divide by meiosis to produce gametes that have half the genetic material of the starting cells. In this unit, we focus on mitosis. We will return to meiosis in Unit 4.
Eukaryote Cell Division
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Cells grow and divide by progressing through a series of stages called the cell cycle. There are two phases in eukaryotes: interphase and mitotic phase. During interphase, cells grow and replicate their DNA. Interphase has three subdivisions:
• G1 (Gap 1) when cells are growing to prepare for DNA replication.
• S phase when cells are synthesizing and replicating DNA and also duplicate centrosomes
• G2 cells check that DNA reproduction occurred correctly and continue to grow and prepare for mitosis.
After G2, cells entire the mitotic phase. During mitosis, the chromosomes and centrosomes that were duplicated in the S phase are now separated into the daughter nuclei. The cell then usually divides the cytoplasm among the two daughter cells, a process called cytokinesis.
Cell Cycle
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Animal cell mitosis is divided into five stage:
• Prophase – chromosomes condense and nuclear membrane breaks down.
• Prometaphase - mitotic spindles from the centrosomes attach to chromosomes
• Metaphase – chromosomes line up in the middle of the cell from the metaphase plate.
• Anaphase – sister chromatids are separated into opposite ends.
• Telophase— the reformation of the nuclear envelope in the daughter cells.
• Cytokinesis – final separate of cells into two daughter cells.
Mitosis
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Animal and plants cells undergo cytokinesis differently. In animal cells (a), a cleavage furrow forms at the former metaphase plate in the animal cell. The plasma membrane is drawn in by a ring of actin fibers contracting just inside the membrane. The cleavage furrow deepens until the cells are pinched in two. In plants (b), Golgi vesicles coalesce at the former metaphase plate and then fuse to form the cell plate. The cell plate grows from the center toward the cell walls. New cell walls are made from the vesicle contents.
Cytokinesis
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Cells that no longer need to divide can exit the cell cycle and enter G
0 . In some cases, this is a temporary condition until
triggered to enter G1. In other cases, the cell will remain in G 0
permanently (e.g. neurons, muscle cells).
G-Zero (G 0
)
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
The cell cycle is controlled at three checkpoints. Integrity of the DNA is assessed at the G1 checkpoint. Proper chromosome duplication is assessed at the G2 checkpoint. Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint. Disruption of these cell cycle check points by say mutations, can lead to uncontrolled growth.
Cell Cycle Regulation
Genome
Mitosis
Cytokinesis
G-Zero (G 0 )
Cell Cycle Regulation
Cancer
Eukaryote Cell Division
Cell Cycle
Prokaryotes: Binary Fission
Cancer can results from mutations in different genes. Most mutations either have no effect or cause enough damage to cause the cell to activate a controlled, self-destruct sequence (apoptosis). However, some mutations will disrupt regulation of the cell cycle leading to uncontrolled growth. One of the most commonly mutated genes is the p53 gene, which encodes a protein that monitors for DNA damage. If the DNA damage is repaired, the cell resumes division. If the p53 gene is mutated, then DNA damage accumulates undetected, which can result in additional loses of cell cycle regulation. Most cancers are believed to require at least two mutations before the cells take on characteristic of cancer cells. Even after the cancer grows into a tumor, some tumors are benign and do not pose a serious risk. However, some tumors can acquire additional mutations that allow cancer cells to travel in the blood to latch on to other organs, a process called metastasis. A cancer that has metastasized is very dangerous. Some treatments for cancer such as radiation therapy and chemotherapy infer with cell division. Because cancerous cells tend to divide faster than noncancerous cells, these treatments should be more damaging to cancerous cells than noncancerous cells. More recent therapies are aimed at better targeting treatments to only cancerous cells and reduce the side effects of other treatments.
Cancer
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