Cell Division

Cell cycle

The cell cycle or cell-division cycle is the series of events that take place in a cell leading to its division and duplication (replication) that produces two daughter cells.

Chromosome

염색체(染色體, chromosome)는 생물체(엄밀히 말하면 진핵세포를 지닌 생물)의 세포분열과정에서만 관측되며, 세포분열기에 들어가면서 유전물질을 안전하게 보호하고 딸세포들에게 형평성있게 유전정보를 분배하기위해 염색사가 꼬이고 뭉쳐져 응축되어 X자형태를 이룬구조물이다.

Chromosome

Mitosis

Interphase

Interphase

a) Interphase: The period of a cell’s growth and development.

I. Before a cell can enter cell division, it needs to take in nutrients. All of the preparations are done during interphase.

II. Interphase is a series of changes that takes place in a newly formed cell and its nucleus, before it becomes capable of division again.

III. Typically interphase lasts for at least 90% of the total time required for the cell cycle.

Interphase

Mitotic Phase

b) Mitotic phase: The period of a cell’s reproduction.

I. Mitosis is the process by which a cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei.

II. Mitosis occurs exclusively in eukaryotic cells. Prokaryotic cells, which lack nucleus, divide by a process called binary fission.

III. Mitotic phase is divided into phases, corresponding to the completion of one set of activities and the start of the next. These phases are sequentially known as:

prophasemetaphaseanaphasetelophasecytokinesis

Why do Cell divide?

1. Growth

2. Reproduction

3. Repair

Some cells never divide (ex. Nerve cell)

DNA vs. Gene vs. Chromosome?

DNA: A material which contains genetic information

Gene: The genetic material inside the DNA

Chromosome: Chromosomes contain DNA

Terms

1. Centromere: 중심립2. Telomere: 말단소립3. Kinetochore: 동원체4. Centrosome: 중심체5. Chromatid: 염색분체6. Spindle: 방추사7. Spindle pole: 방추체극8. Chromosome: 염색체9. Microtubule: 미소관10. Nuclear envelope: 핵외피11. Diploid: 2배체12. Autosome: 상염색체13. Sex chromosome: 성염색체14. Cleavage furrow: 분열구15. Centriole: 중심체

Mitotic Phase

Animal cell vs. Plant cell

Cancer Cells: Growing out of Control

What is Cancer?

• Disease of the cell cycle.

• In all types of cancer, some of the body’s cells begin todivide without stopping and spread into surrounding tissues.

Tumor and Metastasis

• Benign tumor: If the abnormal cells remain at the original site, the lump is called a benign tumor.• Malignant tumor: One that has begun to spread into neighboring tissues and other parts of the body.

• Metastasis: the spread of a cancer or other disease from one organ or part to another not directly connected with it.

Cancer Staging

Primary Tumor (T)TX: Primary tumor cannot be evaluatedT0: No evidence of primary tumorTis: Carcinoma in situT1, T2, T3, T4: Size and/or extent of the primary tumor

Regional Lymph Nodes (N)NX: Regional lymph nodes cannot be evaluatedN0: No regional lymph node involvementN1, N2, N3: Degree of regional lymph node involvement (number and location of lymph nodes)

Distant Metastasis (M)MX: Distant metastasis cannot be evaluatedM0: No distant metastasisM1: Distant metastasis is present

Stage Definition

Stage 0 Carcinoma in situ

Stage I, Stage II, and Stage III

Higher numbers indicate more extensive disease: Larger tumor size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or tissues or organs adjacent to the location of the primary tumor

Stage IV The cancer has spread to distant tissues or organs

Cancer Treatment

• Radiation Therapy: Parts of the body that have cancerous tumors are exposed to concentrated beams ofhigh energy radiation, which can often harm cancer cells more than the normal cells of the body.

• Chemotherapy: The use of drugs to disrupt cell division.

Meiosis

Meiosis

A specialized type of cell division which reduces the chromosome number by half.

• Occurs in all sexually reproducing single-celled and multi-celled eukaryotes.

• In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell.

• In the case of animals, meiosis only happens in testis and ovary.

Meiosis

I. Meiosis I: Homologous chromosomes pair at the metaphase plate, and then the homologues migrate to opposite poles.II. Meiosis II: Chromosomes spread across the metaphase plate and sister chromatids separate and migrate to opposite poles.

Meiosis I

Meiosis II: Homologous chromosomes pair at the metaphase plate, and then the homologues migrate to opposite poles.

Crossing Over

•Genetic material from the homologous chromosomes is randomly swapped•This creates four unique chromatids•Since each chromatid is unique, the overall genetic diversity of the gametes is greatly increased

Meiosis II

Meiosis II: Chromosomes split across the metaphase plate and sister chromatids separate and migrate to opposite poles.

Meiosis

Mitosis vs. Meiosis

Genetic Variation

1. Crossing over

- During prophase I, nonsister chromatids of homologous chromosomes exchange pieces of genetic material.

1. Independent assortment of homologues

- During metaphase I and anaphase I, tetrads of homologues chromosomes separate into chromosomes that go to opposite poles.

2. Random joining of gametes

- Which sperm fertilizes with which egg is a random event.

Regulation of the Cell Cycle

1. Surface to volume ratio (S/V)

- When S/V is large, a cell can efficiently react with the outside environment. For instance, adequate amounts of oxygen can diffuse into the cell, and waste products can be rapidly eliminated. When S/V is small, the surface area might be unable to exchange enough substances with the outside environment.

2. Genome to volume ratio (G/V)

- The genetic material in the nucleus, called its genome, controls the cell by producing substances that make enzymes and other biosynthetic substances. The capacity of the genome to do this is limited by its finite amount of genetic material. As the cell grows, its volume increases, but its genome size remains constant. As the G/V decreases, the cell’s size exceeds the ability of its genome to produce sufficient amounts of materials for regulating cellular activities.

When Meiosis Goes Awry

Nondisjunction: members of a chromosome pair fail to separate at anaphase.

Down Syndrome: An Extra Chromosome 21

Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.

Down Syndrome: An Extra Chromosome 21

- One in every 691 babies in the United States is born with Down syndrome, making Down syndrome the most common genetic condition.

Down Syndrome: An Extra Chromosome 21

- Down syndrome is usually identified at birth by the presence of certain physical traits: low muscle tone, a single deep crease across the palm of the hand, a slightly flattened facial profile and an upward slant to the eyes.

Abnormal Numbers of Sex Chromosomes

Also known as 47,XXY or XXY, is the set of symptoms that result from two or more X chromosome in males.

Abnormal Numbers of Sex Chromosomes

45,X, is a condition in which a female is partly or completely missing an X chromosome.