Term
|
Definition
| The reproduction of cells; what the continuity of life is based on. |
|
|
Term
|
Definition
| The life of a cell from its origin in the division of a parent cell until its own division into two. |
|
|
Term
|
Definition
| A cell's endowment of DNA. Before a cell can divide, all the DNA must be copied and then the two copies separated so that each daughter cell ends up with a complete genome. |
|
|
Term
|
Definition
| The replication and distribution of so much DNA is manageable because the DNA molecules are packaged into chromosomes. |
|
|
Term
|
Definition
| The nuclei of human somatic cells, all body cells except the reproductive cells, each contain 46 chromosomes. |
|
|
Term
|
Definition
| Reproductive cells, sperm cells and egg cells, that have half as many chromosomes as somatic cells, or 23 chromosomes in humans. |
|
|
Term
|
Definition
| The DNA molecule in each eukaryotic chromosome is associated with various proteins that maintain the structure of the chromosome and help control the activity of the genes. This DNA-protein complex, chromatin, is organized into a long, thin fiber. After a cell duplicates its DNA in preparation for division, the chromatin condenses: It becomes densely coiled and folded, making the chromosomes much shorter and so thick that we can see them with a light microscope. |
|
|
Term
|
Definition
| Each duplicated chromosome has two sister chromatids. The two chromatids, containing identical copies of the chromosome's DNA molecule, are initially attached by proteins all along their lengths. |
|
|
Term
|
Definition
| In condensed form, the chromosome has a narrow "waist" at a specialized region called the centromere. |
|
|
Term
|
Definition
| The division of the nucleus. Usually followed immediately by cytokinesis. Mitosis and cytokinesis produced the trillions a somatic cells that now make up your body, and the same processes continue to generate new cells to replace dead and damaged ones. |
|
|
Term
|
Definition
| The division of the cytoplasm. Where there was one cell, there are now two, each the genetic equivalent of the parent cell. |
|
|
Term
|
Definition
| You produce gametes - eggs or sperm cells - by a variation of cell division called meiosis, which yields daughter cells that have half as many chromosomes as the parent cell. Meiosis only occurs in your gonads (ovaries or testes). In each generation of humans, meiosis reduces the chromosome number from 46 to 23. |
|
|
Term
|
Definition
| Includes both mitosis and cytokinesis, and is usually the shortest part of the cell cycle. |
|
|
Term
|
Definition
| Mitotic cell division alternates with a much longer interphase, which often accounts for about 90% of the cycle. It is during interphase that the cell grows and copies its chromosomes in preparation for cell division. |
|
|
Term
|
Definition
| Interphase can be divided into subphases: the G1 phase ("first gap"), the S phase, and the G2 phase ("second gap"). During all three subphases, the cell grows by producing proteins and cytoplasmic organelles. Chromosomes are duplicated only during the S phase (S is for synthesis of DNA). A cell grows (G1), continues to grow as it copies its chromosomes (S), grows more as it completes preparations for cell division (G2), and divides (M). The daughter cells may then repeat the cycle. |
|
|
Term
| Five subphases of mitosis |
|
Definition
| Prophase, prometaphase, metaphase, anaphase, and telophase. |
|
|
Term
|
Definition
| In the G2 phase, microtubules extend from the centosomes in radial arrays called asters. |
|
|
Term
|
Definition
| During prometaphase, each of the two chromatids of a chromosome now has a specialized structure called the kinetochore, located at the centomere region. Each of the two joined chromatids of a chromosome has a kinetochore, a structure of proteins and specific sections of chromosomal DNA at the centromere. |
|
|
Term
|
Definition
| During metaphase, the centrosomes are now at opposite poles of the cell. The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle's two poles. |
|
|
Term
|
Definition
| Many of the events of mitosis depend on the mitotic spindle, which begins to form in the cytoplasm during prophase. While the mitotic spindle assembles, the microtubules of the cytoskeleton partially disassemble, probably providing the material used to construct the spindle. The spindle microtubules elongate by incorporating more subunits of the protein tubulin. |
|
|
Term
|
Definition
| The assembly of spindle microtubules starts in the centrosome, a nonmembranous organelle that functions throughout the cell cycle to organize the cell's microtubules. In animal cells, a pair of centrioles is located at the center of the centrosome, but the centrioles are not essential for cell division. |
|
|
Term
|
Definition
| In animal cells, cytokinesis occurs by a process known as cleavage. The first sign of cleavage is the appearance of cleavage furrow, which begins as a shallow groove in the cell surface near the old metaphase plate. |
|
|
Term
|
Definition
| Cytokinesis in plant cells have no cleavage furrow. During telophase, vesicles derived from the Golgi apparatus move along microtubules to the middle of the cell, where they coalesce, producing a cell plate. |
|
|
Term
|
Definition
| Prokaryotes reproduce by a type of cell division called binary fission, meaning literally "division in half." |
|
|
Term
|
Definition
| Once the DNA of the chromosome begins to replicate, the copies of the first replicated region - called the origin of replication - move apart rapidly. |
|
|
Term
| Cell cycle control system |
|
Definition
| A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle. |
|
|
Term
|
Definition
| A critical point where stop and go-ahead signals can regulate the cycle. |
|
|
Term
|
Definition
| To be active, the kinases that drive the cell cycle must be attached to a cyclin, a protein that gets its name from its cyclically fluctuating concentration in the cell. Because of this requirement, these kinases are called cyclin-dependent kinases, or Cdks. |
|
|
Term
|
Definition
| A protein released by certain body cells that stimulates other cells to divide. |
|
|
Term
| Density-dependent inhibition |
|
Definition
| The discovery of growth factors provided the key to understanding density-dependent inhibition of cell division, a phenomenon in which crowded cells stop dividing. |
|
|
Term
|
Definition
| Most animal cells also exhibit anchorage dependence. To divide, they must be attached to a substratum, such as the inside of a culture jar or the extracellular matrix of a tissue. |
|
|
Term
|
Definition
| The abnormal behavior of cancer cells can be catastrophic when it occurs in the body. The problem begins when a single cell in a tissue undergoes transformation, the process that converts a normal cell to a cancer cell. The body's immune system normally recognizes a transformed cell as an insurgent and destroys it. |
|
|
Term
|
Definition
| If the cell evades destruction, it may proliferate to form a tumor, a mass of abnormal cells within otherwise normal tissue. |
|
|
Term
|
Definition
| If the abnormal cells remain at the original site, the lump is called a benign tumor. Most benign tumors do not cause serious problems and can be completely removed by surgery. |
|
|
Term
|
Definition
| A malignant tumor becomes invasive enough to impair the functions of one or more organs. |
|
|
Term
|
Definition
| The spread of cancer cells to locations distant from their original site. If a tumor metastasizes, treatments may include high-energy radiation and chemotherapy with toxic drugs that are especially harmful to actively dividing cells. |
|
|
