CellDivision: replacement of damaged or lost cells; growth
At least 60,000,000,000 cells in the human body: Cell division starts with a single fertilized egg.
Chromosomes:DNA-containing structures that carry the organism’s genetic legacy
Prior to cell division, chromosomes are duplicated so that each daughter cell receives equal proportions of DNA from the mother cell.
2. Maintains cells in multicellular organisms.
3. Maintains certain species (kinds) of organisms.
Sexual Reproduction: production of off-spring by two parents that involves fertilization of an egg by a sperm.
2. Creates genetic diversity
Chromatin: combination of DNA and protein. Protein helps to organize DNA and control gene activity. DNA’s total length in one cell’s 46 chromosomes = 2 m: Chromosomes are most easily seen during mitosis DNA is coiled, then supercoiled as it is packed in nucleus
Histones (small proteins) are critical in DNA packing
Nucleosome is DNA wound around histone molecules.
2. Prior to cell division, chromosomes are duplicated.
3. Results are genetically identical sister chromatids.
4. Sister chromatids are joined together in the center at the centromere.
Mitosis: nucleus and DNA divide and are evenly distributed between two cells.
Cytokinesis: cytoplasm divides in two. End result is two genetically identical daughter cells.
Centrioles: structures of microtubules that build the spindle in animal cells. Centrioles are not found in plant cells even though plant cells have spindles.
Cell Plate: membranous disk that forms at the equator in plant cells: Vesicles containing cell wall material collect at the equator of the parent cell fusing together until the division into two daughter cells.
Cancer: disease of the cell cycle; excessive cell division that invades other tissues of the body, sometimes resulting in death In tissue culture, cancer cells are “immortal”; most cell lines die out after 20 – 50 cell divisions.
Malignant: lump of abnormal body cells that spreads from the site of origin by way of the circulatory system (metastasis).
1. Radiation therapy: Expose tumors to high-energy radiation - damages DNA, disrupts cell division
2. Chemotherapy: Expose tumors to high-dose drugs - alters spindle function, disrupts cell division.
Apoptosis: genetically programmed cell death (cell suicide) : Controlled by a single gene (p53) in which 1,000+ mutations have been observed (mutations = cancer).
Autosomes: chromosomes NOT directly involved in determining gender. Any of the 22 pairs of chromosomes in humans that are NOT sex chromosomes.
Diploid: homologous pairs of chromosomes found in somatic cells (46 in humans); 2n.
Haploid: single set of chromosomes found in sex cells (23 in humans); n
Meiosis: process that produces haploid daughter cells in diploid organisms.
1. Cuts the chromosome number in half.
2. Increase genetic diversity.
Synapsis: homologous chromosomes align themselves next to one another.
Nondisjunction: situation in which members of a chromosome pair fail to separate during division I or II. Results in abnormal numbers of chromosomes in gametes. Causes unknown.
Down’s Syndrome: results from trisomy 21 – in which the 21st pair of chromosomes
Klinefelter’s Syndrome (XXY): Testes are small; male is sterile often with breast enlargement, other feminine body contours.
Turner’s Syndrome (XO): Short stature, web of skin extending between neck and shoulders; female is sterile due to underdeveloped sex organs along with secondary sexual characteristics.