Bio 004, College of the Desert

• 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.

• Asexual Reproduction: production of off-spring by a single parent that does not

• involve fertilization of an egg by a sperm.

• 1. Parent and offspring share identical genes.

• 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.

• 1. Maintains a constant chromosome number.

• 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.

• Cell Cycle:
• 1. 90% of the cell cycle is dedicated to interphase.
• 2. During interphase, the cell is replicating DNA, cytoplasm, and organelles.

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).

• Cancer Treatment

• 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.

• 3. Surgical removal: duh

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

• have an extra chromosome. Characteristics include: fold of skin at inner corner of eye, round face, flattened nose bridge, small irregular teeth, short stature, heart de-fects, and susceptibility to respiratory infection, leukemia, and Alzheimer’s.

• 1. Incidence increases with a mother’s age.

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.