chapter 12 quizlet Microbiology

Nuclear Division (Eukaryotic Reproduciton) i. Haploid: a nucleus with a single copy of each chromosome (1n) ii. Diploid: One with two sets of chromosomes (2n) A. Two types of nuclear division: *Mitosis: *Meiosis

-a eukaryotic nucleus has either one or two complete copies of the chromosomal portion of a cells genome.

what is a chromosome?

-chromosomes are a pair of chromatids during the first two phases

Reproduction of eukaryotes: -usually invovles two types of divison such as 1. Nuclear Division 2. Cytoplasmic division (also called cytokinesis) also can consider schizogony

-most of the DNA in eukaryotes is packaged with histone proteins as CHROMOSOMES in the form of CHROMATIN FIBERS located within the nuclei. -Remaining DNA in eukaryotic cells is found in mitochondria and chloroplasts, organelles that reproduce by binary fission in a manner similar to prokaryotic production -Eukaryotes have a variety of methods of asexual reproduction, including binary fission, budding, fragmentation, spore formation and schizogony -Many eukaryotes reproduce sexually, via a process that involves the formation of sexual cells called gametes, and the subsequent fusion of two gametes to form a cell called a zygote -Algae, fungi, and some protozoa reproduce both sexually and asexually

Eukaryotic microbes include: -unicellular and mulitcellular protozoa -fungi: prodouce penicillin -algae -water molds -slime molds -both human pathogens and organism that are vital for human life

-the cells of most fungi, many algae and some protozoa are haploid -the cells of most plants and animals and the remaining fungi, algae and protozoa are diploid -typically gametes are haploid and zygote (formed from the union of gametes) are diploid

Sexual Spore Formation: Four basic steps:

1 Haploid (n) cells from a + fungus and a - fungus fuse to form a dikaryon, a cell containg both + and - nuclei. The dikaryotic stage is neither dipoloid nor haploid but instead designated (n+n) 2. After a period of time that typically range from hours t years but can be centuries, a pari of nuclei within a dikaryon fuse to form one diploid (2n) nuceleus 3. Meiosis of the diploid nucleus restores the haploid state 4. the haploid nuclei are partitioned into + and - spres which restablish + and - fungi by mitoses and cell divisions.

why do microbiologists study parasitic helminths? how about arthropod vectors?

-b/c they have microscopic stages -b/c they are intimately involved in the transmission of microbial pathogens

how does the four phases of meiosis II differ form those of mitosis?

the phasees of meioisis II are equivalent to those in mitosis such as: -the crossing over during meiosis I produces genetic recombinations, ensuring that chromosomes resulting from meiosis are different from the parental chromosomes.

Why do cell divides its nucleus?

to pass a copy of its chromosomal DNA to each of its descendants so that each new generation has the necessary genetic instructions to carry on life

T or F: chromosomes are synonymous terms during the latter two phases of mitosis

true

T or F: mitosis is a continous process and there are no clear boundaries between succeding phases..one phase leads seamslessly to the next.

true

Meiosis: -meiosis is a nuclear division that involves the partitioning of chromatids into four nuclei such that each nucleus receives only half the original amount of DNA -Diploid nuclei use meiosis to produce haploid daughter nuclei. -meiosis is a necesssary condition for sexual reproduction (in which nuclei from two different cells fuse to form a single nucleus) b/c if cells lacked meiosis, each nuclear fusion to form a zygote would cause the number of chromosomes to double and their number would soon become unmanageable -occurs in two stages: *Meiosis I *Meiosis II -produces four haploid nuclei from a single diploid nucleus. -can be considere back to back mitoses without the DNA replcation of interphase between them.

1. Early Prophase I (prophase of meoisis I): as with mitosis, DNA replication during interphase has resulted in pairs of identical chromatids, forming chromosomes. But now an additional pairing occurs: homologous chromosomes-- that is, chromosomes carrying similar or identical genetic sequences--line up side by side. Because these are prophase chromosomes, each of them consists of two identical chromatids; therefor, four DNA molecules are involved in this pairing. An aligned pair of homologous chromosmes is known as a tetrad. 2. Late Prophase I: once tetrads have formed, the homologous chromosomes exchange sections of DNA in a random fashion via a process called CROSSING OVER. This results in recombinations of their DNA. It is because of meiotic crossing over that the offspring produced by sexual reproduction have different genetic makeup form their sibligs. Prophase I can last for days or longer. 3. Metaphase I: tetrads align on a plane in the center of the cell and attach to spindle microtubules. Metaphase I differs from metaphase of mitosis in that homologous chromosomes remain as tetrads 4. Anaphase I: chromosomes of the tetrads move apart from one another; however, in contrast to mitotic anaphase, sister chromatids remain attached to one another 5. Telophase I : the first stage of meiosis is compeleted as spindle disintegrates. Typically, the cell divides at this phase to form two cells. Nuclear envelopes may form. Each daughter nucleus is haploid, though each haploid chromosomes consists of two chromatids 6. Prophase II: Nuclear envelopes disintegrate, and new spindles form 7. Metaphase II: the chromosomes align in the middle of each cell and attach to microtubles of the spindles 8. Anaphase II: sister chromatids separate as in mitosis 9. Telophase II: Daughter nuclei form. The cells divide, yielding four haploid cells.

Mitosis: -begins after the cell has duplicated its DNA such that there are two exact DNA copies, the cell partitions its replicated DNA equally b/w two nuclei. -Mitosis maintains the ploidy of the parent nucleus; that is, a haploid nucleus that undergoes mitosis forms two haploid nuclei and a diploid nucleus that undergoes mitosis produces two diploid nuclei - mitosis has four phases: prophase, metaphase, annaphase and telophase -Eukaryotic cells have two main stages in their life cycles, a stage called interphase, in which cells grow and eventually replicate their DNA, and a stage during which the cells nucleus divides

1. Prophase: the cell condenses its DNA molecules into visible threads called CHROMATIDS. Two indentical chromatids, sister DNA molecules, are joined together in a region called a CENTROMERE to form one chromosomes. Also during prophase, a set of microtubles is constructed in the cytosol to form a SPINDLE. In most cells, the nuclear envelope disintergrates during prophase so that mitosis occurs freely in the cytosol; however, many fungi and some unicellular microbes maintain their nuclear envelopes so that mitosis occurs inside their nuclei. 2. Metaphase: the chromosomes line up on a plane in the middle of the cells and attach near their centromeres to microtubules of the spindle 3. Anaphase: Sister chromatids seperate and crawl along the microtubules toward opposite poles of the spindle. Each chromatid is now called a chromosomes. 4. Telophase: the cell restores its chromosomes to their less compact, nonmitotic state, and nuclear envelopes form around the daughter nuclei. A cell may divide during teleophase, but mitosis is nuclear division, not cell division