Ch 5 Cell Division

Describe binary fission in prokaryotic cells. What must occur before any cell can divide?

Binary fission is the method unicellular organisms such as bacteria(prokaryotes) use for reproduction. This form of reproduction is asexual. It produces offspring genetically identical to the parent organism and can occur very quickly. DNA must be copied before binary fission can begin. Once that happens, the cell splits into two new cells.

What is the purpose of cell division in eukaryotic multicellular organisms?

The purpose of cell division in multicellular organisms is to grow, repair, and maintain.

What are the four purposes of cell division in multicellular organisms?

1. Development 2. Growth 3. Repair of damaged tissues 4. Replacement of lost tissues

What is apoptosis? Why is it important in development and in the prevention of cancer?

Apoptosis is programmed cell death. There are three major check points during the cell cycle in which mitosis will not proceed or the cell will die. Often, cell death is associated with faulty or damaged DNA. If the cell would continue to reproduce, the damaged DNA would continue to spread and cancer would develop in the organism.

Briefly describe the cell cycle using the terms interphase, mitosis, and cytokinesis. Do all cells in the human body complete the cell cycle and undergo mitosis and cytokinesis? Give an example of a human cell that does complete the cell cycle and one that does not complete the cell cycle.

The interphase continuum of stages, G1, S, and G2, begins the process in which the cell grows and matures (G1), followed by the S phase in which the DNA is copied. Finally, the G2 phase is when the cell prepares for division. Mitosis occurs when the nucleus of the cell divides into two identical nuclei with the same number and type of chromosomes, followed by cytokinesis when the cytoplasm, for both plant and animal cells, divides, thus creating two daughter cells that are genetically equal and approximately identical in size. Not all cells in the human body complete the cell cycle, such as differentiated neurons and muscle cells that comprise the brain, heart and skeletal muscle. Cells such as skin cells do complete the cell cycle.

What is the definition of mitosis?

Mitosis is the process by which a cell, which has previously replicated each of its chromosomes, separates the chromosomes in its cell nucleus into two identical sets of chromosomes, each set in its own new nucleus.

Describe the events of prophase by describing what happens to the nuclear membrane, nucleolus, chromatin, centrioles, and spindle.

In prophase, chromatin shorten, thicken, and condense into distinct bodies called chromosomes. The nuclear membrane disassembles and the nucleolus is no longer visible. The spindle forms between the centrioles. A pair of centrioles is called a centrosome. Duplicated chromosomes begin migrating toward the center of the spindle.

Describe the structure of a duplicated chromosome using the words chromatid and centromere.

Duplicated chromosomes exist as pairs of sister chromatids joined together by a centromere.

What happens to the duplicated chromosome during metaphase? What is the relationship of the hereditary material on either side of the equator?

Duplicated chromosomes are lined up in the center of equator of the spindle during metaphase. The hereditary material is identical on either side of the equator.

What happens during anaphase?

Duplicated chromosomes separate at the centromere and are pulled by the spindle fibers toward each pole. Each single body is now called a chromosome. Cytokinesis begins at the end of anaphase.

What events occur during telophase?

Single chromosomes are at the poles of the spindle. The spindle disassembles and the nuclear membrane and nucleolus reappear. Cytokinesis continues until two daughter cells result.

What is cytokinesis? During which mitotic phase does cytokinesis begin? When is it completed?

Cytokinesis is the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells. It begins during anaphase and is completed at the end of telophase.

What is the difference between cytokinesis in plant and animal cells? Name the structures that complete cytokinesis in both plant and animal cells.

Animal cells divide by a cleavage furrow. Plant cells divide by a cell plate that eventually becomes the cell wall. Cytoplasm and cell membranes are necessary for cytokinesis in both plants and animals.

In what other way is plant and animal cell mitosis different?

Plant cells do not have centrioles or asters.

What is meiosis? Where and when does it occur? What are the results of meiosis?

Meiosis reduces the chromosome number and is a specialized process because it only produces haploid gametes. Meiosis only occurs in gonads and only occurs after sexual maturation (puberty). Meiosis turns diploids into haploids.

Distinguish between diploid body or somatic cells and haploid gametes or sex cells.

all your body (somatic) cells have 2 copies of each chromosome… and are diploid. Somatic cells contain all 46 chromosomes and are called diploid because they contain all chromosomes of the DNA. Haploid gametes contain half of the full number of chromosomes and are produced by sex cells, either ovum or sperm.

Describe the events occurring during meiosis I. What are homologous chromosomes?

The first cell division in Meiosis is known as Meiosis IIn Meiosis I members of homologous chromosome pairs are separated. This results in the segregation of genes into the two gametes. Homologous chromosomes are chromosomes that are matching but not identical. One homologous chromosome is inherited from the organism’s mother; the other from the organism’s father. They are usually not identical, but carry the same type of information.

What is crossing over and when does it occur? What is the significance of crossing over to genetic variability in a sexually reproducing population?

Crossing over occurs during synapsis and are cross-connections that form from breakage and rejoining between sister chromatids occurs between non sister chromatids, where one chromatid is from the mother and one is from the father (makes one pair of homologous). The crossing over is the shuffling of genetic information and the recombination of it, which allows for genetic variability in families with the same parents.

What is the result of meiosis I in terms of cell number and chromosome number and arrangement?

The chromosome number is cut in half as a result of meiosis I and two haploid cells are produced. Each cell pole has a cluster of chromosomes that corresponds to a complete haploid set, one member of each homologous chromosome pair at the end of meiosis I,.

In humans, how many different ways can the 23 homologous pairs of chromosomes line up at the metaphase plate or equator during metaphase I?

2^23=8,388,608

What is interkinesis? Does the DNA replicate during interkinesis?

It is the period of time between meiosis I and meiosis II. There is no replication of DNA in this stage.

Describe the events of meiosis II. What results after completion of meiosis II?

Once both cell poles have a haploid set of chromosomes clustered around them, these chromosomes divide mitotically (without reshuffling or reducing the number of chromosomes during division) during the second part of meiosis. This time, the spindle fibers bind to both faces of the kinetochore, the centromeres divide, and the sister chromatids move to opposite cell poles. At the end of meiosis II, therefore, the cell has produced four haploid groups of chromosomes. Nuclear envelopes form around each of these four sets of chromosomes, and the cytoplasm is physically divided among the four daughter cells in a process known as cytokinesis.

What is gametogenesis? What is spermatogenesis? Are all four cells resulting from spermatogenesis viable as gametes?

Gametogenesis is the production of gametes, or sex cells, and is the process of meiosis. Spermatogenesis is the name for gametogenesis in males. All four resulting cells from spermatogenesis are viable as gametes.

What is oogenesis? Why does one secondary oocyte get the majority of the cytoplasm, resulting in three useless polar bodies?

Oogenesis is the name for gametogenesis in females. If all four oocytes survived, it would be very possible for all women to have four babies at a time, which the body is not constructed for.

What is a zygote? What is the number of chromosomes in a human zygote? What type of cell division results in the multicellular fetus, child, and adult?

A zygote is a fertilized egg. A human zygote contains 46 chromosomes because it is the combination of two gametes. Mitosis occurs throughout the human life.

What is meant by reduction division in describing meiosis and gametogenesis?

Meiosis reduces the number of chromosomes and divides it in half from that of a normal cell, such as a skin cell. Diploid–> haploid

Describe how both mitosis and meiosis are necessary in the human life cycle.

It is very essential that cells go through mitosis so that each new cell contains the same gentic information. It is also very essential that meiosis occurs because reproduction would cease.