Learning Resource 09. The Learning Resource goal is to use the Internet and become independent of the textbook. It is a project in progress...   Ch. x
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(Source: Dr. Nilsson's old lecture notes, and Mader, S.S. 2010. Biology. Ed. 10. Used for educational purpose.Permission given in 2001 by McGraw-Hills then sales representative, Don Grainger, to use the pictures online on lecture notes.)   Cancer cell dividing.  The hereditary information of all living things is DNA (Deoxyribonucleic acid), contained in chromosomes in the cell nucleus (if eukaryotes). A single molecule of DNA is a long double helix chain of subunits (building blocks) called nucleotides. All cells come from other cells. Cells reproduce by cell division, in which a parent cell give rise to two daughter cells, in which each daughter cell receives a complete set of hereditary material (genes or DNA), and about half the cytoplasm. The type of cell division required for development, growth, maintenance and asexual reproduction is discussed in this chapter. The type of cell division required for sexual reproduction is discussed in next chapter. The Cell Cycle --- The cell cycle is the sequence of events a cell goes through during its lifetime. In Eukaryotes the cell cycle is a set of stages -- two main stages, Interphase and Mitosis, between the time the original cell divides and the time the resulting daughter cells divide. The Interphase is the time when the cell performs it usual functions (which depends what kind of cell it is). It used to be called a "resting stage", but we now know that it is not "resting", and that in addition to its specialized functions, it also prepares for mitosis. It is further divided into three sub-stages, G1 (gap 1 stage), S (synthesis stage), and G2 (gap 2 stage). 
G1. The stage BEFORE DNA replicates. In addition to its normal (like cellular respiration) or special functions preparing for cell division, the cell grows in size, and increases its organelles, and accumulates building blocks for the DNA synthesis. In addition there is a "checkpoint" to assure that the DNA is not damaged. If DNA is damaged or cannot be repaired apoptosis will normally occur. S. Replication of DNA (DNA synthesis -- duplication of the chromosome material) occurs, so that half of the newly formed DNA material can be divided into each new daughter cell. G2. The cell prepares for division. The proteins necessary for the division are synthesized. In addition there is another "checkpoint" to assure that the DNA has replicated properly. If DNA is damaged or cannot be repaired apoptosis will normally occur. M Stage, which includes mitosis (also called karyokinesis -- or the nuclear division) and cytokinesis (or the cytoplasmic division). Mitosis includes Prophase, Metaphase, Anaphase, and Telophase. When division of the cytoplasm is complete, two daughter cells are present. Remember that one of the memorization "brain exercise quizzes" is about the Cell Cycle:  
   
 Mitosis and Cytokinesis --- Cell division in eukaryotes involves mitosis (nuclear division) and cytokinesis (cytoplasm division). The DNA in the chromosomes is associated with various proteins, histones that are involved in organizing chromosomes. When a cell is not dividing the DNA is a tangled mass of thin threads called chromatin. Before mitosis begins, chromatin becomes highly coiled and condensed, and it is easy to see the individual chromosomes. Mitosis is a continuing process that is arbitrarily divided in to four named phases -- Prophase, Metaphase, Anaphase, and Telophase (see the YouTube video below or your textbook pages 156 - 158. Cytokinesis is the division of the cytoplasm, and follows mitosis in most but not all cells. When mitosis occurs but not cytokinesis the result is a multinucleated cell. Division of the cytoplasm begins in anaphase, continues in telophase, and is completed when the following interphase begins. Cytokinesis in animal like cells and plantlike cells vary (see your textbook pages 158 - 159). Stem cells are undifferentiated cells whose daughter cells can differentiate into other cell types. The two main types of stem cells are embryonic stem cells in the developing embryo, and adult stem cells that are found in adult tissues. In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues. In adult organisms, stem cells function to repair the body, to replenishing specialized cells, but also to replace normal cells in organs, blood, skin, or various tissues. The Cell Cycle and Cancer --- Cancer is a cellular growth disorder that occurs when cells divide uncontrollably, primarily due to mutations involved in control of the cell cycle. Mutated tumor suppressor genes no longer inhibit the cell cycle, allowing unchecked cell division. Cancer cells lack differentiation, have abnormal nuclei, do not undergo apoptosis, forms tumors, and undergo metastasis and angiogenesis. Prokaryotic Cell Division --- Cell division in unicellular prokaryotes do not have a nucleus, do not have sexual reproduction, and do not divide by the process we call mitosis. Cell division in prokaryotes (such as bacteria) is called binary fission. The prokaryotic chromosome has a few proteins and a single, long loop of DNA. When binary fission occurs, the chromosome attaches itself to the inside of the plasma membrane and replicates. Inward growth of the plasma membrane and formation of new cell wall material divide the cell in two.
 Haploid vs. Diploid chromosome numbers --- Mitosis is the dividing process that MAINTAINS the normal chromosome number of a species -- the so called "diploid number". Another process, called meiosis is discussed in the next chapter, is the dividing process that REDUCES the normal chromosome number to the number found in gametes (sperms or eggs) -- the "haploid number". To understand this difference you need to know the difference between the two terms diploid vs. haploid, which are two terms used extensively when discussion genetics. Diploid number. For humans the number 46. The number of complete sets of chromosomes in a biological cell. In humans, the somatic (body) cells that compose the body are diploid -- containing two complete sets of homologous chromosomes, one set derived from each parent. Homologous chromosomes are the pair of chromosomes containing the same linear gene sequences, each derived from one parent (one from mom and one from dad), the chromosomes that are paired during meiosis. Usually abbreviated 2N or 2n. Haploid number. For humans the number 23. The number of chromosomes in a sex cell (sperm or egg). Usually abbreviated N or n. Mitosis, discussed in this chapter, is the dividing process maintaining the normal chromosome number of all body cells (somatic cells) -- the so called "diploid number". Meiosis, and how the cell obtains the haploid number (in sex cells), is discussed in the next chapter.
 - Mitosis, Meiosis and Sexual Reproduction (Khan Academy You Tube) -COMMENT ON THE YOUTUBE: this is amazing! simple? and interesting and best of all i really get it!! You have saved my academic life. If you have problems understanding the concept of the "mitosis" here is an excellent YouTube video from Khan Academy, which will help you understand by comparing it to "meiosis" which will be discussed in the next chapter, and explaining the difference between the terms haploid and diploid -- even though some of the information is beyond what is required for this class. It is 18 minutes long; I don't recommend that you try to view it from home unless you are connected via broadband. It takes too long to download via telephone modem. View it at STC instead... Sometimes YouTube videos disappear. Hopefully it will not happen often, but if it does there is nothing that can be done about it...Mitosis, Meiosis and Sexual Reproduction Biology Introduction. Bozeman.
Cell division -- Mitosis -- is a small part of the complex process we call the cell cycle, the life cycle of a cell. Many different kinds of cancer can result when the division process doesn't work properly. Mitosis involved division and distribution of the chromosomes in the nucleus into two daughter cells. Before this can be done the chromosomes are duplicated so that each daughter cell can receive one of each kind of chromosome. In the next chapter, another kind of cell division -- Meiosis -- REDUCES the chromosome numbers in order to produce gametes (eggs and sperms).
(Source: Mader, S.S. 2010. Biology. Ed. 10. Used for educational purpose.)
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