1. The phases of mitosis: interphase, prophase, metaphase, anaphase, and telophase which produce two identical haploid daughter cells.
2. The transcription of DNA and RNA, producing mRNA.
4. A cancer cell
6. The process of fertilization, when a sperm nucleus and an egg nucleus eventually become enclosed within a nuclear envelope.
I. Genetics
A. Chromosomes
1. Description and function
2. Karyotype
B. Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase and cytokinesis
C. DNA replication
D. Gene expression
1. Transcription
2. Translation
E. DNA technology
1. Recombinant DNA
2. DNA sequencing
3. Genetic engineering
II. Cancer
A. Characteristics
B. Development
1. Genetic basis of cancer
a. Normal cells
b. Cancer cells
C. Types of cancer
D. Causes of cancer
1. Genetic causes
2. Environmental causes
a. Bioethical focus: control of tobacco
3. Viruses
E. Detecting skin cancer
1. Seven warning signs
2. Routine screenings
F. Cancer treatments
III. Sexual Reproduction
A. Fertilization
B. Embryonic development
C. Inheritance and natural selection
1. Meiosis
a. Meiosis I
i. prophase
ii. metaphase
iii. anaphase
iv. telophase
b. Meiosis II
i. prophase
ii. metaphase
iii. anaphase
iv. telophase
c. Genotype
i. alleles
d. Phenotype
d. Phenotype
The inter workings that lie within our bodies are occurring at a constant rate. As a person watches a movie, the internal housing system is creating millions of new cells that will continue to carry out their designated functions. It may not seem that complex, but when a person deeply looks into the woven features of their body system, it becomes a realization that their body contains a totally different world. It is in the confines of the microscopic cells that the processes of genetics, cancer, and sexual reproduction are occurring.
Genetics is the study of specific traits received through inheritance. The role of inheritance cannot begin without the influences of the chromosomes. Located within the nucleus of a cell, chromosomes begin as a mass of chromitin that are, "...condese(d)...when cells divide" (Mader 378). They are made of proteins that give them their particular shape and contain the genetic instructions given by DNA. The human species have, "...46 chromosomes that occur in 23 pairs" (Mader 378). Twenty-two of these pairs are made to perform only specific cellular traits, whereas the twenty-third pair of chromosomes is set aside to operate in accordance with the genes for gender. The access to visual understanding of chromosomes is not only available to scientists, but to anyone who is curious. This type of physical evidence is called a karyotype. In the process of creating a karyotype, white blood cells are separated from a sample of a person's blood. It is then isolated and studied until cell division begins from which a chemical is added to the sample to stop the process in order to see the chromosomes clearly. The karyotype is finished and displayed on a computer for a person to see. Another important feature of genetics is the process of cell division. This is called mitosis.
Mitosis is what makes the chromitin in the nucleus into chromosomes. It consists of four phases that complete the cellular duplication and separation. The first phase, prophase, begins when the nuclear envelope begins to breaks away from the nucleus and the nucleolus disappears. After this happens, centrosomes located externally on polar side of the nucleus, begin the development of spindle fibers. The next phase, metaphase, the nuclear envelope has finally disappeared and now the spindle fibers occupy the space where the nucleus existed. The spindle fibers are fully developed and control the whereabouts of the chromosomes, which are now located in the center of the cell. The third phase, anaphase, the chromosomes split in half and move in opposite directions with the navigation of the spindle fibers. This will ensure that, "...each cell receives a copy of each type of chromosome..." (Mader 382). And the last phase, telophase, the spindle fibers begin to disintegrate as the nucleolus and nuclear envelope reassemble. Inside the reformed nuclear envelope, the chromosomes change back to chromitin. This phase gives the appearance of two identical cells held together by a cleavage furrow. Then the process of cytokinesis divides the cytoplasm of the cell and gives a yield of two identical cells. It is within the chromosomes that are developed from cellular division that gene replication and gene expression occur.
The replication of DNA allows for the double helix strand of base pairs to split and use each single strand, "...as a template for recreating the other half..." (http://www.dnaftb.org/). Then, the enzyme, DNA polymerase, completes the double helix strand with new complimentary base pairs inserted into the old base pairs. The backbones of the two new strands are examined by another enzyme and repaired if there are any breaks in the strand. The process is complete as the two identical helices continue with the replication process. After DNA replication, gene expression occurs. Gene expression consists of two steps called transcription and translation. Transcription is, "...the synthesis of mRNA from a DNA late" (faculty.clintoncc.suny.edu). The DNA strand unwinds and an enzyme called RNA polymerase binds to it. During this interlock of DNA and RNA polymerase, the enzyme, "...identifies the start of a gene, which strand is to be copied, and the direction that it is to be copied" (faculty.clintocc.suny.edu). After transcription is completed, the produced mRNA, called mRNA trnascript, is modified and directed to the cytoplasm of the cell. The second step, translation, uses the mRNA transcript produced in transcription for the synthesis of proteins. The mRNA transcript and tRNA, which has a polypeptide chain connected to it, are threaded through a ribosome where complementary base pairs, called codons and anticodons, bind together. After this occurs, another tRNA comes into place of the ribosome and repeats the binding of codons and anticodons. This process continues until the ribosome terminates the process, by, "...reaching a stop codon" (Mader 451). Then, all parts of the process are released and translation is complete. Although these procedures occur naturally within cells, DNA technology has developed other synthetic processes.
DNA technology has discovered three ways of creating genes. The first way, called recombinant DNA, allows genes to be asexually reproduced from two or more different sources. For example, a gene from human DNA and a plasmid from a bacterium are joined together and placed into a host cell, such as the bacterium. Then, the host is cloned and the human gene that was inserted to the bacterium's plasmid now functions within that bacterium. The second way, called DNA sequencing, is a process of using DNA polymerase to make new DNA strands. The chain is then, "...repeatedly replicated..." (Mader 459) from the DNA polymerase. This type of technology can be used in DNA fingerprinting, also known as the human genome project. For example, DNA fingerprinting from a specimen in a crime scene can be used to find and convict the person or people responsible. The last way, called genetic engineering, can enhance a particular substance by splicing genes from another substance and adding it to the original one. For example, certain plants can be given a gene that will make them withstand the use of herbicides and pesticides. Although DNA technology is making headway, the disease, cancer, has not been able to be manipulated and controlled.
Cancer is, "...a cellular disease.." (Mader 404) that differs completely in appearance compared to normal cells. It has many characteristics that sets it apart from normal cells. They are: 1. cancer cells do not contribute to bodily functions 2. they have abnormal nuclei which fail to stop processing their damaged DNA 3. cancer cells never die and keep dividing into infinity (or till the host dies without treatment) 4. they pile up on top of each other forming a tumor 5. cancer cells do not have growth factors because they keep growing and do not stop 6. they can metastasize, which creates new tumors from the original tumor. Also, cancer has a genetic basis for which continues the replication process, like in cell division, but does not terminate. Normal cells within the cell cycle contain proto-oncogenes, which keep the cycle functioning regularly, and tumor suppressor genes, which promote cell death. But when proto-oncogenes mutate and tumor suppressor genes mutate, they produce oncogenes. And oncogenes cause cancer. There are four different types of cancer that can be distinguished by the location of the tumor. The first type, carcinomas are, "...cancers of the epithelial cells" (Mader 407). They can be found in the thyroid, skin, prostate, breast, lung, liver, intestines, and pancreas. The second type, sarcomas, develop in connective tissue such as muscle and bone. The third kind, leukemia, are, "...cancers of the blood..." (mader 407). And the last kind, lymphomas, are found in the lymph tissue. Cancer can be caused by genetics, environmental carcinogens, and viruses. Cancer caused by genetics can occur when a person inherits a mutated tumor suppressor gene in two incidences. For example, in order to have a predisposition to cancer, the person must have received a mutated copy from their father and a mutated copy from their mother. Environmental carcinogens that can cause cancer are radiation (UV light, nuclear fuel, and Xrays), organic chemicals (tobacco smoke), and pollutants (metal, pesticides, and chemicals). For example, the use of tobacco and the link to the cause of cancer has resulted in thousands of deaths each year, that many states are placing high taxes on cigarettes products to hinder the consumer's purchasing of them. And viruses such as hepatitis B and C and HPV have been linked to causing liver and cervical cancer. Although cancer is a very powerful force within the body, there are ways to detect the possibility of early cancer and ways to treat it if necessary.
There are seven warning signs that spell the word CAUTION. They are, "C hange in bowel or bladder habits, A sore that does not heal, U nusual bleeding or discharge, T hickening or lump in breast or elsewhere, I ndigestion or difficulty in swallowing, O bvious change in wart or mole, N agging cough or hoarseness" (Mader 411). There are also routine screening that help keep a look out for developing cancers. They are self examinations for women and men, such as breast and testicles, blood tests, rectal and prostrate examinations fro men, pap tests for women, and the periodic health examination. But, if cancer is detected through routine screenings, there are different types of treatments that can be applied. The first standard method is surgery. Surgery is used when, "...cancer (is) in situ" (Mader 414). But there is always the risk that not all of the cancer cells can be obtained and the second treatment is applied. This is radiation. In this treatment, gamma rays are applied to a part of the infected person's body to break apart chromosomes in the cancer cells. And another common treatment for cancer is chemotherapy. This helps catch cancer cells that have metastasized. This kills the cells by destroying their DNA and DNA synthesis. But chemotherapy can fail, because the cells can build a resistance to the drugs being used. In accordance with cellular production, sexual reproduction creates the very individuals that carry out cellular production.
Sexual reproduction occurs when the sperm from a male is united with an egg of a female, creating a zygote. This is called fertilization. It happens in a series of five steps. In the first step, the sperm navigates it way through the egg's exterior, adhering cells. Then, the sperm's external enzyme caseing breaks down the adhering cells and is able to finally fuse with the egg's internal membrane. The third step consists of the sperm's nucleus entering the cytoplasm of the egg and the outside of the egg releases fertilization enzymes. Lastly, the nucleus of the sperm and egg join together into a nuclear envelope. After fertilization occurs, "...the zygote divides repeatedly as it passes down the oviduct to the uterus" (Mader 356). Then the process of embryonic development occurs. Embryonic development happens within the first couple months of pregnancy. The embryo implants itself within the uterian walls and begins developing the embryonic disk, which contains membranes for blood cell formation, the nervous system, all the major body systems, glands of these body systems. Also the amniotic fluid develops, that protects the embryo. After the membranes have fully developed, the actual start of the heart and nervous system appear. Then, towards the end of the second month of gestation, the umbilical cord connects to the placenta, little limbs begin to pop out of the embryo, sense organs are more defined, and the embryo begins to resemble a human being. Along with the development of a human being, is the importance of inheritance.
Inheritance of particular traits of the father and mother to the offspring consists of a process called meiosis. The beginning of meiosis starts with the pairing of chromosomes inside the parent cell. Then meiosis one begins where prophase, metaphase, anaphase, and telophase one occur. During prophase one, the chromosomes inside the nucleus duplicate and then cross-over, where the identical chromatids are no longer alike. Therefore, "...crossing-over causes the offspring to receive a different combination of instructions than the mother or father received" (Mader 388). Next, in metaphase one, the pairs of the unidentical chromosomes line up at the center of the spindle fibers, which orientates either the mother's chromosomes or father's chromosomes to either pole of the fibers. Then, anaphase one, seperates the chromosome pairs and pulls them to opposite poles of the spindle fibers. Lastly, telophase one, creates the two new diploid daughter cells that contain one chromosome from each pair of chromosomes. But the process of meiosis is not over yet. The process of meiosis two begins where prophase, metaphase, anaphase, and telophase two occur. Each phase happens in the same fashion, but now involve the two daughter cells that were created in meiosis one. Once meiosis is complete, it results in, "...four haploid daughter cells" (Mader 387). It is from the daughter cells created in meiosis that genotypes develop.
Genotype is, "...the genes of an indivdual" (Mader 422) and can be distinguised by their alleles. Alleles are given letters to represent the different types of traits that can be inheritated. For example, if an indivdual inheriates the dominant alleles for brown hair from their father (B) and mother (B), the genotype will be a dominant homozygous pair of BB. The individuals physical appearance or any characteristic of the received genotypes are called phenotypes. For example, an person can either have attached or unattcahed earlobes, a widow's peak or a straight hairline, short fingers or long fingers, freckles or no freckels, color blindness, or a metabolic disorder. These different traits are what creates diversity throughout the existence of life and the basis for natural selection.
It is in the confines of microscopic cells that the processes of genetics, cancer, and sexual reproduction are occuring. The many processes of genetics, such as mitosis, gene replication, and gene expression, can allow the cell to divide through prophase, metaphase, anaphase and telophase,can create new strands of DNA, can transcribe mRNA, and translate mRNA with tRNA. The cell can also mutate and create an immortal cell called cancer. Cancer differs from normal cells by particular characterisitcs and can be caused by several different things, such as genetics, environmental causes, and other viruses. Fortunately, there are ways to detect cancer, such as the mneunoic of CAUTION and examinations. But, if cancer is detected, it can be treated with surgery, radiation, and chemotherapy. The cell can also be produced through fertilization of a sperm and an egg, which leads to embryonic development and the birth of a new individual. While a new indvidual is being created, processes such as meiosis and inheritance are occuring, which passes on the genectic traits of the parents and makes new genotypes and phenotypes. This creates diversity within living things. The individual is an amazing center for natural procedures that connects us back to the beginning of creation.
Sources:
Pictures:
1. img.tfd.com/dorlan/thumbs/mitosis.jpg
2. ghs.gresham.k12.or.us/.../transcript1.gif
3. library.thinkquest.org/C0123260/basic%20knowl...
5. members.thai.net/m6141/lesson5pic/meiosis-big.gif
Works:
1. Human Biology 10e Sylvia S. Mader
3. faculty.clintoncc.suny.edu
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