Genetics/Cell Cycle

1. What is DNA? DeoxyriboNucleic Acid.
2. What are the 4 bases? A (Adenine), T (Thymine), C (Cytosine) & G (Guanine).
3. What 2 peices of information did the scientists need to solve the elusive structure of DNA? In order to solve the elusive structure of DNA, a couple of distinct pieces of information needed to be put together. One was that the phosphate backbone was on the outside with bases on the inside; another that the molecule was a double helix. It was also important to figure out that the two strands run in opposite directions and that the molecule had a specific base pairing.
4. What are the specific base pairs? G can only bind to C and A can only bind to T.
5. How does the pairing rule effect the shape and structure of DNA? According to the biochemist Erwin Chargoff even though different organisms have different amounts of DNA, the amount of adenine always equals the amount of thymine. The same goes for the pair guanine and cytosine. For example, human DNA contains about 30 percent each of adenine and thymine, and 20 percent each of guanine and cytosine. With this information at hand James Watson was able to figure out the pairing rules. On the 21st of February 1953 he had the key insight, when he saw that the adenine-thymine bond was exactly as long as the cytosine-guanine bond. If the bases were paired in this way, each rung of the twisted ladder in the helix would be of equal length, and the sugar-phosphate backbone would be smooth.
6. What does the DNA do during cell division? During cell division, the DNA molecule is able to "unzip" into two pieces. One new molecule is formed from each half-ladder, and due to the specific pairing this gives rise to two identical daughter copies from each parent molecule.
7. How many base pairs does E. Coli have? How long does it take to replicate? How is the DNA packaged in the cell? The DNA in E. coli bacteria is made up of 4 million base pairs and the whole genome is thus one millimeter long. The single-cell bacterium can copy its genome and divide into two cells once every 20 minutes. In order to fit, the DNA must be packaged in a very compact form. In E. coli the single circular DNA molecule is curled up in a condensed fashion.
8. How many base pairs does Human DNA have? How long does it take to replicate? How is the DNA packaged in the cell? The DNA of humans is composed of approximately 3 billion base pairs, making up a total of almost a meter-long stretch of DNA in every cell in our bodies. The human DNA is packaged in 23 distinct chromosome pairs. Here the genetic material is tightly rolled up on structures called histones.

1. What is RNA? How different is it from DNA? RiboNucleic Acid. DNA is made up of double strand while RNA is made up of a single strand. Also the base T (Thymine) in DNA is replaced by U (Uracil) in RNA.
2. How are the RNA messages formed? The alphabet in the RNA molecule contains 4 letters, i.e. A, U, C, G. To construct a word in the RNA language, three of these letters are grouped together. This three-letter word are often referred to as a triplet or a codon. An example of such a codon is ACG. The letters don't have to be of different kinds, so UUU is also a valid codon. These codons are placed after each other in the RNA molecule, to construct a message, a RNA sequence. This message will later be read by the protein producing machinery in the body.
3. How are the RNA messages interpreted? Every organism has an almost identical system that is able to read the RNA, interpret the different codons and construct a protein with various combinations of the amino acids. In fact every RNA word or codon, corresponds to one single amino acid. These codons and their correlation with the amino acids in a protein sequence is what defines the genetic code.

















1. Describe cell cycle. The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication. These events can be divided in two broad periods: interphase—during which the cell grows, accumulating nutrients needed for mitosis and duplicating its DNA—and the mitotic (M) phase, during which the cell splits itself into two distinct cells, often called "daughter cells". The cell-division cycle is an essential process by which a single-celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed.
2. What is nuclear division. The division of the nucleus and its genetic information into more than one cell deriving from a parent cell, either via meiosis or mitosis.
3. What is interphase. A phase of the cell cycle, defined only by the absence of cell division. During interphase, the cell obtains nutrients, and duplicates its chromatids. Most eukaryotic cells spend most of their time in interphase.
4. Cytokinesis. Cytokinesis is the process whereby the cytoplasm of a single cell is divided to spawn two daughter cells. It usually initiates during the late stages of mitosis, and sometimes meiosis, splitting a binucleate cell in two to ensure that chromosome number is maintained from one generation to the next. In animal cells, one notable exception to the normal process of cytokinesis is oogenesis (the creation of an ovum in the ovarian follicle of the ovary), where the ovum takes almost all the cytoplasm and organelles, leaving very little for the resulting polar bodies, which then die. In plant cells, a dividing structure known as the cell plate forms across the centre of the cytoplasm and a new cell wall forms between the two daughter cells.
















5. Homologous chromosomes. (Science: genetics) a pair of chromosomes containing the same linear gene sequences, each derived from one parent. The chromosomes tend to pair or synapse during meiosis. They have the same genes, in the same location, but the genes have different versions (not like in sister chromatids that are exact replicas).
Retrieved from "http://www.biology-online.org/dictionary/Homologous_chromosome"
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6. Phases of mitosis (5 of them).
1. Prophase – In prophase, the chromatin condenses into discrete chromosomes. The nuclear envelope breaks down and spindles form at opposite "poles" of the cell.
2. Metaphase – In metaphase, the chromosomes are aligned at the metaphase plate (a plane that is equally distant from the two spindle poles).
3. Anaphase – In anaphase, the paired chromosomes (sister chromatids) move to opposite ends of the cell.
4. Telophase – In this last stage, the chromosomes are cordoned off in distinct new nuclei in the emerging daughter cells. Cytokinesis is also occurring at this time.
Interphase – G1 phase: The period prior to the synthesis of DNA. In this phase, the cell increases in mass in preparation for cell division. Note that the G in G1 represents gap and the 1 represents first, so the G1 phase is the first gap phase. S phase: The period during which DNA is synthesized.

















7. Phases of meiosis and how it is different from mitosis.
Meiosis begins with Interphase I. During this phase there is a duplication genetic material, DNA replication. Cells go from being 2N, 2C (N= chromosome content, C = DNA content) to 2N, 4C. Cells remain in this active phase 75% of the time. The chromatin remains in a nuclear envelope while a pair of centrioles lies inside a centrosome.
During Prophase I, the chromatin condenses into chromosomes, the nuclear envelope disappears, and a spindle apparatus begins to form. Each chromosome consists of a pair of chromatids connected by a centromere. Cells are now 4N, 4C. The major occurrence in this phase is the coupling of these homologous chromosomes. Two double-stranded chromosomes form a four-stranded tetrad. In some cases, there is crossing-over of the two middle strands, at a site called the chiasma, such that there is genetic recombination. This process is extremely important for creating genetic diversity.
In Metaphase I, the tetrads line up on the "equator" of the cell. The centrosome has replicated and one has moved to each pole. Microtubules that extend out of each centrosome attach to kinetochores in the center of each side of the tetrads that have lined up on the equator.
Anaphase I occurs as the microtubules pull the pairs of homologous chromatids toward each pole, as the tetrad is divided. The cell begins to lengthen.
During Telophase I, the nuclear envelope begins to reform and nucleoli reappear. The cell begins to split, forming a cleavage furrow in the middle.
In Cytokinesis I, the cells finally split, with one copy of each chromosome in each one. Each of the two resulting cells is now 2N, 2C.
Interkinesis has not replication, unlike the previous Interphase I and the interphase of mitosis.Prophase II, Metaphase II, Anaphase II, and Telophase II repeats the same steps as Prophase I-Telophase I, with half as much genetic material.
Cytokinesis II is the final step of meiosis, where each cell splits into two daughter cells, for a total of four gametes, each with half the number of chromosomes. Each of the four resulting cells is 1N, 1C. (30)
In Meiosis the first phase is Interphase but in Mitosis it is last. In addition, Meiosis process are seven stages while Mitosis process are five phases.
8. Describe the process and purpose of crossing over. Crossing over occurs when the sperm and egg chromosomes pair up and swap genetic information, reducing the number of chromosomes to a complete set. It is important because it makes the number of chromosomes the normal number and also allows the genetic information to remain present in the cell.


CITES:
http://en.wikipedia.org/wiki/Cytokinesis
http://biology.about.com/od/mitosis/a/aa051206a.htm
http://www.biology-online.org/dictionary/Homologous_chromosome
http://en.wikipedia.org/wiki/Interphase
http://www.biology-online.org/dictionary/Nuclear_Division
http://en.wikipedia.org/wiki/Cell_cycle
http://nobelprize.org/educational_games/medicine/dna_double_helix/readmore.html