Everything About Molecular Biology - Assignment Example

Genetic and Molecular Biology Mendel’s conclusions: The F1 offspring showed only one of the two parental traits, and always the same trait. Results were always the same regardless of which parent donated the pollen (was male). The trait not shown in the F1 reappeared in the F2 in about 25% of the offspring. Traits remained unchanged when passed to offspring: they did not blend in any offspring but behaved as separate units and finally the reciprocal crosses showed each parent made an equal contribution to the offspring. 2. In 1902, Walter Sutton and Theodor Boveri made a correlation between Mendels conclusions about genes (or inherited traits) and the behavior of chromosomes during mitosis and meiosis. The chromosome theory on inheritance said that Chromosomes are in pairs and genes, or their alleles, are located on the chromosomes. 3. The Genetic Makeup of an organism is its GENOTYPE. The Appearance of an organism as a result of its genotype is called PHENOTYPE. 4. Each of several Alternative forms of a Gene is called an Allele. Letters are used to represent Alleles: Capital Letters refer to a Dominant Allele that masks or hides expression of a recessive allele. Lowercase Letters refer to a Recessive Allele its expression is masked by a dominant allele. Yes, it is possible for more than two alleles of a gene to exist. 5. Scientists gradually learned about DNA in a curiously twisted fashion that is common in science. For one thing, the discovery of DNA required progress on three separate fronts: cytology (the study of cells through a microscope), genetics, and chemistry. Scientists working on DNA in the early 1950s used the term "gene" to mean the smallest unit of genetic information, but they did not know what a gene actually looked like structurally and chemically, or how it was copied, with very few errors, generation after generation. Nevertheless, many scientists continued to believe that DNA had a structure too uniform and simple to store genetic information for making complex living organisms. The genetic material, they reasoned, must consist of proteins, much more diverse and intricate molecules known to perform a multitude of biological functions in the cell. 6. Gene is a hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism. A chromosome is a grouping of coiled strands of DNA, containing many genes. 7. Each strand of DNA is a chain of chemical "building blocks", called nucleotides, of which there are four types: adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These allowable base components of nucleic acids can be polymerized in any order giving the molecules a high degree of uniqueness. The sequence of base pairs along its length determines the genetic information it carries. 8. The central dogma of molecular biology was first enunciated by Francis Crick in 1958. Genes specify structure and function according to a process described by the central dogma of molecular biology. Central dogma of molecules genetic describes that each gene in the DNA molecule carries the information needed to construct one protein, which, acts as an enzyme, and controls one chemical reaction in the cell. This process of protein synthesis has been a turning point in molecular genetics. 9. Amino acids are the basic structural building units of proteins. They form short polymer chains called peptides or polypeptides which in turn form structures called proteins. Twenty amino acids are encoded by the standard genetic code and are called proteinogenic or standard amino acids. The mean mass of the standard amino acids, weighted by abundance in proteins, is roughly 111 Daltons. Combinations of these amino acids produce every single essential protein for the homeostasis of the human body. 1. a. Chromatin: It is a complex of DNA, RNA, Histones and nonhistone protein that make up uncoiled chromosomes characteristic of eukaryotic interphase nucleus. Changes in chromatin structure are affected mainly by methylation (DNA and proteins) and acetylation (proteins). Chromatin structure is also relevant to DNA replication and DNA repair. b. The nucleolus is a nuclear organelle which is a site of ribosome biosynthesis. Since nucleoli carry out the production and maturation of ribosomes, large numbers of ribosomes are found inside them. In addition to ribosome biogenesis, nucleoli are believed to have other roles in cellular activity. c. A ribosome is an organelle composed of ribosomal RNA and ribosomal proteins. It translates Messenger RNA (mRNA) into a polypeptide chain (e.g., a protein). d. A mitochondrion is an organelle found in the cells of eukaryotes. It is a cytoplasmic self reproducing organelle and is sometimes described as "cellular power plants," because they convert organic materials into energy in the form of ATP via the process of oxidative phosphorylation and also helps in Cellular proliferation. e. A centriole is a cytoplasmic organelle composed of nine groups of microtubules, generally arranged in triplets. It functions in generation of cilia and flagella and serves as foci for the spindles in cell division. f. The centromere is a region on chromosomes to which sister chromatids remain attached after replication and the site to which spindle fibers attach during cell division. The centromere plays a role in cellular division and the control of gene expression. 2. Chromosomes that are homologues share many properties such as overall length, position of the centromere, banding pattern, type and location of genes, autoradiographic pattern. All animals have a characteristic number of chromosomes in their body cells called the diploid (or 2n) number. These occur as homologous pairs, one member of each pair having been acquired from the gamete of one of the two parents of the individual whose cells are being examined. The gametes contain the haploid number (n) of chromosomes. 3. Homologous chromosomes are similar in length, except for sex chromosomes in several taxa, wherein the X chromosome is considerably larger than the Y chromosome. These chromosomes share only small regions of homology. 4. Mitosis is simply described as having four stages—prophase, metaphase, anaphase, and telophase. During prophase the two chromatids remain attached to one another at the centromere, but each contracts into a compact tightly coiled body; the nucleolus and, in most cases, the nuclear envelope break down and disappear. During metaphase the chromosomes congregate at a plane midway between the two ends to which the spindle tapers. The ends of the spindle are the poles to which the chromatids will migrate. The chromatids are attached to the spindle fibers at the centromeres. During anaphase the two chromatids of each chromosome separate and move to opposite poles, as if pulled along the spindle fibers by the centromeres. During telophase new nuclear envelopes form around the two groups of daughter chromosomes, the new nucleoli begin to appear, and eventually, as the formation of the two daughter nuclei is completed, the spindle fibers disappear. 5. During prophase there will be 16 structures each consisting of a pair of sister cromatids remain attached to one another at a region called the centromere, but each contracts into a compact tightly coiled body; the nucleolus and, in most cases, the nuclear envelope break down and disappear. Eight chromatids will be seen moving towards each pole during anaphase of mitosis. 15. Spermatogenesis is the process by which stem cells develop into mature spermatozoon (sperm) cells. Where as Oogenesis is the creation of an ovum (egg cell) in the ovarian follicle of the ovary. Polar body is a cell structure found inside an ovum. In plants the fertilized polar bodies create a structure called endosperm which stores nutrients for initial growth of plant seeds. 16. Multicellular organisms grow by way of mitosis and the cytoplasmic division of body cells. On the other hand, meiosis occurs only in germ cells, which are put aside for the formation of gametes (sperm and egg). Reproduction by meiosis allows for species survival and it increases genetic variability. 21. a. Crossing over occurs in the pachytene stage of first meiotic prophase. b. During zygotene phase the pairing of homologous chromosomes begins which is also called synapsis and the resulting structure synaptic complex. c. The chromosomes first become visible as thin threads within the nucleus at the stage called leptotene. This is the stage when it is least condensed. d. The chiasmata become visible during the diplotene stage of prophase I. Read More