Table Of Contents:

2. 14 Transfer RNA (T-RNA) molecules, each consisting of an amino acid (abbreviated by 3 letters within a box), and the base triplet of the corresponding anticodon (outside of the box).

3. The abbreviation and proper spelling of each amino acid.

From left to right, indicate the proper arrangement of the eight amino acids of a polypeptide determined by this sequence of 24 DNA bases. Remember that this problem involves two steps: 1. Transcription and 2. Translation:

Transcription: Construct a strand of Messenger RNA (M-RNA) from the initial gene sequence. Remember that C in DNA becomes G in M-RNA, G in DNA becomes C in M-RNA, A in DNA becomes U in M-RNA, and T in DNA becomes A in M-RNA.

The M-RNA strand should have the following RNA base sequence:

Translation: Match up the anticodons of the T-RNA with the codons of the M-RNA. It might be easier to first divide the M-RNA base sequence into base triplets or codons (3 letter sequences):

The anticodon CCA from the above chart matches up to the complementary codon GGU, making Gly (glycine) the first amino acid in the polypeptide. The anticodon UAA matches up to the codon AUU, making Iso the second amino acid in the polypeptide. The following shows the completed polypeptide with the correct order of amino acids corresponding with the initial DNA base sequence:

The relationship between DNA, M-RNA, T-RNA and each amino acid of the completed polypeptide is shown in the following table:

Mutation: Assume that the initial DNA strand was treated with nitrous acid (HNO₂), oxidizing all the cytosine bases (C) and converting them into uracil bases (U). DNA does not normally contain uracil (U). This mutation in DNA will now have the following base sequence:

The M-RNA strand made from this mutant DNA strand containing U instead of C will have the following base sequence:

The following shows the completed polypeptide with the correct order of amino acids that correspond with the mutant strand of DNA. Note that three amino acids (shown in pink) are different from the original polypeptide made from the original DNA strand. They are different because the codons changed as a result of the substitution of U (uracil) for C (cytosine). In three places along the strand, a different T-RNA anticodon matched up with the altered codons.

The relationship between the mutant DNA, M-RNA, T-RNA and each amino acid of the completed polypeptide is shown in the following table:

Note: The Above Codon Chart Was Used In My Biology Lab Manual During The Previous (2nd) Millennium. Please Refer To Following Updated Chart For A More Detailed Comparison Of DNA & RNA Codons.

Transposons are genes that move from one location to another on a chromosome. In the pigmented aleurone layer of corn grains, the position of transposons may inhibit or block pigment production in some cells. For example, if the transposon moves to a position adjacent to a pigment-producing gene, the cells are unable to produce the purple pigment. This results in white streaks or mottling rather than a solid purple grain. The duration of a transposon in this "turned off" position affects the degree of mottling. If the pigmentation gene is turned off long enough by a transposon, the grain will be completely unpigmented. The reddish-purple patterns caused by transposons may be blotches, dots, irregular lines and streaks.

When the transposon (ace of spades) moves away from the gene for pigment production (jack of diamonds), the production of purple pigment is resumed (continuous purple area). In this example the gene for pigment production (jack of diamonds) is not adjacent to a transposon (ace of spades):

When a transposon moves to different positions within cells of the corn kernel, the coloration gene is "turned on" or "turned off" depending on whether it lands in a position adjacent to the pigmentation gene. Transposons may also have a profound effect on embryonic development and tumor formation in animal cells. Oncogenes (genes that cause tumors) may be activated by the random reshuffling of transposons to a position adjacent to the oncogene. Transposons may also be useful in genetic engineering with eukaryotic cells, by splicing in transposons to activate certain genes. The implications from Barbara McClintock's discovery of transposons may be far-reaching and as significant as Watson and Crick's discovery of the structure of DNA.

In eukaryotic cells, the initial messenger RNA (M-RNA) transcribed from the DNA (gene) is modified (shortened) before it leaves the nucleus. Sections of the M-RNA strand called introns are removed, and the remaining portions called exons are spliced together to form a shortened (edited) strand of mature M-RNA that leaves the nucleus and travels to the ribosome for translation into protein. Perhaps the deleted sections (introns) were needed by our ancestors, but are no longer necessary. In fact, this hypothesis was actually utilized in an episode of Star Trek: The Next Generation. In this episode the crew was reverting back to their ancestral state because their introns were reactivated.

A genome may be defined as all of the functional genes in an organism, including haploid and diploid organisms, and viruses. Total genomic DNA includes genes of the nucleus, nucleolus and cytoplasmic organelles, including chloroplasts and mitochondria. Polyploid organisms also have one genome. For example, a tetraploid plant has one tetraploid genome composed of four haploid sets of chromosomes. The mule genome is composed of one set of donkey chromosomes and one set of horse chromosomes. A lichen genome is composed of the DNA from two symbiotic organisms that live together in one body, the photosynthetic alga (photobiont) and heterotrophc fungus (mycobiont). The Human Genome Project is a worldwide endeavor to map the DNA base sequence of every gene in the human genome. As of February 2001, the total number of functional genes is considerably less than expected, about 30,000 genes per cell compared with previous estimates of 100,000 genes per cell. It has been estimated that a human somatic cell contains about 5 billion base pairs. If the average gene contains 1500 bases, then 30,000 functional genes is only about one percent of the total DNA per cell.

Like tumorous growths, some galls can be very destructive to the host plant. In fact, crown gall (caused by the bacterium Agrobacterium tumefaciens) can cause serious damage to orchard trees. Crown galls are especially interesting because the plasmids of this bacterium (small, circular DNA molecules) contain genetic information that may become incorporated into the nuclear DNA of the infected host cells. These plasmids are referred to as tumor-inducing or Ti plasmids. The Ti plasmid DNA contains genes which cause the host cells to divide uncontrollably. In a sense, the plasmids are like floppy disks containing files or "genes" which are loaded into the host DNA. This explains why these "plant tumors" continue to grow even when the bacteria are eliminated. Ti plasmids are a powerful tool for genetic engineering in plants because the tumor-inducing genes can be replaced with beneficial genes. Agrobacterium tumefaciens containing genetically-engineered (recombinant DNA) plasmids can then be used to transfer the beneficial genes into the host DNA of an infected plant. For example, bacterial genes for insecticidal proteins have been transferred into tomato plants, resulting in transgenic plants that are resistant to ravenous lepidopteran larvae. The protein toxin actually kills the caterpillars feeding on the plant.

The Ti plasmid technique with Agrobacterium tumefaciens as a vector has also been used to introduce a gene into transgenic plants that is resistant to the herbicide Roundup®. This popular herbicide used for weed control blocks a single target enzyme essential to plants for the production of aromatic amino acids. Without aromatic amino acids the plant essentially starves to death after a few weeks. The transgenic plants are resistant to Roundup® because they contain a gene from a Salmonella bacterium that produces a mutant form of the target enzyme that is not blocked by this herbicide. Transgenic plants containing this Salmonella gene and modified target enzyme are immune to Roundup® and still produce the vital aromatic amino acids. Although extremely toxic to plants, Roundup® does not block amino acid enzymes in animals. In fact, aromatic amino acids in people, such as phenylalanine, are among the eight essential amino acids that are not synthesized in cells and consequently must come from our diet. [Although toxic to plants, Roundup® was once thought to be relatively innocuous to people. As of 2017, extensive use of Roundup® over a period of years has been linked to non-Hodgkin lymphoma.]

Another species of bacteria (Bacillus thuringiensis) also referred to as BT, has natural insecticidal properties. This common soil bacterium produces proteins that are especially toxic to alkaline insect stomachs, but not to the acidic stomachs of mammals. These BT proteins have been found to be remarkably effective against a wide range of caterpillars and worms, including peach tree borers, European corn borers, cotton boll worms, cabbage worms and loopers, tomato and fruit hornworms, tent caterpillars, fall webworms, leaf miners, alfalfa caterpillars, leaf rollers, gypsy moth larvae and cankerworms.

According to T.D. Brock and M. T. Madigan (Biology of Microorganisms, 1988), Bacillus thuringiensis forms a crystalline protein during sporulation called a parasporal body. The toxic component of the crystalline body is delta endotoxin. BT bacteria are readily mass-produced by commercial companies and are sold in the form of a stable wettable dust containing millions of spores and crystalline bodies (or just the crystalline toxin). When a caterpillar ingests any plant tissue with BT spores and crystals on it, the delta endotoxin causes deterioration of the intestinal lining and paralysis of the insect's gut. In addition, the bacteria quickly become active and invade the host causing lethal septicemia (blood poisoning due to pathogenic bacteria in the bloodstream).

The use of fungal and bacterial spores as microbial insecticides is becoming an increasingly popular method of "biological control." Advocates of this method of insect control maintain that it is safer and more effective than traditional nonspecific poisons (biocides) that kill many life forms. In addition, the lethal biocides enter the food chain and become concentrated along successive trophic levels, a serious condition known as "biological magnification."

Another potent tool used in genetically modified (GM) plants is the cauliflower mosaic virus (CaMV) 35S promoter. [The promoter is a short sequence of DNA that defines the start of a gene, the direction of transcription, and the strand of DNA to be transcribed. It is one component of an operon, a group of structural and regulating genes that functions as a single unit. Transcription begins when the enzyme RNA polymerase attaches to the promoter.] The CAMV promoter is used in many GM plants because it is more powerful than other promoters, is active in both angiosperms and gymnosperms, and is not greatly influenced by the environment or tissue type. The presence of CaMV promoter DNA in food crops is evidence of transgenic contamination. Other genetic sources of transgenic contamination include DNA sequences from Agrobacterium tumefaciens and Bacillus thuringiensis.

In the everchanging world of biotechnology, the genes for BT proteins have now been isolated and introduced into the DNA of corn plants (Zea mays), tomatoes (Lycopersicon esculentum) and potatoes (Solanum tuberosum). One of the transgenic corn hybrids, called "starlink corn," produces a toxic BT insecticide in its tissues that is lethal to corn borers and other destructive insect pests. Genetically modified (transgenic) food plants (GM plants) have become a controversial issue in recent years, especially in Europe. Many people are very concerned about the potential dangers of altering the genomes of food plants. For example, the transgenic starlink corn was originally designed as animal food, but due to human error it inadvertently got into corn tortilla shells used for human consumption. As of winter 2001, many people are afraid to eat corn chips and other corn products, because of their concern over BT insecticides in the corn. Another concern about transgenic plants containing BT insecticides is that they may be toxic to beneficial insects. For example, it has been shown that pollen from these plants is lethal to the larvae of monarch butterflies, particularly if it lands on nearby milkweeds which the larvae feed upon. The widespread destruction of beneficial insects could be very detrimental to animals that feed on these insects, and could upset the complex food web of an ecosystem. Since corn is wind pollinated, there is also the possibility of BT genes being inadvertently transferred to other varieties of corn plants. This could theoretically contaminate the genomes of other corn plants, including Mexican teosinte, the ancestral corn that provides the natural genetic reservoir for all the hundreds of varieties of modern corn. According to S. Nelson (The SeedHead News, Spring 2002), transgenic DNA (GM corn) was recently found among samples of native corn landraces in the mountains of Oaxaca, Mexico. Whether all these concerns can be substantiated by rigorous scientific investigation remains to be seen.

The genes of sterile transgenic crops, such as bananas, are not as likely to escape into the environment through seeds or pollen. Because edible bananas do not produce seeds, new groves are planted from cuttings of existing stock; however, this asexual propagation also spreads diseases and pests, such as the black sigatoka fungus, nematodes and weevils. Modern tissue culture methods will allow existing strains to be reared in a disease-free environment resulting in clean planting stock. Genes from other banana strains can also be inserted into existing stock to produce disease resistant, transgenic strains.

DNA is such an amazing molecule that it makes great material for "gee-whiz" trivia. Although some of the trivia presented here are based on facts, I have also included some fantastic propositions and preposterous mathematical projections that are impossible to observe, difficult (if not impossible) to prove, and beyond the scope of genuine trivia.

A single human nucleus five micrometers in diameter (0.005 mm) contains 46 chromosomes (2 haploid sets). When completely uncoiled this amounts to an estimated six feet of DNA. With an average of 60 trillion cells per person, this amounts to 68 billion miles of DNA; enough DNA to stretch to the sun and back 365 times or 140,000 round trips to the moon. If the nucleus were enlarged to five feet in diameter, the uncoiled DNA in one nucleus would extend 46 miles, about one mile per chromosome. Each gene would be about five to ten feet long.

The amount of DNA stored in a single human nucleus invisible to the naked eye is enormous. In terms of printed information using a 26 letter Roman alphabet and 12 characters per inch, this information represents about 500 volumes of Encyclopedia Brittanica. All this is stored in a microscopic nucleus five micrometers in diameter (smaller than a human red blood cell). A computer chip is gigantic by comparison and stores much less data.

If a human cell contains five billion base pairs, this represents 4^{5,000,000,000} or 10^{3,000,000,000} different possible base sequences. This astronomical number has three billion digits and would fill about one million pages on a computer printout (12 cpi). This incredible number helps to explain the enormous diversity of life forms on earth, from viruses and bacteria to complex plants and people, all genetically programmed by DNA. Flowering plants alone range from tiny wolffias less than one millimeter long to huge eucalyptus trees over 100 meters tall.

If all the DNA in ten human nuclei were enlarged to a full-sized continuous ladder, it could reach more than 30 million miles, or from the earth to the planet Mars: