Because these planets are so massive and at such wide separations away from their star, it is possible to directly image some of these planets — quite literally taking an image of a planet next to a star. When an image is taken of a planet or brown dwarf, the spectrum of its atmosphere can also be observed helping to understand these objects even more.
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Genetic Mutation. Functions and Utility of Alu Jumping Genes. Transposons: The Jumping Genes. DNA Transcription. What is a Gene? Colinearity and Transcription Units. Copy Number Variation. Copy Number Variation and Genetic Disease. Copy Number Variation and Human Disease. Tandem Repeats and Morphological Variation.
Chemical Structure of RNA. Eukaryotic Genome Complexity.
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RNA Functions. Pray, Ph. The landmark ideas of Watson and Crick relied heavily on the work of other scientists. What did the duo actually discover? Aa Aa Aa. A single nucleotide is made up of three components: a nitrogen-containing base, a five-carbon sugar, and a phosphate group. The nitrogenous base is either a purine or a pyrimidine. Of Avery's work, Chargaff wrote the following: "This discovery, almost abruptly, appeared to foreshadow a chemistry of heredity and, moreover, made probable the nucleic acid character of the gene These features are as follows: DNA is a double-stranded helix, with the two strands connected by hydrogen bonds.
A bases are always paired with Ts, and Cs are always paired with Gs, which is consistent with and accounts for Chargaff's rule. Most DNA double helices are right-handed; that is, if you were to hold your right hand out, with your thumb pointed up and your fingers curled around your thumb, your thumb would represent the axis of the helix and your fingers would represent the sugar-phosphate backbone. The DNA double helix is anti-parallel, which means that the 5' end of one strand is paired with the 3' end of its complementary strand and vice versa. As shown in Figure 4, nucleotides are linked to each other by their phosphate groups, which bind the 3' end of one sugar to the 5' end of the next sugar.
Not only are the DNA base pairs connected via hydrogen bonding, but the outer edges of the nitrogen-containing bases are exposed and available for potential hydrogen bonding as well.
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These hydrogen bonds provide easy access to the DNA for other molecules, including the proteins that play vital roles in the replication and expression of DNA Figure 4. Two hydrogen bonds connect T to A; three hydrogen bonds connect G to C. The bottom four base pairs are shown flattened instead of twisted, so this region can be easily seen in a cut-away showing a close-up view.
The cut-away shows the individual atoms and bonds in the DNA molecule. Phosphate groups are depicted within light brown spheres, and the bonds between the phosphate and oxygen atoms are shown.
The sugars are represented by grey pentagons that show where oxygen atoms and hydrogen atoms are attached to the unmarked carbon atoms at the corners. An oxygen atom from each phosphate molecule is connected by a black line to a carbon atom from the sugar molecule. These black lines represent the covalent bonds between the sugars and phosphate groups.
The sugar molecules are each attached to a nitrogenous base. The nitrogenous bases from the two DNA strands meet in the center of the molecule, where they are connected with hydrogen bonds shown by dotted, red lines. At the top left side, a guanine base with two fused rings G, shown in blue is bound to a cytosine base with a single ring C, shown in gold on the opposite strand.
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These two bases are held together by three hydrogen bonds. Below this base pair, a thymine base with a single ring T, shown in red is bound to an adenine base with two fused rings A, shown in green on the opposite strand. These two bases are held together by two hydrogen bonds. Below this pair, a single-ringed cytosine base is bound to a double-ringed guanine base by three hydrogen bonds. In the final pair, an adenine base with two fused rings is bound to a single-ringed thymine by two hydrogen bonds. A A-DNA is a short, wide, right-handed helix. Genetics: A Conceptual Approach , 2nd ed.
All rights reserved. References and Recommended Reading Chargaff, E. Preface to a grammar of biology.
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Science , — Dahm, R. Human Genetics , — Levene, P. Journal of Biological Chemistry 40 , — Rich, A. Nature Reviews Genetics 4 , — link to article Watson, J. Nature , — link to article Wolf, G. Article History Close.
Keywords Keywords for this Article. Flag Inappropriate The Content is: Objectionable. Email your Friend. This content is currently under construction. Lysosomes are specialized organelles that break up macromolecules, allowing the cell to reuse the materials. In , Christian de Duve, then chairman of the Laboratory of Physiological Chemistry at the University of Louvain in Belgium, was studying how insulin acted on liver cells.
He wanted to determine the location of an enzyme a type of protein involved in chemical reactions called glucosephosphatase inside the cells. He and his group knew that this enzyme played a key role in regulating blood sugar levels. They obtained cellular extracts by blending rat liver fragments in distilled water and centrifuging the mixture at high speeds.