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. RNA Functions. Pray, Ph. Citation: Pray, L. Nature Education 1 1 The landmark ideas of Watson and Crick relied heavily on the work of other scientists.
What did the duo actually discover? Aa Aa Aa. Figure 1: The chemical structure of a nucleotide. 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 Figure 2: What is Chargaff's rule?
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. 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.
Figure 4: Base pairing in DNA. 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. 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. Figure 5: Three different conformations of the DNA double helix. 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. 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. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Nobel Prizes Thirteen laureates were awarded a Nobel Prize in , for achievements that have conferred the greatest benefit to humankind.
See them all presented here. Select the category or categories you would like to filter by Physics. Economic Sciences. Ever the perfectionist, he hesitated for long periods of time between experiments before he published his results in Before then he primarily discussed his findings in private letters to his friends. For many years, scientists continued to believe that proteins were the molecules that held all of our genetic material.
Surely, one type of molecule could not account for all the variation seen within species? Albrecht Kossel was a German biochemist who made great progress in understanding the basic building blocks of nuclein. Albrecht Kossel isolated the five nucleotide bases that are the building blocks of DNA and RNA: adenine, cytosine, guanine, thymine and uracil.
In Albrecht identified nuclein as a nucleic acid and provided its present chemical name, deoxyribonucleic acid DNA. In the early s, the work of Gregor Mendel was rediscovered and his ideas about inheritance began to be properly appreciated.
As a result, a flood of research began to try and prove or disprove his theories of how physical characteristics are inherited from one generation to the next. In the middle of the nineteenth century, Walther Flemming, an anatomist from Germany, discovered a fibrous structure within the nucleus of cells. By observing this chromatin, Walther correctly worked out how chromosomes separate during cell division, also known as mitosis.
Walter Sutton and Theodor Boveri first presented the idea that the genetic material passed down from parent to child is within the chromosomes. The chromosome theory of inheritance was developed primarily by Walter Sutton and Theodor Boveri. They first presented the idea that the genetic material passed down from parent to child is within the chromosomes. Their work helped explain the inheritance patterns that Gregor Mendel had observed over a century before.
Interestingly, Walter Sutton and Theodor Boveri were actually working independently during the early s. Walter studied grasshopper chromosomes, while Theodor studied roundworm embryos.
However, their work came together in a perfect union, along with the findings of a few other scientists, to form the chromosome theory of inheritance.
Walter Sutton left and Theodor Boveri right worked independently to come up with the chromosome theory of inheritance. Image credit: Wikimedia Commons.
From his studies of the roundworm embryo he also worked out that the number of chromosomes is lower in egg and sperm cells compared to other body cells.
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