The darkly staining regions usually contain genes that are not active, and are found in the regions of the centromere and telomeres. The lightly staining regions usually contain genes that are active, with DNA packaged around nucleosomes but not further compacted. Concept in Action. Watch this animation of DNA packaging. The DNA molecule is a polymer of nucleotides.
Each nucleotide is composed of a nitrogenous base, a five-carbon sugar deoxyribose , and a phosphate group. There are four nitrogenous bases in DNA, two purines adenine and guanine and two pyrimidines cytosine and thymine. A DNA molecule is composed of two strands. Each strand is composed of nucleotides bonded together covalently between the phosphate group of one and the deoxyribose sugar of the next.
From this backbone extend the bases. The bases of one strand bond to the bases of the second strand with hydrogen bonds. Adenine always bonds with thymine, and cytosine always bonds with guanine.
The bonding causes the two strands to spiral around each other in a shape called a double helix. Ribonucleic acid RNA is a second nucleic acid found in cells. RNA is a single-stranded polymer of nucleotides. It also differs from DNA in that it contains the sugar ribose, rather than deoxyribose, and the nucleotide uracil rather than thymine. Prokaryotes contain a single, double-stranded circular chromosome.
Eukaryotes contain double-stranded linear DNA molecules packaged into chromosomes. The DNA helix is wrapped around proteins to form nucleosomes.
The protein coils are further coiled, and during mitosis and meiosis, the chromosomes become even more greatly coiled to facilitate their movement.
Chromosomes have two distinct regions which can be distinguished by staining, reflecting different degrees of packaging and determined by whether the DNA in a region is being expressed euchromatin or not heterochromatin. Skip to content Chapter 9: Introduction to Molecular Biology. But as far as their structure is concerned, these RNAs all share the same basic single-stranded chemical structure with, in some cases, higher-order structures obtained through complementary base-pair folding. New functions for RNA, new modifications to RNA, and other surprises undoubtedly await discovery in the years to come.
Figure The "wobble" position. This base-pairing flexibility is also called "wobble. Berget, S. Spliced segments at the 5' terminus of adenovirus 2 late mRNA. Proceedings of the National Academy of Sciences 74 , — Early, P. Cell 20 , — Evans, R. Cell 12, — Holley, R. Structure of a ribonucleic acid. Science , — doi Patel, A. Splicing double: Insights from the second spliceosome.
Nature 4 , — doi Rich, A. A hybrid helix containing both deoxyribose and ribose polynucleotides and its relation to the transfer of information between the nucleic acids. Proceedings of the National Academy of Sciences 46 , — A new two-stranded helical structure: Polyadenylic acid and polyuridylic acid. Journal of the American Chemical Society 78 , — link to article. Schmucker, D. Drosophila Dscam is an axon guidance receptor exhibiting extraordinary molecular diversity. Cell , — Theimer, C.
Structure of the human telomerase RNA pseudoknot reveals conserved tertiary interactions essential for function.
Molecular Cell 17 , — Restriction Enzymes. 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.
RNA Functions. Citation: Clancy, S. Nature Education 7 1 The more researchers examine RNA, the more surprises they continue to uncover. What have we learned about RNA structure and function so far? Aa Aa Aa. Figure 1. Figure Detail. Nucleic acids hold an important role in cellular functions, heredity, and survival of an organism. Apart from being a major component of nucleic acids, adenine is also a vital constituent of adenosine triphosphate ATP , which is adenosine with three phosphate groups attached to it.
ATP is an energy-rich molecule and is used in cellular metabolism and other biological reactions. Uric acid is the metabolic end product of purine metabolism, including adenine. In the diet, purines are found in high amounts in liver, kidney, and other internal organs.
They are also present in meat, seafood, cauliflower, beans, and mushrooms but in moderate amounts. Hyperuricemia is the condition when there is too much uric acid level in the body. Too much uric acid from a high-purine diet could eventually lead to gout inflammation in the joint and kidney stones.
Thus, people with such conditions are advised to eat a rather low-purine diet. It is also further advised to restrain from, or avoid consuming, alcohol and saturated fats because they obstruct the proper metabolism of purines. The isolation and naming of the five nucleobases, including cytosine, is attributed to Albrecht Kossel a German biochemist.
From to he and his students discovered them through chemical analyses of the nucleic acids. DNA is a double helix structure comprised of nucleotides. A nucleotide, in turn, is made up of phosphate molecule, deoxyribose, and a nitrogenous base. Read More. Plants are responsible for incredible feats of molecular transformation. Plant processes, such as photosynthesis, photophosphorylation, chemiosmosis, carbon fixing reactions, respiration, are presented in this tutorial The body is comprised of different elements with hydrogen, oxygen, carbon, and nitrogen as the major four.
This tutorial will help you understand the chemical composition of the body. This will come in handy when considering the various interactions between cells and structures.
Genes are expressed through the process of protein synthesis.
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