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from article Allosteric enzyme

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Model of an allosteric enzyme composed of two subunit monomers. Regulatory effects are obtained by shifting back and forth between the two states—relaxed (R state) and taut (T state). In the R state, the enzyme reacts with substrate and activators;…

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from article Continental drift

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Map of the Earth as Pangea broke up as a result of continental drift. (Copyright © McGraw-Hill)

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from article Heart (invertebrate)

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Invertebrate hearts range from (left) the centralized hearts and open circulatory systems of grasshoppers to (right) the distributed hearts and closed circulatory systems of segmented worms. (Copyright © McGraw-Hill Education)

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from article Heart (invertebrate)

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Circulatory system in a marine snail (Aplysia). Arrows indicate the normal direction of blood flow. (Credit: E. Mayeri, J. Koester, I. Kupfermann, G. Liebeswar, and E. R. Kandel)

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from article Heart (invertebrate)

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Cardiac ganglion of a lobster (Homarus): (a) nerves on the inner dorsal surface of the heart; (b) cell body position of all nine intrinsic neurons. (Credit: D. K. Hartline)

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from article Heart (invertebrate)

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Cross section of a leech (Hirudo), showing its major organs and muscles, including its ventral nerve cord and the four longitudinal coelomic sinuses, which are the main vessels of its circulatory system. The nerve cord is enclosed in the ventral…

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from article Amino acid

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Structural formula for an amino acid. (Copyright © McGraw Hill)

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from article Amino acid

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The 20 amino acids that serve as the building blocks for proteins. These amino acids (shown with their respective three-letter abbreviations) can be divided into nonpolar, polar, and electrically charged groups. (Copyright © McGraw Hill)

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from article Amino acid

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Synthesis of a dipeptide. When an amino group of one amino acid is linked to the carboxyl group of another amino acid, a peptide bond linkage is formed. A molecule of water (H2O) is split out when a peptide bond is formed. (Copyright © McGraw Hill)

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from article Amino acid

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Two-dimensional chromatogram of a protein. (Credit: R. J. Block, E. L. Durrum, and G. Zweig)

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from article Stalactites and stalagmites

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Stalactite and stalagmite deposits. Along the central opening are deposits made by water as it dripped from the crack in the limestone. Outside layers were deposited by water flowing over the surface. Water may drip to the floor and create a…

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from article Mitochondrial replacement therapy

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Spindle transfer involves the excision of the metaphase II spindle from a donor egg and replacing it with the metaphase II spindle from the affected egg. The metaphase II spindle contains the condensed chromosomes of the egg's haploid genome. Terms:…

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from article Mitochondrial replacement therapy

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Cytoplasmic transplantation involves the addition of a donor's ooplasm (cytoplasm in an oocyte) to the recipient oocyte prior to fertilization. Terms: ICSI, intracytoplasmic sperm injection; mtDNA, mitochondrial DNA; nDNA, nuclear DNA. (Credit:…

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from article Mitochondrial replacement therapy

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Pronuclear transfer requires that both the donor and affected eggs be fertilized by the father's sperm simultaneously in vitro. Following fertilization and once pronuclei are visible by microscopy, the two pronuclei from the donor egg are removed,…

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from article Glucose

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Steps involved in the regulation of blood glucose. The pancreas acts as both the sensor and effector organ. (Copyright © McGraw-Hill Education)

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from article Glucose

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Breakdown (catabolism) of glucose. Glucose is catabolized in three steps: glycolysis, Krebs cycle, and oxidative phosphorylation. The final product is ATP (adenosine triphosphate), which is an organic molecule that cells use as a source of energy to…

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from article Glucose

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Glucose and insulin uptake in normal individuals and those with type 1 or type 2 diabetes. (Copyright © McGraw-Hill Education)

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from article Lake

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MODIS (MODerate-resolution Imaging Spectroradiometer) Terra satellite image of the Great Lakes, September 15, 2015. (Credit: NOAA Great Lakes CoastWatch)

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from article Lake

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Oxbows in Bolivia. Landsat satellite image of the Beni River in Bolivia, which resembles a blue ribbon as it flows toward the Amazon River. Scattered along the river are numerous oxbow lakes, which are curved bodies of water that form when a meander…

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from article Oil shale

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C-13 nuclear magnetic resonance characterization of organic matter in two United States oil shale samples. (a) Colorado oil shale, 80% aliphatic carbon content with 69% conversion of organic carbon to oil. (b) Kentucky oil shale, 52% aliphatic…

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from article Oil shale

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Oil shale deposits of the United States. (Courtesy of John Ward Smith)

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from article Oil shale

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Oil shale retorting systems: (a) internally heated, (b) externally heated.

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from article Tuberculosis

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Tuberculosis is caused by the tubercle bacillus Mycobacterium tuberculosis. (Left) Colorized scanning electron micrograph (SEM) depicting some of the ultrastructural details seen in the cell wall configuration of a number of Gram-positive…

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from article Tuberculosis

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Annual number of tuberculosis (TB) cases in the United States from 1992 to 2017. During this time period, there has been a decline in the prevalence of tuberculosis. However, the progression of decline has slowed since 2013 (indicated by the purple…

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