Tài liệu Khoa Học Tự Nhiên

Each eukaryotic chromosome consists of a long, linear DNA molecule. Each chromosome has hundreds or thousands of genes, the units that specify an organism’s inherited traits. Associated with DNA are proteins that maintain its structure and help control gene activity. This DNA-protein complex, chromatin, is organized into a long thin fiber. Afte...

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 602 | Lượt tải: 0

Sutherland’s research team discovered that epinephrine activated a cytosolic enzyme, glycogen phosphorylase. However, epinephrine did not activate the phosphorylase directly but could only act onintact cells. Therefore, there must be an intermediate step or steps occurring inside the cell. Also, the plasma membrane must be involved in transmitt...

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Powered by light, the green parts of plants produce organic compounds and O2 from CO2 and H2O. Using glucose as our target product, the equation describing the net process of photosynthesis is: 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2 In reality, photosynthesis adds one CO2 at a time: CO2 + H2O + light energy -> CH2O + O2 CH2O represents th...

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When these bonds shift from nonpolar to polar, the electrons move from positions equidistant between the two atoms for a closer position to oxygen, the more electronegative atom. Oxygen is one of the most potent oxidizing agents. An electron looses energy as it shifts from a less electronegative atom to a more electronegative one. A redox reacti...

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Membrane molecules are held in place by relatively weak hydrophobic interactions. Most of the lipids and some proteins can drift laterally in the plane of the membrane, but rarely flip-flop from one layer to the other.

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Transmission electron microscopes (TEMs) are used mainly to study the internal ultrastructure of cells. A TEM aims an electron beam through a thin section of the specimen. The image is focused and magnified by electromagnets. To enhance contrast, the thin sections are stained with atoms of heavy metals.

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Mitochondria and chloroplasts are the organelles that convert energy to forms that cells can use for work. Mitochondria are the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen. Chloroplasts, found in plants and eukaryotic algae, are the sites of photosynthesis. They con...

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The magnitude of delta G for an exergonic reaction is the maximum amount of work the reaction can perform. For the overall reaction of cellular respiration: C6H12O6 + 6O2 -> 6CO2 + 6H2O delta G = -686 kcal/mol Through this reaction 686 kcal have been made available to do work in the cell. The products have 686 kcal less energy than the reactan...

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Tertiary structure is determined by a variety of interactions among R groups and between R groups and the polypeptide backbone. These interactions include hydrogen bonds among polar and/or charged areas, ionic bonds between charged R groups, and hydrophobic interactions and van der Waals interactions among hydrophobic R groups.

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Enantiomers are molecules that are mirror images of each other. Enantiomers are possible if there are four different atoms or groups of atoms bonded to a carbon. If this is true, it is possible to arrange the four groups in space in two different ways that are mirror images. They are like left-handed and right-handed versions. Usually one is...

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