Tài liệu Sinh Học

Further evidence that DNA was the genetic material was derived from studies that tracked the infection of bacteria by viruses. Viruses consist of a DNA (sometimes RNA) enclosed by a protective coat of protein. To replicate, a virus infects a host cell and takes over the cell’s metabolic machinery. Viruses that specifically attack bacteria are ca...

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Morgan observed this linkage and its deviations when he followed the inheritance of characters for body color and wing size. The wild-type body color is gray (b+) and the mutant black (b). The wild-type wing size is normal (vg+) and the mutant has vestigial wings (vg). Morgan crossed F1 heterozygous females (b+bvg+vg) with homozygous recessive m...

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In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F1 generation. Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation. It was mainly Mendel’s quantitative analysi...

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In asexual reproduction, a single individual passes along copies of all its genes to its offspring. Single-celled eukaryotes reproduce asexually by mitotic cell division to produce two identical daughter cells. Even some multicellular eukaryotes, like hydra, can reproduce by budding cells produced by mitosis.

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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...

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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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