Biology  5/e   Raven/Johnson
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Structure of DNA and RNA: DNA and RNA are nucleic acids. Both are made of nucleotides, linked by phosphate groups. The sugar in RNA is ribose. The sugar of DNA has one less oxygen atom per molecule, thus, deoxyribose. RNA is single-stranded, whereas DNA is double-stranded. Both contain the bases adenine, guanine and cytosine. DNA also has thymine, whereas RNA has uracil.

Ribosomes: Ribosomes are microstructures found in the cytoplasm and on the rough endoplasmic reticulum. They are the sites of protein synthesis.

Enzymes and enzyme activity: Enzymes are protein catalysts of specific reactions. In order to function, an enzyme must physically conform to the shape of the substrate.

Structure of eukaryotic chromosomes: Eukaryotic chromosomes are very long, often coiled molecules of DNA with some protein. Each contains a constriction, called the centromere, by which sister chromatids are held together, and by which the chromosomes are attached to the microtubules for movement.

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