lecture 1.docx

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Department
Biology
Course
BIOL311
Professor
Kerry Reimer
Semester
Winter

Description
DNA is a molecule encoding thegenetic instructions used in the development and functioning of all known living organisms and many viruses. Along with RNAand proteins, DNA is one of the three major macromoleculesthat are essential for all known forms of life. Genetic information is encoded as a sequence of nucleotides (guanine, adenine,thymine, and cytosine) recorded using the letters G, A, T, and C. Most DNA molecules are double-stranded helices, consisting of two long polymers of simple units callednucleotides, molecules with backbones made of alternatingsugars (deoxyribose) and phosphate groups (related to phosphoric acid), with the nucleobases (G, A, T, C) attached to the sugars. DNA is well-suited for biological information storage, since the DNA backbone is resistant to cleavage and the double-stranded structure provides the molecule with a built-in duplicate of the encoded information. These two strands run in opposite directions to each other and are therefore anti-parallel, one backbone being 3' (three prime) and the other 5' (five prime). This refers to the direction the 3rd and 5th carbon on the sugar molecule is facing. Attached to each sugar is one of four types of molecules callednucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA in a process called transcription. Within cells, DNA is organized into long structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms (animals, plants,fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteriaand archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatinproteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA is a long polymer made from repeating units callednucleotidesDNA was first identified and isolated by Friedrich Miescher and the double helix structure of DNA was first discovered by James D. Watson and Francis Crick. The structure of DNA of all species comprises two helical chains each coiled round the same axis, and each with a pi
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