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Bisc 150 Fall lectures 2009

Bisc 150 Fall lectures 2009 - Bisc 150 Fall 2009 lectures...

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Bisc 150, Fall, 2009, lectures by R. Baker. The following notes are meant to be of help in understanding the lectures. These notes are outlines of a portion of the material presented and do not contain many of the details given in the actual lectures. Readings: page and chapter numbers are for the 8 th edition of Lewis. Lecture # 1 (Readings in Lewis: Chapter 9) Introduction to the Central Dogma of Life : Genes are lengths of chromosomal DNA that code for the synthesis of proteins. DNA replication 1. Genes, DNA structure: the two strands in chromosomal DNA are antiparallel to each other. 2. DNA replication is semiconservative : each daughter cell receives one of the two strands of DNA that were originally in the parent cell. After cell division. each daughter cell has a new companion strand that accompanies the old parental strand (see Figs. 9.14, 9.15, 9.16 in Lewis). 3. Replication of DNA is bidirectional , starting at chromosomal origin positions. Replication takes place on the sides of two “growing forks,” which diverge and travel away from the origin. 4. DNA polymerases move along the parental (old) strands, traveling 3’ toward 5’ on each old strand, creating a new companion strand as each polymerase moves along. Thus, new nucleotides are added to the 3’ ends of all four of the growing new strands within the two growing forks (see Fig. 9.16 in Lewis). 5. Nucleoside triphosphates are pulled in one at time by the DNA polymerases to create the new strands. Each incoming nucleotide is attached (to the 3’ end of a growing strand) as a nucleoside monophosphate. 6. DNA replication is initiated by unwinding double stranded DNA to created the beginnings of growing forks. This accomplished by a helicase protein. A short RNA primer strand is first synthesized and then extended as DNA to form a new DNA strand on each side of a fork. (The RNA primer is eventually removed and replaced with DNA.) 7. On one side of each growing fork, DNA synthesis is discontinuous , forming a series of Okazaki fragments, which are later connected together by the enzyme ligase. Lecture # 2 Protein synthesis, genetic code (Readings in Lewis: chapters 10 and 11) 1. Transcription: One of the two strands in chromosomal DNA is copied by RNA polymerase to form a strand of pre-mRNA. This pre-mRNA strand includes exon and intron sections. Pre-mRNA is then converted to mRNA by removal of the intron sections, leaving only the original exons connected to each other. 2. Transcription begins at promoter DNA sequences located just upstream from genes.
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3. In eucaryotic cells, mRNA strands are exported from a cell’s nucleus into the cytoplasm where they are translated into protein strands. 4. Translation: Ribosomes load onto the 5’ end of mRNA strands and move toward the 3’ end. As a ribosome moves, it takes in, one at a time, a tRNA with a specific amino acid attached to the tRNA. The incoming amino acid is taken from the tRNA and attached to the growing protein strand (polypeptide chain). So, the protein becomes longer the further the ribosome has moved along the mRNA strand.
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