DNA structure

DNA structure - DNA structure: (Fig 7.1) Review DNA...

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DNA structure: (Fig 7.1) Review DNA structure (Ch. 2) Nucleotide made of ribose,phosphate and nitrogenous base Nitrogenous bases: Adenine, Guanine, Thymine, Cytosine Double helix: 2 antiparallel strands held by hydrogen bonds between the bases (Review hydrogen bonds Fig. 2.4) Always A-T, G-C Chain grows from 5' to 3'. Nucleotide attaches at 3' Phosphate is attached at carbon # 5 of ribose. Carbon # 3 is free for next nucleotide to attach by its phosphate. DNA can replicate itself by complementary base pairing Chromosomes: Linear in Eukaryotes. Circular in Prokaryotes Gene - sequence of DNA , defines a characteristic Locus - point on chromosome where a gene is located Alleles - alternate form of a gene Prokaryotes - one chromosome, one allele to a gene Eukaryotes - pairs of chromosomes, 2 alleles to a gene Mutation - alteration in DNA, change in sequence of bases Replication: (fig. 7.4) At point of origin strands separate forming a replication fork.(bidirectional) Each strand is replicated by complementary base paring. Replication is semiconservative. Helicases - open unwind and stabilize strands. DNA polymerase - synthesize strand in 5' to 3' direction. Needs primer to begin Leading strand - forms continues 5' to 3' Lagging strand - forms in Okazaki fragments 5' to 3'. Ligase joins fragments (primer needed) Protein Synthesis: DNA transcription mRNA translation Polypeptide (protein) (Fig. 7.3) Transcription: (Fig. 7.5) RNA: single strand; Uracil substitutes for thymine; synthesis by complementary base pairing in 5' to 3' direction; DNA opens, one strand used as a template. RNA polymerase binds to promoter and transcribes gene: initiation, elongation, termination - RNA released Prokaryotes: transcription and translation in cytoplasm Eukaryotes: transcription in nucleus, translation in cytoplasm Processing of mRNA: (Fig. 7.6) Introns removed, exons spliced - continues mRNA (gene). Cap of GTP at 5', Poly A tail at 3'. mRNA exits nucleus. Translation: Code - sequence of bases in DNA Codon - 3 bases in mRNA specify for one amino acid
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3 bases in DNA - codon in mRNA (3 bases) - one amino acid in polypeptide Genetic code: 64 codons (Fig. 7.8) Start- AUG; Stop - UAA, UAG, UGA; Reading frame - read code in groups of 3 bases during translation. Ribosomes: (Fig. 7.7) Site of protein synthesis Two subunits of rRNA+proteins make functional ribosome Transfer RNA: (tRNA) (Fig. 7.9), (T. 7.1) Brings proper amino acid to ribosomes for protein synthesis. Many tRNAs Site for amino acid attachment Anticodon - complementary to codon in mRNA. Complementary base pairing during polypeptide synthesis Translation process: (Fig. 7.10, 7.12) in 5' to 3' direction Ribosomes coordinate and bring together mRNA and tRNA Initiation: mRNA binds to small subunit; First tRNA-met base pair with start codon AUG; Large subunit binds; tRNA fits into P site; A site ready to receive next tRNA
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This note was uploaded on 04/08/2008 for the course BI 151 taught by Professor Zavras during the Spring '08 term at Fairfield.

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DNA structure - DNA structure: (Fig 7.1) Review DNA...

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