tRNA and Ribosomes

tRNA and Ribosomes - Molecular Biochemistry II tRNA &...

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Copyright © 1999-2008 by Joyce J. Diwan. All rights reserved. Molecular Biochemistry II
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Molecular Biology Familiarity with basic concepts is assumed, including: w nature of the genetic code w maintenance of genes through DNA replication w transcription of information from DNA to mRNA w translation of mRNA into protein.
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Nucleic acids are polymers of nucleotides . Each nucleotide includes a base that is either w a purine (adenine or guanine), or w a pyrimidine (cytosine, uracil, or thymine).
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Some nucleic acids contain modified bases. Examples:
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In a nucleotide , e.g., adenosine monophosphate (AMP), the base is bonded to a ribose sugar, which has a phosphate in ester linkage to the 5' hydroxyl.
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Nucleic acids have a backbone of alternating Pi & ribose moieties. Phosphodiester linkages form as the 5' phosphate of one nucleotide forms an ester link with the 3' OH of the adjacent nucleotide. A short stretch of RNA is shown. N N N N NH 2 O OH O H H H CH 2 H ribose adenine P O O O O OH O H H H CH 2 H N N NH 2 O P O O O O P O O O - - - cytosine 5' 4' 3' 2' 1' ribose 3' 5' 3' end 5' end - (etc) nucleic acid
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Hydrogen bonds link 2 complementary nucleotide bases on separate nucleic acid strands, or on complementary portions of the same strand. Conventional base pairs : ( or T ); . In the diagram at left, H-bonds are in red. Bond lengths are inexact. The image at right is based on X-ray crystallography of tRNAGln. H atoms are not shown.
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Secondary structure Base pairing over extended stretches of complementary base sequences in two nucleic acid strands stabilizes secondary structure , such as the double helix of DNA. Stacking interactions between adjacent hydrophobic bases contribute to stabilization of such secondary structures. Each base interacts with its neighbors above and below, in the ladder-like arrangement of base pairs in the double helix, e.g., of DNA.
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Genetic code The genetic code is based on the sequence of bases along a nucleic acid. Each codon , a sequence of 3 bases in mRNA, codes for a particular amino acid, or for chain termination. Some amino acids are specified by 2 or more codons. Synonyms (multiple codons for the same amino acid) in most cases differ only in the 3rd base. Similar codons tend to code for similar amino acids. Thus effects of mutation are minimized.
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Genetic Code 2 nd base 1 st base U C A G 3 rd base UUU Phe UCU Ser UAU Tyr UGU Cys U UUC Phe UCC Ser UAC Tyr UGC Cys C UUA Leu UCA Ser UAA Stop UGA Stop A U UUG Leu UCG Ser UAG Stop UGG Trp G CUU Leu CCU Pro CAU His CGU Arg U CUC Leu CCC Pro CAC His CGC Arg C CUA Leu CCA Pro CAA Gln CGA Arg A C CUG Leu CCG Pro CAG Gln CGG Arg G AUU Ile ACU Thr AAU Asn AGU Ser U AUC Ile ACC Thr AAC Asn AGC Ser C AUA Ile ACA Thr AAA Lys AGA Arg A A AUG Met* ACG Thr AAG Lys AGG Arg G GUU Val GCU Ala GAU Asp GGU Gly U GUC Val GCC Ala GAC Asp GGC Gly C GUA Val GCA Ala GAA Glu GGA Gly A G GUG Val GCG Ala GAG Glu GGG Gly G *Met and initiation.
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tRNA The genetic code is read during translation via adapter
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This note was uploaded on 09/25/2010 for the course BCH 4024 taught by Professor Allison during the Spring '08 term at University of Florida.

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tRNA and Ribosomes - Molecular Biochemistry II tRNA &...

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