Lecture 18, 19, 20

Lecture 18, 19, 20 - Nucleic Acids The Genetic Code...

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1 Nucleic Acids The Genetic Code Chem 004 - Spring 2006 Transcription, Translation and Replication Blackboard: http://blackboard.gwu.edu Office Hours: MW 3:10 – 3:55 PM, 1957 E street, room 213 or by appointment Deoxyribonucleic acid (DNA) - Mainly found in the cell nucleus - Very large molecules - Double stranded - Store genetic information Ribonucleic acid (RNA) - Found in the nucleus and in the cytoplasm of a cell - Large molecules, but small compared to DNA - Single stranded - Involved in protein synthesis P O - O O - O - Phosphate Chemical units of DNA Chemical units of DNA In RNA, deoxyribose is replaced by ribose, O H H O O O H O H and Thymine by Uracil ( U ) H N N H O O O H H O O O H Sugar Deoxyribose N N N H N H 2 N CH 3 H N N H O O N N H N H 2 O H 2 N H N N N H N O Base Adenine Thymine Cytosine Guanine AC TG N N N N N H 2 O O H O P -O O - O A nucleotide O O O H N N O O N H N N O N H 2 N O O O P O -O O N N N H 2 O O O P O -O O O O H H N N O O P O -O -O P O DNA segment Thymine Cytosine Guanine Thymine
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2 Simplified representation of a single strand of DNA/RNA sugar P sugar P sugar P sugar P sugar P sugar P A G T C A G The Base compositions of DNA of Various Species 21.6 21.0 29.0 28.4 Bacillus subtilis (bacterium) 25.6 25.5 24.3 24.6 Escherichia coli (bacterium) 24.6 24.5 25.3 25.6 Zea mays (corn) 26.6 27.1 23.3 23.0 Neurospora crasa (mold) 22.5 22.5 27.6 27.3 Drosophila melanogaster (fruit fly) 18.4 19.1 31.5 31.0 Homo sapiens (human) Cytosine Guanine Thymine Adenine Species Chargaff’s rules: In every species, the percent of adenine almost exactly equals the percent of thymine, and the percent of guanine is essentially identical to the percent of cytosine. N N N H N N H H Adenine H 3 C N H H N O O Thymine N N H N O H H Cytosine N H N N N H N O H H Guanine Base pairing S S S S S S P P P P P P S S S S S S P P P P P P C T G A A G T C T C A G
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3 DNA is packaged into structures called chromosomes Human body cells have 46 chromosomes (23 pairs) A G C C C C G G G A A A A T T T T T T G C T T C G G T C C T G A A A A A Replication (in the cell nucleus) Double strand of DNA Process by which copies of DNA are made. Catalyzed by the enzyme DNA polymerase How is the genetic information stored in DNA transferred to proteins? DNA RNA Transcription RNA molecules are produced The base sequence is translated to an amino acid sequence Translation Protein
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4 The genetic code is written in groupings of three DNA bases called codons This information is transferred to an mRNA molecule during the transcription process. Each group of three bases (triplet) codifies for one amino acid. There are 64 possible codons and only 20 amino acids. There is redundancy in the code. Alanine Threonine Glutamine Leucine Arginine Serine Termination Transcription (in the cell nucleus) A G C C C C G G G A A A A T T T T T T G C T T C G G T C C T G A A A A A DNA strand A gene in DNA is copied into a messenger RNA (mRNA) molecule A G C C C C G G G A A A A T T T T T T G C T T C G G T C C T G A A A A A C A A A A G G G C C C U U U U A G U mRNA Transcription (in the cell nucleus) A gene in DNA is copied into a messenger RNA (mRNA) molecule C A A A A G G G
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This note was uploaded on 04/10/2008 for the course CHEM 004 taught by Professor Zysmilich during the Spring '06 term at GWU.

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Lecture 18, 19, 20 - Nucleic Acids The Genetic Code...

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