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Chapter 4

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CAS BI 108
Francis Monette

Savan Shah BI 108 Outline Chapter 4 Chapter 4: NucleicAcids and the Origin of Life I. What are the Chemical Structures and Functions of NucleicAcids -NucleicAcids  Polymers specialized for the storage, transmission, and use of genetic info • DNA(DeoxyribonucleicAcid) and RNA(RibonucleicAcid) • Nucleotide  Nitrogen-containing base + Pentose Sugar + 1-3 Phosphate groups oPurines  2 Ring Base (Adenine, Guanine) oPyrimidines  1 Ring Base (Cytosine, Thymine, Uracil) oRNABases:Adenine (A) , Uracil (U), Cytosine (C), Guanine (G) oDNABases:Adenine(A), Thymine (T), Cytosine (C), Guanine (G) oNucleosides  Pentose Sugar + Nitrogen-containing base (No phosphate group) • RNAcontains pentose sugar ribose; DNAcontains pentose sugar deoxyribose • Phosphodiester Linkage  Bond that forms between pentose in last nucleotide of existing chain and phosphate on the new nucleotide oForms through dehydration synthesis oPhosphate on new nucleotide is attached to 5`-carbon atom of its sugar; Linkage occurs between it and 3`-carbon on the last sugar of the existing chain oNucleic acids grow in the 5`-to-3` direction • Oligonucleotides include RNAmolecules that function as “primers” to begin duplication of DNA • Polynucleotides include DNAand most RNA • Complementary base pairing  Adenine always pairs with Thymine; Cytosine always pairs with Guanine; RNA:Adenine always pairs with Uracil • Individual base pairs are relatively easy to break with a modest input of energy • RNA oSingle stranded oBase pairing can occur between different regions of the molecule oPortions of single-stranded RNAmolecule can fold back and forth  Complementary H-bonding between ribonucleotides plays role in 3D shape of RNA • DNA oDouble stranded oUniform oA-T and G-C base pairs are about same size o2 polynucleotide strands form “ladder” that twists into double helix • DNAReplication  Completed by polymerization using an existing strand as base- pairing template oCertain DNAsequences can be copied into RNA Transcription oNucleotide sequence in RNAcan be used to specify sequence of amino acids in polypeptide chain  Translation oTranscription + Translation  Gene Expression Savan Shah BI 108 Outline Chapter 4 o**SEE FIGURE ON PG. 65** oDNAreplication and transcription depend on base-pairing properties of nucleic acids oTranscription produces the complementary strand to the template strand oDNAreplication usually involves entire DNAmolecule  Complete set of DNAin living organism = Genome oSequences of DNAthat are transcribed into RNA Genes • DNAbase sequence reveals evolutionary relationships  Chimpanzee genome is 98% similar to human genome • Nucleotides are used in other important substances other than DNA oUsed in ATP, GTP, cAMP, and as carriers in synthesis and breakdown of
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