Chapter 89Stu - Chapters 8 and 9: Nucleotides and Nucleic...

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Chapters 8 and 9: Nucleotides and Nucleic Acids
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Fundamentals of Nucleic Acids The genetic make-up of living material is stored in either DNA or RNA - A fundamental, scientific definition of life - Prion Gene - Segment(s) of DNA or RNA - May not be a continuous sequence of bases - Contains the information required for the synthesis of a functional biological product: RNA or protein
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Nucelo t ides 3 Components: nitrogenous base + a pentose + phosphate Nucelo s ides 2 Components: nitrogenous base + a pentose Structure of Nucleic Acids 1 3 2
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Nitrogenous bases come from parent compounds : Purine or Pyrimidine Purines A denine and G uanine P y rimidines C y tosine, T h y midine and U racil Structure of Nucleic Acids
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The two pentoses are closed ring forms (-furanose) 2’- deoxy -D-ribose DNA D-ribose RNA Ring : is puckered, not planar Plays a role in complex structures
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Nucleoside phosphates are also nucleotides: ATP Adenylate (the common name of this nucleotide) Adenosine 5’ monophosphate A Nucleotide The Nucleoside (without the phosphate) is Adenosine alone
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Most are methylated forms of the major bases Nomenclature is confusing Do not memorize nomenclature or structures of minor bases Some nucleotides have additional rings Examples : Adenosine 3’-5’cyclic monophosphate (cAMP) Guanosine 3’-5’cyclic monophosphate (cGMP) Minor Bases
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5’ phosphate + 3’ hydroxyl Creates a backbone of pentose – phosphate – pentose – phosphate, etc Oligonucleotide Up to about 50 bases Polynucleotide (old term) More than 50 bases Nucleotides are Joined by Phosphodiester Bonds
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- Bases are considered side-groups (like R-groups of amino acids) - Backbones are hydrophilic -- Pentose hydroxyls form hydrogen bonds with water - Phosphates are completely ionized at pH 7.0 - Nucleotides absorb ultraviolet light (maxima at ~ 260 nm) - All phosphodiester bonds have the same orientation in the chain - Bases “Stack” to minimize contact with water The polarity of the molecule dictates a defined orientation The end without a nucleotide in the 5’ position The end without a nucleotide in the 3’ position By definition, the 5’ end of a pictured molecule is on the left 5’ C 3’ Some Structural Properties of Nucleotides
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Bases are hydrophobic and relatively insoluble in water (near neutral pH) Hydrogen bonds form interactions between nucleotide bases Permits associations between two or more strands of nucleic acids Watson/Crick Model for double-stranded DNA A binds to T G binds to C Some Structural Properties of Nucleotides
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Bases “stack” - Planes of the bases - Minimizes contact with water Properties of Nucleotides Dictate the Structure of the Resulting Nucleic Acids
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Nucleic Acid Primary and Secondary Structure The Structure of DNA was outlined crudely in Edwin Chargaff’s Rules 1. The base composition of DNA varies from species to species 2. DNA from different tissues of the same species have the same base composition 3. The base composition of a given species is constant over time or with
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Chapter 89Stu - Chapters 8 and 9: Nucleotides and Nucleic...

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