Nucleotides and Nucleic Acids

Three principle components of nucleotides

a heterocyclic nitrogenous base, a pentose sugar, and a phosphate

• they are intermediates in virtually all cellular metabolism

Nucleic Acids

linear polymers of nucleotides

• DNA uses 2-deoxyribose; RNA uses ribose

• DNA is the repository of genetic information

• RNA is central to gene expression

What are two nitrogenous bases

found in nucleotides that include purines and pyrimidines.

Purines vs Pyrimidines

• Pyrimidines are single six-membered rings with two nitrogen atoms

• Purines are fused rings resembling pyrimidine and imidazole

• Bases are relatively insoluble to pronounces aromatic character

Common Pyrimidines and Purines

Pyrimidines: Cytosine(C), Uracil (U), Thymine (T, or 5-methyluracil): C and T - DNA; C and U - RNA

Purines: Adenine(A) and Guanine(G): A and G - DNA/RNA

UV detection of nitrogenous bases

Bases strongly absorb UV light around 260nm

• useful for quantitive and qualitative analysis

Nucleosides

Sugar + nitrogenous base

• Link a base to a pentose sugar in the furanose form

• No phosphate group yet

• Linkage is a beta-configuration glycosidic bond

Naming for pyrimidines and purines

Pyrimidines - “-idine”

Purines - “-osine”

Exception: hypoxanthine —> inosine

What are the nucleosides of deoxyribose?

deoxyribonucleic acides (prefixed deoxy)

• Adenine-ribose = adenosine

• Adenine-deoxyribose = deoxyadenosine

• Exceptionfor thymine

  • Thymine-deoxyribose is called thymidine

Adenosine

acts as a local hormone and neuromodulator

• adenosine regulates heartbeat, promotes blood vessel dilation, and promotes sleepiness

  • we have low levels after we wake up and then it increases as the day goes on

• caffeine blocks adenosine receptors

How is a nucleotide formed?

a nucleotide is formed when a phosphoric acid is esterfied, usually at the 5’ - position of the sugar

• due to the phosphate group, nucleotides have acidic properties

Nucleoside diphosphate(NDPs) and triphosphates(NTPs)

are nucleotides with two or three phosphate groups attached, respectively. They play crucial roles in cellular energy transfer and metabolism.

• contain additional phosphates linked by phosphoric anhydride linkages

• NTPS are indispensable carriers of chemical energy

What drives biological work in nucleotides?

The transfer of phosphoryl, pyrophosphoryl, or nucleotidyl(NMP) groups drive biological work

• Different bases (A,G,C, and U) channel energy into different metabolic pathways

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Cyclic Nucleotides

cyclic phosphodiesters —> 3’, 5’-cyclic AMP (cAMP)

• they are important regulators of cellular metabolism

Glucagon Signaling

Glucagon signaling involves the binding of glucagon to its receptor

• leads to the activation of the enzyme Adenylate Cyclase which converts ATP to cAMP

Functions of nucleotides

• building block of nucleic acids

• triphosphates are energy intermediates

• Carrier of metabolic intermediates:

  • UDP in sugar metabolism

  • CDP in phospholipid metabolism

• Chemical Signaling second messengers: cyclic AMP

• Nucleotide derivatives are vital components of coenzymes involved in redox reactions

The polynucleotide chain

• Nucleic Acids are polynucleotides formed by nucleotides linked 3’ to 5’ vis phosphodiester bond

  • This forms directional sugar-phosphate backbone

• This unique identify is determined solely by the sequence of bases

• * read from 5’ to 3’ end (order of polarity)

DNA double helix structure

• DNA has a singular role: preserving information for all functional macromolecules

• DNA consist of two antiparallel polynucleotide strands wound together in a double helix

• Strands held together by interchain hydrogen bonds (base pairing)

DNA base pairing

• A to T —> 2 bonds

• G to C —> 3 bonds

• form spatially equivalent units, giving the helix uniform dimensions

DNA Synthesis*******22

• The process by which DNA is replicated, involving the unwinding of the double helix and the addition of complementary nucleotides to form new strands.

• Nucleic acids are synthesizes starting at the 5’ end and moving toward the 3’ end

• Condensation reaction Between two nucleotides

DNA replication and info storage

• complementary relationship means info is conserved in the opposing strand

• base pairing ensures faithful replication

• DNA encodes information digitally using the four bases

• Eukaryotic DNA is condensed by wrapping around histone proteins to form nucleosomes

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