U01.01.002 Nucleotides

Nucleosides

Definition: Base + (deoxy)ribose (sugar).
Examples:
- Adenosine = Adenine + Ribose
- Thymidine = Thymine + Deoxyribose

Nucleotides

Definition: Base + (deoxy)ribose + phosphate.
Characteristics:
- Linked by 3′-5′ phosphodiester bonds.
Examples:
- ATP = Adenine + Ribose + 3 Phosphates
- dGTP = Guanine + Deoxyribose + 3 Phosphates

Purines vs. Pyrimidines

Base	Structure	Rings
Purines	2 rings	A, G
Pyrimidines	1 ring	C, U, T

Purines vs. Pyrimidines

Purines: Adenine (A), Guanine (G)
Pyrimidines: Cytosine (C), Uracil (U), Thymine (T)

Deamination Reactions

Original Base	Deaminated Product
Cytosine	Uracil
Adenine	Hypoxanthine
Guanine	Xanthine
5-Methylcytosine	Thymine

Deamination Reactions

Uracil is found in RNA; Thymine is found in DNA.
Methylation of uracil makes thymine.

Nucleotide Structure and Bonding

5′ End: Bears the triphosphate (an energy source for the bond).
Triphosphate Bond: Target of 3′ hydroxyl attack.

Points to Remember

Purines (A, G): Two rings.
Pyrimidines (C, U, T): One ring.
Amino Acids for Purine Synthesis: Glycine, Aspartate, Glutamine.
Mnemonic: “Cats purr until they GAG.”
Base Pairing Strength:
- C-G Bond: 3 hydrogen bonds, stronger than A-T bond (2 hydrogen bonds).
- C-G Content: Higher C-G content increases the melting temperature of DNA.
- Mnemonic: “C-G bonds are like Crazy Glue.”
Purine and Pyrimidine Synthesis:

Purine (A, G)	Pyrimidine (C, U, T)
Glycine	CO2
Aspartate	Carbamoyl phosphate
Glutamine	Aspartate
N10–Formyltetrahydrofolate	N10–Formyltetrahydrofolate

Points to Remember

This organized format should help in understanding nucleotide and nucleoside structures, their chemical properties, and important biological reactions.