Understanding nucleic acids is essential for modern pharmacy: genetic diseases, drug targets (e.g., enzymes that copy DNA), vaccines, biotechnology drugs and diagnostic PCR tests all rely on DNA/RNA knowledge. Grasping the basic structures and roles helps link molecular biology to therapeutics and diagnostics.
ACTUAL NOTES:
Nucleic Acids: Bases, Nucleosides, Nucleotides, DNA Structure (Watson–Crick) and RNA Functions
Nucleic acids are the molecules of inheritance. They store and transmit the genetic information that tells cells how to build proteins and carry out life processes. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). These notes explain the basic building blocks—bases, nucleosides and nucleotides—describe the classic Watson–Crick model of DNA and summarize the types and functions of RNA in simple language.
Definition
Nucleic acids are long polymers made of repeating units called nucleotides. Each nucleotide consists of three parts: a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. DNA and RNA differ by the sugar (deoxyribose in DNA, ribose in RNA) and by some bases.
Purine and Pyrimidine Bases
Nitrogenous bases are of two kinds: purines (two-ring structure) and pyrimidines (one-ring structure).
- Purines: Adenine (A) and Guanine (G). Larger, double-ring molecules.
- Pyrimidines: Cytosine (C), Thymine (T) and Uracil (U). Single-ring molecules. Thymine is found in DNA; uracil replaces thymine in RNA.
Components of Nucleosides and Nucleotides
A nucleoside is formed when a nitrogenous base attaches to a sugar (no phosphate). A nucleotide is a nucleoside plus one or more phosphate groups.
- Example of nucleoside: Adenosine = adenine + ribose.
- Example of nucleotide: Adenosine monophosphate (AMP) = adenosine + one phosphate.
Nucleotides are the monomers that link together to form nucleic acid chains. The phosphate group links the 3′ carbon of one sugar to the 5′ carbon of the next sugar, creating a sugar–phosphate backbone.
Structure of DNA: Watson and Crick Model (Simple Explanation)
The Watson–Crick model (1953) describes DNA as a double helix: two long strands wound around each other like a spiral staircase. Key features:
- Two antiparallel strands: One strand runs 5′ → 3′, the opposite strand runs 3′ → 5′.
- Sugar–phosphate backbone: The sides of the “ladder” are alternating sugar and phosphate groups.
- Complementary base pairing: Bases on opposite strands pair by hydrogen bonds: Adenine (A) pairs with Thymine (T) via two hydrogen bonds; Guanine (G) pairs with Cytosine (C) via three hydrogen bonds. This pairing explains accurate replication and genetic code.
- Major and minor grooves: The helix has grooves where proteins can bind to read the genetic code.
Because of complementary pairing, each DNA strand can serve as a template to make a new complementary strand during replication—this is how genetic information is copied and passed on.
Structure of RNA and Its Types
RNA is usually single-stranded and contains ribose sugar and uracil (U) instead of thymine. There are several types of RNA, each with a specific role in the flow of genetic information from DNA to protein:
- mRNA (messenger RNA): Carries genetic instructions from DNA in the nucleus to ribosomes in the cytoplasm. Acts as a working copy of a gene (the recipe).
- tRNA (transfer RNA): Small folded RNA that brings the correct amino acid to the ribosome during protein synthesis; has an anticodon that pairs with mRNA codons.
- rRNA (ribosomal RNA): Structural and catalytic component of ribosomes; helps assemble amino acids into proteins.
- Other RNAs: Regulatory RNAs like microRNA (miRNA) and small interfering RNA (siRNA) control gene expression; long non-coding RNAs have diverse regulatory roles.
Simple Functional Summary
- DNA stores genetic information long-term and passes it to the next generation.
- RNA converts that information into functional proteins and regulates gene expression.
- Nucleotides (ATP, GTP, etc.) also serve as energy carriers and signaling molecules in cells.
