OIA1003 NUCLEIC ACIDS I

Nucleic Acids

Macromolecules that store genetic information and direct protein synthesis (DNA & RNA).

Central Dogma of Molecular Biology

DNA → RNA → Protein explains genetic information flow.

Nucleotide

Basic unit of DNA/RNA, consisting of a sugar, phosphate, and nitrogenous base.

Nucleoside

A molecule containing a sugar and nitrogenous base, but lacking a phosphate group.

Chargaff’s Rule

A = T and G = C in DNA, ensuring base-pair complementarity.

DNA vs RNA

DNA: Double-stranded, deoxyribose sugar, thymine (T).

RNA: Single-stranded, ribose sugar, uracil (U).

Purines

Adenine (A), Guanine (G) - Double-ring structures.

Pyrimidines

Cytosine (C), Thymine (T), Uracil (U) - Single-ring structures.

Phosphodiester Bonds

Link nucleotides via 3’-5’ bonds, forming a sugar-phosphate backbone.

Watson-Crick DNA Model

Double-helix, antiparallel strands, complementary base pairing, hydrogen bonding.

Hydrogen Bonds

A-T (2 bonds), G-C (3 bonds), making GC-rich DNA more stable.

DNA Melting Temperature (Tm)

Higher GC content increases Tm, requiring more energy to denature.

Denaturation vs Renaturation

Denaturation: DNA unwinding by heat/chemicals.

Renaturation: Cooling allows reformation of complementary strands.

Semi-Conservative Model

Each daughter DNA contains one original and one new strand.

Origin of Replication (OriC)

The AT-rich sequence where replication begins.

Replication Fork

The Y-shaped region where DNA is unwound and synthesized.

Leading Strand

Synthesized continuously in the 5' to 3' direction.

Lagging Strand

Synthesized discontinuously, forming Okazaki fragments.

Helicase

Unwinds the DNA double helix.

Topoisomerase (DNA Gyrase)

Relieves supercoiling during DNA unwinding.

Single-Strand Binding Proteins (SSBPs)

Stabilize single-stranded DNA, preventing premature reannealing.

DNA Primase

Synthesizes RNA primers for DNA polymerase to initiate replication.

DNA Polymerase

Adds nucleotides in the 5' to 3' direction.

Exonuclease (Proofreading)

Removes mispaired nucleotides (3’-5’ exonuclease activity).

DNA Ligase

Seals nicks between Okazaki fragments.

Prokaryotic DNA Polymerases

Pol I: Removes primers, fills gaps.

Pol II: DNA repair.

Pol III: Main replication enzyme.

Eukaryotic DNA Polymerases

Pol α: Initiates replication.

Pol δ: Synthesizes lagging strand.

Pol ε: Synthesizes leading strand.

Pol γ: Replicates mitochondrial DNA.

Mitochondrial DNA (mtDNA)

Circular DNA, maternally inherited, essential for electron transport chain.

Telomeres

Repetitive sequences (TTAGGG in humans) protecting chromosome ends.

Telomerase

Extends telomeres, active in stem cells and cancer cells.

RNA Primer Removal

In prokaryotes: DNA polymerase I removes primers.

In eukaryotes: RNase H and FEN1 remove primers.

Okazaki Fragment Processing

DNA polymerase fills gaps; ligase seals the final bond.

Point Mutation

Single nucleotide substitution (e.g., sickle cell anemia).

Frameshift Mutation

Insertion or deletion of nucleotides, disrupting reading frame.

Mismatch Repair

Corrects errors made by DNA polymerase.

Base Excision Repair (BER)

Removes damaged bases (e.g., oxidative damage).

Nucleotide Excision Repair (NER)

Repairs thymine dimers (damage from UV light).

Telomerase & Cancer

Increased telomerase activity in cancer cells, allowing uncontrolled division.

DNA Intercalating Drugs

Actinomycin D binds minor groove, inhibiting replication/transcription.

Topoisomerase Inhibitors

Ciprofloxacin (bacteria), Etoposide (cancer) target topoisomerase activity.