Nucleic Acids

🧬 Nucleic Acids: The Information Molecules

Nucleic acids store, transmit, and express the genetic information of every living organism. The two types are:

• DNA (deoxyribonucleic acid) — the long-term genetic blueprint
• RNA (ribonucleic acid) — the working copy used to make proteins

Element fingerprint

Nucleic acids contain C, H, O, N, and P. The presence of phosphorus distinguishes nucleic acids from carbohydrates and most lipids.

Where you'll meet nucleic acids

Concept Check 🎯

The Monomer: Nucleotide

A nucleotide has three parts:

1. Pentose sugar (5-carbon ring) — ribose in RNA, deoxyribose in DNA
2. Phosphate group — gives the molecule its acidic character
3. Nitrogenous base — purine (A, G) or pyrimidine (C, T, U)

DNA vs RNA: side-by-side

Pairing rules (Chargaff)

In DNA: A pairs with T (2 H-bonds), G pairs with C (3 H-bonds).

In RNA: A pairs with U instead.

Concept Check 🎯

Fill in the Blanks 🔍

Nucleic Acids: DNA & RNA

Nucleotide Structure

Each nucleotide has three components:

1. 5-carbon sugar (ribose in RNA, deoxyribose in DNA)
2. Phosphate group ($PO_4^{3-}$)
3. Nitrogenous base

DNA vs. RNA

Functions Beyond Information Storage

The central dogma

$DNA \xrightarrow{\text{transcription}} mRNA \xrightarrow{\text{translation}} \text{Protein}$

🎯 AP Review: Nucleic Acids

Must-know synthesis points

1. Nucleotides = sugar + phosphate + nitrogenous base.
2. DNA vs RNA — DNA: deoxyribose, T, double-stranded, stable. RNA: ribose, U, usually single-stranded.
3. Chargaff's pairing — A–T (or A–U), G–C; G–C bonds are stronger (3 H-bonds).
4. Antiparallel orientation enables semiconservative replication and accurate copying.
5. Central dogma — DNA → mRNA → protein (transcription → translation).
6. Nucleotides also serve as energy carriers — ATP, NAD⁺, FAD, cAMP all share a nucleotide backbone.

Common AP traps

• mRNA is the photocopy, not the original. The DNA stays in the nucleus (in eukaryotes).
• A nucleotide is the monomer; nucleic acid is the polymer.
• Both DNA and RNA contain phosphate groups — phosphate isn't unique to one.

Workshop Problem 📐

Workshop Problem 📐

AP Synthesis 🔬