DNA and RNA Overview

Overview

This lecture compares DNA and RNA at the molecular level, highlighting their structural differences, types of nitrogenous bases, functional roles, and evolutionary context.

DNA Structure and Features

• DNA consists of two strands forming a double helix.
• The backbone of DNA contains deoxyribose sugar, which lacks an oxygen atom at the 2' carbon.
• DNA uses the nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
• Adenine and Guanine are purines (double-ringed), while Cytosine and Thymine are pyrimidines (single-ringed).

Converting DNA to RNA

• RNA contains ribose sugar, which has a hydroxyl group attached at the 2' carbon.
• To represent RNA, replace the 2' hydrogen in deoxyribose with a hydroxyl group.
• RNA typically exists as a single strand.

Differences in Nitrogenous Bases

• DNA uses Thymine; RNA uses Uracil in its place.
• Uracil is structurally similar to Thymine but is less stable and more error-prone.
• Uracil, like Thymine, pairs with Adenine.

Functional Orientation and Transcription

• mRNA (messenger RNA) is synthesized during transcription using DNA as a template.
• mRNA and DNA strands are antiparallel; mRNA has a 5' to 3' orientation opposite to DNA’s 3' to 5'.
• mRNA carries genetic information from DNA for protein synthesis.

Types and Roles of RNA

• Messenger RNA (mRNA) transfers genetic information from DNA to ribosomes for translation.
• Transfer RNA (tRNA) brings amino acids to the ribosome and has anticodons that pair with mRNA codons.
• Ribosomal RNA (rRNA) forms the structural and functional core of ribosomes.
• MicroRNA (miRNA) regulates gene expression by affecting translation.

Evolutionary Notes on RNA

• RNA likely predates DNA in evolutionary history.
• RNA’s instability may have favored the later development of DNA for stable genetic storage.

Key Terms & Definitions

• Deoxyribose — five-carbon sugar in DNA lacking an oxygen at the 2' carbon.
• Ribose — five-carbon sugar in RNA with a hydroxyl group at the 2' carbon.
• Purines — double-ring nitrogenous bases; Adenine and Guanine.
• Pyrimidines — single-ring nitrogenous bases; Cytosine, Thymine (DNA), and Uracil (RNA).
• mRNA — messenger RNA; carries genetic code from DNA for protein synthesis.
• tRNA — transfer RNA; matches amino acids to mRNA codons during translation.
• rRNA — ribosomal RNA; structural and catalytic component of ribosomes.
• miRNA — microRNA; short RNA molecules that regulate gene expression.

Action Items / Next Steps

• Review structural differences between DNA and RNA.
• Memorize the nitrogenous base pairing rules for DNA and RNA.
• Study the functional roles of different RNA types.