3.5 Nucleic Acids - Biology 2e | OpenStax

Learning Objectives

• Describe nucleic acids' structure and define the two types of nucleic acids.
• Explain DNA's structure and role.
• Explain RNA's structure and roles.

Importance of Nucleic Acids

• Nucleic acids are crucial macromolecules for life.
• They carry genetic information and instructions for cellular function.

Types of Nucleic Acids

• Deoxyribonucleic Acid (DNA):
  • Genetic material in all living organisms.
  • Located in nucleus of eukaryotes, chloroplasts, mitochondria, and in prokaryotes (not enclosed by a membrane).
  • Forms chromatin with histone proteins in eukaryotes.
  • Controls cellular activities by gene regulation.
• Ribonucleic Acid (RNA):
  • Primarily involved in protein synthesis.
  • Acts as intermediary between DNA and cellular machinery.

Structure of Nucleic Acids

• Nucleotides: Basic units consisting of:
  • Nitrogenous base
  • Pentose sugar (ribose in RNA, deoxyribose in DNA)
  • Phosphate group
• Types of Nitrogenous Bases:
  • Purines (Adenine, Guanine) – two rings.
  • Pyrimidines (Cytosine, Thymine, Uracil) – one ring.
• Pentose Sugars:
  • DNA contains deoxyribose; RNA contains ribose.
• Phosphodiester Linkage: Joins nucleotides via dehydration reaction.

DNA Double Helix Structure

• DNA is a double helix with sugar-phosphate backbone and nitrogenous bases inside.
• Base pairing rule: A with T, G with C.
• DNA strands are antiparallel and complementary.
• During replication, each strand acts as a template for new strands.

RNA Structure and Types

• Single-stranded with ribonucleotides linked by phosphodiester bonds.
• Types of RNA:
  • Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes.
  • Ribosomal RNA (rRNA): Component of ribosomes, facilitates mRNA and ribosome interaction.
  • Transfer RNA (tRNA): Transfers amino acids to ribosomes during protein synthesis.
  • MicroRNA (miRNA): Regulates gene expression.

DNA vs. RNA

• Function:
  • DNA stores genetic information.
  • RNA involved in protein synthesis.
• Location:
  • DNA remains in the nucleus.
  • RNA functions outside nucleus.
• Structure:
  • DNA is a double helix.
  • RNA is usually single-stranded.
• Sugar:
  • DNA contains deoxyribose.
  • RNA contains ribose.
• Bases:
  • DNA: Adenine, Cytosine, Guanine, Thymine.
  • RNA: Adenine, Cytosine, Guanine, Uracil.

Central Dogma of Life

• Information flows from DNA to RNA to protein.
• Transcription: DNA to mRNA in nucleus.
• Translation: mRNA to protein in cytoplasm.
• Exceptions exist in viral mechanisms.

For further learning, animations on DNA are available through the Howard Hughes Medical Institute BioInteractive.