Chapter 3: Nucleic Acids

Overview

• Final type of biological macromolecule discussed: nucleic acids.
• Nucleic acids make up genetic material of all living organisms.
• Two types: DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).
• Found in:
  • Nucleus of eukaryotic cells
  • Mitochondria and chloroplasts of eukaryotic cells
  • Cytoplasm of prokaryotic cells

DNA

• All DNA in a cell is known as the cell's genome.
• DNA is organized by wrapping around histone proteins in eukaryotes (similar proteins in prokaryotes).
• DNA and histone complex: Chromatin.
• Chromatin condenses into chromosomes.
• Thousands of genes in DNA contain instructions for building proteins and other molecules.
• DNA controls cellular activities by turning genes on/off.

RNA

• Involved in protein synthesis.
• Three main types:
  • Messenger RNA (mRNA): Intermediary for protein synthesis.
  • Transfer RNA (tRNA): Bridge between nucleotides and amino acid chains.
  • Ribosomal RNA (rRNA): Part of the structure involved in translation.

Nucleotides

• Monomers of nucleic acids (DNA and RNA).
• Composed of:
  • Nitrogenous base
  • Pentose sugar
  • One or more phosphate groups

Nitrogenous Bases

• Organic molecules (CHON).
• Two groups:
  • Pyrimidines: Single-ring (cytosine, thymine, uracil).
  • Purines: Double-ring (adenine, guanine).

Sugars

• DNA contains deoxyribose sugar.
• RNA contains ribose sugar.
• Difference lies in the group attached to carbon number 2 (Hydrogen in DNA, Hydroxyl in RNA).

Structural Differences: DNA vs. RNA

• DNA is usually double-stranded (double helix), RNA is usually single-stranded.
• RNA is less stable due to hydroxyl groups.
• DNA contains thymine, RNA contains uracil.
• DNA strands are anti-parallel (5’ to 3’ and vice versa).

Base Pairing

• A pairs with T, G pairs with C (DNA).
• Base pairing is via hydrogen bonds (2 bonds A-T, 3 bonds G-C).
• DNA regions with more G-C pairs are more stable.

From DNA to Protein

• Central Dogma: DNA -> RNA -> Protein.
• Steps:
  • Transcription: DNA transcribed to mRNA, using uracil in place of thymine.
  • Translation: mRNA translated to proteins.

Codons

• Sets of three bases on mRNA correspond to amino acids.
• tRNA assists in translation by matching its anticodon to mRNA codons and carrying appropriate amino acids.
• Ribosome facilitates the process.

Differences Between DNA and RNA

• Function: DNA carries genetic info; RNA is involved in protein synthesis.
• Location: DNA in nucleus (eukaryotes), cytoplasm (prokaryotes); RNA can leave the nucleus.
• Structure: DNA double-stranded, RNA single-stranded.
• Sugar: DNA (deoxyribose), RNA (ribose).
• Bases: DNA (Cytosine, Thymine); RNA (Cytosine, Uracil).

Applications and Exceptions

• Retroviruses (e.g., HIV) reverse the central dogma using reverse transcriptase to convert RNA to DNA.
• Laboratory applications for cloning.

Next Steps

• Transition to Chapter 4: Exploring cell structure, both prokaryotic and eukaryotic.