Biology Chapter: Molecular Genetics Quiz

Nucleic Acids: Overview, Composition, and Functions

• Nucleic acids are essential biomolecules forming the genetic blueprint for all living organisms
• They are long polymers made of repeating nucleotides
• Each nucleotide consists of three key components: a nitrogenous base, a pentose sugar, and a phosphate group

Classification of Nucleic Acids

• Deoxyribonucleic Acid (DNA): The primary genetic material in most organisms
  • Found in the nucleus, mitochondria, and chloroplasts
  • Double-stranded helix with complementary base pairing (adenine with thymine, guanine with cytosine)
  • Stores genetic information, provides a template for RNA synthesis, and facilitates replication
• Ribonucleic Acid (RNA): Involved in protein synthesis and gene regulation
  • Single-stranded, contains uracil (U) instead of thymine (T)
  • Classified into different types based on function:
    • Messenger RNA (mRNA) (approximately 1-5% of total RNA): Carries genetic instructions from DNA to ribosomes for protein synthesis
    • Transfer RNA (tRNA) (approximately 10-15% of total RNA): Transports specific amino acids to the ribosome during translation
    • Ribosomal RNA (rRNA) (approximately 80-90% of total RNA): Forms the structural and catalytic components of ribosomes responsible for protein synthesis
    • Regulatory RNAs (miRNA and siRNA) (approximately 1-2% of total RNA): Regulates gene expression by binding to mRNA to inhibit translation or promote degradation

The Central Dogma of Molecular Biology

• Outlines the flow of genetic information in a biological system
• The flow follows a one-way path: DNA → RNA → Protein

DNA Replication

• The process by which a cell copies its DNA before cell division
• Ensures that daughter cells inherit identical genetic material

Transcription

• The process by which a segment of DNA is copied into RNA, specifically mRNA

Translation

• The process by which mRNA is translated into proteins at the ribosome
• Where amino acids are assembled according to the mRNA sequence

Differences Between DNA and RNA

Composition of Nucleic Acids

• Nucleic acids are complex macromolecules composed of nucleotides
• 1. Nitrogenous Bases: These are organic molecules with nitrogen atoms;
  • Purines (larger, double-ring structures): Adenine (A), Guanine (G)
  • Pyrimidines (smaller, single-ring structures): Cytosine (C), Thymine (T), Uracil (U)
• 2. Pentose Sugar:
  • Deoxyribose: Found in DNA (lacks hydroxyl group at the 2′ carbon)
  • Ribose: Found in RNA (has a hydroxyl group at the 2′ carbon)
• 3. Phosphate Group: Contributes to the acidic nature and negative charge of nucleic acids and forms the sugar phosphate backbone through phosphodiester bonds between the 5' and 3' carbons

Nucleosides

• Formed when a nitrogenous base is attached to a pentose sugar via a beta-N-glycosidic bond

Nucleotides

• Formed when a nucleoside is esterified to a phosphate group

Functions of Nucleic Acids

• Genetic Information Storage: DNA serves as the repository of genetic instructions
• Replication: DNA replicates itself to ensure accurate inheritance during cell division
• Transcription and Translation: DNA directs RNA synthesis which subsequently instructs protein synthesis.
• Energy Transfer: Nucleotides like ATP and GTP are essential for cellular energy transfer
• Role in Coenzymes: Nucleic acids participate in redox reactions, metabolism, and energy production by forming part of coenzymes
• Cell Signaling: Nucleic acids like cAMP act as second messengers in cell signaling
• Catalysis (Ribozymes): Certain RNA molecules (ribozymes) act as enzymes, catalyzing biochemical reactions.