Nucleic Acids: DNA and RNA Overview

Nucleic Acids

• Nucleic acids are essential for storing and transmitting genetic information
• Two primary types: DNA and RNA

DNA (Deoxyribonucleic Acid)

• Structure: Double-stranded molecule composed of nucleotides
• Nucleotides: Sugar (deoxyribose), phosphate group, nitrogenous base
• Nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
• Double helix: Twisted ladder structure
• Base pairs: A with T, C with G
• Function: Carries genetic instructions for all living organisms
• Location: Nucleus of eukaryotic cells
• Replication: DNA replicates itself during cell division

RNA (Ribonucleic Acid)

• Structure: Single-stranded molecule made up of nucleotides
• Nucleotides: Sugar (ribose), phosphate group, nitrogenous base
• Nitrogenous bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)
• Uracil (U) replaces Thymine (T) in RNA
• Function: Plays a key role in protein synthesis
• Types of RNA:
  • mRNA (messenger RNA): Carries genetic instructions from DNA to ribosomes
  • tRNA (transfer RNA): Brings amino acids to ribosomes during protein synthesis
  • rRNA (ribosomal RNA): Combines with proteins to form ribosomes, the site of protein synthesis

Protein Synthesis

• Process by which cells synthesize proteins using information encoded in DNA
• Two main stages: Transcription and Translation

Transcription

• Location: Nucleus (eukaryotic cells)
• Process: Creates an mRNA molecule from a DNA template
• Steps:
  • RNA polymerase binds to a specific DNA region (promoter)
  • RNA polymerase moves along the DNA, separating strands
  • RNA polymerase uses one strand as a template to synthesize mRNA
  • mRNA is complementary to the DNA template (A with U, C with G)
  • mRNA detaches from DNA, and DNA strands rejoin
  • mRNA exits the nucleus and enters the cytoplasm

Translation

• Location: Cytoplasm at ribosomes
• Process: Uses mRNA as a template to create proteins
• Steps:
  • mRNA binds to ribosome
  • Ribosome reads mRNA codons (three-nucleotide sequences)
  • tRNA molecules with matching anticodons bring specific amino acids to the ribosome
  • Ribosome adds amino acids to the growing protein chain, linking them with peptide bonds
  • Process continues until a stop codon is reached, releasing the protein

The Genetic Code

• Codons: Sets of three nucleotide bases that correspond to specific amino acids
• Redundancy: Some amino acids are coded by more than one codon
• Start codon (AUG): Signals the beginning of translation
• Stop codons (UAA, UAG, UGA): Signal the end of translation

Mutations in DNA

• Definition: Changes in DNA sequence
• Types:
  • Point mutations: Changes in a single nucleotide base
  • Frameshift mutations: Insertion or deletion of nucleotides, altering the reading frame
  • Silent mutations: Do not affect the amino acid sequence
  • Nonsense mutations: Change a codon into a stop codon, prematurely ending protein synthesis

Importance of Protein Synthesis

• Proteins are the building blocks of life
• Crucial cellular functions:
  • Enzymes: Catalyze chemical reactions
  • Structural support: Provide structure to cells and tissues
  • Transport: Move molecules within cells and across membranes

Regulation (of Cellular Processes)

• Controlling cellular processes, such as gene expression