Molecular Biology Lecture 1 - Nucleic Acids

Molecular Biology Lecture 1

• Topic: Molecular Biology Level 2, Lecture 1
• Instructor: Prof. Sami Mohamed
• Location: Badr University in Cairo, School of Biotechnology
• Lecture Focus: Nucleic Acids, the Genetic Code, and the Synthesis of Macromolecules

Central Dogma

• Concept: DNA directs the synthesis of RNA, which in turn directs the synthesis of proteins.
• Process: DNA → Transcription → RNA → Translation → Protein
• RNA Types: mRNA, rRNA, tRNA

Structure of Nucleic Acids

• Nucleic Acids: Composed of nucleotides.
• Nucleotide Components:
  • Phosphate group
  • Sugar (ribose in RNA, deoxyribose in DNA)
  • Nitrogenous base (purines or pyrimidines)
• Polymerization: Nucleotides link via phosphodiester bonds to form nucleic acid strands.
• Purines: Adenine (A) and Guanine (G)
• Pyrimidines: Cytosine (C), Thymine (T) in DNA and Uracil (U) in RNA
• Nucleosides: Base + Sugar
• Nucleotides: Nucleoside + Phosphate group (mono-, di-, or triphosphate)

Structure of DNA

• DNA Structure: Double helix formed by two antiparallel strands.
• Base Pairing:
  • Adenine (A) pairs with Thymine (T)
  • Guanine (G) pairs with Cytosine (C)
• Antiparallel Strands: One strand runs 5' to 3', the other 3' to 5'.
• DNA Forms: B-form (most common), A-form, and Z-form
• Features: Helix axis, base stacking, major and minor grooves.

DNA Denaturation and Renaturation

• Denaturation (Melting): DNA strands separate due to breakage of hydrogen bonds.
• Factors: High temperature, alkaline solutions, formamide or urea.
• Renaturation (Reannealing): DNA strands rejoin.
• Conditions: Specific conditions required (temperature, ion concentration)

DNA Characteristics and Structure

• Melting Temperature (Tm): Temperature at which half of the DNA strands are denatured.
• G-C Content: Higher G-C content = higher Tm (stronger hydrogen bonds)
• Important Considerations: DNA molecules can be linear or circular.

RNA Structure

• Conformation Diversity: RNA molecules exhibit diverse conformations.
• Secondary Structure: Stem-loop structures, hairpins.
• Tertiary Structure: Complex three-dimensional shapes, pseudoknots.

Synthesis of Biopolymers

• Monomer Addition: Proceeds from a specific starting point and in a defined direction.
• Examples:
  • Proteins: Amino (NH2) to Carboxyl (COOH)
  • Nucleic Acids: 5' to 3'
• Modification: Products can undergo cleavage, ligation, splicing, and cross-linking.

Nucleic Acid Synthesis

• Template Dependence: DNA and RNA synthesis are based on copying template DNA strands.
• Directionality: Strands grow in the 5' to 3' direction.
• Enzyme Role: RNA polymerases initiate RNA synthesis; DNA polymerases do not.

Gene Organization

• Prokaryotes (Operons): Genes for related functions are grouped together in operons.
• Eukaryotes: Genes are not clustered; contain introns and exons.
• Processing of Primary Transcripts in Eukaryotes: Pre-mRNA is processed to remove introns and connect exons, creating mature mRNA.

Protein Synthesis

• Components: mRNA, tRNA, Ribosomes

• Translation: mRNA sequence is translated into amino acid sequence to create protein.

• tRNA: Specific for each amino acid and has an anticodon to pair with the appropriate codon on the mRNA.

• Aminoacyl-tRNA Synthetases: Couple specific amino acids to tRNA

• Ribosomes: Protein synthesis machinery, composed of rRNA and proteins.

• Genetic Code: Set of rules for translating mRNA sequences into amino acid sequences

• Redundancies/Universality: Multiple codons can specify the same amino acid - almost universal across species.