Molecular Biology,Molecular Genetics & OmpathStudy

GOOD LUCK Gene structure: Eukaryotic genes are composed of exons (coding sequences) and introns (non-coding sequences), with introns being removed during RNA splicing. Promoter region: Upstream of the coding sequence lies a promoter containing specific sequences (e.g., the TATA box ) essential for the initiation of transcription by RNA polymerase II. Regulatory elements: Eukaryotic genes are also controlled by enhancers , silencers , and insulators , which regulate the level, timing, and tissue-specific expression of genes. Chromatin packaging: DNA is wrapped around histone proteins to form nucleosomes , enabling compaction into chromatin; gene accessibility depends on the degree of chromatin condensation (euchromatin vs. heterochromatin). Post-transcriptional modification: After transcription, primary RNA undergoes capping , polyadenylation , and splicing to form mature mRNA before translation. Ingestion of oocysts: Consuming food or water contaminated with mature oocysts from cat feces. Ingestion of tissue cysts: Eating undercooked or raw meat containing tissue cysts (especially from pigs, sheep, or goats). Congenital transmission: Vertical transmission from an infected mother to her fetus across the placenta during pregnancy. Mutation: Spontaneous changes in DNA introduce new alleles into a population, altering genotype frequencies. Natural selection: Differential survival and reproduction favor certain genotypes over others, leading to changes in allele frequencies. Genetic drift: Random fluctuations in allele frequencies, especially in small populations, can lead to loss or fixation of alleles. Gene flow (migration): Movement of individuals between populations introduces new genetic material, affecting allele frequencies. Non-random mating: Mating preferences (such as assortative or disassortative mating) can alter genotype distributions by increasing homozygosity or heterozygosity. Denaturation (94–98°C): Double-stranded DNA is heated to separate into two single strands. Annealing (50–65°C): Short DNA primers bind (anneal) to complementary sequences on the single-stranded templates. Extension (72°C): Taq DNA polymerase synthesizes new DNA strands by adding nucleotides to the primers. Importance: Taq DNA polymerase is thermostable , meaning it remains active at the high temperatures used in PCR, allowing continuous DNA synthesis without denaturation of the enzyme. Source: It is derived from Thermus aquaticus , a thermophilic bacterium found in hot springs. Mediating virus entry: Virus receptors on host cells enable attachment and entry of viruses, initiating infection. Tropism determination: The type and distribution of receptors determine the host range and tissue specificity of the virus (e.g., HIV uses CD4 receptors found on T-helper cells). Disease pathogenesis: Viral binding to specific receptors can influence disease severity and clinical manifestations . Therapeutic targets: Virus-receptor interactions are targeted in drug development (e.g., receptor blockers to prevent viral entry). Vaccine development: Knowledge of receptors aids in vaccine design by focusing immune responses on blocking virus attachment. 1. Initiation Chromatin remodeling opens DNA (via HATs and remodeling complexes). Core promoter : Usually has a TATA box (~25 bp upstream). Pre-Initiation Complex (PIC) : TFIID binds TATA (TBP subunit). TFIIA , TFIIB , TFIIF (brings RNA Pol II), TFIIE , and TFIIH assemble. TFIIH : Helicase : Unwinds DNA. Kinase : Phosphorylates RNA Pol II CTD → activates transcription. Promoter clearance : RNA polymerase II escapes the promoter and starts RNA synthesis. --- 2. Elongation RNA polymerase II synthesizes RNA 5’ → 3’, reading DNA 3’ → 5’. Uses ribonucleotide triphosphates (NTPs) . Co-transcriptional processing : 5’ Capping (7-methylguanosine). Splicing (introns removed, exons joined). Elongation factors help polymerase move efficiently. --- 3. Termination Polyadenylation signal (AAUAAA) triggers termination. Cleavage of RNA transcript downstream. Poly-A tail (~200 As) added at 3’ end. RNA polymerase II disengages from DNA. --- 4. Post-Transcriptional Modifications 5’ cap : Protects RNA, aids translation. Splicing : Removes introns; can allow alternative splicing . Poly-A tail : Stabilizes RNA, helps export from nucleus. --- QUICK MEMORY TIP: "CRP → PIC → TFIIH → Cap-Spin-Tail" (Chromatin Remodeling → Pre-Initiation Complex → TFIIH activation → Capping, Splicing, Tail addition) --- --- Protein Translation (8 Marks) Definition: Translation is the process of protein synthesis where the ribosome reads the mRNA codon sequence and assembles amino acids into a polypeptide chain. --- Stages of Translation 1. Initiation mRNA binds to the small ribosomal subunit . Initiator tRNA (carrying methionine) binds to the start codon (AUG) . Large ribosomal subunit joins → functional ribosome formed. 2. Elongation Ribosome reads mRNA one codon at a time . tRNA delivers correct amino acids based on codon-anticodon ma