Lecture_6_-_Molecular_Biology_of_Microorganisms_Spring_2023

Lecture Overview Lecture 6: Focus on the Molecular Biology of Microorganisms.

Replication: Essential for transferring genetic information between generations, relying on multiple enzymes to unwind DNA, synthesize new strands, and correct errors. Proper segregation ensures each daughter cell receives an identical genome.
Cell Division: Following accurate segregation, cell division occurs through binary fission in prokaryotes and mitosis in eukaryotes, ensuring new cells inherit a complete genetic copy.

Central Dogma: Describes the pathway DNA → RNA → Protein, highlighting the unidirectional flow of information.
Transcription: The synthesis of RNA from DNA, primarily by RNA polymerase, with transcription factors influencing gene expression.
Translation: The nucleotide sequence in mRNA is translated into amino acids at ribosomes, involving tRNA and rRNA in assembling polypeptides.

Polycistronic messages: In prokaryotes, multiple genes are transcribed into a single mRNA, unlike the monocistronic mRNAs in eukaryotes.
Non-coding sequences in ORFs: Prokaryotic ORFs have uninterrupted coding sequences, while eukaryotic genes contain introns that must be spliced out.
mRNA Processing: Eukaryotic mRNAs undergo 5' capping, polyadenylation, and splicing; prokaryotic mRNAs don't require such modifications.
5' and 3' ends: Modifications at both ends protect against degradation and enhance stability and translation.

Pairing Rules: Nucleotides pair via hydrogen bonding, with G-C pairs forming three bonds for greater stability than A-T pairs with two.
Significance of A-U Base Pair: Important in RNA structures, especially in transcription termination.
Structure of DNA Ends: Distinct 5' (phosphate group) and 3' (hydroxyl group) ends are critical for replication.
Antiparallel Strands: Ensures proper base pairing and supports replication and transcription.

Double Helix: DNA's double helix structure features anti-parallel, complementary strands crucial for genetic encoding and replication.
Grove Regions: Major groove allows for sequence-specific protein binding; the minor groove permits non-specific interactions.

Inverted Repeats: Essential for forming secondary structures like hairpins that affect gene regulation.
Stem-loop Structures: Significant for regulating gene expression and transcription termination.

Nucleoid: A region in prokaryotes where the chromosome is densely packed, lacking a surrounding membrane.
Chromosome Packaging: Due to its larger size, the bacterial chromosome organizes in supercoiled loops affecting gene expression and replication.
Lysis Evidence: Observable chromosome extents beyond the cell indicate organized loop formations vital for function.

Plasmids: Circular DNA molecules that replicate independently of chromosomal DNA, often carrying genes for traits like antibiotic resistance, crucial in biotechnology.

Multiple Enzymatic Steps: Involves helicases, primases, DNA polymerases, and ligases, working in concert to ensure accuracy and efficiency in DNA synthesis.

Helicase Activity: DnaB enzyme unwinds DNA using ATP energy to create single-stranded templates.
Leading and Lagging Strands: Leading strand synthesized continuously; lagging strand forms in Okazaki fragments, necessitating complex coordination.

Cis-acting factors: Termination relies on specific motifs and protein interactions, indicating sophisticated control mechanisms.

Restriction Enzymes: Cut DNA at palindromic sequences, creating “sticky” or “blunt” ends for recombinant DNA technology.

Operons: Clusters of co-regulated genes producing polycistronic mRNA, enabling simultaneous expression under a single promoter—characteristic of prokaryotic regulation.

mRNA Codons: Three nucleotide sets representing specific amino acids or termination signals; among 64 codons, some denote start and stop.
Degeneracy: Multiple codons can correspond to a single amino acid, providing mutation tolerance.

L Structure: All tRNAs adopt an L-shaped structure crucial for amino acid binding and ribosome interaction for translation.

Three Stages: Consist of initiation, elongation, and termination, with specific factors aiding in both prokaryotic and eukaryotic systems, which differ in molecular players and timing.

No Compartmentalization: In prokaryotes, absence of a nuclear membrane allows simultaneous transcription and translation, enabling rapid responses to environmental changes.

Role of Chaperones: Assist nascent polypeptides in folding correctly during synthesis, preventing misfolding, with distinct types for co- and post-translational processes.