Overview of Transcription Process

• Transcription Begins:

  • Involves a promoter that initiates transcription by signaling where to start. The promoter typically has a TATA box, a sequence with multiple 'T's and 'A's, which are easier to separate due to weaker hydrogen bonds.

• RNA Processing:

  • Eukaryotic cells transcribe pre-mRNA, which is then processed in the nucleus. This includes:
  • Adding a 5' cap and Poly-A tail: These modifications protect mRNA from degradation in the cytoplasm, much like sealing both ends of a moccasin.
  • Introns and Exons:
    • Introns: Non-coding sequences that are removed during processing.
    • Exons: Coding sequences that remain and are expressed.
  • The trimmed mRNA is smaller, making transport and processing more efficient.

Differences between Eukaryotes and Prokaryotes

• Size and Complexity:

  • Eukaryotes are more complex than prokaryotes, often multi-cellular and containing organelles, leading to longer DNA strands. More genes means more energy and resources needed for expression and maintenance.

• Gene Expression Efficiency:

  • Eukaryotes require efficient energy usage. Excess long sequences in DNA create inefficiencies in protein synthesis.

Genetic Code and Nucleotide Pairing

• Nucleotide Combinations:
  • DNA: A-T, G-C
  • RNA: A-U, G-C (Thymine (T) is replaced by Uracil (U) in RNA)
• Codons: Three-letter sequences in mRNA that code for amino acids in protein synthesis.

Transcription and Translation Flow

• RNA Transcription:
  • mRNA is synthesized from DNA templates. Enzymes and various mechanisms ensure the correct sequence is created.
• Translation Process:
  • mRNA is translated in ribosomes into proteins via tRNA molecules matching codons to amino acids. tRNA has an anticodon that pairs with mRNA's codon.

Gene Regulation Mechanisms

• Operon Model:
  • A cluster of genes controlled by a single operator that can turn gene expression on or off depending on the presence of regulatory molecules (co-repressors).
• Chromatin Modification:
  • Histone Acetylation:
    • Acetyl groups attach to histone tails, relaxing chromatin and promoting transcription.
  • DNA Methylation:
    • Addition of methyl groups condenses chromatin and reduces transcription, thus silencing genes.

Importance of Enzyme Production Control

• Cells can regulate enzyme levels based on environmental needs, enabling adaptation and efficiency in response to metabolic requirements.

Viruses and Their Structure

• Definition of Viruses:
  • Non-living infectious particles consisting of genes protected by a protein coat; they cannot reproduce without a host.
• Capsid Structure:
  • Protein shell enclosing viral genomes, structured from capsomeres. Viral envelopes may also be present in some viruses, aiding in infection.
• Bacteriophages: Viruses specifically targeting bacteria, with an elongated head and tail for injecting genetic material into host cells.

Key Concepts on Viruses

• Living vs. Non-Living: Viruses do not possess metabolism, leading to the classification as non-living entities requiring host cells to replicate and survive. Obligate intracellular parasites that need to be inside host cells to function.
• Molecular Biology Applications: Understanding these processes provides insight into genetic expression strategies, virus transmission and infection processes, enhancing biotechnological developments and therapeutic strategies.