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biologia
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This biology document covers fundamental molecular biology concepts. It details DNA structure (nucleotides, phosphodiester bonds, anti-parallel strands, H-bonds, B/A/Z conformations), DNA replication (semi-conservative mechanism, origins, polymerases, primers, Okazaki fragments, topoisomerases, telomerase function in eukaryotes), and gene expression (transcription, RNA processing including 5' cap formation). Additionally, it explores cytoskeleton components like Actin (G-actin to F-actin, bundles, networks, interaction with Myosin 2) and Intermediate Filaments, essential for cell shape, movement, and structural integrity. Key proteins and enzymatic activities crucial for these processes are highlighted for university students in biotechnology.
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- Nucleotide & DNA Structure:
- Nucleotides are monomers composed of a pentose sugar and a nitrogenous base.
- DNA features 4 bases (A, C, G, T), anti-parallel strands, and stable hydrogen bonds between complementary bases (3 for C-G, 2 for T-A).
- The constant diameter of DNA ensures stability, recognized by repair systems.
- Phosphodiester bonds are strong covalent linkages forming the DNA backbone (5'-3' direction).
- DNA Conformations & Denaturation:
- DNA exists in B, A, and Z forms, differing in shape and accessibility of grooves for protein interaction.
- DNA denaturation (strand separation) is carried out by helicases, breaking hydrogen bonds, and can be induced in labs by heat or ionic changes.
- Histones:
- Found in eukaryotes, histones are proteins that compact DNA into a cylindrical structure, forming nucleosomes. Histone H1 helps maintain DNA wrapping.
- DNA Replication:
- A semi-conservative process, where each parental strand serves as a template for a new identical daughter molecule.
- Requires RNA primers for initiation, DNA polymerases for synthesis (5'-3' direction), and various proteins like topoisomerases (to relieve supercoiling) and SSB proteins (to stabilize single strands).
- In eukaryotes, replication starts at multiple origins, producing Okazaki fragments on the lagging strand.
- Key Replication Proteins (Eukaryotes):
- DNA Polymerase α (primer synthesis), DNA Polymerase δ (DNA synthesis), PCNA (processivity), Replication factors C and A (elongation/SSB), Topoisomerases I and II (strand separation), FEN1 (RNA primer removal), DNA Ligase (nick sealing).
- Telomerase:
- A specialized DNA polymerase that uses an RNA template (reverse transcriptase activity) to synthesize DNA at telomeres, compensating for end replication problems and preventing DNA damage due to shortening.
- Transcription:
- The process of synthesizing RNA from a DNA template, occurring in a 5'-3' direction.
- In eukaryotes, primary transcripts (pre-mRNA) undergo modifications like splicing (removal of non-coding sequences) and the addition of a 5' cap.
- The 5' cap protects mRNA from degradation and aids in ribosome binding.
- Actin:
- A key cytoskeleton protein existing as G-actin (monomer) and F-actin (polymerized filament).
- F-actin forms bundles and networks, providing structural support and enabling cell contraction through interaction with myosin 2.
- ATP hydrolysis to ADP is crucial for G-actin to F-actin conversion.
- Intermediate Filaments:
- Cytoskeletal components found in all cells, providing structural integrity. Nuclear lamins are a specific type of intermediate filament.
- Myosin:
- Motor proteins, like Myosin II, interact with actin to facilitate cell movement and contraction, utilizing ATP for energy (e.g., “colpo di frusta” mechanism).
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