La DNA Polimerasi può commettere errori

La DNA Polimerasi può
commettere errori
• Nei batteri: 1 errore ogni 109 basi in ogni
generazione
La correzione
delle bozze
Le basi si possono alterare
spontaneamente
Correzione
delle
Bozze n2
Alterazioni del DNA indotte da
agenti fisici
Alterazioni
da
Agenti
Chimici
Il DNA
danneggiato
viene riparato
Due sistemi di riparazione
Le DNA polimerasi sono tante
α
β†
γ
δ
ε
Polymerization: 5′ → 3′
+
+
+
+
+
Exonuclease proofreading activity:‡ 3 → 5′
−
−
+
+
+
RNA primer
+
−
−
+
?
DNA primer
+
+
+
+
+
Associated DNA primase
+
−
−
−
−
Sensitive to aphidicolin (inhibitor of cell DNA synthesis)
+
−
−
+
+
Nuclei
+
+
−
+
+
Mitochondria
−
−
+
−
−
Mammalian Cells*
Synthesis from:
Cell location:
Yeast DNA polymerase I, II, and III are equivalent to polymerase α, β, and δ, respectively. I and III are essential for cell
viability.
† Polymerase β is most active on DNA molecules with gaps of about 20 nucleotides and is thought to play a role in DNA
repair.
‡ FEN1 is the eukaryotic 5′ → 3′ exonuclease that removes RNA primers; it is similar in structure and function to the
domain of E. coli polymerase I that contains the 5′ → 3′ exonuclease activity.
*
Malattie ereditarie legate a difetti
della riparazione del DNA
Classificazione del DNA Eucariotico
•
•
•
Protein-coding genes
Solitary genes
Duplicated and diverged genes (functional gene families and
nonfunctional pseudogenes)
Tandemly repeated genes encoding rRNA, 5S rRNA,
tRNA, and histones
Repetitious DNA
Moderately repeated DNA (mobile DNA elements)
•
•
•
Transposons
Viral retrotransposons
Simple-sequence DNA (Satellite DNA: eg telomeres)
Long interspersed elements (LINES; nonviral retrotransposons)
Short interspersed elements (SINES; nonviral retrotransposons)
Unclassified spacer DNA
Classificazione del DNA Eucariotico
Genomi a Confronto
Struttura “tipo” di un Cromosoma Umano