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TLS Online TPP Program

#Id: 6503

These two mechanisms, (1) binding of the capping enzyme to RNA polymerase II specifically through its unique CTD phosphorylated on serine 5 of the heptapeptide repeat during transcription initiation by TFIIH, and (2) activation of the capping enzyme by the serine 5–phosphorylated CTD, result in specific capping of RNAs transcribed by RNA polymerase II.



#Unit 3. Fundamental Processes #Eukaryotic Transcription #Part B Pointers
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TLS Online TPP Program

#Id: 3186

#Unit 3. Fundamental Processes

Mitochondria use different origin sequences to initiate replication of each DNA strand

Replication of the H strand is initiated in a D loop.

Replication of the L strand is initiated when its origin is exposed by the movement of the first replication fork.
TLS Online TPP Program

#Id: 3187

#Unit 3. Fundamental Processes

Replication starts at a specific origin in the circular duplex DNA. Initially, though, only one of the two parental strands (the H strand in mammalian mitochondrial DNA) is used as a
template for synthesis of a new strand. 

Synthesis proceeds for only a short distance, displacing the original partner (L) strand, which remains single-stranded,
TLS Online TPP Program

#Id: 3188

#Unit 3. Fundamental Processes

A single D loop is found as an opening of 500 to 600 bases in mammalian mitochondria.
TLS Online TPP Program

#Id: 3189

#Unit 3. Fundamental Processes

Some mitochondrial DNAs possess several D loops, reflecting the use of multiple origins. The same mechanism is employed in chloroplast DNA, where (in complex plants) there are two D loops.
TLS Online TPP Program

#Id: 3190

#Unit 3. Fundamental Processes

To replicate mammalian mitochondrial DNA, the short strand in the D loop is extended. The displaced region of the original L strand becomes longer, expanding the D loop
TLS Online TPP Program

#Id: 3191

#Unit 3. Fundamental Processes

In mtDNA, The existence of D loops exposes a general principle: An origin can be a sequence of DNA that serves to initiate DNA synthesis using om strand as a Template.