Noggin is a secreted protein that is able to accomplish two of the major functions of the organizer:  It induces dorsal ectoderm to form neural tissue It dorsalizes mesoderm cells that contribute to the ventral mesoderm

TLS Online TPP Program

#Id: 6129

#Unit 3. Fundamental Processes

When the initial removal involves lyase action, the endonuclease APE1 instead recruits DNA polymerase b to replace a single nucleotide. The nick is then sealed by the ligase XRCC1/ligase-3. This is called the short-patch pathway.

TLS Online TPP Program

#Id: 6130

#Unit 3. Fundamental Processes

Alkyladenine DNA glycosylase (AAG), recognizes and removes a variety of alkylated substrates, including 3-methyladenine, 7-methylguanine, and hypoxanthine. 

TLS Online TPP Program

#Id: 6131

#Unit 3. Fundamental Processes

1-methyladenine and 3MC is corrected by an enzyme that uses an oxygenating mechanism alkB by reversal mechanism

TLS Online TPP Program

#Id: 6132

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6133

#Unit 3. Fundamental Processes

The oxoG adduct is highly mutagenic because it can base-pair with adenine as well as with cytosine. If it base-pairs with adenine during replication, it gives rise to a G:C to T:A transversion, which is one of the most common mutations found in human cancers.

TLS Online TPP Program

#Id: 6134

#Unit 3. Fundamental Processes

The modified base can be repaired before replication by DNA glycosylase via the base excision pathway. If replication occurs before the oxoG is removed, resulting in the misincorporation of an A, then a fail-safe glycosylase can remove the A, allowing it to be replaced by aC. This provides a second opportunity for the DNA glycosylase to remove the modified base.