Irreversible DNA damage

["Bjorn Cedervall" <bcradsafers@HOTMAIL.COM>]

>What is "irreversible" DNA damage?  DNA repair also occurs at the molecular 

>levels.

---

Examples of irreversible damage are point mutations and chromosomal 

aberrations (which partly can be the result of misrepair).



Many tumors seem to begin their track from heterozygotic situation where the 

loss of one functional gene can be enough for a penetration of the trait 

("loss of heterozygosity - LOH"). What this means that there is no backup 

gene - if the functional one is lost there is no return. The loss can occur 

by many mechanisms: Loss of a whole chromosome (by non-disjunction), loss of 

a part of a chromosome having the critical gene, point mutations, small 

deletions (anything from a few base pairs to say millions of base pairs), 

inversions, insertions or certain types of translocations - all these are 

events that require events like recombinational repair or end-joining. This 

can be the initiation step. Some oncogenes often have point mutations at 

specific sites (codons).



For some tumors specific translocations occur with a high probability and 

are directly related to the development of a particular type of tumor.



In a few cases one such step is enough for the tumor to develop 

(retinoblastoma is the classical example) but for most tumors more such 

types of events are necessary for the final development of the tumor.



Bjorn Cedervall    bcradsafers@hotmail.com





_________________________________________________________________

Chat with friends online, try MSN Messenger: http://messenger.msn.com



************************************************************************

You are currently subscribed to the Radsafe mailing list. To unsubscribe,

send an e-mail to Majordomo@list.vanderbilt.edu  Put the text "unsubscribe

radsafe" (no quote marks) in the body of the e-mail, with no subject line. You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/