Senior Online Assessment (OSA) An announcement of the OSA will be released this week to seniors through their Texas Tech e-mail address. A follow up e-mail will provide the same students the OSA link. There are four OSA versions covering most of the categories in the General Education curriculum. The assessment activity will take approximately 20-25 minutes to complete. Students who complete the OSA will be entered into a drawing for three awards of $1,500 to use toward their fall 2008 tuition and fees, or, if they are g raduating this spring, the awa rd will be applied retroactively to their spring 2008 account. Award recipients will be notified by e-mail no later than April 15, 2008. The reports and research that result from students responses to the Online Senior Assessment will include only aggregated data which is not linked to individual students.
Telomerase: a molecular fossil that is a ribonucleoprotein; whose function is to cap chromosomes
The RNA sequence adds ~ 1.5 x the repeat with each binding and polymerase event
Fig. 8.37
Adding telomere copies allows replication of sequences at the end of a chromosome and cell division to continue throughout the life of the cell; in many cancers it also allows immortality
Fig. 8.38
The telomerase reaction
(From Weaver, 2007, Molecular Biology)
Watch the animation on telomerase action on the web site or cd
Telomere binding proteins in lower eukaryotes - among the tightest protein-DNA associations ever found; these protect the ends of the telomere from degradation
The likely organization of the mammalian telomere; their telomere binding proteins do not bind to single stranded, but to duplex DNA (see next slide) forming a structure called the t-loop
(From Weaver, 2007, Molecular Biology)
Telomere length is determined in part by telomere-binding proteins
Few protein complexes bound
More protein complexes
Fig. 8.40
(Act indirectly by binding to Rap1)
Yeast
All three proteins Inhibit telomerase
(binds ssDNA and recruits telomerase) (binds to ds telomere repeat DNA)
All of these are proteins thought to associate directly with TRF1 and/or TRF2 (also binds ss telomere repeat)
Humans
Fig. 8-39
Some telomere binding protein similarities in humans and yeast (see later slide for TRF 1 and 2)
The mammalian t-loop, showing the invasion of the single stranded 3 end of the G-rich strand (red). The model suggests that it invades dsDNA upstream, forming a long tloop and a D-loop (~75-200 nt) at the junction of the between the loop and the tail.
Electron micrographs of (a) an isolated t-loop, showing TRF-1 bound to the loop, but not the tail; (b) SSB bound to the tail-loop junction, where the ssDloop should be
(From Weaver, Molecular Biology, 2007)
Telomere-binding proteins in mammals, the TRF family
Get strand invasion of free 3 end in presence of TRF2; this hypothesis has been verified by binding of invading strand by SSB
t-loop is now resistant to degradation
(From Weaver, 2007, Molecular Biology)
Reducing the amount of POT1 by RNA interference leads to telomere lengthening; the binding of all of these other proteins is thought protect the end of the telomere from degradation or additional telomerase activity
POT1 = Protection of Telomeres, discovered by Baumann and Cech in 2001, preferentially...