Lunch & Learn

Lunch & Learn student led discussion and presentations are held on Thursdays from 12-1:30 in Howey. These sessions are an informal gathering of PoLS students and faculty in which one student presentation will be given followed by a discussion. If you would like to sign up to give a talk this semester please fill in your name in the spreadsheet below.

Fall 2012 Schedule

Date	Speaker	PPT
10/11	Tung Le (Kim Lab)	-
10/18	Nick Gravish (Goldman lab)	-
10/25	Open	-
11/1	Gabriel Mitchel (Weitz Lab)	-
11/8	James Waters (Kim Lab)	-
11/15	Open	-
11/29	Open	-
12/6	Open	-

Link to editable google doc here.

Fall 2012 Abstracts

 
Lunch & Learn 10/18/2012

STABILIZING FALLS IN CONFINED ENVIRONMENTS
Nick Gravish (Goldman lab)

Subterranean animals must rapidly navigate unpredictable and perilous underground environments. Nests of the fire ant \em{Solenopsis invicta} (average body length 0.35  \pm 0.05 cm) consist of a subterranean network of large chambers and tunnels which can reach 2 meters into the earth and house up to 250,000 workers. Laboratory investigations of fire ants reveal that digging workers typically climb up and down tunnels slightly wider than the largest ant hundreds of times per hour. However the principles of locomotion within confined environments such as tubes have been largely unexplored. We hypothesize that the ability to engineer underground habitats provides opportunities to facilitate movement. We conducted laboratory experiments to monitor upward and downward tube climbing of isolated fire ant workers. Fire ants were challenged to climb in 9.4 cm long glass tunnels (diameter D = 0.1 – 0.9 cm) that separated a nest from an open arena with food and water. During ascending and descending climbs we induced falls by a rapid, short, translation of the tunnels downward. We monitored induced falls over 24 hours in groups from five separate colonies. The tunnel diameter has a significant affect on the ability of ants to rapidly recover from perturbations. Falls in smaller diameter tunnels were arrested through the use of rapid jamming of limbs, body and antennae against the tunnel walls, arresting in as low 30 ms. Falls in larger diameter tunnels were not arrested. We find that the transition to stable fall arrest occurs in tunnels equal to 1.4 BL. This tunnel size is  comparable to the natural tunnel diameter found near nest entrances. Our data indicates that fire ants moving through natural tunnels can employ antennae, limbs, and body to rapidly stabilize falls.

 
Lunch & Learn 10/11/2012

MEASURING LOOPING KINETICS OF SHORT DOUBLE-STRANDED DNA
Tung Le (Kim Lab)

Bending of double-stranded DNA (dsDNA) is associated with fundamental biological processes such as genome packaging and gene regulation, and
therefore studying sequence-dependent dsDNA bending is a key to understanding biological impact of DNA sequence beyond the genetic code. Average mechanical behavior of long dsDNA is well described by the wormlike chain model, but the behavior of dsDNA at length scales
around or below the persistence length remains controversial. Here we used single-molecule FRET (Förster Resonance Energy Transfer) to measure spontaneous looping kinetics of 100~200 bp dsDNA in the absence of proteins. We showed that in this length regime, the apparent looping rate increased as dsDNA became more curved and longer, suggesting that the energy component dominates the free energy of looping. We also calculated the predicted dependence of looping rate as a function of deflection angle and length based on a dinucleotide wormlike chain model, and showed that the observed length and curvature dependence is much weaker than predicted. Our results suggest that dynamics of dsDNA deviates from the wormlike chain behavior below 200 bp.