Download Biology 52: Problem Set for Lectures 9, 10, and 11

Biology 205: Problem Set for Lectures 9, 10, and 11
1. Name the three primary cytoskeletal filaments in order of decreasing
diameter.
A. Microtubules
B. Intermediate filaments
C. Actin filaments (microfilaments)
2. Receptor-activated G-proteins interact with a variety of downstream effectors
such as adenylyl cyclase and Phospholipase C. What second messenger
molecule(s) is/are generated by activation of phospholipase C and what is/are
the downstream effector(s)?
Inositol trisphosphate (IP3), which causes the release of calcium from
internal stores in the ER, and diacylglycerol (DAG). The combined effect of
a calcium transient and DAG production is to activate protein kinase C and
recruit it to the membrane for phosphorylation of its downstream targets.
3. Of the two types of signaling molecules we discussed in class (large
hydrophillic ligands and small or hydrophobic molecules), which mediates the
most direct signaling pathway and why?
Steroids and NO. Since they are membrane permeable and bind and
directly activate their cytoplasmic receptors, they are most direct - there
are no intermediate proteins orsecond messengers involved.
4. Most tyrosine kinase receptors must oligomerize to be activated. Why is this
necessary and how is it achieved?
The receptors must oligomerize (dimerize) in order to autophosphorylate.
Autophosphorylation occurs between receptor monomers that are
clustered in the membrane upon ligand binding to the extracellular domain
of the receptor.
5. The growth factor PDGF activates a signaling pathway in cells via a receptor
tyrosine kinase, yet the downstream effector of receptor activation is MAP
kinase. How is this acheived?
Activation of the PDGF receptor tyrosine kinase leads to the recruitment
and activation of Ras. Activated Ras converts the tyrosine kinase cascade
to a serine/threonine kinase cascade by activating the MAP kinase
pathway.
6. You are working in a lab to examine the cellular responses to a new drug.
You treat cells with the drug and measure the intracellular level of cAMP and find
it to be increased in response to this treatment. With what type of receptorwould
you predict the drug interacts? How is this rise in cAMP used to change cellular
physiology or metabolism?
A G-protein coupled receptor (GPCR, 7TMD receptor). cAMP activates
protein kinase A (PKA) by binding to its inhibitory subunit and releasing
the active kinase subunit to phosphorylate downstream targets in the
cytoplasm that alter gene expression.
7. A common technique used to study microtubule-based motor proteins is to
attach them to a microscope slide by their tails (which stick avidly to glass) and
then add polymerized microtubules to them. The microtubules are moved along
the glass as the motors "walk" along their length in what is known as a
"microtubule gliding assay".
In which direction will microtubules glide on a coverslip coated with kinesin and
on a coverslip coated with dynein (i.e. plus end first or minus end first)?
Kinesin - minus end first, dynein - plus end first.
8. Dynamic instability causes microtubules to either grow or shrink rapidly. If
you have an individual microtubule that's in a shrinking phase:
A. What must happen at the microtubule plus end for it to stop shrinking and start
growing?
GTP-charged tubulin must begin assembling on the plus end to restore the
GTP cap. Also, the conformation of the microtubule tip must structurally
interconvert from the "peeled-bannana" or "ram's-head" structure in which
the protofilaments peel away from the microtubule into the flat 2dimensional sheet associated with microtubule growth.
B. How would a change in monomeric tubulin (heterodimers of alpha- and betatubulin) affect this switch?
Low tubulin would make rescue less likely, while higher concentrations
would increase the probability.
C What would happen if GDP but no GTP were present in the solution?
The microtubule would never rescue to a growing phase.