Lecture 16 Flashcards by Ava Stark

What different conformations of adhesion proetins are there

Open/active and closed/inactive conformation

How well did you know this?

Not at all

Perfectly

focal adhesions respond to what

mechanical stress and cluster

How well did you know this?

Not at all

Perfectly

Name the two main structural proteins that connect Integrins to the Actin cytoskeleton

Talin and Vinculin

How well did you know this?

Not at all

Perfectly

What are the two main “layers” of function within a Focal Adhesion as shown in the diagram?

Actin linkage & force transduction layer. Intra-cellular signaling layer.

How well did you know this?

Not at all

Perfectly

Talin

a dimer that binds integrin and actin with active and inactive conformations

How well did you know this?

Not at all

Perfectly

What does the Talin Head domain bind to?

It binds to PIP2, F-actin, FAK, and the $\beta$-integrin tail.

How well did you know this?

Not at all

Perfectly

Talin buffers forces through the what

folding and unfolding of its various rod domains.

How well did you know this?

Not at all

Perfectly

What happens to Talin when it is subjected to mechanical force (tension)?

It acts as a mechanosensor; the rod domains unfold.

How well did you know this?

Not at all

Perfectly

Cell-matrix adhesions respond to what

mechanical stress

How well did you know this?

Not at all

Perfectly

What is the specific consequence of Talin unfolding under mechanical stress?

Unfolding exposes cryptic Vinculin-binding sites (specifically on helix 12), allowing Vinculin to bind.

How well did you know this?

Not at all

Perfectly

What is the function of Vinculin in Focal Adhesions?

It stabilizes Talin and Integrin, opens up to aid in integrin clustering, and supports focal adhesion growth.

How well did you know this?

Not at all

Perfectly

What is the role of Calpain in Talin regulation

Calpain is a protease that has a cleavage site on Talin (between the head and rod)

How well did you know this?

Not at all

Perfectly

What is the role of Calpain in Talin regulation?

Calpain is a protease that has a cleavage site on Talin (between the head and rod).

How well did you know this?

Not at all

Perfectly

What defines a “Protein Domain” in molecular biology?

A region of a polypeptide chain that is self-stabilizing and folds independently into a compact 3D structure

How well did you know this?

Not at all

Perfectly

Vinculin stabilizes

talin and integrin at the FA

How well did you know this?

Not at all

Perfectly

Vinculin does what

opens up and aids integrin clustering for FA growth. open and closed conformations Integrins

How well did you know this?

Not at all

Perfectly

Integrins recruit what

intracellular signaling proteins

How well did you know this?

Not at all

Perfectly

What is FAK and what is its role? A: Focal Adhesion Kinase

Talin brings it to the focal adhesion to phosphorylate substrates (signaling).

How well did you know this?

Not at all

Perfectly

What reaction do Kinases catalyze?

hey transfer a phosphate group from ATP to a substrate (phosphorylating it).

How well did you know this?

Not at all

Perfectly

Contrast “Focal Adhesions” with “Myotendinous Junctions”.

Focal Adhesions: Short-lived, dynamic, found between migrating cells and ECM. Myotendinous Junctions: Strong, permanent attachment sites between muscles and tendons.

How well did you know this?

Not at all

Perfectly

What is Apical-Basal Polarity?

differential distribution of phospholipids, protein complexes, and cytoskeletal components between the various plasma membrane domains, reflecting their specialized functions

How well did you know this?

Not at all

Perfectly

What are the three major protein complexes that establish Apicobasal polarity?

Par Complex Crumbs (Crb) Complex Scribble (Scrib) Complex

How well did you know this?

Not at all

Perfectly

How do these three complexes interact to maintain polarity?

They exhibit mutual antagonism (repulsive interactions); they inhibit each other to maintain domain identity

How well did you know this?

Not at all

Perfectly

The exact position of the three complexes vary slightly between what?

tissues and species.

How well did you know this?

Not at all

Perfectly

What structures maintain the separation between the Apical and Basolateral domains?

Tight Junctions (or Cadherins/Apical Junctions) act as "fences" to prevent transmembrane diffusion and lock asymmetry in place

Antagonistic interactions

Antagonistic interactions between polarity factors that maintain the identity and control the size of the apical, junctional and lateral domains

Which GTPase activates the Par Complex?

Cdc42.

In the diagram of antagonistic interactions, what does Yurt do?

Yurt inhibits the Crb-Par-6-aPKC complex (limiting apical domain size).

What is the enzymatic function of aPKC in polarity?

It is a kinase that phosphorylates junctional/lateral factors (like Lgl and Par-3/Baz) to exclude them from the apical domain.

aPKC is the main effector what

of apical identity

What are the components of the Par Complex?

Par-3 (Bazooka/Baz), Par-6, and aPKC

What are the components of the Scribble Complex?

Scribble (Scrib), Discs large (Dlg), and Lethal giant larvae (Lgl)

Where is the Scribble complex localized?

In the Lateral (or Basolateral) domain

How does aPKC exclude Lgl from the apical domain?

aPKC phosphorylates Lgl, which inactivates it and inhibits its association with the complex.

How does the Scribble complex affect aPKC?

It inhibits aPKC activity (mutual antagonism).

Phosphorylation of Lgl inhibits what

its association with the other proteins in the complex

All the proteins are cytoplasmic except for what

Crumbs

What is the role of Bazooka (Par-3) in polarity establishment?

It is a scaffold for cadherins that helps propagate polarity in epithelia so all cells are polarized equally.

What is unique about the Crumbs protein compared to the other polarity proteins?

It is the only transmembrane protein (links aPKC to the membrane).

What happens if the Crumbs complex is non-functional (mutant)?

There is no apical membrane (tissue loses apical identity).

How is the loss of Apicobasal polarity linked to cancer?

Loss of polarity leads to overproliferation and metastasis.

What is EMT?

Epithelial-Mesenchymal Transition. A process where epithelial cells lose their polarity and cell-cell adhesion to gain migratory/invasive properties

What is a "Tumor Suppressor Gene"?

A gene that, when mutated (lost), leads to uncontrolled proliferation.

Which Drosophila gene was the first "Tumor Suppressor" to be discovered?

Lethal giant larvae (l(2)gl).

What phenotype is seen in scribble or dlg mutant larvae?

The larvae become huge masses of tissue due to cell overproliferation (tumors).

Cell in scribble complex mutants

overproliferate

What is an "Imaginal Disc"?

A sac-like epithelial structure found inside insect larvae that undergoes metamorphosis to become adult parts (like eyes/legs).

What happens to Imaginal Discs if polarity genes (like scrib, dlg, lgl) are mutated?

They lose polarity, overproliferate, and form tumors

What is the synergistic effect of RasV12 (oncogene) and scrib (polarity) mutation?

While RasV12 alone causes overgrowth, RasV12 plus a Scribble mutation causes massive, aggressive metastatic tumors.

AP polarity and cancer are what

linked

What is Asymmetric Cell Division?

A division that produces two daughter cells with different cellular fates.

What is the purpose of Symmetric Division vs. Asymmetric Division?

Symmetric: Proliferation (Two Stem Cells). Asymmetric: Generates diversity (One Stem Cell + One Differentiated Cell).

What determines if a division is asymmetric?

The segregation of Cell-fate determinant proteins (e.g., Numb) to one side.

What structural machinery must be aligned with the polarity axis for asymmetric division to occur?

The Mitotic Spindle (Orientation of the spindle!).

The major purpose of symmetric divisions is what

What analogy did the lecturer use to explain the "Inside-Out" activation of proteins (like Talin)?

A cord/rope analogy. When the cord is slack/folded, binding sites are hidden. When you stretch the cord (mechanical tension), it elongates and reveals binding sites for other proteins.

How does a cell "know" if a focal adhesion is strong enough?

Through mechanical signaling. If the adhesion is weak, the proteins stretch/unfold, signaling for recruitment of more proteins (reinforcement). If strong enough, the tension is diffused, proteins don't stretch, and recruitment stops.

What happens to Talin when it is stretched by forces of less than 10 piconewtons?

It begins to unfold domain by domain (like a spring snapping out), which provides mechanical buffering and exposes binding sites.

Why are myotendinous junctions described as "hyper strong adhesions"?

Because they are permanent attachments (unlike short-lived focal adhesions) that must withstand the constant, high pressure of muscle contraction against tendons.

Where exactly are Integrins located in a polarized epithelial cell?

In the Basal domain (bottom), not the lateral or apical domains.

What is the specific phenotype of Lethal Giant Larvae mutants?

The larvae die (lethal) and become giant (twice the size of wild type) because their cells lose polarity and overproliferate.

What are "Imaginal Discs" in insect larvae?

Sacs of epithelial cells that eventually develop into adult organs like wings and legs.

Why is asymmetric cell division crucial for stem cells?

It allows a stem cell to produce one differentiated daughter cell (e.g., neuron) while the other daughter remains a stem cell to maintain the pool (regeneration).

How does a dividing cell "know" whether to divide symmetrically or asymmetrically?

By sensing its apical-basal polarity. This allows it to orient the mitotic spindle to either split determinants equally (symmetric) or segregate them to one side (asymmetric).

Lecture 16 Flashcards

(64 cards)