bio 211 lecture 9 - microtubules and intermediate filaments

What is EB1 and what is its function?

EB1 is a protein that binds specifically to the plus ends of growing microtubules. It helps track microtubule growth, as microtubule plus ends typically point towards the cell periphery.

What are the key functions of microtubules in cells?

Microtubules help move cargo and signaling proteins around the cell, are highly dynamic, and their plus ends point towards the cell periphery. They form important cellular structures and participate in intracellular transport.

What is the basic building block of microtubules?

The basic subunit is the tubulin heterodimer, composed of α (alpha) and β (beta) tubulin bound to a guanine nucleotide. These heterodimers polymerize to form microtubules.

What is the GTP cap and why is it important?

The GTP cap helps control microtubule growth. When GTP hydrolyzes to GDP on tubulin, it leads to rapid depolymerization of microtubules due to a conformational change that weakens the polymer bonds.

What is dynamic instability in microtubules?

Dynamic instability refers to the rapid switching between growing and shrinking states within the microtubule polymer. This allows microtubules to rapidly change their network architecture in response to extracellular and intracellular signals.

What is γ-tubulin and its role in microtubule formation?

γ (gamma) tubulin is localized around centrosomes and forms the γ-TuSC (gamma tubulin small complex). It helps nucleate microtubules by forming their minus ends.

How do centrosomes organize microtubules in animal cells?

Centrosomes serve as the main microtubule organizing centers in animal cells, from which microtubules emanate outward. They contain γ-tubulin and help organize the cellular microtubule network.

What is the function of stathmin in microtubule regulation

Stathmin is similar to thymosin in that it limits the availability of subunits to reduce polymer growth. However, it differs in that it binds to two tubulin heterodimers instead of a single monomer.

What are the two main types of microtubule motor proteins?

The two main types are kinesins and cytoplasmic dynein. These motors move along microtubules to transport cargo within the cell.

What is unique about intermediate filament structure?

Intermediate filaments are non-polarized when assembled in cells, due to their unique assembly process involving lateral bundling and twisting of coiled-coils. This structure gives them their mechanical strength.

How do intermediate filaments provide mechanical strength?

Their rope-like structure of overlapping subunits creates many bonds within the polymer, allowing them to stretch and bend without breaking, providing mechanical stability to cells and tissues.

What is the relationship between keratin mutations and disease?

Mutations within the keratin gene can lead to abnormally weak intermediate filaments, resulting in diseases like epidermolysis bullosa, which causes skin blistering.

What is plectin and its function?

Plectin (appearing green in immunofluorescence) is a linker protein that cross-links different cytoskeleton polymers together, helping to integrate the cellular cytoskeleton.

What are septins and what structures can they form?

Septins are cytoskeletal proteins that can form filaments, sheets, and/or rings. They help regulate cell polarity and can form diffusion barriers.

How do septin structures function in cells?

Septins can form diffusion barriers in dividing yeast cells and at the base of cilia, helping to compartmentalize cellular components and maintain cell polarity.

What is the role of microtubule plus-end-binding proteins?

They modulate microtubule dynamics and attachments by targeting the GTP-bound tubulin dimers at the plus end of the polymer, affecting catastrophe and stabilization.

How do microtubules and motors coordinate organelle movement?

Motor proteins like kinesin and dynein move along microtubules, carrying organelles and vesicles as cargo, facilitating intracellular transport.

What is the nuclear piston mechanism?

It's a mechanism of 3D cell migration where myosin II pulls the nucleus forward to pressurize the cytoplasm and generate lobopodia, facilitating cell movement through 3D matrices.

How does matrix dimensionality affect septin localization?

Septin localization patterns differ between 2D and 3D matrices, showing that the cellular environment influences septin organization and function.

What is the role of linker proteins in nuclear positioning?

Linker proteins connect cytoskeletal filaments and bridge the nuclear envelope, allowing forces to be applied to the nucleus for proper positioning and movement within the cell.

What are the main characteristics of microtubules?

They are large, polarized filaments capable of rapid growth and collapse, nucleated by gamma tubulin within centrosomes.

How do intermediate filaments differ from microtubules?

Intermediate filaments are non-polar, relatively static, and provide mechanical strength to cells and tissues, while microtubules are polar and highly dynamic.

What role do microtubule-binding proteins play?

They modulate filament dynamics and organization by nucleating microtubules, connecting them to other structures, and governing their dynamics.

What happens during microtubule catastrophe?

Catastrophe occurs when the GTP cap is lost, leading to rapid depolymerization of the microtubule due to the inherent instability of GDP-tubulin.

How do intermediate filaments contribute to tissue integrity?

They provide mechanical strength to cells and tissues through their rope-like structure and ability to resist mechanical stress without breaking.

What is the relationship between nuclear movement and cytoskeletal elements?

Cytoskeletal elements, connected by linker proteins, apply forces to the nucleus to move and position it within the cell, which is crucial for cell migration and organization.

How do septins contribute to cell organization?

Septins form barriers that help compartmentalize cellular components and maintain cell polarity, particularly in processes like cell division and cilium formation.

What is the role of GTP in microtubule dynamics?

GTP hydrolysis to GDP on tubulin affects microtubule stability, with GTP-tubulin promoting growth and GDP-tubulin promoting depolymerization.

How do microtubule-severing proteins affect microtubule organization?

They destabilize microtubules by breaking them apart, helping to reorganize the microtubule network and regulate microtubule dynamics.

What is the significance of cytoskeletal integration?

The integration of different cytoskeletal elements (microtubules, intermediate filaments, and septins) through linker proteins allows for coordinated cellular processes like movement, organization, and mechanical stability.