L4 Cytoskeletons

What is Cytoskeleton made up of?

Microtubules, Microfilament, Intermediate Filaments.

What are the 3 functions of Microtubules?

1. Chromosomal Movements during nuclear divisions (mitosis/meiosis)

2. Formation of Cilia and Flagella in certain cell types

3. Intracellular Transport of Materials.

Elaborate Microtubules’ role in Chromosomal Movements.

MTs pull and push chromosomes to enable genetic material separation into daughter cells.

What is a Mitotic Spindle?

Disassembled Cytoplasmic MTs which are later reassembled.

What is Cilia?

Slender protuberances that project from a larger cell body to provide movement in fluids and across epithelial cells of the respiratory tract.

What are Flagella?

Lash-like appendage, longer than cilia, that protrudes from a cell body and helps move an entire cell through fluids.

What are Dynein and Kinesin?

MT Motor Proteins that facilitate movement of intracellular cargo such as membrane-bound organelles and transport vesicles on MT tracks.

What are Microtubules composed of?

Alpha and Beta Tubulin Heterodimers that form into linear chains called Protofilaments.

What structure can form from Protofilaments?

13 protofilaments form the outer wall of a cylindrical microtubule structure with a GTP cap that is immediately hydrolyzed to GDP after being added to the structure.

What is a Centrosome?

The major Microtubule Organizing Center (MTOC) of the cell by regulating MTs by number, location, and cytoplasmic orientation; origin of most microtubules (MTs).

What is the purpose of Microfilaments?

Involved in the movement of the cell.

What is the purpose of Intermediate Filaments?

Located in the cytosol, between the nuclear envelope and plasma membrane, to provide support to the cell and resist mechanical stress; has 6 categories: Types I-VI.

What is Actin?

Present in most cell types and forms microfilaments that radiate from the nucleus to the plasma membrane to regulate the physical state of the cytosol.

What type of tissue is Actin typically known to be found in?

Muscle cells to help with muscle contraction.

What is Actin Polymerization?

Globular Actin (G-Actin) monomers are polymerized to form a Filamentous Actin (F-Actin) molecule.

What energy is required for actin polymerization?

ATP is hydrolyzed to ADP + Pi.

Explain the structure of F-Actin.

Two strands of G-Actin monomers wrap around each other to form a mature F-Actin microfilament with a + end for new added monomers and a - end to subtract monomers.

What are the phases of Actin Polymerization?

Lag Phase, Polymerization, Steady State.

What is treadmilling?

The process of addition to the + end and subtraction from the - end of G-Actin monomers at an equal rate.

What are the 2 possible physical nature of cytosol?

Gel and Soluble — 'Gel-Sol'.

Describe the Gel State.

A more firm state due to more structured actin.

Describe the Soluble state.

A more soluble state due to less structured or more fragmented actin.

In which state of Gel-Sol is actin continuously treadmilling?

Both gel and sol states.

What are Actin-Binding Proteins?

Regulators of the gel-sol nature of the cytosol.

What is Cofilin?

An Actin-Binding protein that PREVENTS F-Actin lengthening to create a more STABLE structure.

What roles is Cofilin a part of?

Cell Motility, Migration, Shape, and Metabolism.

What is Gelsolin?

An Actin-Binding protein that FRAGMENTS the F-Actin to create a more SOLUBLE state of the cytosol.

What is Spectrin?

An actin-binding protein family that binds to F-Actin to strengthen and support the Erythrocyte membrane.

How does Spectrin contribute to erythrocytes’ shape?

Maintains its Biconcave Disc Shape which maximizes the Hemoglobin and Oxygen carried by each RBC.

What can occur when there is an absence or presence of abnormal Spectrin?

Hereditary Spherocytosis.

What can Spherical Erythrocytes cause?

Hemolytic Anemia due to its low membrane pliability, making it susceptible to lyse; can be life-threatening and require frequent blood transfusions.

What is Dystrophin?

An actin-binding protein that provides tensile strength to muscle fibers and contributes to the framework for signaling molecules.

What are can possibly be a result due to defects in Dystrophin?

Muscular Dystrophy (MD), muscle wasting, Duchenne MD (DMD) and Becker MD; mutation in the dys gene.

What function can Actin participate in in nonmuscle cells?

Contractile functions due to the effects of an ATP hydrolyzing motor protein of the Myosin family.

Explain how Myosin II and F-Actin interacts to mediate local contractions.

Myosin slides F-Actin over each other which can create a contractile ring to divide a cell into two daughter cells in mitosis.

How does Myosin II and F-Actin affect cells?

Provides stiffness to cell cortex and prevent deformation of the plasma membrane.

Why is Contraction important?

Wound healing, cell division, cytokinesis, and cytoplasmic division following nuclear division of mitosis.