Notes 1: Intro, Components of the cytoskeleton

Skeleton

_______ are two types in nature.

Exoskeleton

Invertebrates usually have an _______.

Vertebrates

_______ have an endoskeleton.

Transition

There are _______ organisms that are the bridge between a fully developed exoskeleton.

Mollusks

_______ are the linking whatever in the chain that goes from exoskeleton to fully developed to endoskeleton.

Cuttlefish

This is the skeleton of the _______.

Endoskeleton

The cuttlefish's skeleton is an example of an _______.

cytoskeleton

Cells have their own skeleton too; for animal cells it's an endoskeleton because it's inside the cell and it's called the ______.

Microtubules

There are three main components of the cytoskeleton:intermediate filaments, ______, and actin filaments.

Actin filaments

There are three main components of the cytoskeleton:intermediate filaments, microtubules, and ______.

Intermediate filaments

______ are very strong in the sense that they have great tensile strength.

Intermediate filaments

They allow cells to sustain mechanical stress.

Intermediate filaments

They are found almost in all animal cells.

Intermediate filaments

They mostly form a mesh throughout the cytoskeleton and even within the nucleus.

Intermediate Filaments

______ are structured like ropes.

Strong

Intermediate filaments are so ______ because of structure.

Rope

The basic structure of an intermediate filament is the same as that of a ______.

Coiling

It's basically a filament that keeps ______ with another filament.

Tetramer

The two filaments align together and form a ______.

Group of Eight Tetramers

Tetramers align together to form a ______ _________ _________ _____

Composed

Tetramer ______ by two filaments.

Align

Tetramers ______ head to tail.

C Terminus and N Terminus

The parts that are loose on the ______ and the ______ let's say if, if you take one, the first one is a reference, they get together like this you know like the parts that are loose like if you're crossing your fingers of the two hands in this way and this goes along with the entire length of the filament.

Coiled-Coil Helices

In the end, it's pretty strong because there are all these filaments wrapped around in this ___-____ __ and they're wrapped around each other, they also interact like this so it becomes really strong.

Intermediate filaments

Two different types of ________.

Cytoplasmic

Intermediate filaments that are ________.

Nuclear

Intermediate filaments that are ________.

Keratin

The most common cytoplasmic intermediate filaments are ________ found in every epithelial cell.

Epithelial cells

Cells that need to be strong because they are the layer outside every organ and inside, including our skin, made of _____ ___.

Vimentin

Another intermediate filament present in all connective tissues, muscle cells, and glial cells, besides keratin.

nerve

A type of intermediate filaments specific for ________ cells.

Lamins

The nuclear filaments, mostly the so-called ________, such as Lamin AC and Lamin B.

Nuclear Intermediate Filaments

_____ ______ ___ are the only ones that don't form the rope-like structure.

Coiled-coil Structure

They make this ___-___ ____ but not the rope structure.

Mesh

They form this ______.

Nuclear Lamina

The ____ __, just underneath the intranuclear side of the nuclear envelope, interacts with anchoring dimers that are formed.

KASH-Domain Protein

There's that __-____ ____ which has one end in the intraperinuclear space and the other end towards the cytosol.

SUN-Domain Proteins

Then there's the __-_ ___ which are the other way around with one end in the perinuclear space and the other end inside the nucleus.

Chromatin

Importantly, the SUN-domain proteins also directly interact with ______ so with the chromosomes.

Nuclear Envelope

Everything that is in the nucleus is anchored to the _ _____.

Mutations

When there are ______ in these proteins that stabilize the nuclear envelope, these mutations can cause very severe diseases.

Muscular Dystrophy

For example, some kind of ___ ___ are caused by mutations in lamin proteins.

Microtubules

The ______ are in the cytoplasm only.

Actin filaments

The microtubules and __ ____ are in the cytoplasm only.

Microtubules

______ are the biggest in terms of size, filaments of the cytoskeleton.

Microtubules

They're very stiff ______.

centrosomes

Microtubules always grow and shrink from the same end which is called the plus end, whereas the minus end is anchored to a structure called the ______.

two

In non-dividing cells, there's only one centrosome and one pole of the cell; in dividing cells, there are ______.

mitotic spindle

The first step of mitosis is the duplication of the centrosome and the migration of the second centrosome to the other pole of the cell, followed by the formation of the ______.

centrosomes

In ciliated cells, the basal body, where the microtubules originate from, is located in the apical end of the cell, instead of the ______.

Microtubule

The components of the eukaryotic cytoskeleton that are made up of dimers of alpha and beta tubulin.

Alpha and Beta Tubulin

The components of the microtubule that form dimers and stack one on top of the other with alpha towards the minus end and beta towards the plus end.

Gamma Tubulin

A component found in the basal body in the centrosome but not in the microtubule.

Filament

The structure formed by stacking alpha and beta tubulin dimers in a microtubule.

Spiral

The arrangement of microtubule filaments with other filaments in a ___ manner.

13

The number of filaments that make up one microtubule, a prime number.

Lumen

The space inside the microtubule structure where the filaments are arranged.

Electromyography

A technique used to visualize the structure of microtubules with tubulin dimers.

Microtubule Dynamics

______ Require GTP Hydrolysis

GTPase

An enzyme that hydrolyzes GTP into GDP plus phosphate and the hydrolysis gives the energy to remain attached within the microtubule

Alpha Beta Tubulin Dimer

The dimer is a GTPase

GTP

The addition of ___ bound alpha beta dimers at the plus end of the microtubule

GDP

After hydrolysis of GTP, dimers remain bound to ___ and are stable within the microtubule

Stabilization

The hydrolysis of GTP is important to ______ the microtubule

GTP Cap

If hydrolysis of GTP is faster than the kinetics of addition of alpha beta tubulin dimers, the ______ is lost

Shrinking

When hydrolysis of GTP is faster than the kinetics of addition of dimers, the microtubule starts ______

Capping

There are proteins that associate with the growing microtubule, that stabilize the microtubule. In the absence of this ______ protein, the microtubule might shrink back.

Microtubule Polymerization and Growth

Sometimes it depends on whether the microtubule has reached the end of the line, like it's touched the plasma membrane or whatever is under the plasma membrane, could be a layer of actin for example covering the intracellular side of the plasma membrane. So, the bottom line is it is interactions with other proteins, other structures that determine whether the microtubule is going to grow or shrink because it's going to determine whether the hydrolysis of GTP is gonna be faster or whether the addition of the dimers is gonna be faster. But the important thing to learn is to remember because this is different to what we're gonna see shortly about actin is that microtubules can only grow and shrink at one end which is the plus end. The minus end is anchored in the centrosome and it starts from this gamma tubulin rings remember I mentioned that just 5 minutes ago the gamma tubulin so within the centrosome there are these gamma tubulin rings which are really the beginning of the assembly of a microtubule and then the microtubule grows towards the plus end in any direction of the cell. Can grow and shrink grow and shrink.