MCB Exam 3: Cytoskeleton

Cytoskeleton

Dynamic system of protein fibers that can be reorganized as needed which allows for physical support and movement

Microfilaments

Another term for actin filaments. They are about 7nm in width.

G-actin (globular)

The monomers for actin filaments are:

affinity, polarity, conserved, abundant

Actin filaments:

Can accommodate ATP or ADP which affects ______

It has _________/directionality

Is highly __________

Very __________

Nucleation

This has nothing to do with the term nucleus, it just means forming a unit

Polymerization, depolarization

For actin filaments, _______ occurs usually on the barbed end while _______ is favored on the pointed end. Both occur on both sides, but because of physical structure, one is favored over the other.

Pointed, Barbed

The (-) side of G actin is also called ______ and the (+) of G actin is also called ______.

ATP, ADP,

When G actin has ___, it has a high affinity for actin so polymerization is easier. When it has _____, G actin’s affinity for other actin is low so it depolymerizes.

Actin Binding Proteins (ABP)

These are proteins that allow severing, bundling, hiding, capping, anchoring, and cross linking of actin filament. Actin filaments are always subject under polymerization and depolymerization but some of these allow them to stop (temporarily or however needed)

Bundling Proteins

A type of ABP which is cross linked with actin filaments; a real life example is microvilli in intestinal epithelial cells.

Networks

This occurs when actin filaments are cross linked with flexible arm proteins (ABPs). A real life example is the terminal web below the microvilli to anchor the (-) end of actin filament.

Contractile Elements

This is created when actin filaments are cross linked with motor proteins; this allows for crawling, cell division, and muscle contraction.

Myosin

A family of motor proteins that work together with actin filaments. They use ATP hydrolysis to be powered. They convert chemical energy into mechanical energy.

empty

Step 1 for Movement:

Myosin head attached to actin. When a myosin head is attached to actin its nucleobinding site is ______.

ATP

Step 2 for Movement:

_____ is attached to the myosin head which makes it have no affinity for actin, so it detaches from it.

Hydrolysis

Step 3 for Movement:

______ of ATP into ADP and phosphate group, which pulls the myosin head back a little bit; has a little bit of affinity for actin.

Power Stroke

Step 4 for Movement:

Myosin head grabs onto the actin and holds on which ejects the phosphate group causing a _______.

ADP

Step 5 for Movement:

________ falls off, back to confirmation, back to the original position but closer to the plus end.

Myosin II

This is a type of motor protein that works with actin. Its job is to get closer to the positive end and works in a pair (two of their tails connected). It’s considered conventional.

Cytokinesis, Crawling, Vesicle transport, contraction,

What are the four things that the combination of actin and myosin can do?

1.) ________

2.) Cell __________

3.) _____ _______

4.) ________ of muscles

Cleavage of Furrow

During cytokinesis, this is formed with myosin and actin

Substratum

This refers to the surface of what the cell that is crawling/moving is resting on.

substratum, adhesion, organelles, retraction

Steps for Cell Crawling:

1.) Cell is on the _______ and extends the leading edge of the cytoplasm

2.) Cell attaches to a new part of the substratum; a new ______ point

3.) The whole cell body moves forward towards the new spot bringing all of its ______.

4.) ______ of the trailing edge; breaking the old adhesion point and gliding forward.

Lamellipodium

This refers to the leading edge/part of the cell that it’s extending when it’s crawling.

Myosin 1

Type of motor protein that works with actin. Considered unconventional because it doesn’t work with a pair, but works alone. Multiple of these surround vesicles when transporting things

Muscle Fibers

This is another term that refers to muscle cells

Multinucleate

Muscle cells are _______ and push their organelles toward the periphery.

Sarcomere

This is also referred to as the “unit of contraction” in muscle cells. It’s composed of myosin and actin along with “bands” and “discs” that refer to various regions of this. It extends from one Z disc to another. During contraction, this decreases in width.

I band

This refers to the region in a sarcomere where only actin is present. During contraction, this band decreases in width.

H Zone

This refers to the region in a sarcomere where only myosin is present. During contraction, this zone decreases in width.

A band

This refers to the entire length of myosin in a sarcomere.

Thin, Thick

In a sarcomere, the actin filaments are referred to as the ____ filaments and the myosin are referred to as the ____ filaments.

Contraction

This is when the sarcomere, H zone, and I band decrease in width and is caused by tons and tons of power strokes by the myosin.

Positive

Each actin has its _____ end attached to the z disc, which is the direction the myosin are going towards.

Microtubules

These can be used for guiding intracellular movement, segregating chromosomes during mitosis, and overall movement. They are 25nm in width.

Tubulin

This is the monomer for microtubules. It’s a heterodimer that’s made up of an alpha and beta subunit.

beta

This is the subunit in tubulin whose GTP gets hydrolyzed. If the other one was to be hydrolyzed, it would loose its affinity for the other part of the dimer and the tubulin dimer would fall apart.

ATP, GTP

Actin use _____ as a power source while tubulin use ____ as a power source.

13 Protofilaments

Tubulin dimers that are GTP bound polymerize into ______________ that look like toothpicks.

GTP cap

This is not a physical structure when referring to tubulin. It’s just the outer tubulin ring.

Binding Tubulin

These are molecules that actually bind to the tubulin monomers and induce depolymerization. This is because they “lock up” the free tubulin so when the molecular countdown ends for the polymerized tubulin, there’s nothing preventing them from depolymerizing because GTP was hydrolyzed into GDP.

Colchicine and Colcemid

These are two drug examples that bind to tubulin and non-specifically affect all tubulin.

Vincristine and Vinblastine

These are two drug examples that bind to tubulin and target rapidly dividing cells.

Binding Microtubules

These are molecules that directly bind to microtubules (polymerized) to prevent depolymerization, which is crucial for cell division. Therefore, cell cannot divide.

Taxol

This is an example of a drug that binds to microtubules and targets rapidly dividing cells.

100%

The ability to do cell division ____ depends on being able to break down microtubules and make new cells.

Microtubule-organizing centers (MTOC)

Where is the origin of microtubules (overall, umbrella term)

Centrosome

This is made up of a pair of centrioles positioned perpendicular to each other, microtubules, and pericentriolar material (PCM)

In animals, this is the primary MTOC

9 triplet

The centrioles are made up of microtubules that are in a ______ arrangement

PCM

This refers to the things surrounding the centrioles and microtubules in the centrosome and is composed of a variety of proteins and material.

Because it contains molecules like gamma tubulin, it can be said that the microtubules originate from this area.

Gamma Tubulin

This is located in the PCM. It’s job is to facilitate the formation of new microtubules by helping start the process.

Dyneins, Kinesins

There are two motor proteins that microtubules work with.

______ always go towards the (-) end of the microtubule which is the end that is usually attached to something.

______ always go towards the (+) end of the microtubule.

(This is for purposes of MCB150, there are classes that don’t follow this but most of the time it’s these rules)

Intracellular, organelle, color, separation

Functions of Motor Proteins + Microtubules:

________ vesicle transport

___________ movement and positioning

______ changes

Bending of cilia and flagella

_________ of sister chromatids and centrosomes during M phase.

Basal Body

This is usually located near the plasma membrane. Its structure is so similar to centrioles that location must be given to see if its this or centrioles. In other words, they also have the 9 triplet arrangement.

Axoneme

This is a central part/strand of a cilium or flagellum (cross image/section)

9+2

The axoneme is in a _____ arrangement.

Dyneins, nexin

In a flagellum or cilium, the ____ are always anchored/attached into the A tubule and interact with the B tubule.

____ are “linker” proteins between the tubules.

Shorter, Slower, more

In comparison to flagella, cilia are much ______, and in terms of speed they are much ______, but there are ____ of them than flagella.

G0

Some cells stop dividing but are still alive and are metabolically active. When this happens, they exit from G1 to _____. Some cells are able to come out of this phase.

Quiescent

This refers to how cells are peacefully inactive

95, 11, 8, 4, 1

Human cells are ____% of the time in interphase. They spend ___hrs in G1, ___ hrs in S, ___ hrs in G2, and only ____ hr in M phase.

Prophase, spindle poles, nuclear envelope

Step 1 in M phase: _______

This is when microtubules disassemble and new ones are made. ________ begin to travel to opposite sides and DNA condenses. At this point the ____ _____ is gone.

Prometaphase

Step 2 in M phase: ___________

This is when the chromosomes begin doing “ballet” in order to try and line up at the middle.

Metaphase

Step 3 in M phase: ___________

This is when all the chromosomes are lined up in the middle along the metaphase plate (imaginary line)

Anaphase

Step 4 in M phase: ___________

This is occurs as soon as all the proteins holding the sister chromatids are broken and the chromosomes are pulled to opposite sides of the cell.

Telophase

Step 5 in M phase: ___________

The nuclear envelope beings to form around the chromosomes

Cytokinesis

Step 6 in M phase: ___________

This is the only step in mitosis where actin and myosin are used. A contractile ring of actin is formed with myosin motors on the inside to create a cleavage furrow and pinch away to create two daughter cells.

Nuclear Envelope

This surrounds the nucleus and is made of the inner and outer cell membrane

Pores

These are embedded into the nuclear envelope and are not covalently attached to each other.

Nuclear Lamina

This is a type of an intermediate filament. It gives the nucleus its shape and stability and are held together non-covalently. It’s a point of attachment for heterochromatin.

Phosphorylated, B, A and C

Disassemble of the nuclear envelope:

In order to disassemble the nuclear envelope, the nuclear lamina are __________. Lamin ___ continue to be bound to the now free-floating vesicles while _______ are free-floating.

Single bilayer, surround, flatten

The vesicles from the nuclear envelope and lamina are ________. To form the nuclear envelope back, they are dephosphorylated and completely _____ the chromosomes since their affinity returns. Then they ______ all fuse together, and the DNA begins to unwind again. This occurs during telophase.

Kinetochore MT, Polar MT, Astral MT

The microtubules that are sent out/extended by the centrosome have three different fates:

They either hit the kinetochore of the chromosome, so they are called __________; they go in the direction of the chromosomes and don’t hit the kinetochore so they’re called ___________; ones that don’t even go in that direction are called ___________.

Plus, negative

The ____ ends of the microtubules are the ones extended out. The _______ ends are attached/bound to the centrosomes.

Spindle Poles

These are centrosomes but are referred to as this when going through M phase.

Anaphase A

This is when the sister chromatids are taken and moved to apart from each other; for this, dyneins are needed since they’re going towards the (-) end.

Anaphase B

This is when the microtubules don’t hit the kinetochore, but allow for moving the spindle poles farther apart from each other; polar MTs push and astral MTs pull.

the same

Anaphase A and Anaphase B occur at ________ time!!

Beta, Alpha 8

On a tubulin, the ___ part of the dimer is the positive end and the _____ part of the dimer is the negative end. They are also ___ nm in thickness.