Cytoskeleton - IV

Intermediate filaments

• Form structural connections between cells

• Maintain cell shape and anchor organelles in place

• Provide tensile strength and mechanical stability, helping cells resist stretching forces

• average in diameter

Microtubules

• Serve as tracks for intracellular transport of vesicles and organelles

• Contribute to cell structure and enable movement via cilia and flagella

• Form the mitotic spindle to separate chromosomes during cell division

Intermediate

Which type of filament?

• strong and ropelike

• strengthen cells against mechanical stress

Nucleolus

where rRNA synthesis occurs

Nuclear lamina

determines the shape of nucleus and is a meshwork of intermediate filaments

Tetramers

can pack together into a helical array containing eight tetramer strands

coiled-coil

Pairs of monomers associate to form a dimer through a _______-______ dimer

a-helical

The intermediate filament monomer consists of an _-_____ central.

Keratin filament

• the most diverse of intermediate filaments

• Every epithelium in the vertebrate body has its own of these filaments

• Most prominent examples include: hair, feathers and claws

2D-meshwork

Intermediate filaments found in the nucleus are ____-_____

lamins

The nuclear envelope’s subunit protein

• is removed and recreated during every cell division

kinases

Lamin phosphorylation by protein ______ weakens their stability

Actin filaments

Support cell shape, especially at the cell cortex

• Enable cell movement and changes in cell shape

• Allow cells to move (taxis), engulfing (phagocytosis) and division (cytokinesis)

Actin filaments

Participate in processes like cytokinesis during cell division

Actin

Which filament?

Thinnest and more flexible

actin binding proteins

When actin filaments bind to what, they can:

• Create microvilli (gut epithelial cells)

• Contractile bundles (muscle contraction)

• Contractile rings (cytokinesis)

polar

Actin filaments are polar/non-polar.

ATP

Each monomer of actin binds to the actin filament with what molecule?

• each end binds, but the plus end has a faster rate of growth

plus end

Which end of the actin filament has faster rate of growth?

ADP

Once a monomer with ATP is bound to the actin filament, the ATP is hydrolyzed into ______, and the monomer would dissociate.

ADP-actin

• less stable

• more prone to dissociation

• doesn’t immediately leave the filament

plus end

Which end of the actin filament?

• ATP-actin monomers are added rapidly

• filament growth promoted

minus end

Which end of the actin filament?

• dissociation occurs more frequently

grows

If the critical concentration (cc) is high, the actin filament _____ at the plus end.

shrinks

If the critical concentration (cc) is low, the actin filament _____.

treadmills

If the critical concentration (cc) is intermediate, the actin filament _______.

T

T or F?

While the rate of actin addition at the plus end equals the rate of loss at the minus end, the filament maintains a constant overall length.

treadmilling

Individual actin monomers continuously cycle through the filament, adding at the plus end and dissociating at the minus end

Actin

What protein makes up actin filaments?

a.) Tubulin

b.) Actin

c.) Keratin

d.) Dynein

Structural support

Intermediate filaments primarily provide:

a.) Movement

b.) Structural support

c.) Energy

d.) Transport

ATP

What molecule binds actin during polymerization?

a.) GTP

b.) ATP

c.) ADP

d.) NADH

Plus end

Which end of actin grows faster?

a.) Minus end

b.) Plus end

c.) Both equal

d.) Neither

Myosin

What type of protein moves along actin filaments?

a.) Kinesin

b.) Dynein

c.) Myosin

d.) Tubulin

shortening

Contraction of a muscle is caused by a simultaneous _______ of all the cell’s sarcomere

Stabilize microtubules

Blocking GTP hydrolysis would:

a.) Increase shrinkage

b.) Stabilize microtubules

c.) Stop actin

d.) Stop myosin

Vesicle transport to the positive end

A kinesin defect would affect:

a.) DNA replication

b.) Vesicle transport to the positive end

c.) Vesicle transport to the negative end

d.) Translation

Shrinkage happens

If GTP cap is lost:

a.) Growth happens

b.) Shrinkage happens

c.) Stability occurs

d.) No change

Actin-binding proteins

allow for caping, crossing or even severing proteins

• e.g.,formin or actin-related proteins (ARP) allow for nucleation (or growth at positive end)

Myosin

• bind to and hydrolyze ATP to move along actin

Actin

Myosin binds to:

a.) DNA

b.) Actin

c.) Tubulin

d.) Intermediate filaments

Myosin-I

Myosin-I or Myosin-II?

• has a single globular head that attaches to actin filaments

• has a tail that attaches to another molecule such as an organelle, cargo or even the plasma membrane

• The head hydrolyzes ATP and can detach and reattach so that cargo moves along actin in a unidirectional way

Myosin-II

Myosin-I or Myosin-II?

• a dimer protein that has two globular heads (ATPases) and a coiled-coil tail

• Clusters of these molecules bind to each other through their coiled-coil tails, forming a bipolar myosin filament that has heads on each end

Myosin-I

Myosin-I or Myosin-II?

The head hydrolyzes ATP and can detach and reattach so that cargo moves along actin in a unidirectional way

Myosin-II

Myosin-I or Myosin-II?

forms a bipolar myosin filament that has heads on each end

Myosin-II

Myosin-I or Myosin-II?

Each head can bind to actin filaments and moves the filament in the opposite direction.

myofibrils

Most animal muscle cells are large multinucleated individual cells that contain _______ in their cytoplasm.

• composed of a chain of identical units

sarcomere

gives the myofibrils a stripped look

• composed of two filaments

  • Actin

  • Myosin-II

myosin

Thick or thin?

myosin

thin

Thick or thin?

actin

both

Thick myosin filaments are _____ positioned, and the thin actin filaments are extended inward from ____ end of the sacromere.

Z disc

Actin filaments are anchored by their plus end to a structure known as the

actin; myosin-II

Which two filaments is a sacromere composed of?

no change

Change or no change?

Muscle contraction is achieved by the sliding action of actin past the myosin filaments with _______ in the length of either type of filament

hydrolysis

The sliding motion in muscle contractions is generated by _____ of one ATP molecule by the head of myosin which causes a conformational change and the movement of the tip by a short distance.

unidirectional; shorten

The sliding motion in muscle contraction is repeated by each round of ATP hydrolysis, which propels myosin in a _______ way to ______ the sarcomere