Cytoskeleton

Question 1

How can you describe the epithelium?

Answer 1

-A tight,pavement like layer of brick-shaped cells

Question 2

Name the functions of the cytoskeleton
HINT:
Shape, proteins, organisation, vertebrates

Answer 2

• keeps the SHAPE, INTERNAL ORGANISATION and POLAARITY of cell
  • Made up of FILAMENTOUS PROTEINS
  • Provides a FRAMEWORK for organising cell components and processes
  • Like a “BONY SKELETON” in vertebrates

Question 3

Answer these questions about microfilaments:

1. What protein makes up microfilaments?
2. What protein organises microfilaments?

Answer 3

• polymers of the protein actin
• Organised into functional bundles by actin-binding proteins

Question 4

Answer these questions about microtubules:

1. What protein makes up microtubules?
2. Give an example of microtubules in cells
3. What proteins transport cargo along microtubules?

Answer 4

• Polymeric tubes formed from the protein TUBULIN
• Make up MITOTIC SPINDLES, FOR MITOSIS
• Proteins called KINESINS AND DYNEINS transport cargo along microtubules

Question 5

Answer these questions about intermediate filaments:
1. What are intermediate filaments assembled of?
2. What do they lend structural support to?
3. What do they as barriers to?

Answer 5

• polymers assembles by TISSUE SPECIFIC SUBUNITS
• Lend structural support to NUCLEAR MEMBRANE
• Serve structural and barrier functions in SKIN, HAIR AND NAILS

Question 6

SIGNALS IN CYTOSKELETON

• Cell organisation depends on cells ability to _____________
• Signals come from ____________ etc.
• Signals are detected by ______________ that activate _________________ to the cytoskeleton

Answer 6

• Cell organisation depends on cells ability to SENSE SIGNALS
• Signals come from ECM, ADJACENT CELLS etc.
• Signals are detected by CELL SURFACE RECEPTORS that activate SIGNAL TRANSDUCTION PATHWAY to the cytoskeleton

Question 7

NAME SIX PLACES WE FIND MICROFILAMENTS

Where do we see microfilaments
1. A tight bundle of filaments making the ____________
2. microfilaments form band around cell, ______________
3. Found at the front of the cell, ____________________
4. Bundles of filaments protrude from the lamellipodium called =____________
5. =________________ also attatch to the substratum

Answer 7

Where do we see microfilaments
1. A tight bundle of filaments making the MICROVILLI
2. microfilaments form band around cell, ADHERENS BELT
3. Found at the front of the cell, LEADING EDGE
4. Bundles of filaments protrude from the lamellipodium called FILOPODIA
5. STRESS FIBBERS also attatch to the substratum

Question 8

STRUCTURE OF G-ACTIN MONOMERS

• seperated into ___________ by _____________
• At the base of cleft is an __________ , which is where ___ and ____ binds.

Answer 8

• seperated into TWO LOBES by DEEP CLEFT
• At the base of cleft is an ATPase fold , which is where ATP and Mg2+ binds.

Question 9

STRUCTURE OF F-ACTIN
Structure is _________.

One end of filament (+) is designated for_________ of actin subunits

Other end of filament ____ is favored for _________ of subunits

On the ______ end, cleft is _________ to surrounding solution

Answer 9

STRUCTURE OF F-ACTIN
Structure is HELICAL.

One end of filament (+) is designated for ADDITION of actin subunits

Other end of filament (-) is favored for REMOVAL of subunits

On the (-) end, cleft is _______ to surrounding solution

Question 10

What are the three steps of actin polymerisation in vitro?

Answer 10

1. Nucleation
2. Elongation
3. Steady state

Question 11

NUCLEATION PHASE

• marked by a _________, (represents a delay) in which G-actin subunits combine into an _________.
• Acts as a “______”

Answer 11

NUCLEATION PHASE

• marked by a LAG PERIOD (represents a delay) in which G-actin subunits combine into an OLIGOMER.
• Acts as a “SEED” .

Question 12

ELONGATION
• short oligomer increases in length by addition of____________ to both ends.
• Concentration of addition decreases until ___________ is reached, a ________ state reached

Answer 12

• short oligomer increases in length by addition of ACTIN MONOMERS to both ends.
• Concentration of addition decreases until EQUILIBRIUM is reached, a STEADY state reached

Question 13

What occurs in steady-state phase?

Answer 13

Steady-state phase
• There is NO NET CHANGE in total length of filaments

Question 14

What needs to be reached in order for Nucleation of actin filaments to start?

What happens below this level?

What is the formula for this term?

Which side of the actin filaments have a lower critical concentration?

Answer 14

• Critical Concentration (Cc)
• Below this concentration filaments won’t form
• Critical concentration = rate of dissociation/rate of assembly
• ATP-actin units are added faster at the (+) end than at the (-) end of an actin filament, resulting in a lower critical concentration AT THE (+) END

Question 15

TREADMILLING
What is treadmilling?

What is it powered by?

Steps of treadmilling:
1. ___________ binds to the end of a filament
2. ATP is hydrolysed to ____________ and ___.
3. Pi is slowly released so filament is organised into three regions: 1. ___________, 2._______________, 3.___________.

Answer 15

1. ATP-G-ACTIN binds to the end of a filament
2. ATP is hydrolysed to ADP AND Pi (INORGANIC PHOSPHATE).
3. Pi is slowly released so filament is organised into three regions: 1. ATP-actin subunits (+)
4. ADP-Pi-actin in the middle
5. ADP-actin at the (-).

Question 16

Name the two actin-binding proteins we see help the process of treadmilling actin filaments

Answer 16

PROFILIN AND COFILIN

Question 17

PROFILIN
1. What does Profilin do? Name the two steps

2. How does Profilin benefit actin filaments?

Answer 17

• small protein that BINDS to ADP-actin.
• It opens the cleft and GREATLY ENHANCES LOSS OF ADP.
• DOES NOT ENHANCE treadmilling rate, but ensures a constant supply of ATP-actin formed from release of ADP-actin

Question 18

COFILIN
1. What does Cofilin bind to?

2. What does Cofilin do? 2 steps !

Answer 18

1. binds to ADP-actin subunits within F-actin

• BRIDGES two actin monomers
• BREAKS the filament into SHORT PIECES, generating more free (-) ends
• ENHANCING the NET ASSEMBLY of the filament.

Question 19

What does thymosin Beta-4 do?

Answer 19

1. Acts as a BUFFER for unpolymerised actin,
   - Makes ATP-ACTIN SUBUNITS AVAILABLE when they are needed

Question 20

What are the two proteins that block assembly and diassembly of actin filaments?

Answer 20

CAPZ and TROPOMODULIN

Question 21

MATCH the term to the definition
_________ a protein that inhibits the addition or loss on the (+) end of F-actin.

__________ inhibits filament assembly and disassembly by binding to the (-) end of an actin filament.

___________ can insert itself between subunits of the helix, and break the filament apart

1. CapZ 2.Tropomodulin 3. Gelsolin

Answer 21

MATCH the term to the definition
CAPZ a protein that inhibits the addition or loss on the (+) end of F-actin.

TROPOMODULIN inhibits filament assembly and disassembly by binding to the (-) end of an actin filament.

GELSOLIN can insert itself between subunits of the helix, and break the filament apart

1. CapZ 2.Tropomodulin 3. Gelsolin

Question 22

What do actin-nucleating proteins do?

What are the two major classes of actin-nucleating proteins?

Answer 22

1. INITIATE FORMATION of actin
2. Provide a SCAFFOLD or TEMPLATE for assembly
3. PROMOTE the formation of actin subunits

FORMIN and ARP2/3 COMPLEX

Question 23

What is the structure Formin?
HINT; donut , landing site

Answer 23

1. Two adjacent domains FH1 and FH2, they associate to form a “donut shape”
2. FH1 acts as a landing site for ATP-G-actin which are then fed into FH2 domain

Question 24

Arp2/3 Complex nucleate the assembly of ________ actin filaments
Needs to be activated by _____________________.

Answer 24

Arp2/3 Complex nucleate the assembly of BRANCHED actin filaments
Needs to be activated by NUCLEATION PROMOTING FACTOR (NPF)

Question 25

Arp2/3 activation and actin filament Nucleation 1. Two ____ domains bind to an two______ monomers. 2. Then ______ complex binds to the NPF-actin complex 3. Activated Arp2/3 complex binds to an ______________ and binds the ___ ends of actin subunits 4. Additional ________ assemble onto the __ end of new acting filament, which makes a characteristic _____ angle with old filament

Answer 25

Arp2/3 activation and actin filament Nucleation 1. Two NPF domains bind to two ACTIN monomers. 2. Then ARP2/3 complex binds to the NPF-actin complex 3. Activated Arp2/3 complex binds to an EXISTING ACTIN FILAMENT and binds the (-) ends of actin subunits 4. Additional G-ACTINS assemble onto the (+) end of new acting filament, which makes a characteristic 70 DEGREE angle with old filament

Question 26

What bacteria is able to use actin filaments to move? The bacteria _____ a normal cell mobility process, it forms a ________ that protrudes onto a neighboring cell and delivers _______ to that cell

Answer 26

Listeria Bacteria What bacteria is able to use actin filaments to move? The bacteria HIJACKS a normal cell mobility process, it forms a FILOPODIUM that protrudes onto a neighboring cell and delivers BACTERIUM to that cell

Question 27

Cross-linking proteins Name the four types of crosslinking proteins that assemble actin filaments

Answer 27

1. Fimbrin 2. Filamin 3. Spectrin 4.Alpha actin

Question 28

Match the crosslinking protein to the description 1. two f-actin binding sites / Builds bundles of filaments, forming a stereocilium 2. Has a flexible region binding between binding sites / forms stabilising cross links 3. Spans a large distance between filaments 4. Generates short rigid rods for stress fibers A. Filamin B. Spectrin C. Alpha-actinin D. Fimbrin

Answer 28

1. Fimbrin = two f-actin binding sites / Builds bundles of filaments, forming a stereocilium 2. Filamin = Has a flexible region binding between binding sites / forms stabilising cross links 3. Spectrin = Spans a large distance between filaments 4. Alpha-actinin = Generates short rigid rods for stress fibers

Question 29

What are the two proteins that bind to Spectrin molecules that attatch actin filaments to the membrane?

Answer 29

Ankyrin = binds halfway along a spectrin Glycophorin C - binds at actin binding domain of spectrin

Question 30

Contractile rings _____ the cell midway between the poles of __________ in a cell. When rings contract is pulls __________ apart, cytoplasm is divided, this process is called ___________.

Answer 30

Contractile rings ENCIRCLES the cell midway between the poles of MITOTIC SPINDLES in a cell. When rings contract it pulls PLASMA MEMBRANE apart, cytoplasm is divided, this process is called CYTOKENISIS.

Question 31

What are the four steps of cell migration?

Answer 31

1. Extension 2. Adhesion 3. Translocation 4. De-adhesion 5. Endocytic recycling

Question 32

Cell migration Part 1 In the extension step of cell migration, ______ is nucleated by __________ and so the filament _________. In the adhesion step, plasma membrane becomes firmly attatched to ___________. ___________ connect actin bundles to the cytoplasm In translocation, contents of the cell body are translocated forward. The ________ and other organelles move forward

Answer 32

Cell migration Part 1 In the extension step of cell migration, ACTIN is nucleated by ARP2/3 COMPLEX and so the filament ELONGATES. In the adhesion step, plasma membrane becomes firmly attatched to SUBSTRATUM INTEGRINS connect actin bundles to the cytoplasm In translocation, contents of the cell body are translocated forward. The NUCLEUS and other organelles move forward

Question 33

Cell migration Part 2 After translocation in cell migration, the ______ of the cell is brought forward, tail is seen to “__________” from its connections The next steps is ____________. Adhesion molecule at the rear of cell are transported by ____________ to the front of the cell to make new ______________. “Like a ______ rolling”

Answer 33

Cell migration Part 2 After translocation in cell migration, the TAIL of the cell is brought forward, tail is seen to “ SNAP LOOSE” from its connections The next steps is ENDOCYTIC RECYCLING. Adhesion molecule at the rear of cell are transported by ENDOCYTIC CYCLE to the front of the cell to make new SUBSTRATUM. “Like a TANK rolling”

Question 34

What is the definition of Chemotaxis

Answer 34

- movement of cell or organism toward or away from certain chemicals