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Cell Biology > Chapter 17 > Flashcards

Chapter 17 Flashcards

1
Q

What are the three classes of filaments?

A

Intermediate filaments, microtubules, actin filaments

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2
Q

What is the structure of intermediate filaments?

A

Many strands twisted together. 2 monomers to dimers, then non covalent bonds creates tetramer from two dimers, and two tetramers are put end to end. Then they are twisted together.

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3
Q

True or False. Both ends of an intermediate filaments look identical.

A

true

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4
Q

Main function of intermediate filaments

A

Resists stretching/ tensile strength

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5
Q

What type of cells are intermediate filaments found in?

A

animal cells

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6
Q

Where are intermediate filaments found?

A

nucleus and cytosol

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7
Q

Are intermediate filaments dynamic?

A

no-they cannot shrink and grow

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8
Q

Are intermediate filaments polar?

A

No-the ends are identical

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9
Q

Do intermediate filaments have motor proteins?

A

No, because there is no polarity

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10
Q

Do intermediate filaments use energy?

A

No, since there are no motor proteins to use energy

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11
Q

List the types of intermediate filaments?

A

keratins (most diverse) , vimentin (connective tissues, muscle cells, and neuroglial cells), neurofilaments (nerve cells), nuclear lamins (animal cells). ONLY one in nulceus are the nuclear lamins the rest are found in the cytoplasm.

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12
Q

Why is it important that intermediate filaments resist stretching?

A

the cells would rupture without the intermediate filaments. (Epidermolysis Bullosa)

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13
Q

What type of junction join two intermediate filaments together?

A

desmosomes

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14
Q

What is plectin?

A

cross links filament bundles- connects intermediate filaments to actin and microtubules - holds intermediate filaments to desmosomes/hemidesmosomes

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15
Q

Where are microtubules found?

A

Interphase cells, dividing cells, ciliated cells

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16
Q

Explain the structure of microtubules.

A

Alpha and beta components
Beta- positive end
Alpha- negative end

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17
Q

How do microtubules grow and shrink in vitro?

A

They grow and shrink from both ends but grow faster at the plus end

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18
Q

How do microtubules grow and shrink in a cell?

A

They only add on the positive end (Beta)

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19
Q

Microtubules growing around a centrosome.

A

13 strands around the circle, (-) end at the centrosome. The nucleating sites are starting sites, the rings act as the starting place.

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20
Q

What are the functions of microtubules?

A

intracellular transport (cargo), cilia and flagella, and divide chromosomes during mitosis and meiosis

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21
Q

Are microtubules dynamic?

A

yes, dynamic instability
in cells
1/2 tubulin is free as dimers
1/2 tubulin is in microtubules

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22
Q

Are microtubules polar?

A

yes beta(+) and alpha (-)

23
Q

Do microtubules have motor proteins?

A

yes
kinesin- (+) end directed
dynein- (-) end directed

24
Q

Do microtubules use energy?

A

Yes

25
Q

Conditions to growing microtubule.

A

Addition needs to stay ahead of hydrolysis. (Hydrolyzed is not stable and curl away.) The addition of GTP then P leaves and become GDP, this process must stay ahead of the hydrolysis

26
Q

What is the shrinking of microtubules called?

A

Catastrophe- when the GTP cap falls off it leads to rapid shrinkage then a rescue occurs and it regains the GTP cap and then rapid growth with the GTP capped end

27
Q

Why is shrinking and growing of microtubule important?

A

the shrinking and probing allows them to probe and it allows for flexibility (movement of cells)

28
Q

How are microtubules involved in the cell cycle?

A

they pull the sister chromatids apart during the M phase.

29
Q

how are microtubules involved in moving cargo?

A

They act as tracks for moving around the cell. can move 10cm/day

30
Q

Microtubules motors

A

They walk, not run. (something is always bound -processive) The lagging head loses a phosphate and the ATP becomes ADP then it wraps tighter and the leading head becomes the lagging head and it starts moving the other direction. And repeat.

31
Q

What happens if there is no ATP in the in the microtubules motors?

A

Stuck in step 2. the heads could not switch.

32
Q

Which motor proteins moves which direction on the microtubule?

A

Kinesins- moves to the positive end

dyneins- move toward the negative ends

33
Q

Which motor proteins move orgenelles

A

Kinesine moves the ER

Dyneins moves the golgi

34
Q

True of False bacteria cilia is different from other cilia

A

True

35
Q

Explain the structure of cilia and flagella microtubules

A
  • 9+2 array-9 doublets and 2 singlet
  • Outer and inner dynein arms that act as motors
  • the radial spoke controls which walks and when (regulator)
  • nexin attaches to doublets to keep it from falling apart
36
Q

What happens to the motor dynein with and without nexin?

A

Without- produces microtubule sliding

With- bends not slides, flagellum dynein causes microtubule bending

37
Q

What do actin filaments do?

A

Help cells move and adopt different shapes

i.e. microvilia and cleavage furrow

38
Q

Explain the structure of actin

A 
One type of subunit-actin
two double stranded helix
polar- (+) and (-) end
flexable
Smallest
39
Q

What is treadmilling?

A

Actin adds faster on the (+) end, lose faster on the (-) end.
ATP- instead of G protein -> bound tightly

40
Q

What are the functions of actin?

A

nucleating protein, monomor sequestering protein, bundling protein in filopodia, motor protein, side binding protein, capping end blocking protein, cross linking protein in cell cortex, severing protein.

41
Q

How much of all protein is actin? and the monomer to filament ratio?

A

5%

50/50

42
Q

How do actin filaments grow?

A

Adds to the plus end
Adds to radio labeled actin
Put subunits in a mixture of actin filaments when conditions favor polymerization-> determines positive end. (NOT REAL CHARGES)

43
Q

Explain Actin Nucleation and Polymerization

A

The (+) end looks just like actin (+) end.
ARP- actin related protein
The (-) end has the ARP and actin monomers add to the positive end.
This is faster than tread milling because you will not lose and have a start point.
The actin branches at 70 degree angles

44
Q

Explain the cell cortex and cell movement with actin?

A 
The leading edge has actin polymerizing 
The back end has actin depolymerizing 
This pulls the cell forward (ameoboid movement) 
lamellipodium- sheet of membrane 
filopodium- finger like
45
Q

How does the actin orientate itself in actin in lamellipodia?

A

Heads to the leading edge (+) they all point upward

They stretch in the front while disasembleing in the back end which pulls it up

46
Q

Small G protein regulators of actin dynamics

A

Quiescent- quiet non stimulated
Rho- Contractile bundle
Rac- lamellipodia
Cdc42 filopodia

GTP bound is active

47
Q

Actin modifying drugs

A
  • caps filament plus end- limits growth
  • severs filaments- breaks apart
  • binds subunits and prevents their polymerization- prevent new from forming
48
Q

What are the units in a contracting myofibrils in muscle cells?

A

repeating linear array of contractile units call sacromers.

49
Q

Myosin motors

A 
Plus end directed 
ATP is the energy source
Not persessive- no double head
Use multiple myosins 
ATP-hydrolysis
Myosin motors walk along actin
50
Q

Myosin motors walk along actin

A
  • either actin or myosin moved- they move in relation to each other
  • Myosin head attached to actin with ATP
  • the ATP lets go
  • Hydrolosis of ATP occurs and ADP and P are produced
  • A power stroke occurs and starts back in the start of the new cycle
  • at the end of the cycle the myosin head is again locked tightly to the actin filament
51
Q

Muscle myosin

A

the heads go in two different directions.

the cytoplasm is filled with myofibrils made of actin and myosin

52
Q

Muscle contraction

A
  • Troponin- binds calcium
  • Calcium- required for muscle contraction
  • Sarcoplasmic reticulum- stores calcium
  • Tropomyosin- inhibits myosin binding
53
Q

Ca2+ activatates contraction

A
  • releases ca2+ from the sarcoplasmic reticulum
  • Ca2+ binds to protein and the protein binds to actin and blocks myosin
  • Tropoinin will move and drag tropomyosin with it.

Cell Biology (2 decks)

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