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Cell Bio 1-4 > Cell Bio 7 > Flashcards

Cell Bio 7 Flashcards

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1
Q

Actin filaments location

A

Found in the cortex near the outside of the cell, at the plasma membrane.

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2
Q

Actin can… (2 functions)

A

Receive signals soming from the outside of the cell, it receives signals from the extracellular matrix.

Critical for allowing cell movement. Cells can move in different ways, involving actin assembly + disassembly.

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3
Q

Actin Based Structures (3 cell types/functions)

A

Epithelial Cells
-Microvili; cell cortex; adherence belt

Migrating Cells

  • Filopodia
  • Lamellipodium
  • Stress fibers

Muscle

  • Phagocytosis
  • Moving endocytic vesicles
  • Contractile ring
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4
Q

Actin distribution in the plasma membrane

A

is not equally distributed in the plasma membrane.

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5
Q

Actin forms

A

different structures; bundles and networks.

more capabilities to form different structures.

bundles and networks are constantly changing as the cell moves

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6
Q

Adherens belt and stress fibers

A

Adherens belt: structure to epithelial cells.

Actin sturctures and stress fibers are responsible for movement.

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7
Q

Actin Structure

A

4 alpha in muscles
4 beta in cortex
4 gamma in stress fibers

Globular actin polymerizes into filamentous actin i.e microfilaments.

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8
Q

Globular protein

A

forms a protein with four domains; asymmetrical clover leaf with a cleft.

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9
Q

Cleft gives the protein polarity.

A

monomers polymerize in the same orientation so the cleft is on the same side.

non cleft end is always at one side.

(-) end is the cleft end; double helix that is completed after 72nm, one helix is turn is 36 nm.

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10
Q

When you isolate actin

A

You can add different proteins to it and these proteins will bind to actin.

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11
Q

Myosin S1

A

Coats actin, creates these arrowhead structure always pointing to the minus end.

Under the microscope this patterns shows barbed heads pointing to the minus end.

Myosin stabilizes actin, it is no longer dynamic now it is stable.

S1 coated piece of actin can be used as a nucleus.

Arrowheads point towards the minus end.

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12
Q

_____ ____ can be added to the stable piece of actin

Polymerization location + requirement

A

actin monomers

polymerization occurs fastest at the plus end.

you need to be above the critical concentration to get polymerization.

Actin monomers are growing into the filament, concentration of monomers is stable because the monomers are all being added to the filament.

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13
Q

Actin Assembly: Nucleation

A

If you have actin monomers above concentration they will polymerize.

It involves formation of a nucleus leading to a lag phase.

Proceed to elongation quicker if the nucleus is present.

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14
Q

The nucleus could be

A

An actin monomer

Or formin

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15
Q

Actin that’s being polymerized

A

Needs to be in the ATP form.

It needs to be energized + above cc.

You don’t need ATP hydrolysis for polymerization, ATP hydrolysis occurs after polymerization.

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16
Q

Plus end and minus end

A

Have different critical concentrations.

Both ends are exposed.

Minus end CC: 0.60 micrometers

Plus end CC: 0.12 micrometers

Plus end polymerizes faster because it has a lower critical concentration.

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17
Q

CC at 0.7

A

You get polymerization at both ends.

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18
Q

CC at 0.1

A

You don’t get any polymerization, you get depolymerization.

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19
Q

CC at 0.4

A

you will get polymerization the plus end and depolymerization at the minus end.

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20
Q

CC at 0.4

A

you will get polymerization the plus end and depolymerization at the minus end.

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21
Q

Treadmilling

A

You can add to one end and subtract from the other end, cc in between the two ccs.

Adding to one side (-) and removing from the (+) end.

It looks like the nucleus is moving to the other end.

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22
Q

Regulation of actin polymerization: Cellular concentration of G-actin is about 400 micrometers but CC is 0.12 micrometers…

A

Thymosin: binds to actin, the actin cannot polymerize even at a high concentration of free actin, lowering the amount of free actin by binding to it.

Profilin: promotes actin polymerization by charging G-ADP into G-ATP actin; actin can now polymerize

Cofilin: enhances depolymerization; it will cause depolymerization at critical concentration

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23
Q

Actin capping proteins

A

Blocking assembly and disassembly.

CapZ: binsd to the plus end leaving the minus end exposed; it can still polymerize but only above the CC.

Tropomodulin: binds the minus end.

By capping we regulate which end is going to grow and at what speed.

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24
Q

Actin-disrupting drugs

Study These Flashcards
A

Phalloidin comes from plants; it binds to and stabilizes actin in live cells, it is very specific to actin binding anc can be used to label fixed cells.

cytochalasin: depolymerizes actin filaments

25
Formin
Can bind to monomers and act as a nucleation site to increase the rate of polymerization. Acts only at the plus end Can only function when activated by Rho-GTP on the plasma membrane regulates the speed of growth and depolymerization
26
Arp2/3
Mediates filament branching Requires nucleation promoting factor (NPF) which both need to be activated In this state it will bind to an actin filament and cause branching. Arp2/3 forms a branch point and you get growth of a new filament at the plus end.
27
NPF
Nucleating promoting factor WASp or WAVE both bind to arop2/3. WASp is activated by cdc24 (in the plasma membrane) and WAVE works with RAC
28
Branching
Growth of a new plus end. A very powerful way to move things.
29
Listeria
Has a protein called Act/a causing the activation of arp2/3 causing rapid branching of actin moving the listeria quickly around in cells.
30
Arp2/3-dependent actin assembly can aid endocytosis
Branching is crucial to the movement of lots of things. Endocytic vesicles are being pushed around by actin polymerization. As the vesicle buds inwards actin is polymerized and branching (arp2/3) is responsible for pulling on the membrane and once the vesicle is formed we're moving the new vesicle around. arp2/3 is necessary for endocytosis
31
Arp2/3 dependent actin assembly can also aid phagocytosis
Actin can pull a membrane inqard or push a membrane outward. branching is pushing the membrane outwards.
32
Actin Binding Proteins
Give rise to different actin structures. Bind actin filaments and form bundles of networks Parallel actin bundles are held together by proteins
33
Microvili
Are projections of actin that push the PM outwards, actin needs to hold onto the PM. Actin bundles are held to the plasma membrane Ezrin Held together by fimbrin and alpha-actin.
34
Fimbrin
microvili filopedia focal adhesion
35
alpha-actin
stress fibers filopedia muscle Z line
36
Spectrin
cell cortex
37
Filamin
Loading edge Stress fibers Filopedia
38
Red Blood Cells Shape
Biconcave Actin Cortical skeleton just below the PM Shape is due to the actin cortical skeleton underneath the PM. ACS: actin network formed of short actin bundles linked together by spectrin. Ankyrin anchors the actin and spectrin network to the PM.
39
Muscle Cells
Use actin and myosin to work. Bound to the PM and extracellular matrix. Actin network is bound to the plasma membrane by the protein dystrophin. Allows the muscle cell to contract and pull on a ligament or a tendon.
40
If dystrophin is not working
The work done when the contractile unit contracts is not transmitted. Dystrophin needs to link the actin filament to the plasma membrane.
41
Myosin
Only Motor Protein Actin's Motor Protein Plus end directed. Myosin heavy chain has the head domain with ATPase activity that can move to the plus end of actin. Light chain regulate the step size and speed of movement, light chains bind the neck. Tail domain is apart of the light chain and can bind cargo (myosin doesn't bind cargo) Cleavage with proteases at different domains helps elucidate the function of myosin.
42
Myosin II
Main myosin in muscle cells. Contraction Forms thick filament. found between actin filaments; bipolar with head domains on both sides Two tails meet with head domains at the very end. Abundant and easy to purify. 8 nm
43
Myosin S1
Head domain is S1 myosin, that decorates the actin molecule that forms a certain shape and binds to the minus end. Head and neck domain with associated light chains (regulatory/essential) S1 can move but it needs ATP; so it binds and does not move; only decorates actin.
44
Myosin I
Can bind to membranes (no tail), it can move the actin filamed or the plasma membrane.
45
Myosin V
Binds to actin and uses ATP to move to the plus end and is involved in vesicle transport. 72 nm stepsize Each head is 36 nm apart
46
Sliding Filament Assay
Used to detect myosin powered movement; speed and components of movement Myosin fragments bind to a glass coverslip or glass slide. BSA washes unboud molecules. Fluorescently labeled actin filaments are added to the chamber. Some bind to myosin, in the presence of ATP myosin head is activated to walk towards the plus end of actin. Myosin is tethered to the glass slide, actin will slide. The fluorescent actin can be seen sliding.
47
Long neck
Faster velocity; more light chains is more velocity.
48
Rigor State
Myosin bound to actin in the absence of ATP; This myosin will bind to actin and remain bound.
49
Actin-Myosin Cycle
ATP binds to the myosin causing a conformational change. Myosin will release the actin. ATP hydrolysis occurs but the phosphate is not released hydrolysis causes a conformational change in the head. The head moves towards the plus end of the actin, binding to a new position at the plus end Hydrolysis allows the myosin head to bind a new molecule of ATP. Binding of a new ATP releases the Pi. Release of Pi causes another conformational change called the powerstroke; the head moves and moves the actin with it. Back to the rigor state
50
Skeletal Muscle Sarcomere Banding
Myosin II filaments are the A bande (no change in size) Z disks come closer together during contractions I bands decrease in size.
51
Sarcormere
Made up of actin and myosin in these specific structures
52
Z-disk
Vertical strcutures they dileneate one sarcormere from the other (one sarcormere between two Z-disks) Actin filaments are polymerized away from the Z-disk. (+) end of actin are at the Z disks. Myosin overlaps with actin. Myosin head bind the actin and move towards the plus end
53
A Band
Thick filament
54
I Band
Represents where actin is present but no myosin.
55
Shortening of the sarcormere
Muscle contractions
56
Actin filaments in skeletal muscles
Capped at the plus end by CapZ. Tropomodulin caps the (-) end to stabilize the actin. No polymerization/ depolymerization. Nebulin stabilizes actin. Actin filaments are overlapping with myosin thick filaments. These thick filaments sit in the center of the sarcormere. Titin is responsible for keeping the thick filaments at the center.
57
NMJ
AP travels down the pre synaptic neuron axon causing the opening of Ca+ channels. Ca+ rushes down into the cell and causes the release of acetylcholine. acetycholine binds to receptors on the sarcolemma causing a local depolerization (EPP). EPP travels on the membrane causing an action potential that travels down the t-tubules into the cell. AP travels near the sarcoplasmic reticulum and triggers the release of Ca++
58
Ca++ Release
almost instantly as the calcium comes out it is pumped back into the sarcoplasmic reticulum. Calcium is a secondary messenger, there is little calcium in the cytoplasm because phosphate and calcium form minerals in the cytoplasm, which we don't want.
59
Calcium + Actin
Calcium binds to troponin C resulting in a change in conformation that triggers tropomyosin to slide off of actin uncovering myosin binding sites on actin.

Cell Bio 1-4 (4 decks)

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