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Week 9 Flashcards

1
Q

3 types of cytoskeletal polymers

A

actin filaments, intermediate filaments, and microtubules

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2
Q

cytoskeleton is made of

A

protein polymers

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3
Q

Cytoskeleton can form….

A

polarized, highly dynamic, self-organizing structures

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4
Q

Microtubule function

A

function in concert with molecular motors that generate force and move vesicles and other complexes along the microtubule surface.

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5
Q

Cells use microtubules to provide…

A

structural support because microtubules are the strongest of the cytoskeletal polymers

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6
Q

Do microtubules have polarity?

A

Yes. Positive end is crowned by β-tubulin and assembles faster.
The negative end is crowned by α-tubulin and assembles slower

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7
Q

Tubulin Polymerization

A

Microtubule polymerization begins with the formation of a small number of nuclei (small polymers).

Microtubules polymerize by addition of tubulin subunits to both ends of the polymer.

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8
Q

critical concentration

A

A critical concentration of tubulin subunits always remains in solution. The concentration of tubulin must be above the critical concentration (Cc) for assembly to occur.

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9
Q

is there a net change in polymerization at critical concentration?

A

No. There is no net change

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10
Q

Dynamic Instability

A

the process where microtubules are constantly switching between phases of growth and shortening
Driven by GTP hydrolysis

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11
Q

microtubule rescue

A

The transition from shortening to growing

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12
Q

microtubule catastrophe

A

The transition from growing to shortening states

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13
Q

Straight proto-filaments indicate…

A

the growing end and have lateral and longitudinal bonds to stabilize them

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14
Q

curled proto-filaments indicate…

A

the shortening end. They bend back & away form the microtubule lattice. Eliminates the lateral bonding

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15
Q

how GTP Hydrolysis Drives Dynamic Instability

A

Growing microtubules have a cap of GTP-tubulins at their tip because the GTP associated with β-tubulin is hydrolyzed to GDP shortly after a subunit adds to a microtubule

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16
Q

Why Do Cells Have Dynamic Microtubules?

A

Dynamism of microtubules is vital for cell function

slide 15

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17
Q

Interactions Between Microtubules and Actin Filaments

A

Microtubules and actin filaments function together during cell locomotion and cell division.

In general, microtubules direct where and when actin assembles or generates contractile forces.

Microtubules influence the actin cytoskeleton through direct binding or indirect signaling.

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18
Q

Actin

A

Exists as both a monomer called G-actin and as a filamentous polymer called F-actin

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19
Q

Actin structure

A

The actin filament is structurally polarized and the two ends are not identical.

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20
Q

Actin Polymerization

A

De novo actin polymerization is a multistep process that includes nucleation and elongation steps.
The rates of monomer incorporation at the two ends of an actin filament are not equal

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21
Q

When do Actin Subunits Hydrolyze ATP

A

after polymerization.
Actin monomers can be bound to ATP, ADP+Pi, or ADP alone.

The critical concentration for actin assembly depends on whether actin has bound ATP or ADP

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22
Q

Actin-Binding Proteins

A

Regulate actin polymerization and organization
Associate with monomers or filaments and influence the organization of actin filaments in cells
The cell uses these proteins to regulate motility

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23
Q

G-protein Regulation of Actin Polymerization

A

Members of the Rho family of small G proteins regulate actin polymerization and dynamics.

Activation of Rac, Rho, and Cdc42 proteins induces formation of lamellipodia, contractile filaments, and filopodia, respectively

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24
Q

Myosins cellular role

A

Myosin proteins are energy transducing machines that use ATP to power motility and generate force along actin filaments.
Some myosins power muscle and cellular contractions, whereas others power membrane and vesicle transport, regulate cell shape and polarity and participate in signal transduction and sensory perception pathways.

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25
myosin
actin-based molecular motors with essential roles in many cellular processes.
26
myosin head/motor domain
Contains the ATP- and actin-binding sites and is responsible for converting the energy from ATP hydrolysis into mechanical work.
27
Myosin regulatory domain
Acts as a force transducing lever arm.
28
Myosin tail domain
Interacts with cargo proteins or lipid and determines its biologic function
29
Mechanochemical Pathway of Myosin
Myosin’s affinity for actin depends on whether it’s bound to ATP, ADP-Pi, or ADP. Myosins with bound ATP or ADP-Pi are in weak binding states, and will rapidly associate and dissociate from actin Myosins with either bound ADP or no nucleotide are in strong binding states.
30
Myosin regulation
regulated by phosphorylation and by interactions with actin- and myosin-binding proteins
31
Intermediate Filaments
are major components of the cytoplasmic and nuclear cytoskeletons. Essential in maintaining correct tissue structure and function.
32
Extracellular Matrix (ECM)
Network of material secreted from the cells forming a complex meshwork outside of cells Major component of certain parts of plants and animals (Bone and cartilage of animals Woody parts of plants)
33
Adhesive ECM proteins
Fibronectin and laminin | Adhere ECM components together and to the cell surface
34
Structural ECM proteins
Collagen provides tensile strength Main protein found in bone, cartilage, tendon, skin Elastin provides elasticity Expands and returns to original shape
35
Collagens | common structure, what differentiates a collagen
Many different genes encode procollagen All collagens have a common triple helix structure Similar yet different amino acid sequences affect structure and function of each specific type of collagen
36
Laminins | location, function
Found in virtually all tissues of vertebrate and invertebrate animals. The principal functions of laminins are to provide an adhesive substrate for cells and to resist tensile forces in tissues.
37
Types of animal cell junctions
tight, gap, and anchoring junctions
38
``` Tight Junctions (function, components/structure, location) ```
Forms tight seal between adjacent cells Prevents ECM from leaking between cells Made by occludin and claudin Bind to each to form tight seal Not mechanically strong, not strongly associated to cytoskeleton
39
``` Gap Junctions (function, components/structure, location) ```
Small gap between plasma membranes of cells at junction Six connexin proteins in one cell align with six connexin proteins in an adjacent cell to form a connexon Connexon allows passage of ions and small molecules Allow adjacent cell to share metabolites and directly signal each other
40
``` Anchoring Junctions (function, components/structure, location) ```
Attach cells to each other and to the ECM Rely on cell adhesion molecules (CAM) Cadherin and integrin
41
4 categories of Anchoring junctions
Adherins junctions Desmosomes Hemidesmosomes Focal adhesions
42
``` Adherens Junctions (function, components/structure, location) ```
junctions are a family of related cell surface domains that link neighboring cells together. Adherens junctions contain transmembrane cadherin receptors and link the cells actin cytoskeletons together
43
Desmosomes | function, components/structure, location
intermediate filament-based cell adhesion complexes. The principal function of desmosomes is to provide structural integrity to sheets of epithelial cells by linking the intermediate filament networks of cells.
44
desmosomes can function as both...
adhesive structures and as signal transducing complexes
45
Hemidesmosomes | function, components/structure, location
Hemidesmosomes, like desmosomes, provide structural stability to epithelial sheets. Hemidesmosomes are found on the basal surface of epithelial cells, where they link the ECM to the intermediate filament network via transmembrane receptors.
46
Anchoring Junction Proteins: Cadherins | function, components/structure, location
Cell Adhesion Molecules (CAMs) that create cell-to-cell junctions Ca2+ dependent adhering molecule Extracellular domain of two cadherins, each in adjacent cells, bind to each other to promote cell-to-cell adhesion
47
Anchoring Junction Proteins: Integrins | function, components/structure, location
Integrins are a type of CAM that connect cells to the ECM Extracellular portion binds ECM Intracellular portion binds cytoskeleton and signaling proteins
48
Integrin structure
Integrins are composed of two distinct subunits, known as α and β chains.
49
intern function
Integrins are signaling receptors that control both cell binding to ECM proteins and intracellular responses following adhesion. Integrins have no enzymatic activity of their own. Instead, they interact with adaptor proteins that link them to signaling proteins.
50
affinity modulation
varying the binding strength of individual receptors
51
avidity modulation
varying the clustering of receptors
52
Integrins and Inside-Out Signaling
Changes in receptor conformation result from intracellular signals that originate elsewhere in the cell (e.g., at another receptor).
53
Components of biological membranes
phospholipid bilayer, proteins, and carbohydrates
54
Fluid-Mosaic Model
Membrane exhibits properties that resemble a fluid because lipids and proteins can move relative to each other within the membrane
55
Fluidity
individual molecules remain in close association yet have the ability to readily move within the membrane
56
types of membrane proteins
integral/intrinsic and peripheral/extrinsic
57
Semifluid
most lipids can rotate freely around their long axes and move laterally within the membrane leaflet
58
Flipflop” of lipids
lipids from one leaflet to the opposite leaflet does not occur spontaneously
59
Flippase requires what molecule to transport lipids from one leaflet to the other
ATP
60
Factors Affecting Fluidity
Length of fatty acyl tails. Presence of double bonds in the acyl tails. Presence of cholesterol. Cholesterol tends to stabilize membranes. Effects depend on temperature.
61
Fatty acid saturation
refers to amount of Hydrogens bonded to Carbon | Saturated means no C=C double bonds
62
Experiments on Lateral Transport
Larry Frye and Michael Edidin conducted an experiment that verified the lateral movement of membrane proteins
63
What cells were fused in the Frye and Edidin experiments
Mouse and human cells
64
How is the movement of some integral membrane proteins restricted?
may be bound to components of the cytoskeleton, which restricts the proteins from moving laterally. Also, membrane proteins may be attached to molecules that are outside the cell, such as the interconnected network of proteins that forms the extracellular matrix
65
what type of microscopy can be used to study membranes?
Transmission electron microscopy (TEM) and Freeze fracture electron microscopy (FFEM), specialized form of TEM, can be used to analyze the interiors of phospholipid bilayers
66
How is the transfer of Lipids to Other Membranes possible?
Lipids in ER membrane can diffuse laterally to nuclear envelope Transported via vesicles Lipid exchange proteins
67
Cholesterol stabilization of membrane at high temperatures
Lipid becomes more fluid | Cholesterol becomes more rigid
68
Cholesterol stabilization of membrane at low temperatures
Lipid becomes more rigid | Cholesterol becomes more fluid
69
where can you find cholesterol in the membrane?
between phospholipids. Polar OH group by the heads and aromatic groups by the tails
70
K+ channels function
function as water-filled pores that catalyze the selective and rapid transport of K+ ions.
71
What do K+ channels catalyze?
catalyze selective and rapid ion permeation
72
K+ channels-Selectivity Filter
catalyzes dehydration of ions, which confers specificity and speeds up ion permeation.
73
What regulates K+ channels?
Membrane potential

BCMB (8 decks)

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