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BCMB > Week 9 > Flashcards

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
Q

myosin

A

actin-based molecular motors with essential roles in many cellular processes.

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26
Q

myosin head/motor domain

A

Contains the ATP- and actin-binding sites and is responsible for converting the energy from ATP hydrolysis into mechanical work.

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27
Q

Myosin regulatory domain

A

Acts as a force transducing lever arm.

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28
Q

Myosin tail domain

A

Interacts with cargo proteins or lipid and determines its biologic function

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29
Q

Mechanochemical Pathway of Myosin

A

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.

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30
Q

Myosin regulation

A

regulated by phosphorylation and by interactions with actin- and myosin-binding proteins

31
Q

Intermediate Filaments

A

are major components of the cytoplasmic and nuclear cytoskeletons.

Essential in maintaining correct tissue structure and function.

32
Q

Extracellular Matrix (ECM)

A

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
Q

Adhesive ECM proteins

A

Fibronectin and laminin

Adhere ECM components together and to the cell surface

34
Q

Structural ECM proteins

A

Collagen provides tensile strength
Main protein found in bone, cartilage, tendon, skin
Elastin provides elasticity
Expands and returns to original shape

35
Q

Collagens

common structure, what differentiates a collagen

A

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
Q

Laminins

location, function

A

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
Q

Types of animal cell junctions

A

tight, gap, and anchoring junctions

38
Q 
Tight Junctions
(function, components/structure, location)
A

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
Q 
Gap Junctions
(function, components/structure, location)
A

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
Q 
Anchoring Junctions
(function, components/structure, location)
A

Attach cells to each other and to the ECM
Rely on cell adhesion molecules (CAM)
Cadherin and integrin

41
Q

4 categories of Anchoring junctions

A

Adherins junctions
Desmosomes
Hemidesmosomes
Focal adhesions

42
Q 
Adherens Junctions
(function, components/structure, location)
A

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
Q

Desmosomes

function, components/structure, location

A

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
Q

desmosomes can function as both…

A

adhesive structures and as signal transducing complexes

45
Q

Hemidesmosomes

function, components/structure, location

A

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
Q

Anchoring Junction Proteins: Cadherins

function, components/structure, location

A

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
Q

Anchoring Junction Proteins: Integrins

function, components/structure, location

A

Integrins are a type of CAM that connect cells to the ECM
Extracellular portion binds ECM
Intracellular portion binds cytoskeleton and signaling proteins

48
Q

Integrin structure

A

Integrins are composed of two distinct subunits, known as α and β chains.

49
Q

intern function

A

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
Q

affinity modulation

A

varying the binding strength of individual receptors

51
Q

avidity modulation

A

varying the clustering of receptors

52
Q

Integrins and Inside-Out Signaling

A

Changes in receptor conformation result from intracellular signals that originate elsewhere in the cell (e.g., at another receptor).

53
Q

Components of biological membranes

A

phospholipid bilayer, proteins, and carbohydrates

54
Q

Fluid-Mosaic Model

A

Membrane exhibits properties that resemble a fluid because lipids and proteins can move relative to each other within the membrane

55
Q

Fluidity

A

individual molecules remain in close association yet have the ability to readily move within the membrane

56
Q

types of membrane proteins

A

integral/intrinsic and peripheral/extrinsic

57
Q

Semifluid

A

most lipids can rotate freely around their long axes and move laterally within the membrane leaflet

58
Q

Flipflop” of lipids

A

lipids from one leaflet to the opposite leaflet does not occur spontaneously

59
Q

Flippase requires what molecule to transport lipids from one leaflet to the other

A

ATP

60
Q

Factors Affecting Fluidity

A

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
Q

Fatty acid saturation

A

refers to amount of Hydrogens bonded to Carbon

Saturated means no C=C double bonds

62
Q

Experiments on Lateral Transport

A

Larry Frye and Michael Edidin conducted an experiment that verified the lateral movement of membrane proteins

63
Q

What cells were fused in the Frye and Edidin experiments

A

Mouse and human cells

64
Q

How is the movement of some integral membrane proteins restricted?

A

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
Q

what type of microscopy can be used to study membranes?

A

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
Q

How is the transfer of Lipids to Other Membranes possible?

A

Lipids in ER membrane can diffuse laterally to nuclear envelope
Transported via vesicles
Lipid exchange proteins

67
Q

Cholesterol stabilization of membrane at high temperatures

A

Lipid becomes more fluid

Cholesterol becomes more rigid

68
Q

Cholesterol stabilization of membrane at low temperatures

A

Lipid becomes more rigid

Cholesterol becomes more fluid

69
Q

where can you find cholesterol in the membrane?

A

between phospholipids. Polar OH group by the heads and aromatic groups by the tails

70
Q

K+ channels function

A

function as water-filled pores that catalyze the selective and rapid transport of K+ ions.

71
Q

What do K+ channels catalyze?

A

catalyze selective and rapid ion permeation

72
Q

K+ channels-Selectivity Filter

A

catalyzes dehydration of ions, which confers specificity and speeds up ion permeation.

73
Q

What regulates K+ channels?

A

Membrane potential

BCMB (8 decks)

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