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MCB 3010 > The extracellular matrix of animal connective tissues > Flashcards

The extracellular matrix of animal connective tissues Flashcards

1
Q

The classes of macromolecules that constitute the ECM are broadly similar, but it is the variation in their ___________and their _________ that give rise to diversity of tissues.

A

Relative amounts, organization

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2
Q

The ECM can become

A

can become calcified to become bone or teeth or it can become the transparent substance of the cornea or the rope-like organization of tendons

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3
Q

Matrix molecules are secretes by cells called

A

fibroblasts

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4
Q

In certain specialized connective tissues such as cartilage and bone, fibroblasts have specific names such as ________ and ________, respectively.

A

Chondrocytes, osteoblasts

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5
Q

The matrix in connective tissue is constructed from the same two main classes of macromolecules as in basal laminae:

A

1) glycosaminoglycan (GAG) polysaccharide chains usually covalently linked to proteins in the form of proteoglycans
2) fibrous proteins such as collagen.

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6
Q

Polysaccharides

A

resists compressive forces on the matrix while permitting rapid diffusion of nutrients, metabolites, and hormones between the blood and tissue cells

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7
Q

Collagen fibers

A

strengthen and help organize the matrix, while other fibrous proteins such as elastin (rubber-like) give it resilience.

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8
Q

Major protein of the extracellular matrix

A

Collagens

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9
Q

Collagens are secreted in large quantities by _______ and small quantities by _______

A

Connective tissue cells, many other cell types

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10
Q

What is the principal collagen of skin and bone

A

Type I collagen

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11
Q

After being secreted into the extracellular space, these collagen molecules assemble into higher order polymers called

A

collagen fibrils

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12
Q

Primary feature of a typical collagen molecule

A

its long, stiff, triple-stranded helical structure, in which three collagen polypeptide chains called α chains are wound around one another in a rope-like superhelix.

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13
Q

What are collagens extremely rich in that are found every 3rd a.a

A

Glycine

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14
Q

What does glycine allow for

A

allows the three helical α chains to pack tightly together to form the final collagen superhelix

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15
Q

What is found under the fibroblast cell

A

Long strands of collagen fibrils

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16
Q

Post-translational modifications collagen chains undergo

A

Individual collagen polypeptide chains are synthesized on membrane-bound ribosomes and injected into the lumen of the rough endoplasmic reticulum as large precursors called pro-α chains. After being trimmed, hydroxylated and glycosylated, each pro-α chain then combines with two others to form the triple-stranded, helical procollagen

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17
Q

________ and ________ are infrequently found in other animal proteins

A

Hydroxylysines and hydroxyprolines

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18
Q

What gives tissues their elasticity

A

Elastin

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18
Q

Vertebrate tissues need to be both ______ and ______

A

strong, elastic

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19
Q

What makes vertebrate tissue strong and elastic

A

Strong: collagen
Elastic: elastin

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20
Q

A network of elastic fibers in the ECM of these tissues
gives them the required __________- so that they can recoil after transient stretch.

A

Resilience

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21
Q

How is stretching and tearing limited

A

Long, non-elastic collagen fibrils are interwoven with elastic fibers

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22
Q

Like collagen, elastin is

A

unusually rich in proline and glycine

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23
Q

Unlike collagen, elastin is

A

not glycosylated and contains hydroxyproline but not hydroxylysine

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24
Q

The precursor of elastin

A

Soluble tropoelastin

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25
Q

How are elastic fibers assembled at the PM?

A

Soluble tropoelastin is secreted into the extracellular space and assembled into elastic fibers

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26
Q

What happens after secretion of tropoelastin

A

Tropoelastin becomes highly crosslinked to one another between lysines

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27
Q

The elastin protein is composed largely of WHAT two types of short segments that alternate along the polypeptide chain

A

1). hydrophobic segments which are responsible for the elastic properties
2 alanine- and lysine-rich alpha-helical segments which form cross-links between adjacent molecules

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28
Q

Fibronectin

A

an extracellular protein that helps cells attach to the matrix

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29
Q

The ECM contains a number of

A

non-collagen proteins with
binding sites for other matrix macromolecules and for cell-surface receptors

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30
Q

Fibronectin is found where an is important for

A

large glycoprotein found in all vertebrates and important for many cell-matrix interactions

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31
Q

What happens to mice that cant synthesize fibronectin

A

die early in embryogenesis because their endothelial cells are unable to form proper blood vessels.

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32
Q

Fibronectin is a dimer composed of

A

two very large subunits joined by disulfide bonds at one end

33
Q

What regulates the assembly of fibronectin fibrils

A

Tension exerted by cells

34
Q

Fibronectin in soluble form

A

Circulates in the blood and other bodily fluids

35
Q

Fibronectin in insoluble form

A

Fibronectin dimers are cross-linked to one another by additional disulfide bonds in the ECM

36
Q

Difference between fibrillar collagen and fibronectin molecules (form and assembly)

A

Fibrillar collagen can form fibrils in test tubes alone, fibronectin molecules only assemble into fibrils on the surface of cells and only where the cells possess appropriate binding partners such as integrins

37
Q

Integrins provide

A

A linkage from the fibronectin outside of a cell to the actin cytoskeleton inside

38
Q

Fibronectin binds to cells through an

A

RGD motif that bind integrins

39
Q

What molecules assemble into fibrils where cells possess integrins or binding partners

A

Fibronectin

40
Q

The ability to cut through the matrix is crucial in two ways

A

1) it enables cells to divide while embedded in the
matrix;
2) it enables them to travel through it

41
Q

Matrix degradation is exploited by __________ to spread through the body

A

Cancer cells

42
Q

Cells degrade matrix components through extracellular ___________ that act close to the cells that produce them

A

cancer cells

43
Q

Many of these proteases belong to one of two general classes:

A
  • 1) matrix metalloproteases, which depend on bound
    Ca 2+ and Zn2+
  • 2) serine protease, which have a highly reactive serine
    in their active site
44
Q

Some are highly specific and only cleave particular
proteins in a few sites such as _________

A

collagenases

45
Q

Less specific proteases

A

Act just where needed as they are anchored to the plasma membrane

46
Q

We can restrict the breakdown of the ECM by

A
  1. Having the protease be very specific in which type of ECM it is going to break down
  2. Limit its location by anchoring the protease to a specific structure
47
Q

Local activation

A

Many proteases are secreted as inactive
precursors that can be activated when needed.
Plasminogens are inactive proteases in the blood that,
when cleaved by plasminogen activators, yield the active protease plasmin which helps break up blood clots.

48
Q

Confinement by cell-sruface receptors

A

Many cell-surface
receptors bind to proteases confining the enzyme to
where it is needed. An example is urokinase plasminogen
activator which is found at the leading edge of migrating cells. (limited by location)

49
Q

Secretion of inhibitors

A

Secreting protease inhibitors such as tissue inhibitors of metalloproteases (TIMPs) and the serine protease inhibitors known as serpins.

50
Q

The matrix exerts powerful influences on the cells through

A

Transmembrane cell adhesion proteins that act as matrix receptors

51
Q

The principal receptors on animals cells for binding
most ECM proteins are the

A

Integrins

52
Q

Integrins bind

A

Laminins and fibronectins

53
Q

Integrins (large family of transmembrane adhesion molecules) have the ability to

A

transmit signals in both directions across the cell membrane

54
Q

Integrins are _______ that link to the cytoskeleton

A

Transmembrane heterodimers

55
Q

An integrin molecule is composed of

A

Two non-cavalently associated glycoproteins called alpha and beta

56
Q

Integrin: The __________ portion binds to ECM proteins such as laminin or fibronectin, or to ligands on the surface of other cells

A

Extracellular

57
Q

Integrins: the intracellular portion binds to _______ via

A

Binds to actin via the protein talin and a set of anchorage proteins

58
Q

True or false: integrins can switch between an active and an inactive conformation

A

True

59
Q

What does a cell crawling through a tissue have to be able to do

A

has to be able to make and break attachments to the matrix and to do so rapidly if traveling quickly.

60
Q

If force is to be applied where it is needed, the
making and breaking of attachments has to be

A

coupled to the assembly and disassembly of
cytoskeletal attachments inside the cell.

61
Q

As an integrin binds to or detaches from its ligands,
it undergoes _________________ that affect
both the intracellular and the extracellular end of
the molecule.

A

conformational changes

62
Q

Outside-in integrin activation

A

Stimulus binds to the RGD domain of fibronectin, inducing a structural change that causes the talin binding domain to be revealed which allows the integrin (and ECM via fibronectin) to be linked to the cytoskeleton inside the cell

63
Q

Talin links

A

The integrin to the cytoskeleton

64
Q

Inside-out integrin activation

A
65
Q

In _________ and ______, the ability to regulate integrin activity via inside-out signalling is particularly important

A

White blood cells, platelets

66
Q

Repeated adhesion allows

A

A cell to circulate
unimpeded until it encounters an appropriate
stimulus

67
Q

True or false: Integrins do not need to be synthesized de novo therefore the signal is rapid

A

True

68
Q

True or false: In inside-out integrin signalling, the signal could still have originated from outside the cell BUT the activation of the integrin specifically is going in an inside out order

A

True

69
Q

Inside-out signalling PIP2

A

PIP2 activated Talin, Talin binds b-integrin, conformational change to open integrin, binds ECM

70
Q

Integrins differ from RTK’s in that

A

they bind their ligand with lower affinity and are therefore more abundant (10-100-fold) at the cell surface

71
Q

The Velcro principle

A

Many receptor ligand interactions give increased
strength to the adhesion between cell and ECM
–> multiple low affinity bonds cause higher strength

72
Q

ECM attachments act through ________ to control
cell proliferation and survival

A

Integrins

73
Q

Integrins activate ______________ to allow a cell to behave according to its
surrounding matrix

A

Intracellular signalling pathways

74
Q

What happens when cells lose contact with their ECM

A

They initiates apoptosis
ANCHORAGE-DEPENDENCE

75
Q

FAK is recruited by

A

intracellular anchor proteins such as talin

76
Q

How is docking site for the Src family of tyrosine kinases (Fyn)

A

The clustered FAK molecules cross-phosphorylate each other on a specific tyrosine

77
Q

What does FAK do

A

FAK helps disassemble focal adhesions

78
Q

Outside-in signaling is relayed from integrins, via
_____ and ________- kinases into the cell.

A

FAK and Src-family kinases

79
Q

Mutant mice lacking FAK

A

their fibroblasts still adhere to fibronectin and form focal adhesions. But they
form too many focal adhesions and do not migrate

MCB 3010 (20 decks)

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