Topic 6: ECM and Integrins Flashcards by Bernice Baah

what are the main classes of the ECM?

Basal Lamina
connective tissue

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what is the ECM made from?

network of polysaccharides and proteins secreted by cells and embed other cells

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what is the function of the ECM?

hold the shape of cell and mechanical properties
holds cells and tissues together

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what is the function of connective tissue?

to support the structure of the body

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what are the 4 functions of the basal lamina?

filters what comes form epithelial cells and goes to the connective tissue
scaffold for the regenerating cells
support to overlying epithelium or endothelium
guide cells for embryonic development

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what is the Basal lamina?

aka the basement membrane
a thin sheet of extracellular matrix that separates the epithelial cells and the connective tissue and provides a connection between them
(under the epithelial cells)
kind of a filter between them

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what is connective tissue made from?

made from fibers and proteins to create a framework and support structure for body tissues and organs
- majority of the ECM volume in connective tissue is secreted by fibroblasts cells

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what are the 2 types of specialized connective tissue?

bones and cartilage

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what are the 3 types (classes) of molecules in the ECM?

proteoglycans
structural proteins
adhesive glycoproteins

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what is GAG and what is the usual animo acid it contains?

a unbranded chain of alternating polysaccharides of an animo sugar and uric acid that are both usually sulphated

N-acetylglucoamine or N-acetygalatosmine

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what is proteoglycan?

is it a group of glycoproteins that contain a one or more of the core protein glycosaminoglycan (GAG)

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an example of proteoglycan?

perlecan

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what is the characteristics of GAG?

highly charged
very hydrophilic
fills up most of the extracelluar space
attracts water and cation to create gel for collagen to get stuck in
water in it makes it withstand compressive forces

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what are the 4 types of GAGs and which is the simplest?

hyaluronan (simplest)
heparin sulfate
chondroitin sulphate
keratan sulfate

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describe hyaluronan and the characteristics

D- glucuronic acid
N-acetyl-D- glucosamine
B(1-3) linkage
simplest
not sulphated
not linked to any core protien

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describe chondroitin (or dermatan)

D-glucuronic acid/L-iduronic acid
N-acetyl-D-galactosamine
a/B(1-3) linkage
O linked

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describe heparin sulfate

D-glucuronic acid/L-iduronic acid
N-acetyl/N-sulfo -D-glusamine
a/B(1-4) linkage
O- linked

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describe keratan sulfate

D-galactose
N-acteyl-D-glucoamine
B(1-4) linkage
N-linked

what is the difference between proteoglycans and other glycoproteins

at least one of the sugars in a glycoprotein have to be a GAG
the long chain if unbranched GAG can comprise most of the weight of the molecule
they are very diverse

what is aggrecan?

it is a major component of cartilage
- its backbone is mostly made up of hyaluronan and can be modified by GAG
- gel like properties
- attaches toothed aggrecan non covalently

what is the function of proteoglycan and what does it bind to?

bind to other matrix proteins like collagen and adhesive glycoproteins
regulate the activity of secreted signalling proteins by functioning as a cell surface co receptor

what are the types of structural protein

collagen
elastins

what is collagen?

the most abundant protein in mammals (25%) used as structure for cells

what are the important types of collagen (where are they found?)

type 1 - skin, tendons and internal organs
type 4- basal lamina
type 9 & 12 - cartilage

describe the structure and function of Type 1 collagen

- long strong fibers with huge TENSILE STRENGH to withstand the force of the bones - construction of bone (30%) - secreted by fibroblast in connective tissue

describe the structure and function of Type 4 collagen

form a branching network that is founding he basal lamina

what types of collagen help co assemble type 1 collagen

Type 5 and 9 (minor fibrillar collagens)

describe the structure and function of Type 9 and 12 collagen

in cartilage, they are covalently bound at regular intervals along the type 2 fibrils to allow them to be more loosely associated to the cartilage

what is the formation of collagen fibril

1) synthesis of individual alpha chain in the pro peptides in the rough ER 2) the pro peptides associate to form trimers and selected proline and lysine residues get hydroxylated 3) those modifications allow trimer formation and the being of chaperone Hsp47 4-6) secretion of the pro peptidase 7) the N & C terminus are cleaved by extracelluar proteases 8) the trimers get staggered by 67 nm in fibrils and covalently cross linked

what is elastin?

it forms the elastic fibers in the ECM to give the tissue strechness (skin, blood vessels & lung) - very hydrophobic

what are adhesive glycoproteins and where are they found? (examples)

they are proteins that anchor cells to the basal lamina eg. laminin and fibronectin

explain laminin function

it is the main adhesive glycoprotein and is the ligand that binds the basal lamina to integrins

explain fibronectin function

an adhesive glycoprotein that helps organize and attach cells to the matrix

how does fibronectin attach cells to the matrix?

it binds collagen and herapan sulfate and to the cell adhesion receptor called integrins each specific integrin can influences the shape, movement and underlying cytoskeleton of the cell

how is fibronectin turn into fibrils produced and travel?

the dimeric forms are produced by cells and circulate in the blood the are turning into fibrils on the surface of cells when they bind to integrins. This is because the integrin are attached to actin filaments so this causes a stretch in the firbonectin and exposes the site for more integrins to bind turning into more fibrils

what are the 2 main type of connection inetgrin make with cytoskeletons?

focal adhesion: linked to actin filaments (stress fibers) hemisomes - linked to intermediate filaments

what is the structure of inetgrin?

they are transmembrane heterodimer composed of alpha and beta subunit a mixmatch of 8 types of beta subunits and 18 alpha subunits

what's the difference between beta1 and beta2 sub its of integrins?

beta 1 is found on the surface of vetebraes cells beta 2 is found on the surface of white blood cell

what is the function of integrins?

bind the ECM proteins in animal cells

how do integrins get activated?

by allosteric regulation causing inside out and outside in signalling

what are inside out signalling

comes from intracellular signal changing the conformation of the inetgrin to extended close it does this by talon opening and attaching to the integrin along with kindling and RIAM.

what is outside in signalling?

after inside our signalling, the integrin binds to the ECM and the attcahment to he cytoskeleton drives the integrins to the extended open confirmation which causes vinculin to bind to the talin and bind to the actin filament

how does mechanical force affect cell matrix adhesion?

it opens up the talin to allow vindullin to bind

why is cell attachment needed?

cell proliferation and survival