PPT 5 - Chapter 19: Cell Junctions and Extracellular Matrix

epithelial tissue

Covering or lining tissue

epithelial

No blood vessels = avascular

gets nutrients from diffusion

cells are very close

sits on basement membrane

connective

good blood supply

cells scattered further apart

gaps between cells are filled w/ fibers and ground substance

tight junction

seals gap between epithelial cells

waterproof seal

adherens junction

connects actin filament bundles in one cell to bundles of another cell

basic type of junction adhering cells together

desmosome

connects intermediate filaments in one cell to those in the next cell

strongest

gap junctions

allows the passage of small water soluble molecules from cell to cell

connect 2 cells together with small openings

allow communication between neighboring cells

hemidesmosome

anchors intermediate filaments in cell to extracellular matrix

anchor cell to basement membrane

generally, what are junctions made up of?

specific proteins that interact with each other and the cytoskeleton

intracellular adaptor proteins and transmembrane adhesion proteins

intracellular adaptor protein

interact with transmembrane adhesion proteins and holds them to the cytoskeleton

transmembrane adhesion proteins

positioned in the membrane and interact with extracellular matrix or neighboring proteins to anchor cells

Cadherins

Require Calcium (Ca) + adhere (bind to each other)

What is the property of cadherins where they only bind to the same cadherins

Homophilic

What is cadherin binding similar to?

velcro

What are cadherins 2 conformations and what causes them?

Folded up = no calcium

Linear = calcium present

Is cadherin attachment rigid or flexible?

Attachment is flexible allowing for some shifting

What causes the sorting of cells found in embryotic development?

Sorting depends on the type of cadherins present

similar types of cells sort themselves out

What do cadherins attach to?

Cadherins attach to actin in the cytoskeleton

What attaches a cadherin to an actin filament?

catenin

What interacts with catenin to bundle actin filaments together in the adherens junction?

vinculin

What structure do adherens junctions form in order to connect specific cells together with cadherins?

Actin rings

What is an actin ring?

A band of actin that surrounds a cell and provides structure and an anchoring point for adherens junctions

What is an adhesion belt?

a layer of epithelial cells connected with adherens junctions on actin rings

What structure is made by pinching off facilitated by adhesion belts?

neural tube

Are tight junctions attached to the cytoskeleton?

Nope

What are the names of the 2 tight junctions proteins?

claudin and occludin

How do claudin and occludin interact?

claudin to claudin, occulin to occludin

What is the main function of a tight junction?

makes a waterproof seal between 2 cells

Where are tight junctions often seen?

Places like the bladder and stomach

What are scaffold proteins?

proteins that bind to claudin and occludin inside the cell

restrict or inhibit items from traveling between cells

What ways do gap junctions allow neighboring cells to “communicate”

Electronically (Ions)

Metabolically (i.e. hormones)

What kind of molecules do gap junctions allow entry?

small and dissolved in cytosol (water soluble)

What kind of junction is a connexon?

gap junction

What monomers form a connexon and how many?

six connexins

Can there be different types of connexins be used to form a connexon?

Yes

What do plants have instead of gap junctions?

plasmodesmata

What is the structure of a plasmodesmata?

a gap in the cell walls of neighboring cells

has a tube of smooth ER in the pore

What does the addition of smooth ER in a plasmodesmata allow for?

allows for the transport of lipid soluble and water soluble molecules between cells

What do selectins mediate?

cell to cell adhesions in the bloodstream

Selectins on epithelial cells use ____ domain and bind to ____ on white blood cells to slow them down?

lectin domain

bind to specific sugars

What is immunoglobulin another name for?

antibody

What are NCAM, ICAM, and Nectin?

immunoglobulin (Ig)

Where is NCAM and what does ICAM bind to?

NCAM- only in nervous tissue

ICAM- bins to integrins

What do nectins work with and why?

can work with cadherins in order to promote cell-cell attachment

What forms the protein fibers of the extracellular matrix?

The cells within the matrix

What are GAGS?

glycosaminoglycan

diverse in size, mostly used to fill up space in the matrix

can determine the properties of the matrix

What does sulfation do?

presence of charged sulfate groups attracts lots of water

What is the GAG called hyaluronan’s job?

fills in space

What is the structure of hyaluronan?

a long single chain of up to 25,000 disaccharides

no sulfation

fewer charges

What is a proteoglycan?

a core protein with GAG chains attached

What links a core protein and GAG together?

a 4 sugar linkage

What tissue is known to have large amounts of proteoglycan complexes?

cartilage

What is the most abundant protein in mammals and where is it found?

collagen

found in the extracellular matrix

What are collagen molecules made up of?

three α-chains, form a triple helix

What causes the triple helix structure of a collagen fiber?

glycine R group interactions

How are collagen types named?

Roman numerals

What are collagen fibrils and how are they held together?

many triple helices of collagen covalently bonded together, very strong

What allows collagen fibrils to organize into layers?

Fibril-associated collagens

How is amphibian skin unique?

specific layering of collagen fibrils which allows for permeable skin which they can breathe through

What kinds of collagen form structures like thick ropes?

I, II, and III

What give tissue is elasticity?

elastin

What does elastin make up and what are its properties?

Elastic fibers

able to stretch and snap back

What does matrix composition depend on?

The types of cells generating it, therefore it is dynamic

What helps organize the matrix?

fibronectin

What does fibronectin contain that allows it to organize the matrix?

many specific binding domains

What is the structure of fibronectin like?

exists as a dimer, held together by disulfide interaction

What is a specific molecule which binds to fibronectin?

Integrins

What regulates the assembly of fibronectin fibrils?

Tension

What are the two major components of the basal lamina?

Laminin and Type IV Collagen

What is the structure of a laminin?

a lower case t shaped molecule which contains 3 polypeptides

a β chain and γ chain wrapped around an α chain

How are laminins named?

named for their specific kind of α, β, and γ chains

i.e. laminin-111 = α1, β1, and γ1 chains

How do type IV collagen, laminin, and integrin interact?

integrins interact with laminins, laminins bind to type IV collagen

What allows for the regeneration of muscle tissue at a neuromuscular junction?

the basal lamina

What do cells have to do in addition to creating matrix?

degrade it

What degrades the extracellular matrix?

Matrix Metalloproteases

What does the name Matrix Metalloproteases mean?

Matrix

Metallo- require metal ions for active site to work

protease- break down proteins

What regulates Matrix Metalloproteases?

TIMPS, they inhibit them

How do cancer and Matrix Metalloproteases connect?

Cancer often increases the production of these proteases when metastasizing because it allows them to spread

What do integrins link together?

link the extracellular matrix to the cytoskeleton of cells

Do integrins exist as heterodimers or homodimers?

heterodimers, contain α subunit and β subunit

What happens when integrins are activated?

they stand up and bind to an extracellular matrix protein

What connects integrin to the cytoskeleton?

talin

What connects multiple actin filaments to the talin, making the integrin connection stronger?

vinculins

What attaches epithelial cells to basement membranes?

hemidesmosomes

What is the structure of a hemidesmosome?

transmembrane integrins and type XVII collagen interact with laminins in the basal lamina and with keratin inside of the cell

What does an inactive integrin look like?

α subunit and β subunit interact, fold up and hide binding site

What does an active integrin look like?

subunits stand up and expose binding site

What is the process for activation of integrin?

1. signaling molecule activates Rap1 (a G protein: any protein that can bins and hydrolyze GTP)

2. kindlin binds to β subunit and causes α and β subunits to separate

3. Rap1 and RIAM together interact with the α subunit

4. RIAM causes inactive talin to become linear

5. Linear talin binds to the β subunit

6. Talin binds to an actin filament

7. vinculin binds to talin and more actin filaments strengthening the connection with the cytoskeleton

What do integrin clusters adhere together?

Cells to the extracellular matrix

What are talin proteins able to sense?

mechanical forces, i.e. stretching of cells

How does talin react to stretching?

As it it pulled and stretched, talin binds to more vinculin, these vinculin bind to more actin, and the actin starts to bundle

What is turgor pressure in plants?

internal pressure caused by water filling cells

What is the cell wall made of?

primarily complex carbohydrates called cellulose

Why is cellulose an effective cell wall component?

it is incredibly strong and resistant to breakdown

What is the structure of cellulose?

a series of glucose molecules linked in a special way that are difficult to break.

Makes strong linear structures

What links cellulose molecules together?

pectin

What orients cellulose in the cell wall?

microtubules connected to cellulose synthase

microtubules inside of the membrane guide cellulose deposition