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Define a junctional interaction.
one that can be seen as a specialized region of contact by conventional and/ or freeze-fracture electron microscopy
__ and __ are involved in both nonjunctional and junctional cell-cell (__) and cell-matrix (__) contacts.
Cadherins generally do what?
Integrins generally do what?
- mediate homophilic interactions
- mediate heterophilic interactions
Both cadherins and integrins do what?
For this reason, most __ and __ are __.
- act as transmembrane linkers adn depend on extracellular divalent cations to function
- cell-cell and cell-matrix contacts
__ and __ can also act as __cell-cell adhesion molecules: the __ bind to carbs, while the __ bind to members of hte __.
- cell-binding integrins
What is homophilic binding?
binding of two like molecules
What is heterophilic binding?
binding of two different molecules
What is the third type of binding?
binding through an extracellular linker molecule located in the cytoplasm; least common
What are hte five types of cadheriin molecules in mammalian cells.
- E (epithelial cells)
- P (trophoblast, heart, lung, intestine)
- N (nervous system)
- R (retinal nerve and glial)
- M (myoblasts)
Cadherins: The extracellular part of the protein is __.
The extracellular domain farthest from the membrane is thought to mediate __.
The cytoplasmic tail interacts with te __ via a number of __, including three __ proteins.
__ is structurally related to __.
- folded into five similar domains, three of which contain Ca2+ binding sites
- cell-cell adhesion
- actin cytoskeleton
- intracellular attachment proteins
- alpha catenin
What does Ca2+ do in the cadherin?
What would happen if it weren't there?
- form bridges between the domains
- if it were nt there, the external portion will be the wrong shape and will be hydrolyzed
What do linker proteins in the cytosol do in cadherin?
attach the cytoplasmic portion of cadherin to actin microfilaments, leading to an influence of arrangement of actin
In N-CAM, the extracellular part of the polypeptide chain in each case is __. __ connect the ends of each loop forming each __.
- folded into five immunoglobulinlike domains (and one or two other domains called fibronectin type III repeats)
- disulfide bonds
- Ig-like domain
Explain the extracellular portion of the N-CAM (quantity)
How many carbs?
N-CAMs play a huge role in __.
- huge EC portion
- vertebrate development of embryos
True or False:
N-CAMs have been seen to have no cytoplasmic portions at all.
Binding of selectin is __. Explain the proportions of their molecules?
- veery large EC portions/ very small cytoplasmic portions
True or False:
Selectins are not attached to the cytoskeleton.
The EC portion of selectins have __.
repeat domains (one portion toward end similar to EGF
The lectin domain of selectin binds to __.
Selectin is calcium- (independent or dependent).
- the lectin domain won't be the right shape if the Calcium isn't there
A circulating __ adheres weakly to the surface of the specialized high __ in a postcapillary venule in a lymph node. This initial adhesion, mediated by __ on the lymphocyte surface, is sufficiently weak that it enables the lymphocyte to __ the surface of the endothelial cells. The lymphocyte rapidly activates a __, mediated by an __, that enables the cell to stop __ and migrate out of the venule between the __.
- endothelial cells
- roll along
- stronger adhesion system
- endothelial cells
What is the shape of an integrin cell-surface matrix receptor.
globular head projecting more than 20 nm from the lipid bilayer
By bindign to the matrix protein outside the cell adn to the __ inside the cell, the protein serves as a __.
- actin cytoskeleton (via the attachment proteins talin and alpha-actinin)
- transmembrane linker
The __ and __ chains are both __ and are held together by __. The __ is made initially (in the figure) as a single 140k dalton polypeptide chain, which is then __.
- alpha beta
- noncovalent bonds
- cleaved into one small transmembrne chain and one large extracellular chain that remain held by a disulfide bond
Explain the extracellular chain after cleavage.
is folded into four divalent-cation binding domains
The extracellualr aprt of the B chain contains a repeating __, where __ bonding occurs; te beta chain has a mass of about 100,000 daltons.
- cysteine-rich region
- intrachain disulfide bonding
The integrin is a __. There are at least __ of them and are based on __.
- 24 different heterodimers
Each chain int he integrin cell-surface matrix receptor is coated for by __.
a different gene
Binding in the integrin is dependent on what?
It also depends on the __ what what binds.
- divalent cations
- alpha chains
The cytosolic part of the integrin receptor is what?
- - small, cytosplasmic portion
- - can be actin or vinculin
- - you find actin microfilaments being bound to in the cytoplasmic skeletom
Heterophilic binding can occur in integrin proteins because?
they can bind more than one protein
If any __ is exerted on adjacent cell at one end, what?
the moleclues must be attached to the matrix
Advantage of cytoskeletal attachment
- stabilize--> cluster
- weak attachment unless you have alot of cadherins--> stabilize whole system
True or False:
N-Cams are permanent.
- they can appear and siappear
Why do NCAMs lose themesleves in cell migraiton of the neural test.
they bind together, which will inhibit movemetn
What must occur in order for robust cell-cell or cell-matrix adhesion to occur? Why?
- cell-adhesion molecuels must be linked to the cytoskeleton
- they would probably be pulled from the cell with bits of attached membrane and the holes left in the membrane would reseal
Integrins have two forms. What?
inactive and active
__ have a great effect on integrins. Why?
- without talins, the outside is bent
What is talin?
Actvation of talin
- one of the protiens that link to actin microfilaments
- via a signal from either out or in, the integrins are activated