Passgeways from cell to cell and Basal Lamina Flashcards
What blocks passageways through gaps between cells
Tight junctions
What to tight junctions prevent
extracellular molecules from leaking from one side of an epithelium to the other
Name of junctional structure that bridges gaps between adjacent cells to create passageways from cytoplasm of one to another
Gap junctions (animals)
Plasmodesmata (plants)
Gap junction and plasmodesmata allow neighbouring cells to exchange _______ but not _________
small molecules, macromolecules
Gap junctions couple cells both ______ and ________
electrically, metabolically
The gap is spanned by channel-forming proteins, of which there are two distinct families, called the _______ and the _________.
connexins, innexins
Differences and similarities between connexins and innexins
Unrelated in sequence but similar in shape and function
Do connexins or innexins predominate in vertebrates
Connexins
Summarized explanation of channels formed by gap-junction proteins
The channels formed by the gap- junction proteins allow inorganic ions and other small water-soluble
molecules to pass directly from the cytoplasm of one cell to the cytoplasm of another, coupling the
cells both electrically and
metabolically.
A gap-junction connexon is made up of
six transmembrane connexin subunits
When connexons in the plasma membrane of two cells in contact are aligned, what is formed?
A continuous aqueous channel that connects the two cell interiors
How is a hemichannel formed
when one connexon from one cell does not line up with one from another cell, instead it opens up to the extracellular space.
What happens in regard to ions when hemichannels form
case ions can move into or out of the cell (depending on the concentration gradient) through this hemichannel, this essentially creates a pore
What conformation are hemichannels generally kept in
Closed conformation, we want to control what goes in and out
Why can gap junctions in different tissues have different properties
They are formed from different combinations of connexins, creates channels differing in permeability
True of false: Adjacent cells expressing
different connexins cant form intracellular channels
False, they can.
What mutation is the most common of all genetic causes of congenital deafness and how does it do that
Connexin-26
-Death in the organ of Corti through the disruption of the flow of ions in the organ’s sensory epithelium
Can cells regulate the permeability of their gap junctions
Yes
Gap-junction channels close when
a cell’s plasma membrane is damaged causing ions to leak in
What happens when gap-junction channels close due to damaged PM
Isolates the cell, prevents its neighbors from harm
What neurotransmitter reduced gap-junction communications between a class of neurons in retina in response to increase in light intensity
Dopamine
What does dopamine do in retina
reduces gap-junction communication between a class of neurons in the retina in response to an increase in light intensity
What does the reduction in retina gap-junction permeability do
Helps retina switch from using rod receptors to cone receptors, detects color and fine detail in bright light
The matrix is composed of various _____ and _____
proteins and polysaccharides
Proteins and polysaccharides (that make up matrix) are secreted
locally
In our own bodies, the most plentiful forms of extracellular matrix are found in
bulky connective tissues such as bone, tendon, and the dermal layer of the skin
Basal lamina is also referred to as the
basement membrane
The basal lamina surrounds what cells (3)
Muscle cells, fat cells and Schwann cells
True or false: the basal lamina is a type of ECM
True
Basal lamina differences in muscle vs epithelium cells
Muscle:
-basal lamina wraps around cell, following striated muscle path
-basal lamina surrounded by connective tissues
Epithelium:
-more polar
-sheath of villi on one polar (apical), basal attached to basal lamina, connective tissue under
Functions of the basal lamina
-Determines cell polarity
-Influences cell metabolism
-Organize the proteins in adjacent PM
-Promotes cell survival, proliferation, and differentiation
In the skin, the epithelial outer layer (epidermis) depends on the strength of the ____ to keep it attached to underlying connective tissue (dermis)
Basal lamina
Defects in certain basal lamina proteins cause the epidermis to
Become detached from the dermis
What is the primary component of the basal lamina
Laminin
The basal lamina is synthesized by the cells on each side of it,which are:
Epithelial cells and cells underlying the bed of connective tissue (stroma)
2 main classes of basal lamina
Fibrous proteins (glycoproteins with short oligosaccharide side chains) and polysaccharide chains of the type called glycosaminogylcans (GAG), linked covalently to specific core proteins to form proteoglycans
Basal lamina composition varies between tissues but typically contains the glycoproteins:
laminin, type IV collagen, and nidogen along with the proteoglycan perlecan
Basal lamina is closely associated with
-collagen XVII
-fibronectin
Collagen XVII
core protein of a proteoglycan
fibronectin
a fibrous protein important in the adhesion of connective-tissue cells to matrix)
Fibrous proteins
glycoproteins with short oligosaccharide side chains)
Laminin-1 structure
a large, flexible protein composed of three very long polypeptide chains (α, β, and γ) held together by disulfide bonds.
True or false: heterotrimers can self-assemble through interactions with their tails
False: interactions with their heads
What is a component of most laminin heterotrimers
Laminin γ-1 chain
Structure of a laminin molecule
-3 polypeptide chains (alpha, beta, gamm) coiled around eachother
-Integrin binding site
-Perlecan binding site
-Dystroglycan binding site
-Nidogen binding site at bottom
-Another integrin bind site on N terminal
-self assembly sites
Integrin binding site
membrane proteins present on cells, shows that molecule can interact with other cells through integrins
Perlecan and dystroglycan bind site
can interact with other ECMs
N terminal binding site
means that this molecule can be organized between 2 cells through interaction with integrins on both of them, while stil binding the ECM
Self-assembly site
the laminin molecule can be bound to another laminin molecule while still being bound to other cells and ECM components- gives us nice sheath lining
What gives the basal lamina tensile strength
Type IV collagen
What is the second essential component of the mature basal lamina
Type IV collagen
Why does type IV collagen exist in several isoforms
it consists of three separately synthesized long protein chains. They assemble via terminal domains into flexible, felt-like networks that give basal lamina tensile strength.
The kidney glomerulus
has an unusually thick basal lamina that acts as a molecular filter preventing the passage of macromolecules from the blood into the urine.
Mutations in type IV collagen genes
result in an irregularly thickened and dysfunctional glomerulus filter (hereditary kidney disorder - Alport
Syndrome).
The basal lamina can act as a ______ for the movement of cells
Selective barrier
The basal lamina prevents what from contacting epithelial cells
prevents fibroblasts in the underlying connective tissue from contacting epithelial cells
The basal lamina does not prevent what from passing through, and how
macrophages or lymphocytes, use specialized proteases to cut a hole for transit
Basal lamina plays a role in what after injury and how
Tissue regeneration, basal lamina survives injury and creates a scaffhold along which regenerating cells can migrate
What is responsible for many forms of muscular dytrophy
Defects in components of the basal lamina or in proteins that tether muscle cells to the basal lamina at the synapse
Basal lamina also gives information to cells about
Gives lots of information to cells in repect to where to traffic receptors to, where to extend axons, etc
True or False. Unlike conventional ion channels, individual gap junction channels remain open continuously once they are formed.
False
True or False. A sheet of basal lamina underlies all epithelia.
True
Certain bacteria secrete enzymes that can digest protein or carbohydrate components of the basal lamina. Why do you suppose they do so?
Tissue invasion
When you wake up in the morning and turn on the light, is dopamine release increased or decreased? How does dopamine alter the neuronal activity in the retina?
Closes gap junction
What does cell metabolism do
