Membrane 3 (cell bio) Flashcards
CELL JUNCTIONS (imp. to understand about intergrins etc. to understand this)
Some cell types move freely in the body
? cells, and some ? system cells but
Many others are packed into tight communities
?
Fundamental ? between cells in a multicellular organism are those that hold ? together such as list the 4 tissues
A tissue is an assembly of similar cells and their ** ? ** from the same ? that work together carrying out ? functions.
CELL JUNCTIONS (imp. to understand about intergrins etc. to understand this)
Some cell types move freely in the body
blood cells, and some immune system cells but
Many others are packed into tight communities
tissues
Fundamental social interaction between cells in a multicellular organism are those that hold cells together such as
1. epithelial tissue 2. CT 3. Muscle T. 4. nervous tissue
A tissue is an assembly of similar cells and their ** ECM ** from the same origin that work together carrying out specific functions.
CELL JUNCTIONS
DEFINITION
Cell junctions consist of * ? * that provide contact between:
1. ? cells
2. between a cell and the ?
DIFFERENT FUNCTIONS
1. Bond ? together
2. Reduce ? placed upon cells
3. Build up the * ? * barrier of epithelia
4. Control the ? transport
5. Enable ? between neighboring cells
6. ? of cells to extracellular matr
para: means around (so paracellular = around cells)
DEFINITION
Cell junctions consist of * multiprotein complexes * that provide contact between:
1. neighbouring cells
2. between a cell and the ECM
DIFFERENT FUNCTIONS
1. Bond cells together
2. Reduce stress placed upon cells
3. Build up the * paracellular * barrier of epithelia
4. Control the paracellular transport
5. Enable adhesion between neighboring cells
6. adhesion of cells to extracellular matrix
CELL JUNCTIONS
Important tissue types found in all animals where cell junctions are particularly abundant:
- EPITHELIAL TISSUES
Cells are ? bound together into sheets called ?
Attachments between cells are made by ?-? junctions
Cells are anchored onto the basal lamina through cell-? junctions
(reminder: there are “diff. types of epithelium tissue” so single squamous epithelium, e.g. lungs performing diff functions so diff. types of epithelial tissue)
CELL JUNCTIONS
Important tissue types found in all animals where cell junctions are particularly abundant:
- EPITHELIAL TISSUES
Cells are tightly bound together into sheets called epithelia
Attachments between cells are made by cell-cell junctions
Cells are anchored onto the basal lamina through cell-matrix junctions
(reminder: there are “diff. types of epithelium tissue” so single squamous epithelium, e.g. lungs performing diff functions so diff. types of epithelial tissue)
- CONNECTIVE TISSUES
Formed by ? produced by cells that are distributed sparsely in the interstitial matrix (fibroblasts)
It is the matrix (rather than the cells) that bears most of the ? to which the tissue is subjected
(imp: note that fibroblasts will NOT be attached to each other and will be floating around in interstitial fluid)
Direct attachments between cells are common or rare?
Epithelial tissue cells have important ?
to the matrix (cell-matrix junctions)
i.e., Bone or tendons, adipose tissue, cartilage
note: ECM incorporates basal lamina and interstitial fluid
- CONNECTIVE TISSUES
Formed by ECM produced by cells that are distributed sparsely in the interstitial matrix (fibroblasts)
It is the matrix (rather than the cells) that bears most of the mechanical stress to which the tissue is subjected
(imp: note that fibroblasts will NOT be attached to each other and will be floating around in interstitial fluid)
Direct attachments between cells are rare!
Epithelial tissue cells have important attachments
to the matrix (cell-matrix junctions)
i.e., Bone or tendons, adipose tissue, cartilage
note: ECM incorporates basal lamina and interstitial fluid
2 main ways in which animal cells are bound together are through lateral junctions and cell matrix junctions
(BBB: have tight junctions bc the transport between the blood and brain is diff. as compared to epithelial of small intestine for molecules to pass through SO CELL JUNCTION DIFF. BASED ON TYPE OF TISSUE!)
CELL JUNCTIONS ARE ALSO PRESENT IN OTHER TISSUES i.e., muscle, nervous tissue
**TYPES OF CELL-CELL JUNCTIONS
1. ? JUNCTIONS
2. ? ANCHORING JUNCTIONS
a. ? JUNCTIONS
b. ?
3. ? JUNCTIONS (communicating junctions)
-> ?-forming junctions
TYPES OF CELL-MATRIX JUNCTIONS
1. CELL-MATRIX ? JUNCTIONS
a. ? CELL-MATRIX JUNCTIONS
b. ? **
**TYPES OF CELL-CELL JUNCTIONS
1. TIGHT JUNCTIONS
2. CELL-CELL ANCHORING JUNCTIONS
a. ADHERENS JUNCTIONS
b. DESMOSOMES
3. GAP JUNCTIONS (communicating junctions)
-> channel-forming junctions
TYPES OF CELL-MATRIX JUNCTIONS
1. CELL-MATRIX ANCHORING JUNCTIONS
a. ACTIN LINKED CELL-MATRIX JUNCTIONS
b. HEMIDESMOSOMES **
BOTTOM PIC in ANS:
JUNCTIONAL COMPLEX
1. ? junction
2. ? junction
3. ?
(tight junction is more on apical lateral side and adherens more in middle and desmosome on bottom of cell; their morphology and transmembrane protein (in between F-actin and E-cadherin) is quite diff. as seen in pictures; thus perform diff. functions due to diff. structures)
CELL-CELL JUNCTIONS
- TIGHT JUNCTIONS (zonula occludens, or occluding junction)
** Seal ? between ? cells **
* Seal the intercellular space from luminal environment
* Seal is not ** absolute (? barrier) **
Impermeable to ?
Permeability to ? and other ? molecules varies
Serve as selective ? barriers for ? transport (for this transport refer to pic in ans.)
the tight junctions are mostly located at basal or apical location?
found in ? cells
i.e.; lining of the ? mucosa, ?, ? tract..
CELL-CELL JUNCTIONS
- TIGHT JUNCTIONS (zonula occludens, or occluding junction)
** Seal gap between epithelial cells **
* Seal the intercellular space from luminal environment
* Seal is not ** absolute (diffusion barrier) **
Impermeable to macromolecules
Permeability to ions and other small molecules varies
Serve as selective permeability barriers for paracellular transport (present between epithelial cells)
the tight junctions are mostly located at apical location
found in epithelial cells
i.e.; lining of the intestinal mucosa, bladder, digestive tract..
the proteins that make up the tight junctions are ? and ?
the proteins that make up the tight junctions are claudin and occludin (they are made by epithelial cells and later go to inter-membrane space, they poke out of e.g. A cell and the proteins, claudin and occludin, poke out of B cell thus forming connection between B and A cell).
- CELL-CELL ANCHORING JUNCTIONS
The lipid bilayer is flimsy and cannot by itself transmit ? forces from cell to cell, or cell to ? matrix
Anchoring junctions solve this problem by
o Forming ?, ? structures that are tethered inside the cell to the tension-bearing filaments of the cytoskeleton
o Anchoring junctions are ? distributed in animal tissues and most abundant in tissues that are subjected to severe ? stress, such as ? ? and ?
Occur in two functionally different forms:
* ? junctions and
* ?
Hold cells together and are formed by transmembrane adhesion proteins that belong to the ? family (?-dependent adhesive proteins)
CELL-CELL ANCHORING JUNCTIONS
Depends on ? proteins
CADHERINS - “?-dependent adhesion“
Cadherins span the plasma membrane:
* One end linking to the ? and
* Other end linking to structures inside or outside? it
“FLEXIBLE SPOT WELDS”
Form strong ? connections between cells
- CELL-CELL ANCHORING JUNCTIONS
The lipid bilayer is flimsy and cannot by itself transmit large forces from cell to cell, or cell to extracellular matrix
Anchoring junctions solve this problem by
o Forming strong, membrane-spanning structures that are tethered inside the cell to the tension-bearing filaments of the cytoskeleton
o Anchoring junctions are widely distributed in animal tissues and most abundant in tissues that are subjected to severe mechanical stress, such as heart, epidermis and skeletal muscle
Occur in two functionally different forms:
* Adherens junctions and
* Desmosomes
Hold cells together and are formed by transmembrane adhesion proteins that belong to the cadherin family (calcium-dependent adhesive proteins)
CELL-CELL ANCHORING JUNCTIONS
Depends on transmembrane adhesive proteins
CADHERINS - “calcium-dependent adhesion“
Cadherins span the plasma membrane:
* One end linking to the cytoskeleton and
* Other end linking to structures outside it
“FLEXIBLE SPOT WELDS”
Form strong structural connections between cells
(note: in pic, cadherin is linking actin filaments from 2 different epithelium -> “E-cadherin”;
bottom pic: desmoglein (cadherin, so is also calcium dependent) have a diff. arrangment than cadherin, has bigger structure involving intermediate filaments, the 2 lines on the ends of the purple thingies, thus they are STRONGER than cadherin!)
A. ADHERENS JUNCTIONS
(Zonula adherens, intermediate junction, “belt desmosome” or adhesion belt -> synonyms will NOT be on exam!)
- Connect one actin filament ? in one cell
with that in the next cell
o Provide ? site for cytoskeleton - Help ? the shape of ? structures
o Guide the organization of ? tissues EX: construction of vertebrate nervous system
o Important in ? remodeling - Located more ? than tight junctions which are present on apical side
- Found in most ? and ? tissues
(pic: shows that it acts as a belt)
A. ADHERENS JUNCTIONS
(Zonula adherens, intermediate junction, “belt desmosome” or adhesion belt -> synonyms will NOT be on exam!)
- Connect one actin filament bundle in one cell
with that in the next cell
o Provide anchorage site for cytoskeleton -
** Help to model the shape of multicellular structures **
o Guide the organization of developing tissues EX: construction of vertebrate nervous system
o Important in tissue remodeling - Located more basally than tight junctions which are present on the apical side
- Found in most epithelial and endothelial tissues
(pic: shows that it acts as a belt)
B. DESMOSOMES or macula adherens
Connect ? filaments in one cell to those in the next cell
* Provide ? site for cytoskeleton
* Structurally similar to ? junctions but contain specialized ? (?) that link with intermediate filaments instead of ?
Main function is to provide ? strength
* Located in tissues that suffer a lot of ?/stretch like skin, ?, intestines, ?, bladder…
B. DESMOSOMES or macula adherens
Connect intermediate filaments in one cell to those in the next cell
* Provide anchorage site for cytoskeleton
* Structurally similar to adherens junctions but contain specialized proteins (desmogleins) that link with intermediate filaments instead of actin
Main function is to provide MECHANICAL strength
* Located in tissues that suffer a lot of stress/stretch like skin, muscles, intestines, stomach, bladder…
- GAP JUNCTIONS
Allow the passage of small hydrophilic molecules
from cell to cell
* Without having to pass through the plasma membrane
* EX: ?, ?, ? messengers
The gap is narrow or wide? (2 – 4 nm)
Very important in tissues containing electrically excitable cells
* Action potentials can spread rapidly from cell to cell
* EX: cardiac contraction, peristaltic movements of intestines
Located in: connective tissue, epithelial tissue, cardiac muscle, smooth muscle, neurons…
- GAP JUNCTIONS
Allow the passage of small hydrophilic molecules
from cell to cell
* Without having to pass through the plasma membrane
* EX: ions, glucose, second messengers like calcium
The gap is narrow (2 – 4 nm)
Very important in tissues containing electrically excitable cells (present in neurons, skeletal muscles, cardiac muscle cells)
* AP can spread rapidly from cell to cell
* EX: cardiac contraction, peristaltic movements of intestines
Located in: connective tissue, epithelial tissue, cardiac muscle, smooth muscle, neurons…
(intercalated disk in muscle heart, contains a lot of gap junctions and desmosomes connecting cardiac cells together bc those cells receive lots of mechanical stress and so gap junction help to propagate the AP of the heart for these cells so gap junctions allows the passage of small hydrophilic molecules and not only ions (e.g. second messenger, calcium,; peristalsis movements help emulsify lipids and chyme through GI)
there are lots of desmosomes and gap junctions present in intercalated disks to keep them together and for mechanical strength and also allows ions to go through it so u have AP done quickly and some neurons showing up helping in communication between cells
** smtms some cytokines (molecules) going out of whole inflammatory process so some molecule go through gap junction so next cell in tissue is aware something going wrong there so it can avoid the infection can keep going as it triggers apoptosis
permeability depends on tissue it is in
“adheren” linking actin filaments with “cadherin” protein and
‘desmosomes’ intermediate filament with ‘desmoglands’
desmosomes are STRONGEST or WEAKEST? JUNCTION to resist? force!
and then gap function v diff structurally as it functions differently and so it doesn’t keep molecules together but allows the passage of certain molecules which could ions, glucose, and inflammatory signals. THESE CONNECTIONS MAINLY ON EPITHELIAL tissue, therefore lateral part of cell -> epithelial tissue now we discuss how epothelial cells get together with basal lamina and rest of tissue
Tight junctions: permeable or impermeable? junctions prevent molecules from passing through the ? space
Desmosomes: Anchoring junctions bind adjacent cells together like a molecular “?” and help form an internal ?-reducing network of fibers.
Gap junctions: Communicating junctions allow ? and ? molecules to pass for intercellular communication.
desmosomes are STRONGEST JUNCTION to resist mechanical force
Tight junctions: impermeable junctions prevent molecules from passing through the intercellular space
Desmosomes: Anchoring junctions bind adjacent cells together like a molecular “velcro” and help form an internal tension-reducing network of fibers.
Gap junctions: Communicating junctions allow ions and small molecules to pass for intercellular communication.
CELL MATRIX JUNCTIONS
CELL-MATRIX ANCHORING JUNCTIONS
Depend on ** ? ** - transmembrane proteins bridging cell-matrix interactions.
Sense and respond to ? forces acting across the junction
must know! -> INTEGRIN, the transmembrane proteins, are also v imp for cellular communication too!
CELL MATRIX JUNCTIONS
CELL-MATRIX ANCHORING JUNCTIONS
Depend on ** INTEGRIN ** - transmembrane proteins bridging cell-matrix interactions.
Sense and respond to mechanical forces acting across the junction
NOTE! desmosomes (use desmoglein proteins) are present laterally while “hemi”desmosomes (use INTEGRIN to hold things together)
- hemidesmosomes are the junction present between the cell and the basal lamina (in red box)
- fibronectin - have many diff. active sites so will serve many different functions
- basal lamina (laminin protein makes it!)
INTEGRINS
Are activated after binding ? activator proteins, and produce intracellular signals that can influence almost any aspects of cell behavior:
? development
?
?
?
?
?
INTEGRINS
Are activated after binding intracellular activator proteins, and produce intracellular signals that can influence almost any aspects of cell behavior:
embryonic development
signalling
proliferation
survival
migration
blood clotting
CELL-MATRIX ANCHORING JUNCTIIONS
A. ACTIN-LINKED CELL-MATRIX JUNCTIONS or focal adhesion
Anchor ? filaments in cell to ? matrix
Can be small and transient or large and durable (rlly depends on the cell)
actin binding to integrin and integrin in turn binding to ? to get the connection done
B. HEMIDESMOSOMES
Hemidesmosomes anchor ? and NOT actin filaments in a cell to extracellular matrix
They are similar in form to ?
* however Hemidesmosomes use ** ? **, instead of desmogleins (which is used by desmosomes)
* Facilitate a stable adhesion of ? side of the epithelial cells to the ? membrane
- Anchor actin filaments in cell to the extracellular matrix
if cell moving then small and transient but if needs to be in that place then needs to be large and durable so depending on what cell is doing!
actin binding to integrin and integrin in turn binding to laminin to get the connection done
B. HEMIDESMOSOMES
Hemidesmosomes anchor intermediate filaments and NOT actin filaments in a cell to extracellular matrix
They are similar in form to desmosomes
* however Hemidesmosomes use INTEGRINS, instead of desmogleins (which is used by desmosomes)
* Facilitate a stable adhesion of basal side of the epithelial cells to the basement membrane
