Week 11: Interactions Between Cells and their Environment Flashcards
Section 2 Week 5
In order to form tissues, how do epethelial cells interact with each other and the extracellular matrix?
They interact through junctions
What do epethelial cells cover?
Epethelial cells cover external surfaces and organs and they line internal body cavities
What is the order of the junctions present (from apical to basal) in epithelial cells?
tight junction > adherens junction > desmosome > gap junctions > hemidesmosome
What are the functions of all the junctions?
- tight junction: seals neighboring cells together in an epithelial sheet to prevent leakage of extracellular molecules between them; helps polarize cells
- adherens junctions: joins an actin bundle in one cell to a similar bundle in a neighbouring cell
- desmosome: joins the intermediate filaments in one cell to those in a neighbour
- gap junction: forms chennels that allow small, intracellular, water-soluble molecules, including inorganic ions and metabolites, to pass from cell to cell
- hemidesmosome: anchors intermediate filaments in a cell to the basal lamina
Which of the junctions are specifically for holding things together? What do they hold together?
Adherens junction (cell-cell), desmosome (cell-cell), hemidesmosome (cell-ECM)
Why are tight junctions not considere done of the junctions specifically for holding things together?
The function of a tight junction is less about holding cells together and more about keeping things out of the space between two cells
True or false: A hemidesmosome is half of a desmosome
FALSE!!
True or False: Though they are anchored at adherens junctions, the actin of one cell does not crossover into the next cell
True
Mature epithelial cells are ______________
Polarized
Tight junctions create a tight seal between cells to prevent the mixing of what?
The extracellular environments
In the membrane it can be said that tight junctions act as ________, in order to prevent the mixing of ______________ ____________
fences; membrane proteins
Tight junctions form ____________ ___________
sealing strands (which are called the tight junction belt)
What two transmembrane proteins are tight junctions composed of? How do they interact with the same transmembrane proteins in the neighbouring cell?
The two transmembrane proteins are claudin and occuldin. They are required in both cells and the extracellular domain in one cell interacts with the extracellular domain of the same protein in the neighbouring cell. This means that they take part in homophilic interactions, occludin only interacts with occludin as clauding only interacts with claudin.
What is another name for the type of junction adherens, desmosomes, and hemidesmosomes are?
achoring junctions
Anchoring junctions provide ____________ strength to epithelium
mechanical
How are the anchoring junctions similar to one another? How are they different?
All anchoring junctions have the same layout of their proteins. What’s different is the exact protein that correspond with a specific anchoring junction.
What are the two general components of anchoring junctions?
Transmembrane adhesion proteins and intracellular linker proteins
What is are transmembrane adhesion proteins in anchoring junctions?
Transmembrane adhesion proteins have extracellular domains that interact with (depending on the type of achoring junction) either the adhesion proteins of the neighbouring cells or the ECM
What are intracellular linker proteins in anchoring junctions?
Intracellular linker proteins are cytosolic proteins that interact with the intracellular domains of transmembrane adhesion proteins in order to link them to cytokeletal filaments
Adherens junctions form an ____________ ________ that encircles the inside of the _____________ ______________
adhesion belt; plasma membrane
What is the name of the transmambrane adhestion protein for adherens junctions?
Cadherins (each type of Cadherin is distinguished by letters and/or numbers - i.e. E Cadherin or Cadherin 18)
What type of interactions do cadherin proteins undergo?
Homophilic interactions - which means something like E Cadherin would only interact with E Cadherin
The intracellular linker proteins of adherens junctions links what two things together?
Cadherin proteins and actin filaments
Hemidesmosomes and desmosomes link to what kind of filament?
Intermediate filaments (like Keratin)
Intermediate filaments provide the most ____________ strength
structural
What is the difference between desmosomes and hemidesmosomes?
While they are both linked to something like keratin, desmosomes connect to a neighbouring cell while hemidesmosomes anchor keratin filaments to the basal lamina (which is a special type of ECM)
What are the names of the transmembrane adhesion proteins associated with desmosomes?
They are specific cadherin family members called desmoglein and desmocollin
What kind of binding does the transmembrane adhesion proteins associated with desmosomes undergo?
Both homophilic and heterophilic - meaning desmogleins and desmocollins don’t need to always only interact with the same proteins (i.e. desmoglein-desmoglein)
What is the name of the transmembrane adhesion protein associated with hemidesmosomes? What is their function?
Integrins - they bind to laminin in the basal lamina (ECM)
What do the intracellular linker proteins associated with hemidesmosomes link together?
They link integrins to ketarin filaments inside the cell
What is the function of gap junctions?
Gap junctions: Allow for communication between cells
Describe the levels of structure for gap junctions
- 1 subunit: connexin
- 6 connexins: connexon (hemichannel - which is CLOSED)
- 2 connexons: intracellular channel
Why must a connexon be closed?
A connexon is half a gap junction, without the other half things flowing through the connexon would just fly out
What does it mean when it is said that gap junctions couple cells?
This means that gap junction couple cells electrically and metabolically
What do gap junctions allow the passage of?
They allow the passage of ions and metablolites < 1000 daltons. They are not very selecting as to what passes through.
What can and cannot pass through a gap junction? What constitutes for something that can or cannot pass though?
Passes through: cAMP, nucleotides, glucose, amino acids. Does not pass: macromolecules, proteins, nucleic acids. What can pass through are often smaller pieces of bigger things that cannot pass though
Gap junctions are ________. What is an example of this?
gated; an example of this is the treatment of dopamine and how there is a difference between what neurons you can and cannot see when gap junctions are closed or opened.
How are gap junctions opened or closed?
Through an extracellular or intracellular signal
Explain the cystolic Ca2+ gap junction example
- A dramatic increase in cyctolic Ca2+ closes gap junctions
- When there is membrane damage in a cell, gap junctions will close to prevent the loss of metabolites in adjacent cells
- This is caused by the leak of Ca2+ within the cell with the damaged membrane where there is supposed to be low Ca2+
How do intercellular junctions in plant cells differ from animal cell junctions?
Plan cells lack the cell junctions found in animal cells. They are instead surrounded by cell walls which hold cells together and provide mechanical strength.
What is the name of the intercellular junction within plant cells? What is their function?
The name of the intercellular junction within plant cells is plasmodesmata. Their function is to allow for communication between cells. But there is a need to cross the cell wall - this makes it different from gap junctions.
What is present in plant cells that you wouldn’t see in animal cells?
The amount of sharing that occurs in plant cells. Planct cells share their membranes, tranmembrane proteins, lipids, smooth endoplasmic reticulum, and cytoplasm
What is lamella?
The “cement” that sticks one cell to another
True or False: ALL plant cells share their cytosol
False - some, not all
What kind of things move freely between plant cells using the plasmodesmata?
Small soluble molecules (< 1000 daltons) such as sugars, ions, other essential nutrients
What is plasmodesmata in terms of its structure?
Plasmodesmata is a cytoplasmic channel which allows for the continuous plasma membrane and ER
How is movement through the plasmodesmata controlled?
The sharing of larger soluble molecules are controlled though gating, proteins, and regulatory RNAs
What is callose? What is it used for?
Callose is a plant polysaccharide. It is used for permeability control though revserible callose desposition. Callose can grow and shrink, the bigger the less movement of larger soluble molecules.
What are the layers of a cell?
Epithelium, basal lamina, connective tissue
Differentiate between epithelial and connective tissue
Epithelial Tissue:
* e.g. intestinal lining, skin epidermis
* cells closely associated
* cells are attached to each other
* limited ECM (a thin basal lamina)
* Cytoskeletal filaments provide resistance to mechanical stress
Connective Tissue:
* e.g. skin dermis, bone, tendon, cartilage
* cells are rarely connected
* cells are attached to the matrix
* plentiful ECM
* ECM provides resistance to mechanical stress
What are the 3 major classes of macromolecules in the ECM?
- Glycosaminoglycans (GAGs) and proteoglycans
- Fibrous proteins (collagens, elastin)
- Glycoproteins (laminin, fibronectin)
ECM is the ______________ __________ in connective tissues
primary components
What do the different compositions of ECM allow for?
It gives tissues different properties
What are glycosaminoglycans (GAGs)?
- long, linear, chains of a repeating disaccharide
- highly negatively charged (attract Na+ and water)
- form hydrated gels, resist compression
- space filling
- most GAGs synthesized inside cell and released by exocytosis
What is an example of a GAG?
Hyaluronan is a simple GAG. It is a long chain of repeating disaccharide subunits (up to 25K) and it is highly negative. Hyaluronan is spun directly from cell surface by a plasma membrane enzyme complex.
True or False: All proteoglycans are glycoproteins but not all glycoproteins and proteoglycans
TRUE!!!!!!!!!!! (and you better know it bcs it’s on the exam)
What are protoglycans?
- subclass of glycoproteins
- protein with at least one sugar side chain which must be a GAG
- typically, more extensive addition of sugars (up to 95% of total weight)
What are glycoproteins?
Protein with ANY kind of sugar on it
What is collagen?
- fibrous protein
- provides tensile strength and resists strethcing
What is a typical collagen?
Fibril-forming collagen:
* three chains wound around each other in a triple helix
* they assemble into ordered polymers to form collagen fibrils - collagen fibrils can pack together into collagen fibers
Collagen is secreted as ____________ by ____________ (skin, tendon, other connective tissue) and ____________ (bone)
procallagen; fibroblasts; osteoblasts
What happens once procollagen is secreted?
It is processed to collagen and they assemble into large structure - collagen fibrils
What is a visible example of too much collagen in one area?
Scars on your skin
Connective tissue that secrete collagen also ____________ collagen in ECM. How does it do this?
organize; it does this by binding to collagen in ECM integrein (cell surface adhesion receptor) and firbonectin (glycoprotein)
What does fibronectin bind to?
Fibronectin, a glycoprotein, binds to both collagen and integein
What does integrin bind to?
Integrin, a cell surface adhesion receptor, binds to both fibronectin (on its extracellular domain) and adaptor proteins (on its intracellular domain) - which are bound to actin filaments
What is elastin? What is a network of elastin used for?
Elastin is a fibrous protein. Networks of elastin gives tisues elasticity which makes it stretch and relax like a rubber band. This gives tissues resiliance.
What do other components of the ECM do for a tissue?
It provides strength, preventing the tissue from excessive stretching
What is the basal lamina?
- Specialized type of ECM
- underlies all epithelia
- thin (40-120 nm thick)
- ECM is secreted by the epithelial cells
- influences cell polarity by favouring things like hemidesmosomes (which are basal)
What does the basal lamina separate?
It separates the epithelia from underlying tissue
What does the basal lamina prevent? What does it allow?
It prevents fibroblasts in underlying connective tissue from interacting with epitherlial cells. It allows passage of macrophages and lymphocytes
Describe the position of the basal lamina in relation to what it is attached/achored by.
The basal lamina is the attachement site for epithelia. It is anchored by hemidesmosomes. It is organized by laminin
What does laminin do in the ECM? (besides interact with the basal lamina)
It interacts with the other components of the ECM such as how it links integrein (transmembrane adhesion protein) to type IV collagen (fibrous protein)
The supportive matrix of the plant cell is the ______ _______
cell wall
True or false: ECM of animal tissues is more rigid than plant cell wall
F a l s e
What are the main components of a plant’s cell wall? What are they classified as?
The main components of a plant’s cell wall are cellulose and pectin. They are polysaccarides
What do cellulose microfibrils do for a plant’s cell wall?
It provides tensile strength
What does pectin do for a plant’s cell wall?
It is space filling, this provides resistance to compression
Where is cellulose synthesized?
It is synthesized at the plasma membrane via a cellulose synthase complex
Where are other cell wall components besides the cellulose synthesized?
They are synthesized in Golgi and exported by exocytosis
