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BIO130: Molecular and Cell Biology > Week 11: Interactions Between Cells and their Environment > Flashcards

Week 11: Interactions Between Cells and their Environment Flashcards

Section 2 Week 5

1
Q

In order to form tissues, how do epethelial cells interact with each other and the extracellular matrix?

A

They interact through junctions

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2
Q

What do epethelial cells cover?

A

Epethelial cells cover external surfaces and organs and they line internal body cavities

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3
Q

What is the order of the junctions present (from apical to basal) in epithelial cells?

A

tight junction > adherens junction > desmosome > gap junctions > hemidesmosome

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4
Q

What are the functions of all the junctions?

A
  • 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
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5
Q

Which of the junctions are specifically for holding things together? What do they hold together?

A

Adherens junction (cell-cell), desmosome (cell-cell), hemidesmosome (cell-ECM)

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6
Q

Why are tight junctions not considered one of the junctions specifically for holding things together?

A

The function of a tight junction is less about holding cells together and more about keeping things out of the space between two cells

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7
Q

True or false: A hemidesmosome is half of a desmosome

A

FALSE!!

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8
Q

True or False: Though they are anchored at adherens junctions, the actin of one cell does not crossover into the next cell

A

True

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9
Q

Mature epithelial cells are ______________

A

Polarized

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10
Q

Tight junctions create a tight seal between cells to prevent the mixing of what?

A

The extracellular environments

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11
Q

In the membrane it can be said that tight junctions act as ________, in order to prevent the mixing of ______________ ____________

A

fences; membrane proteins

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12
Q

Tight junctions form ____________ ___________

A

sealing strands (which are called the tight junction belt)

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13
Q

What two transmembrane proteins are tight junctions composed of? How do they interact with the same transmembrane proteins in the neighbouring cell?

A

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.

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14
Q

What is another name for the type of junction adherens, desmosomes, and hemidesmosomes are?

A

achoring junctions

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15
Q

Anchoring junctions provide ____________ strength to epithelium

A

mechanical

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16
Q

How are the anchoring junctions similar to one another? How are they different?

A

All anchoring junctions have the same layout of their proteins. What’s different is the exact protein that correspond with a specific anchoring junction.

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17
Q

What are the two general components of anchoring junctions?

A

Transmembrane adhesion proteins and intracellular linker proteins

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18
Q

What are transmembrane adhesion proteins in anchoring junctions?

A

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

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19
Q

What are intracellular linker proteins in anchoring junctions?

A

Intracellular linker proteins are cytosolic proteins that interact with the intracellular domains of transmembrane adhesion proteins in order to link them to cytokeletal filaments

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20
Q

Adherens junctions form an ____________ ________ that encircles the inside of the _____________ ______________

A

adhesion belt; plasma membrane

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21
Q

What is the name of the transmambrane adhesion protein for adherens junctions?

A

Cadherins (each type of Cadherin is distinguished by letters and/or numbers - i.e. E Cadherin or Cadherin 18)

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22
Q

What type of interactions do cadherin proteins undergo?

A

Homophilic interactions - which means something like E Cadherin would only interact with E Cadherin

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23
Q

The intracellular linker proteins of adherens junctions links what two things together?

A

Cadherin proteins and actin filaments

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24
Q

Hemidesmosomes and desmosomes link to what kind of filament?

A

Intermediate filaments (like Keratin)

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25
Intermediate filaments provide the most ____________ strength
structural
26
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)
27
What are the names of the transmembrane adhesion proteins associated with **desmosomes**?
They are **specific** cadherin family members called **desmoglein** and **desmocollin**
28
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)
29
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)
30
What do the intracellular linker proteins associated with **hemidesmosomes** link together?
They link integrins to ketarin filaments (type of intermediate filament) inside the cell
31
What is the function of **gap junctions?**
**Gap junctions:** Allow for **communication** between cells
32
Describe the levels of structure for gap junctions
* 1 subunit: **connexin** * 6 connexins: **connexon** (hemichannel - which is CLOSED) * 2 connexons: **intracellular channel**
33
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
34
What does it mean when it is said that gap junctions couple cells?
This means that gap junction couple cells **electrically** and **metabolically**
35
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.
36
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
37
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.
38
How are gap junctions opened or closed?
Through an extracellular or intracellular **signal**
39
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+
40
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.
41
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.
42
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
43
What is lamella?
The "cement" that sticks one cell to another
44
True or False: ALL plant cells share their cytosol
False - some, not all
45
What kind of things move freely between plant cells using the plasmodesmata?
Small soluble molecules (< 1000 daltons) such as sugars, ions, other essential nutrients
45
What is plasmodesmata in terms of its structure?
Plasmodesmata is a cytoplasmic channel which allows for the continuous plasma membrane and ER
46
How is movement through the plasmodesmata controlled?
The sharing of larger soluble molecules are controlled though gating, proteins, and regulatory RNAs
47
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.
48
What are the layers of a cell?
Epithelium, basal lamina, connective tissue
49
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
50
What are the 3 major classes of macromolecules in the ECM?
1. **Glycosaminoglycans** (GAGs) and **proteoglycans** 2. **Fibrous** proteins (collagens, elastin) 3. **Glycoproteins** (laminin, fibronectin)
51
ECM is the ______________ __________ in connective tissues
primary components
52
What do the different compositions of ECM allow for?
It gives tissues different properties
53
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
54
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.
55
True or False: All proteoglycans are glycoproteins but not all glycoproteins are proteoglycans
TRUE!!!!!!!!!!! (and you better know it bcs it's on the exam)
56
What are proteoglycans?
* 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)
57
What are glycoproteins?
Protein with ANY kind of sugar on it
58
What is collagen?
* fibrous protein * provides tensile strength and resists strethcing
59
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
60
Collagen is secreted as ____________ by ____________ (skin, tendon, other connective tissue) and ____________ (bone)
**procollagen**; fibroblasts; osteoblasts
61
What happens once procollagen is secreted?
It is processed to **collagen** and they assemble into large structure - **collagen fibrils**
62
What is a visible example of too much collagen in one area?
Scars on your skin
63
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)
64
What does fibronectin bind to?
Fibronectin, a glycoprotein, binds to both **collagen** and **integein**
65
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
66
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.
67
What do other components of the ECM do for a tissue?
It provides strength, preventing the tissue from **excessive stretching**
68
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)
69
What does the basal lamina separate?
It separates the epithelia from underlying tissue
70
What does the basal lamina prevent? What does it allow?
It prevents **fibroblasts** in underlying connective tissue from **interacting with epithelial cells**. It allows passage of **macrophages and lymphocytes**
71
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**
72
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)
73
The supportive matrix of the plant cell is the ______ _______
cell wall
74
True or false: ECM of animal tissues is more rigid than plant cell wall
F a l s e
75
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**
76
What do cellulose microfibrils do for a plant's cell wall?
It provides **tensile strength**
77
What does pectin do for a plant's cell wall?
It is **space filling**, this provides **resistance to compression**
78
Where is cellulose synthesized?
It is synthesized at the plasma membrane via a cellulose synthase complex
79
Where are other cell wall components besides the cellulose synthesized?
They are synthesized in Golgi and exported by exocytosis

BIO130: Molecular and Cell Biology (16 decks)

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