Cell Adhesion: Lectures 17-20

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Questions and Answers

What is the primary characteristic of connective tissues compared to epithelial tissues?

High cell density

Absence of extracellular matrix

Cell-cell contacts are frequent

Abundant extracellular matrix (correct)

Which component of the extracellular matrix is primarily responsible for providing mechanical strength?

Polysaccharide chains only

Cell membranes

Both proteins and polysaccharide chains (correct)

Proteins only

Which statement about the extracellular matrix (ECM) is correct?

Different tissues have unique ECM compositions (correct)

ECM has roles only in disease

The ECM is purely cellular material

All cells produce the same ECM

How does the extracellular matrix influence cell behavior?

Through binding of growth factors and interaction with cell-surface receptors Signup and view all the answers

What role does the extracellular matrix play in protection?

It buffers against extracellular changes and retains water Signup and view all the answers

What is the typical length range of sugar residues in proteoglycans?

20-200 sugars residues long Signup and view all the answers

Which components typically make up the core protein of aggrecan?

Around 100 chondroitin and 30 keratan chains Signup and view all the answers

What role does heparan sulfate play in the extracellular matrix?

Binds chemokines, enhancing white-cell attraction Signup and view all the answers

What is the primary structure of collagen?

A triple helix of three α-chains Signup and view all the answers

What is a common feature of all glycosaminoglycans (GAGs)?

They contain repeating disaccharide units Signup and view all the answers

What is the primary purpose of cell adhesion in multicellular organisms?

To create connections and allow communication between cells Signup and view all the answers

Which structure is responsible for initial cell attachment in bacteria?

Pili (fimbrae) Signup and view all the answers

What is the extracellular matrix (ECM)?

A network that provides support and structure to tissues Signup and view all the answers

How do specialized domains in cells contribute to tissue function?

By allowing different sides of a cell to perform distinct roles Signup and view all the answers

What distinguishes multicellular organisms from unicellular organisms in terms of cell adhesion?

Multicellular organisms rely on extensive cell adhesion for structure and function Signup and view all the answers

What is a characteristic of tissues in multicellular organisms?

They consist of similar cells and their extracellular matrix Signup and view all the answers

Why do cells have differing roles in a multicellular organism?

Different sides of a cell interact with various environments Signup and view all the answers

Which of the following is an outcome of effective cell adhesion?

Enhanced communication and specialized domain formation Signup and view all the answers

What is the primary function of the highly mineralised matrix of bone and teeth?

To withstand compression Signup and view all the answers

Which cells are responsible for secreting the macromolecules of the extracellular matrix in most connective tissues?

Fibroblasts Signup and view all the answers

Which of the following GAGs is known for being unbranched and having a large molecular size?

Hyaluronan Signup and view all the answers

What is one of the key properties of glycosaminoglycans (GAGs)?

They attract positive ions and promote gel formation Signup and view all the answers

What role does hyaluronan play in the extracellular matrix?

Provides compressive strength Signup and view all the answers

Which of the following is NOT a characteristic of glycosaminoglycans (GAGs)?

They are mostly branched polymers Signup and view all the answers

Which of the following types of connective tissue matrix is highly elastic?

Tendon matrix Signup and view all the answers

What are the components that provide cartilage its structure and support?

Chondroblasts and glycosaminoglycans Signup and view all the answers

What are the components of the collagen chain represented by GXY repeats?

Glycine, Proline, Hydroxyproline Signup and view all the answers

Which factor is essential for the hydroxylation of proline during collagen synthesis?

Vitamin C Signup and view all the answers

What is the primary role of hydroxylation in collagen synthesis?

To stabilize the triple helix structure Signup and view all the answers

Which type of collagen is the most common and found in skin, bones, and tendons?

Type I Signup and view all the answers

What consequence does a vitamin C deficiency have on collagen-containing tissues?

Weakened tissues due to unhydroxylated collagen destruction Signup and view all the answers

How are collagen fibrils formed during synthesis?

Through oxidative deamination of hydroxylysine and lysine Signup and view all the answers

Which types of collagen do not form fibers but are associated with fibril structures?

Type IX and XII Signup and view all the answers

What is the approximate lifespan of collagen fibrils as compared to most enzymes?

Collagen lasts about 10 years Signup and view all the answers

What is the primary role of collagen in the extracellular matrix?

Gives tensile strength Signup and view all the answers

Which characteristic is associated with elastin in the extracellular matrix?

Provides elasticity Signup and view all the answers

What is one of the main components of microfibrils that coat elastin cores?

Fibrillin Signup and view all the answers

Which gene defect is primarily associated with Marfan syndrome?

FIBRILLIN 1 Signup and view all the answers

Which component of the basal lamina is responsible for determining cell polarity?

Laminin Signup and view all the answers

What role do GAGs like heparan sulfate play in the basal lamina?

Provide structural integrity Signup and view all the answers

What is the primary structural feature of elastin that contributes to its extensibility?

Loose random coil conformation Signup and view all the answers

Which of the following correctly describes the composition of the extracellular matrix?

Consists of collagen fibers, proteoglycans, and polysaccharides Signup and view all the answers

What is the primary function of occluding junctions in epithelial cells?

Seal cells together to form a barrier Signup and view all the answers

How do anchoring junctions contribute to cellular function?

Provide mechanical support through attachments Signup and view all the answers

Which feature distinguishes epithelial cells in terms of their organization?

They possess apical and basal surfaces. Signup and view all the answers

What role do tight junctions play in epithelial functionality?

Preventing uncontrolled fluid flow Signup and view all the answers

What is a characteristic of specialized absorptive epithelial cells?

They utilize passive glucose carriers on basal and lateral faces. Signup and view all the answers

What is the primary role of adherens junctions in multicellular structures?

To determine the shape and coordination of cell activities Signup and view all the answers

In which part of epithelial cells are zonula adherens located?

Below the apical face of epithelial cells Signup and view all the answers

What type of cytoskeleton do desmosome junctions primarily link to?

Intermediate filaments Signup and view all the answers

What structural ability do adherens junctions provide due to the presence of myosin motor proteins?

Reshaping and contractility of epithelial cell sheets Signup and view all the answers

How do desmosomes differ from adherens junctions in terms of their function?

Adherens junctions link to actin, while desmosomes link to intermediate filaments Signup and view all the answers

What effect does methylation have on pectin?

It prevents crosslinking Signup and view all the answers

What are the predominant components of the secondary cell wall in plants?

Cellulose, hemicellulose, and lignin Signup and view all the answers

What role do pectin methylesterases (PMEs) play in pectin functionality?

They demethylate pectin, allowing for crosslinking Signup and view all the answers

Which layer of the secondary cell wall contains differently oriented cellulose microfibrils?

All three layers: S1, S2, and S3 Signup and view all the answers

What is a characteristic of the bacterial extracellular matrix (ECM)?

It includes a capsule made of high molecular weight polysaccharides Signup and view all the answers

How does the extracellular polymeric substances (EPS) contribute to biofilms?

They provide mechanical stability and immobilize cells Signup and view all the answers

What type of cell junctions are essential for preventing leakage in epithelial cells?

Tight junctions Signup and view all the answers

What main components characterize the primary cell wall of plants?

Cellulose, pectin, and cell wall proteins Signup and view all the answers

What is the primary function of cellulose in plant cells?

To provide strength and rigidity Signup and view all the answers

Which of the following best describes hemicellulose?

A crosslinker of cellulose microfibrils Signup and view all the answers

What is the role of pectins in the primary cell wall?

To allow for cell expansion and flexibility Signup and view all the answers

Which of the following components primarily make up the secondary cell wall?

Cellulose and lignin Signup and view all the answers

How does xyloglucan contribute to the primary cell wall?

By crosslinking cellulose microfibrils Signup and view all the answers

What is a significant feature of cellulose microfibrils?

They consist of 1-4 linked β-D-glucose residues Signup and view all the answers

Which component is not found in the primary cell wall structure?

Lignin Signup and view all the answers

Which type of sugar residue is typically found in xyloglucan?

Glucose Signup and view all the answers

What is the primary consequence of antibodies against desmosomal cadherin proteins?

Weakened cell adhesions Signup and view all the answers

Which of the following accurately describes gap junctions?

They create channels between adjacent cell cytoplasms. Signup and view all the answers

Which cells utilize gap junctions to synchronize contractions?

Cardiac muscle cells Signup and view all the answers

What type of junctions are responsible for providing electrical coupling in excitable tissues?

Gap junctions Signup and view all the answers

Which type of protein subunit primarily constitutes gap junctions in vertebrates?

Connexins Signup and view all the answers

What is one of the key functions of plasmodesmata in plant cells?

Creating channels between cell cytoplasms Signup and view all the answers

How can gap-junction plaques rapidly change?

By assembling and disassembling connexons Signup and view all the answers

Which of the following statements about gap junctions is true?

They allow selective movement of signals between cells. Signup and view all the answers

What role does Ca2+ play in the function of cadherins?

It is required for cadherin-mediated cell-cell adhesion. Signup and view all the answers

Which of the following statements about cadherins is accurate?

Cadherins can provide adhesive properties to various cell types. Signup and view all the answers

What is the significance of desmocollin among cadherins?

It helps regulate cell polarity in Drosophila. Signup and view all the answers

How do cadherins primarily contribute to multicellular structure stability?

Through the formation of numerous weak adhesive links. Signup and view all the answers

Which of the following is NOT a property of classical cadherins?

They are involved exclusively in desmosome formation. Signup and view all the answers

What is the effect of EDTA on cell adhesion related to cadherins?

It disrupts cadherin interactions by removing Ca2+. Signup and view all the answers

What distinguishes non-classical cadherins from classical cadherins?

Non-classical cadherins utilize a GPI anchor instead of a transmembrane domain. Signup and view all the answers

What might the presence of over 180 different cadherins in humans indicate?

Diverse functional roles of cadherins in various tissues. Signup and view all the answers

Which component primarily facilitates adhesion between plant cells?

Pectins Signup and view all the answers

What role does the middle lamella play in plant cell structure?

Provides mechanical strength Signup and view all the answers

Which of the following describes a function of oligogalacturonides (OGAs)?

Functions as signaling molecules Signup and view all the answers

How does the transient expression of Fascicilin3 affect motor neurons?

Promotes abnormal synapse formation Signup and view all the answers

Which of the following is a component of plant cell walls that provides structural and mechanical support?

Cellulose Signup and view all the answers

What is a characteristic of homogalacturonan (HGA) in pectin structure?

Linear arrangement Signup and view all the answers

What is the role of cadherins in synapse formation?

Holding pre- and postsynaptic membranes together Signup and view all the answers

Which superfamily of proteins is responsible for mediating cell-cell attachments?

Cadherins Signup and view all the answers

Which factor can lead to varied adhesion strengths among cells?

Cell wall composition Signup and view all the answers

What is the primary function of integrins in cell adhesion?

Mediate cell-matrix attachments Signup and view all the answers

Which component is crucial for the formation of adherens junctions?

Actin Signup and view all the answers

Which junction structure is composed of claudin and occludin proteins?

Tight junctions Signup and view all the answers

Which of the following statements about cadherins is true?

They mediate cell-cell adhesion in animals. Signup and view all the answers

What distinguishes the adhesion methods between animal cells and plant cells?

Animal cells utilize cadherins and integrins, while plant cells use pectin. Signup and view all the answers

What do selectins primarily mediate in the process of cell adhesion?

Adhesion under high shear forces Signup and view all the answers

Which statement correctly describes the function of the zonula occludens (TJ)?

They form a barrier to prevent the passage of molecules. Signup and view all the answers

What results from the binding of an extracellular ligand to an integrin?

Transmembrane signal transmission to cytoskeleton Signup and view all the answers

Which molecules are involved in the inside-out activation of integrins?

Phosphoinositides (PIP2) Signup and view all the answers

Which combination of integrin chains represents a fibronectin receptor?

α5β1 Signup and view all the answers

What characterizes selectins in the context of cell adhesion?

Transient cell-cell adhesion Signup and view all the answers

What is a primary function of NCAMs (Neural Cell Adhesion Molecules)?

Influence fine-tuning of structures in the nervous system Signup and view all the answers

How do ICAMs and VCAMs differ from NCAMs in binding behavior?

ICAMs and VCAMs have heterophilic binding characteristics Signup and view all the answers

What effect do mutations in integrin subunits generally have?

Lead to genetic disorders Signup and view all the answers

How do cadherins and NCAMs compare in terms of adhesion strength?

Cadherins provide stronger adhesion than NCAMs Signup and view all the answers

What characteristic is associated with E-selectin?

Found on activated endothelial cells Signup and view all the answers

What role does Fascicilin3 play in neuronal activity?

Aids in axon outgrowth Signup and view all the answers

What prevents the flexible hinge regions of cadherins from flexing?

Ca2+ binding Signup and view all the answers

During neural tube development in chicks, what change occurs in cadherin expression?

Cells lose E-cadherin and gain N-cadherin Signup and view all the answers

Which protein acts as a link between cadherins and the actin cytoskeleton?

α-catenin Signup and view all the answers

What happens to β-catenin when adherens junctions break down?

It enters the nucleus and regulates transcription Signup and view all the answers

What is the role of vascular endothelial cadherin (VE Cadherin)?

Mediates the response to VEGF Signup and view all the answers

How do integrins facilitate dynamic cell adhesion?

By allowing conformation changes upon ligand binding Signup and view all the answers

What triggers a conformational change in integrins during receptor binding?

RGD peptide mimicking ligand Signup and view all the answers

What effect does the absence of Wnt signaling have on β-catenin?

It initiates β-catenin phosphorylation and degradation Signup and view all the answers

What is the primary role of catenins in relation to cadherins?

Linking cadherins to the cytoskeleton Signup and view all the answers

Study Notes

Lectures 17-20: From Cells to Tissue - ECM

Lectures 17-20 cover the extracellular matrix (ECM) and its role in connecting cells to form tissues, including cell adhesion and communication.
The ECM is a complex network of proteins and polysaccharides secreted by cells. It plays critical roles in normal tissue development, function, and disease.
Different tissues have distinctive ECM compositions adapted to their specific functions.
The ECM provides mechanical support, protection (e.g., buffering against changes and retaining water), and regulates cell behavior.
The ECM is vital for cell communication and interactions and forms pathways for cell migration.

Cell Adhesion and Communication

Cell adhesion is necessary for cells to "stick" together, forming tissues. This is achieved through cell-to-cell contacts and interactions with the ECM.
Bacteria can be planktonic (free-floating) or sessile (attached to a surface or within a biofilm). Initial attachment can be mediated by pili.
Cells transition from unicellular to multicellular organisms, posing challenges in terms of cell-cell adhesion and communication.
Adhesion is vital for cell-cell communication and the building of complex cellular structures.
Major superfamilies of proteins important in cell adhesion include cadherins, integrins, selectins, and immunoglobulin superfamily members.

Extracellular Matrix (ECM) Definition

The ECM comprises any material produced by cells and secreted into the surrounding medium, but commonly referring to the non-cellular portion of animal tissue. Plants and fungi also secrete ECM in the form of walls.
Common components include:
- Glycosaminoglycans (GAGs): Unbranched polymers of repeated disaccharide derivatives, including amino sugars.
- Fibrous proteins: Members of the collagen family; important for tensile strength.
- Non-collagen glycoproteins: Examples include fibronectin and laminin.
- Other components include elastin.

Properties of GAGs

GAGs are acidic and negatively charged, attracting positive ions (e.g., Na+) and water, creating a gel-like substance.
GAGs make up 10% of the ECM mass but 90% of the ECM volume.
They provide compressive strength to the ECM, serve as a metabolically cheap bulking agent, and play a vital role in gel formation.
A specific example of a GAG is Hyaluronan, an important component of the ECM that is spun out from cell membranes. It is large, lacks sulfation, and can exist independently of protein connections.

Proteoglycans (e.g., Aggrecan)

Proteoglycans are serine-rich proteins decorated with hundreds of O-linked GAGs.
Aggrecan is a common proteoglycan in the ECM. Its core protein is decorated with chondroitin and keratan chains.
Aggrecan binds to hyaluronan via adaptor proteins, making aggregates as large as bacteria (5 µm in length).
Heparan sulfate proteoglycans are important in cell growth, prolonging white blood cell activity at inflammatory sites, and binding to and blocking proteases. They also bind to growth factors such as fibroblast growth factor (FGF).

Collagen and other ECM Proteins

Collagen is a fibrous protein composed of three alpha-chains that form a triple helix. It provides tensile strength to the ECM.
Collagen chains consist of repeated GXY units, with Glycine, proline (and commonly hydroxyproline), and provides great tensile strength and stability to the ECM.
Collagen molecules crosslink to form fibrils, which eventually assemble into fibers. Collagen fibers are extremely stable, potentially lasting up to ten years.
Deficiencies in collagen synthesis/structure can lead to scurvy (due to vitamin C, which is critical for proline hydroxylation).

Collagen Synthesis

Collagen is synthesized in the rough endoplasmic reticulum (RER) as a pro-alpha chain.
Procollagen is formed, then secreted.
Terminal propeptides are cleaved to form 100nm long collagen chains.
Hydroxylation and glycosylation of selected prolines and lysines (and the resulting crosslinking of collagen molecules) are essential to producing active collagen.

Other ECM Components

Elastin, a protein found in elastic tissues, provides elasticity to the ECM.
Elastin is composed of around 750 amino acids, rich in proline and glycine, and hydrophobic.
Elastin's structure allows for stretching and recoiling, facilitating elasticity.
Fibrillin is a glycoprotein essential for elastin deposition and function. Fibrillin 1 defects cause Marfan syndrome, a connective tissue disorder affecting organs like the heart and lungs, and the skeletal system.

Basal Lamina

The basal lamina is a specialized ECM found underlying most epithelial cells. It also regulates cell polarity, cell-cell organization, and cell migration.
Typical basal lamina compositions include:
- Glycosaminoglycans (GAGs)
- Heparan sulfate
- Proteins: Laminin, Type IV collagen, nidogen (or entactin), and perlecan.
The specific interactions between these proteins are crucial for the overall function of the basal lamina.

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Explore the crucial role of the extracellular matrix (ECM) in connecting cells to form tissues, as discussed in Lectures 17-20. Understand how cell adhesion and communication facilitate tissue development, function, and the adaptation of ECM compositions for various tissue types. This quiz also highlights the importance of ECM in cell behavior regulation and migration pathways.