ECM: L17

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Questions and Answers

What is a key characteristic of connective tissues?

Low cell density with an abundant extracellular matrix (correct)

High cell density with abundant cell-cell contact

Uniformity of cell types throughout the tissue

Thick basal lamina supporting epithelial cells

Which statement accurately describes the extracellular matrix (ECM)?

It is solely comprised of proteins without any polysaccharides.

It consists of materials secreted by cells into their surroundings. (correct)

It is synthesized only by plant cells.

Its primary function is solely for structural support.

How does the extracellular matrix contribute to tissue function?

By preventing the attachment of cells to the matrix

By accelerating cell division exclusively

By solely providing a protective barrier to pathogens

By influencing cell behavior through binding growth factors (correct)

What distinguishes epithelial tissues from connective tissues?

Epithelial tissues feature closely bound cells with a thin extracellular matrix. Signup and view all the answers

What role does the extracellular matrix play in mechanical strength?

It offers tensile and compressive strength as well as elasticity. Signup and view all the answers

What is the primary composition of the GAG chain in a proteoglycan?

A repeating disaccharide unit Signup and view all the answers

What is the role of heparan sulfate proteoglycans in the body?

They assist in cell growth and can bind chemokines Signup and view all the answers

Which of the following statements about aggrecan is true?

Aggrecan has a core protein that is decorated with several GAG chains Signup and view all the answers

What structure do collagen proteins form?

A triple helix configuration Signup and view all the answers

How long can aggrecan-hyaluronan aggregates be?

As big as bacteria, up to 5 µm long Signup and view all the answers

What is one of the primary reasons for cell adhesion in multicellular organisms?

To allow cells to communicate with one another effectively Signup and view all the answers

Which of the following statements accurately describes a characteristic of the extracellular matrix (ECM)?

Components of the ECM consist of various proteins and polysaccharides. Signup and view all the answers

How do bacteria achieve the initial attachment to surfaces?

By employing pili (fimbrae) Signup and view all the answers

What challenge does the transition from unicellular to multicellular life present?

Establishing permanent connections with other cells Signup and view all the answers

What is one key functional role of the extracellular matrix in tissues?

To define specialized domains and ensure proper cell adhesion Signup and view all the answers

Which of the following best describes how tissues are formed?

From cells of the same origin along with their extracellular matrix Signup and view all the answers

What distinguishes 'planktonic' bacteria from 'sessile' bacteria?

Sessile bacteria attach themselves to surfaces or a biofilm. Signup and view all the answers

Which of the following is NOT a function of cell adhesion?

Increasing the number of independent cells Signup and view all the answers

What are the common components of the GXY repeat in collagen chains?

Glycine, proline, hydroxyproline Signup and view all the answers

Which modification is essential for stabilizing the collagen triple helix?

Hydroxylation of proline Signup and view all the answers

What is the result of oxidative deamination of hydroxylysine and lysine in collagen?

Creation of reactive aldehyde groups Signup and view all the answers

How does vitamin C affect collagen synthesis?

It acts as a cofactor for proline hydroxylase. Signup and view all the answers

What happens to collagen in the absence of vitamin C?

Unhydroxylated collagen is destroyed prior to secretion. Signup and view all the answers

Which type of collagen is predominantly found in skin, bones, and tendons?

Type I Signup and view all the answers

Which type of collagen is associated with cartilage?

Type II Signup and view all the answers

What role does glycosylation play in collagen synthesis?

It occurs on hydroxylysines after hydroxylation. Signup and view all the answers

What is a major function of the ECM in the cornea of the eye?

To create a transparent structure Signup and view all the answers

Which cells are primarily responsible for secreting matrix macromolecules in connective tissues?

Fibroblasts Signup and view all the answers

Which type of glycosaminoglycan (GAG) is not sulfated and acts as a standalone molecule?

Hyaluronan Signup and view all the answers

What percentage of the extracellular matrix mass is made up of glycosaminoglycans (GAGs)?

10% Signup and view all the answers

Which component of the ECM is primarily responsible for providing compressive strength?

Glycosaminoglycans, especially hyaluronan Signup and view all the answers

What is the primary role of blood plasma in relation to the extracellular matrix?

Liquid form of ECM Signup and view all the answers

Which of the following statements about fibrous proteins in the ECM is true?

They include various members of the collagen family. Signup and view all the answers

What is a significant property of glycosaminoglycans (GAGs)?

They are negatively charged and attract positive ions. Signup and view all the answers

Which statement accurately describes the structure of elastin?

Elastin has alternating stretches of hydrophobic residues and alanine/lysine-rich α helices. Signup and view all the answers

What is the role of fibrillin in elastin deposition?

Fibrillin acts as a scaffold that guides subsequent elastin formation. Signup and view all the answers

What condition is associated with defects in the FIBRILLIN 1 gene?

Marfan syndrome Signup and view all the answers

Which function does the basal lamina NOT perform?

Stores genetic material for cell functions. Signup and view all the answers

What are the primary components of the extracellular matrix (ECM)?

Collagen fibers, proteoglycans, and polysaccharides. Signup and view all the answers

Which of the following is NOT a characteristic of type IV collagen?

Rich in hydrophobic residues. Signup and view all the answers

What effect does the hydrophobic nature of elastin have on its structure?

It contributes to the loose random coil conformation of hydrophobic domains. Signup and view all the answers

What is the primary role of glycosaminoglycans (GAGs) like heparan sulfate in the basal lamina?

To attract and bind growth factors. Signup and view all the answers

Study Notes

Lectures 17-20: From Cells to Tissue: ECM

ECM (Extracellular Matrix): A material produced by cells and secreted into the surrounding medium. Primarily found in animal tissues.
Tissue Definition: A tissue is an assembly of similar cells and their extracellular matrix, all from the same origin, working together to perform a specific function.
Cell Adhesion: Essential to form multicellular organisms
Cells exist alone – unicellular organisms, like some bacteria.
Planktonic bacteria – float freely in solutions.
Sessile bacteria – attach to surfaces or within biofilms.
Cell attachments to surfaces, foods and other cells.
Virulence factors in bacteria aid attachment and resistance to the immune response, such as pili (fimbrae).
Cell Interactions: Different sides of a cell possess different roles and interactions.
Cells need to stick together for communication and transport.
Cells need to form specialized domains.
Animal Tissues: Two broad categories:
Connective tissues (bones, tendons) with low cell density and abundant ECM (extracellular matrix). The ECM carries loads and withstands forces.
Epithelial tissues (gut lining, skin epidermis) with cells closely bound together (sheets). Thin extracellular matrix (ECM) is on one side only, known as the basal lamina.

ECM Definition

ECM Definition: Any material produced by cells and secreted into the surrounding medium; usually refers to the non-cellular components of animal tissues.
Plants and Fungi: Produce an extracellular matrix or walls, distinct from animal ECM. Arthropods (insects, crustaceans) produce chitin.
Biopolymers: Chitin and cellulose are the most abundant biopolymers on Earth.

The Extracellular Matrix (ECM)

Component: Complex network of proteins and polysaccharides.
Origin: Produced by cells.
Formation: Secreted and modified outside the cells by different enzymes.

Functions of the Extracellular Matrix (ECM)

Mechanical: Provides tensile and compressive strength and elasticity
- Example: Bone matrix is highly mineralised to withstand compression, tendons are highly elastic; cornea of eye has transparent ECM.
Protection: Buffers against extracellular changes and retains water within tissue space
Organization: Controls cell behavior by binding to growth factors and interacting with cell-surface receptors.

ECM Specializations

Bone and Teeth: Highly mineralised ECM to withstand compression.
Tendons: High elasticity ECM
Eye Cornea: Transparent ECM

ECM Components

Connective Tissues: Fibroblasts secrete the majority of the matrix macromolecules.
Osteoblasts: Form bone
Chondroblasts: Form cartilage
Major ECM Components: Glycosaminoglycans (GAGs) (acidic polysaccharide derivatives), fibrous proteins (e.g., collagen family members), non-collagen glycoproteins (e.g., fibronectin, laminin), and miscellaneous proteins (e.g., elastin)

Glycosaminoglycans (GAGs)

Structure: Unbranched polymers of repeated disaccharide derivatives. Featuring amino sugars, sulfated amino sugars, and uronic acids.
Properties: Acidic and negatively charged, attracting positive ions (e.g., Na+) and causing water retention (gel formation). Making up 10% of the ECM mass but accounting for 90% of the ECM volume. Provide compressive strength. Metabolically cheap bulking agent.
Example: Hyaluronan: A major GAG, spun out from cell membranes, huge size compared to other GAGs; does not attach to proteins covalently. Often added and removed to modulate cell function.
Other GAGs: Include chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate. Typically chemically bound to proteoglycans.

Proteoglycans

Definition: Serine-rich proteins, decorated with hundreds of glycosaminoglycans (GAGs), covalently attached.
Aggrecan: A common proteoglycan in the ECM. Its core protein is decorated with many chondroitin and keratan sulfate chains, and then attached to hyaluronan via adaptor proteins.

Heparan Sulfate Proteoglycans

Function: Important in cell growth processes. Bind to chemokines at inflammatory sites (and so prolong white blood cell attraction). Bind and block certain proteases. Oligomerize fibroblast growth factor (FGF), providing easier binding to its tyrosine kinase receptor.

Collagen and Other ECM Proteins

Collagen: Fibrous protein made up of three alpha chains forming a triple helix, providing tensile strength to the ECM
Collagen synthesis:
- Pro-alpha chains synthesized in RER
- Procollagen assembled
- Procollagen secreted into the ECM
- Terminal propeptides cleaved
- Collagen fibrils self-assemble
- Collagen molecules crosslinked
Collagen fibrils (strength) Highly stable and stable lasting up to 10 years
Types of Collagen: Many forms with different functions
Type I: Primarily in skin, bones and tendons
Type II: Similar tensile strength to cartilage.
Type IX and XII are fibril-associated, linking I or II fibrils and imparting flexibility.
Type IV and VII: Form a mesh in the basal lamina.

Other ECM Components: Elastin

Structure: A fibrous glycoprotein, primarily comprised of a repetitive hydrophobic amino acid sequence. Contains non-glycosylated amino acids like proline and glycine.
Property: Extensible (due to loose conformation). Cross-linked via helical regions.
Fibrillin: A glycoprotein, crucial for the proper arrangement and stability of elastin during deposition
Genetic defects in fibrillin related proteins causes Marfan Syndrome.

The Basal Lamina

Definition: A specialized ECM found underlying epithelial cells, also known as the basement membrane.
Function: Controls cell polarity, organizes and binds cells, provides a barrier to certain cells and a highway/pathways for cell migration.
Components: Heparan sulfate proteoglycans, type IV collagen, laminin , nidogen, perlecan.

Interactions between Basal Lamina proteins

Interactions: Proteins within the basal lamina, e.g. type IV collagen, perlecan, laminin, and nidogen, interact to form the basal lamina structure.

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Dive into the intricate world of the extracellular matrix and how it forms the foundation of animal tissues. This quiz covers key concepts such as cell adhesion, types of bacteria, and the roles of cell interactions within multicellular organisms. Test your understanding of how cells work together to form specialized functions.