ECM

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Questions and Answers

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

To allow cells to remain isolated from one another

To prevent tissues from forming

To enable cells to be unicellular in function

To facilitate communication and transport between cells (correct)

Which component is primarily involved in the initial attachment of bacterial cells?

Cell wall

Pili (fimbrae) (correct)

Plasma membrane

Extracellular matrix

What differentiates the extracellular matrix (ECM) in various tissues?

The mechanical properties it provides (correct)

The type of cells present in the tissue

The presence of immune cells

The genetic makeup of the cells

How do tissues form in a multicellular organism?

By a collection of similar cells and their ECM working together Signup and view all the answers

What is one significant challenge faced when moving from unicellular to multicellular forms?

Achieving communication and transport between cells Signup and view all the answers

Which of the following best describes the composition of a tissue?

An ensemble of cells and their extracellular matrix from the same origin Signup and view all the answers

What role do extracellular matrix components play in tissues?

To provide structural support and mechanical properties Signup and view all the answers

Which statement about the extracellular matrix is incorrect?

ECM is solely composed of cells. Signup and view all the answers

What characteristic of the extracellular matrix (ECM) in bone and teeth allows it to withstand compression?

High mineralization Signup and view all the answers

Which component of the ECM is primarily responsible for its elastic properties?

Elastin Signup and view all the answers

What is the main role of glycosaminoglycans (GAGs) within the ECM?

Gel formation and compressive strength Signup and view all the answers

What is distinctive about hyaluronan compared to other glycosaminoglycans?

It is not covalently attached to proteins. Signup and view all the answers

What percentage of the volume of the ECM do glycosaminoglycans (GAGs) typically comprise?

90% Signup and view all the answers

What is the primary function of the ECM in the cornea of the eye?

Maintaining transparency Signup and view all the answers

Which cells are responsible for secreting the macromolecules that form the extracellular matrix?

Fibroblasts Signup and view all the answers

Which of the following GAGs is not sulfated?

Hyaluronan Signup and view all the answers

What is a characteristic feature of a proteoglycan?

It is a serine-rich protein decorated with acidic, sulfated GAGs. Signup and view all the answers

Which GAG is primarily associated with Aggrecan in the extracellular matrix?

Chondroitin Signup and view all the answers

What role does heparan sulphate proteoglycan play in cellular functions?

Facilitates binding of fibroblast growth factor to its receptor. Signup and view all the answers

What is the typical size range of sugar residues in glycosaminoglycans (GAGs)?

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

What is the composition of collagen in the extracellular matrix?

Three α-chains forming a triple helix. Signup and view all the answers

What forms the core structure of collagen chains?

GXY repeats Signup and view all the answers

What stabilizes the triple helix structure of collagen?

Hydrogen bonding between -OH groups of hydroxyproline Signup and view all the answers

What happens to procollagen after it is secreted into the extracellular space?

Terminal propeptides are cleaved Signup and view all the answers

What is the consequence of a vitamin C deficiency on collagen synthesis?

Improper hydroxylation of prolines Signup and view all the answers

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

Type I Signup and view all the answers

How long do collagen fibrils typically last in the body?

Years Signup and view all the answers

Which property distinguishes type IX and XII collagen from type I and II?

They don’t form fibers Signup and view all the answers

What role does proline hydroxylase play in collagen synthesis?

Formation of hydroxyproline Signup and view all the answers

What provides the extracellular matrix (ECM) with its elasticity?

Elastin Signup and view all the answers

What role does fibrillin play in elastin deposition?

Acts as a scaffold for elastin formation Signup and view all the answers

Which glycosaminoglycan (GAG) is mentioned as part of the basal lamina?

Heparan sulfate Signup and view all the answers

What characterizes the structure of elastin?

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

How do type IV and type VII collagen contribute to the basal lamina?

They form a mesh structure in the basal lamina Signup and view all the answers

What condition is caused by defects in the FIBRILLIN 1 gene?

Marfan syndrome Signup and view all the answers

What component is crucial for organizing and binding cells within the basal lamina?

Laminin Signup and view all the answers

Which of the following statements about the extracellular matrix (ECM) is incorrect?

The ECM is always heavily glycosylated Signup and view all the answers

Study Notes

Need for Cell Adhesion

Unicellular organisms exist on their own
Bacteria can be planktonic (free-floating) or sessile (attached)
Multicellular organisms face challenges with cell adhesion, communication, and specialization

Cell Adhesion & Tissues

A tissue is a group of similar cells and their ECM that perform a specific function.
Organs are formed by multiple tissues working together.
Cells can be linked through direct interaction or through the ECM.
The ECM can be specialized for different tissues:
- Bone and teeth have a highly mineralized ECM for compression resistance.
- The cornea of the eye has a transparent ECM.
- Tendons have a highly elastic ECM.
- Blood plasma is a liquid form of ECM.

ECM Components

Fibroblasts secrete ECM components in connective tissues
Osteoblasts form bone, chondroblasts form cartilage
Main ECM components:
- Glycosaminoglycans (GAGs): acidic polysaccharide derivatives, form proteoglycans
- Fibrous proteins: including collagen family members
- Non-collagen glycoproteins: like fibronectin and laminin
- Others: such as elastin

Glycosaminoglycans (GAGs)

Unbranched polymers of repeating disaccharide derivatives (amino sugars, sulfated acetylamino sugars, uronic acids)
Acidic and negatively charged, attract positive ions (Na+), leading to gel formation
Comprise 10% of ECM mass but 90% of volume
Provide compressive strength (especially hyaluronan)
Metabolically cheap bulking agent

Hyaluronan (GAG)

Spun out from the cell membrane
Enormous (10^7 kDa, much larger than other GAGs)
Not sulfated
Not covalently linked to protein ('stand alone')
Often added to the ECM to hold open spaces for cell migration, then removed by hyaluronidase

Other GAGs

Usually bound to proteoglycans
20-200 sugar residues long
Types:
- Chondroitin-4-sulphate
- Chondroitin-6-sulphate
- Dermatin sulphate
- Heparan sulphate
- Heparin
- Keratan sulphate

Proteoglycans

Serine-rich proteins with hundreds of O-linked acidic, sulfated GAGs
Link tetrasaccharide is assembled on a serine side chain, followed by GAG chain synthesis
Aggrecan (common proteoglycan):
- Core protein with ~100 chondroitin and 30 keratan chains
- Binds to hyaluronan (100:1) through adaptor proteins
- Forms large aggregates with hyaluronan (up to 5µm long)

Heparan Sulphate Proteoglycans

Important role in cell growth
Bind chemokines at inflammatory sites, prolonging white cell attraction
Bind and block certain proteases
Oligomerize FGF, promoting binding to its tyrosine-kinase receptor

Collagen

Fibrous protein of three α-chains forming a triple helix
Provides tensile strength to the ECM
α-chains consist of GXY repeats:
- G: Glycine
- X: commonly proline
- Y: commonly hydroxyproline
Hydrogen bonding between -OH groups of hydroxyproline stabilizes the triple helix
Lysines can be hydroxylated and glycosylated

Collagen Synthesis

Pro-α-chains synthesized on RER
Assembly into procollagen
Procollagen secreted into extracellular space
Terminal propeptides cleaved to form 100nm long collagen chains
Collagen molecules cross-linked to form fibrils (oxidative deamination of hydroxylysine and lysine)
Fibrils self-assemble into fibers
Fibrils are highly stable and last around 10 years

Collagen Defects and Scurvy

Scurvy: weakened collagen tissues due to deficiency in vitamin C
Vitamin C: cofactor for proline hydroxylase, which creates hydroxyproline
Unhydroxylated collagen: destroyed before secretion, leading to weakened tissues

Collagen Types

Type I: most common fibrillar form, found in skin, bones, and tendons
Type II: similar tensile strength, found in cartilage
Type IX and XII: fibril-associated, don't form fibers, more flexible
Type IV and VII: form a mesh structure in the basal lamina

Elastin

Provides elasticity to the ECM
~750 amino acids long, highly hydrophobic, rich in proline and glycine
Non-glycosylated
Alternating stretches of hydrophobic residues and alanine/lysine-rich α-helices
Cross-linking via α-helical regions
Hydrophobic domains are extensible due to loose random coil conformation

Fibrillin and Elastin Deposition

Elastic fibers have an elastin core coated with microfibrils
Microfibrils are made of glycoproteins like fibrillin
Microfibrils act as a scaffold for elastin formation
Marfan syndrome: defects in FIBRILLIN 1 gene, resulting in weak elastic tissues (e.g., Abraham Lincoln)

Basal Lamina

Specialized ECM underlying epithelial cells
Roles:
- Structural support
- Determination of cell polarity
- Organization and binding of cells
- Barrier for certain cells
- Cell migration pathways
Components:
- GAGs: heparan sulphate
- Proteins: laminin, Type IV collagen, nidogen (entactin), perlecan

Lecture Summary

Tissues are groups of similar cells and their ECM that perform a specific function.
The ECM provides structure and support, and its composition varies between tissues.
The basal lamina is a specialized ECM found beneath epithelial cells.

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Description

Explore the fascinating world of cell adhesion and the extracellular matrix (ECM) in this quiz. Understand the roles of tissues, the unique properties of various ECM components, and how cells collaborate to form complex structures in multicellular organisms.

ECM