Biology Quiz on Fibronectin Structures

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Questions and Answers

What type of collagen does not form fibrils or fibers?

Type II

Type V

Type I

Type IV (correct)

Which amino acid is MOST prevalent in collagen composition?

Hydroxyproline

Hydroxylysine

Glycine (correct)

Proline

What type of collagen is classified as linking or anchoring collagen?

Type IV

Type II

Type I

Type VII (correct)

How can the amount of collagen in a tissue be determined?

By measuring the hydroxyproline content Signup and view all the answers

What characteristic amino acids contribute to the synthesis of collagen but are not incorporated into the protein itself?

Hydroxyproline and Hydroxylysine Signup and view all the answers

What characteristics define glycosaminoglycans?

They are linear polysaccharides made of repeating disaccharide units. Signup and view all the answers

Which statements accurately describe laminin?

Laminin has a cross-shaped structure and is found in basal laminae. Signup and view all the answers

What role do integrins play in the extracellular matrix?

Integrins connect cells to specific sequences on extracellular matrix proteins. Signup and view all the answers

What property of glycosaminoglycans contributes to their hydrophilic nature?

The presence of hydroxyl, carboxyl, and sulfate groups Signup and view all the answers

How are fibronectin and laminin similar?

Both proteins have binding sites for collagen and cell receptors. Signup and view all the answers

What is a key feature of the molecular structure of fibronectin?

It has multiple binding sites for different extracellular components. Signup and view all the answers

Which statement is false regarding integrins?

Integrins are exclusively located on immune cells. Signup and view all the answers

What type of cells primarily synthesize fibronectin?

Fibroblasts and epithelial cells Signup and view all the answers

What is a primary characteristic of elastic fibers?

They can stretch up to 150% of their length. Signup and view all the answers

Which component is not part of elastic fibers?

Collagen type I Signup and view all the answers

What staining method produces a black color for elastic fibers?

Aldehyde-fuchsin Signup and view all the answers

What is the role of lysyl oxidases in the context of fibrillar structures?

They catalyze the formation of covalent crosslinks. Signup and view all the answers

What is a distinguishing feature of reticular fibers during embryogenesis?

They are replaced by regular collagen fibers eventually. Signup and view all the answers

Which of the following statements about elastic fibers is true?

They form an irregular network and have a characteristic yellow color. Signup and view all the answers

What type of fibers create flexible networks in organs subject to increased volume?

Elastic fibers Signup and view all the answers

What color do elastic fibers appear when stained using Resorcin-fuchsin?

Purple Signup and view all the answers

What is the molecular weight of proelastin before it polymerizes to form elastin?

70,000 Signup and view all the answers

Which statement accurately describes the amino acid composition of elastin compared to collagen?

Elastin has a greater quantity of valine and alanine than collagen. Signup and view all the answers

Which of the following best describes the stability of elastin's structure?

Stabilized by hydrophobic interactions among non-polar peptide chains. Signup and view all the answers

What unusual amino acids are formed in elastin through covalent reactions?

Desmosine and isodesmosine Signup and view all the answers

What type of cells primarily produce elastin in the body?

Fibroblasts Signup and view all the answers

Which of the following statements about mast cells is accurate?

Mast cells are involved in both local inflammatory responses and innate immunity. Signup and view all the answers

What characterizes dense connective tissue compared to loose connective tissue?

Dense connective tissue has fewer cells and a predominance of collagen fibers. Signup and view all the answers

Which of the following bioactive substances is NOT typically released by mast cells?

Prostaglandins Signup and view all the answers

How do connective tissue mast cells differ from mucosal mast cells?

Mucosal mast cells contain proteoglycan chondroitin, while connective tissue mast cells contain heparin. Signup and view all the answers

What is the primary function of mast cells in the context of tissue repair?

To release mediators that influence the inflammatory response. Signup and view all the answers

Which of the following features is characteristic of all mast cells?

Mast cells have a high concentration of basophilic granules. Signup and view all the answers

What is the function of leukotrienes released by mast cells?

To regulate the immune response and attract other immune cells. Signup and view all the answers

Which type of connective tissue is characterized by having fibers arranged in a parallel manner?

Dense regular connective tissue. Signup and view all the answers

Study Notes

Fibronectin

Highly hydrated, observed as empty spaces upon dessication in mounted slides.
Molecular Weight between 235 - 270 kDa; exists in dimeric form.
Synthesized by fibroblasts and epithelial cells.
Contains binding sites for cells, collagen, and glycosaminoglycans.
Facilitates normal cell adhesion and migration.

Glycosaminoglycans (GAGs)

Also termed mucopolysaccharides; consist of linear polysaccharides with repeating disaccharide units.
Comprised of hexosamine (glucosamine or galactosamine) and uronic acids (glucuronic or iduronic acid).
Heparan sulfate is notable for its high molecular weight (hundreds to thousands of kDa).
GAGs are intensely hydrophilic, bind cations, and are crucial in maintaining tissue hydration.

Laminin

Trimeric glycoprotein with a molecular weight of 200 - 400 kDa; possesses a cross-shaped structure.
Primarily found in the basal laminae, aiding the adhesion of epithelial cells.

Integrin

Functions as matrix receptors that recognize specific sequences on laminin, fibronectin, and various extracellular matrix proteins.
Composed of heterodimers with α and β chains; acts as a crucial link between cells and the ECM.

Types of Collagen

Type IV collagen forms sheet-like structures in basal laminae; does not form fibrils or fibers but exists as unpolymerized procollagen.
Fibrillar collagens (Types I, II, III) are significant structural proteins that form fibrils.
Type VII collagen serves as linking/anchoring collagen, connecting fibrillar collagens and ECM components; prevalent across numerous cells.

Collagen Composition

Major amino acids include glycine (33.5%), proline (12%), and hydroxyproline (10%).
Tissue collagen content can be quantified via hydroxyproline measurement.
Unique characteristics include hydroxylation of proline and lysine, yielding hydroxyproline and hydroxylysine.

Elastic Fibers

Composed of thin, branching fibers that form irregular networks, characterized by their yellow color in fresh samples.
Capable of stretching up to 150% of their length while readily returning to the original shape (recoil).
Composed of an amorphous region with elastin and a sheath of 14nm microfibrils.

Elastin

Secreted as proelastin (molecular weight of 70,000), polymerizes to form elastin.
Highly resistant to boiling and chemical extraction; not digested by trypsin.
High in valine and alanine, and contains unique amino acids desmosine and isodesmosine.

Cells of Connective Tissue

Connective tissue cells support epithelial structures and fill spaces between fibers and muscle sheaths.
Most notable cell types include fibroblasts and macrophages, responsible for tissue maintenance and immune responses.

Mast Cells

Oval to round cells (20-30μm), filled with basophilic granules; central, small nucleus.
Metachromatic properties allow for color change of basic dyes from blue to purple/red.
Key players in local inflammatory responses, releasing leukotrienes and various bioactive substances (e.g., histamine, heparin).
Two subtypes: connective tissue mast cells (primarily heparin) and mucosal mast cells (primarily chondroitin).

Dense Connective Tissue

Similar components to loose connective tissue but dominated by collagen fibers.
Features fewer cells, with fibroblasts being predominant.
Types include dense irregular connective tissue (fibers orient randomly) and dense regular connective tissue (provides multi-directional stress resistance).

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Description

This quiz covers the properties and structures related to fibronectin, including its hydration status and molecular weight. Participants will explore how fibronectin functions in the body, particularly in relation to fibroblasts and epithelial cells. Test your understanding of this essential protein!