Biochemistry: Fibrous Proteins

Questions and Answers

Which type of collagen is primarily associated with tendon and corneal structures?

Type III

Type II

Type I (correct)

Type IV

What characterizes a triple-helical structure in collagen?

A linear arrangement of amino acids

Single polypeptide chain

Two intertwined polypeptide strands

Three polypeptide α-chains (correct)

What role do hydroxyproline and hydroxylysine play in collagen?

They function solely as a source of energy.

They are amino acids that inhibit cross-linking.

They are involved in degrading collagen.

They are crucial for stabilizing the collagen structure. (correct)

Glycosylation in collagen biosynthesis is important for what reason?

It influences the stability and structure of collagen. Signup and view all the answers

How many types of collagen are known to exist?

More than 25 types Signup and view all the answers

What is the main function of fibril-associated collagens?

They provide structural support and stability. Signup and view all the answers

What is the primary structure of collagen defined by?

A unique sequence of amino acids Signup and view all the answers

Which types of collagen are classified as fibril-forming collagens?

Type I, II, and III Signup and view all the answers

Degradation of collagen is generally associated with which physiological processes?

Tissue repair and remodeling Signup and view all the answers

What is the significance of the half-life of normal collagens?

It can last as long as several years. Signup and view all the answers

What initiates the formation of procollagen from pro-α chains?

Formation of interchain disulfide bonds. Signup and view all the answers

Which enzymes are primarily responsible for the initial breakdown of procollagen?

Collagenases Signup and view all the answers

What is the outcome of the extracellular cleavage of procollagen?

Release of triple-helical tropocollagen molecules. Signup and view all the answers

Which part of the procollagen molecule is flanked by nonhelical amino acids?

Central region Signup and view all the answers

Which family of proteins is involved in the further degradation of collagen into amino acids?

Metalloproteinases Signup and view all the answers

What are the resulting fragments after the cleavage of procollagen?

¾ + ¼ length fragments Signup and view all the answers

What role do propeptides play in the structure of procollagen?

They flank the central region of procollagen, assisting in stability. Signup and view all the answers

What type of collagen can be specifically degraded by collagenases as mentioned in the content?

Type I collagen Signup and view all the answers

How does the collagen structure respond to tissue growth or injury?

It undergoes dynamic remodeling. Signup and view all the answers

What is the primary physiological role of α1-antitrypsin in the body?

To inhibit the activity of neutrophil elastase Signup and view all the answers

Which enzyme's activity is inhibited by α1-antitrypsin?

Neutrophil elastase Signup and view all the answers

Where is α1-antitrypsin primarily synthesized?

Liver Signup and view all the answers

What characteristic makes alpha-keratins important in forming tough fibers?

The presence of disulfide bonds Signup and view all the answers

What structural role do alpha-keratins play in the body?

They are components of intermediate filaments Signup and view all the answers

What is a key feature of α1-antitrypsin that contributes to its function in proteolytic inhibition?

It constitutes 90% of α1-globulin Signup and view all the answers

What is the role of glycine in the structure of collagen?

Found in every third position of the polypeptide chain. Signup and view all the answers

Which amino acids can undergo hydroxylation during collagen biosynthesis?

Only proline and lysine. Signup and view all the answers

What is required for the hydroxylation of proline and lysine in collagen?

Hydroxylating enzymes and ascorbic acid. Signup and view all the answers

The repeating sequence found in collagen is denoted as Gly – X – Y. What does 'X' represent?

Proline. Signup and view all the answers

What is the consequence of ascorbic acid deficiency in collagen synthesis?

Impaired interchain H-bond formation. Signup and view all the answers

In collagen, what effect does glycosylation of hydroxylysine have?

It stabilizes the triple-helical structure. Signup and view all the answers

Which cells are primarily responsible for the synthesis of collagen precursors?

Fibroblasts. Signup and view all the answers

How does hydroxyproline contribute to collagen's structure?

It enhances interchain hydrogen bond formation. Signup and view all the answers

What specific modification occurs to prepro-α chains during collagen synthesis?

Cleavage to yield pro-α chains. Signup and view all the answers

Collagen's triple-helical structure is primarily characterized by which of the following features?

Fibrous and elongated configuration. Signup and view all the answers

What is the role of lysyl oxidase in collagen formation?

It forms covalent cross-links in the collagen fibrils. Signup and view all the answers

Which type of Ehlers-Danlos syndrome is most clinically important due to its impact on blood vessels?

Type III Signup and view all the answers

What is a characteristic symptom of Osteogenesis Imperfecta Type II?

Pulmonary hypoplasia leading to early infant mortality Signup and view all the answers

What mutation is associated with Osteogenesis Imperfecta Type I?

Decreased production of α1 and α2 chains Signup and view all the answers

Which of the following is NOT a characteristic feature of Ehlers-Danlos syndrome?

Mutations in pro-α1 and pro-α2 chains Signup and view all the answers

What is the primary defect in Menkes disease?

Copper deficiency affecting collagen maturation Signup and view all the answers

Which cross-linking enzyme requires copper as a cofactor?

Lysyl oxidase Signup and view all the answers

Which collagen type is primarily affected in Ehlers-Danlos syndrome?

Type I Signup and view all the answers

What is a common complication observed in individuals with Osteogenesis Imperfecta?

Bone fractures from minimal trauma Signup and view all the answers

Which of the following results from the mutation of the amino acid sequence in collagen types I, III, or V?

Ehlers-Danlos syndrome Signup and view all the answers

Study Notes

Collagen

Over 25 types of collagen identified, categorized into three main groups based on structure and function.
Fibril-forming collagens (Types I, II, III) provide high tensile strength, forming supportive structures such as tendons and corneas.
Network-forming and fibril-associated collagens serve different structural purposes in connective tissues.

Structure of Collagen

Amino acid sequence rich in proline and glycine; repeating pattern of Gly-X-Y, where X is often proline and Y is hydroxyproline or hydroxylysine.
Triple-helical structure formed by three polypeptide α-chains, contributing to collagen's fibrous and elongated shape.
Hydroxyproline stabilizes the triple helix through interchain hydrogen bonds; not commonly found in other proteins.

Biosynthesis of Collagen

Pro-α chains are synthesized in fibroblasts, osteoblasts, and chondroblasts and begin with an N-terminal signal sequence.
Hydroxylation of proline and lysine is essential for stability, requiring enzymes, oxygen, iron, and vitamin C.
Pro-α chains form procollagen which moves to the Golgi, where it is packaged and secreted.
Extracellular cleavage by procollagen peptidases converts procollagen to tropocollagen, leading to fibril formation.

Collagen Degradation

Collagen is highly stable with a long half-life, constantly remodeled by collagenases (metalloproteinases) in response to tissue growth or injury.
Specific cleavage points lead to tropocollagen fragments, which are further degraded by proteinases.

Collagen Diseases (Collagenopathies)

Ehlers-Danlos syndrome: Hereditary defect leading to a generalized connective tissue disorder affecting Types I, III, or V collagen. Symptoms include fragile skin and easy joint dislocations.
Osteogenesis Imperfecta: Brittle bone syndrome causing fractures with minimal trauma. Two main types:
- Type I: Less severe, presenting in infancy with decreased collagen production.
- Type II: Most severe and fatal in utero or neonatally due to mutations in collagen genes.

α1-Antitrypsin and Elastin Degradation

α1-antitrypsin (A1AT) acts as a protease inhibitor, particularly for neutrophil elastase that degrades elastin and other structural proteins.
Predominantly synthesized in the liver, crucial for preventing tissue injury by controlling enzymatic activity in various tissues.

Alpha-Keratins

Tough fibrous proteins found in hair, nails, and the outer layer of the epidermis.
Constituent of intermediate filaments, distinguished by high cysteine content, providing disulfide bonds that enhance their insolubility and resistance to stretching.

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Description

Dive into the fascinating world of fibrous proteins with a focus on collagen. This quiz covers various types of collagen, including their structures and amino acid sequences, essential for understanding protein biology. Enhance your knowledge about collagen's unique triple-helical structure and its significance in biochemistry.

Biochemistry: Fibrous Proteins - Collagen Types