Biochemistry: Fibrous Proteins Overview
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Questions and Answers

What is the function of fibrous proteins?

Fibrous proteins provide support and aid in structure.

Which of the following are examples of fibrous proteins?

  • Hemoglobin
  • Keratins (correct)
  • Elastins (correct)
  • Myoglobin
  • Collagens (correct)

    • What is the primary function of collagen molecules?

    To provide structural support to tissues.

    Collagen is composed of a single polypeptide chain.

    <p>False</p> Signup and view all the answers

    What is the name of the basic unit of collagen?

    <p>Tropocollagen</p> Signup and view all the answers

    Every ______ amino acids in collagen contains glycine.

    <p>three</p> Signup and view all the answers

    Which amino acid is responsible for the kinks in the collagen helix?

    <p>Proline</p> Signup and view all the answers

    What is the role of hydroxyproline in collagen?

    <p>Hydroxyproline stabilizes the helical conformation of collagen and contributes to its thermal stability.</p> Signup and view all the answers

    What happens to collagen at temperatures above 40 degrees Celsius?

    <p>Denaturation of collagen occurs due to loss of hydrogen bonds.</p> Signup and view all the answers

    What are the two types of modified lysine found in collagen?

    <p>Hydroxylysine and allysine</p> Signup and view all the answers

    What is the main function of cross-linking in collagen fibers?

    <p>To provide strength and prevent tissues from tearing.</p> Signup and view all the answers

    What are the two enzymes involved in the formation of modified lysine?

    <p>Lysyl hydroxylase and lysyl oxidase</p> Signup and view all the answers

    What enzyme helps maintain the helical shape of collagen?

    <p>Prolyl hydroxylase</p> Signup and view all the answers

    What is the name of the disease caused by a deficiency of vitamin C?

    <p>Scurvy</p> Signup and view all the answers

    Scurvy can lead to spontaneous bleeding of the gums and loose teeth.

    <p>True</p> Signup and view all the answers

    What is the main component of elastic fibers?

    <p>Elastin</p> Signup and view all the answers

    What are the two main types of segments found in elastin?

    <p>Hydrophobic segments and alanine- and lysine-rich helical segments</p> Signup and view all the answers

    Elastin is glycosylated.

    <p>False</p> Signup and view all the answers

    What is the name of the cross-link formed between four allysyl side chains and one unaltered lysyl side chain?

    <p>Desmosine</p> Signup and view all the answers

    What type of bond is formed between cysteine residues in keratin?

    <p>Disulfide bond</p> Signup and view all the answers

    Which of the following is NOT a characteristic of keratin?

    <p>It is a component of elastin fibers</p> Signup and view all the answers

    What is the name of the smaller, twisted structure of a-keratin?

    <p>Dimer</p> Signup and view all the answers

    How many protofibirls combine to form one microfibril?

    <p>Eight</p> Signup and view all the answers

    What process can harden a-keratin in nails?

    <p>The introduction of disulfide cross-links</p> Signup and view all the answers

    How do hot or cold water affect the structure of hair?

    <p>Hot or cold water can affect the hydrogen bonds in hair, leading to temporary changes in hair style.</p> Signup and view all the answers

    What is the purpose of a reducing substance in the permanent hair waving process?

    <p>To reduce some of the disulfide cross-links in hair.</p> Signup and view all the answers

    What is used to reform the disulfide cross-links in the permanent hair waving process?

    <p>An oxidizing agent</p> Signup and view all the answers

    Keratin is used to straighten hair.

    <p>True</p> Signup and view all the answers

    What is the final product of the polymerization of five protocollagen molecules?

    <p>A microfibril</p> Signup and view all the answers

    What are the types of bonds that strengthen the formation of collagen fibrils?

    <p>Covalent cross-links between lysine residues</p> Signup and view all the answers

    What is the most common type of collagen found in bones and cartilage?

    <p>Type I collagen</p> Signup and view all the answers

    What does the term 'resilient' mean in the context of tissues?

    <p>Resilient tissues have the ability to return to their original shape after being stretched or deformed.</p> Signup and view all the answers

    What is the primary feature of a typical collagen molecule?

    <p>Its stiffness</p> Signup and view all the answers

    The amount of cross-linking in a tissue decreases with age.

    <p>False</p> Signup and view all the answers

    What is the major difference between a-keratin and b-keratin?

    <p>a-keratin is found in mammals, while b-keratin is found in birds and reptiles.</p> Signup and view all the answers

    A-keratin is the major protein of hair and fingernails in mammals.

    <p>True</p> Signup and view all the answers

    Elastin is present in the extracellular matrix.

    <p>True</p> Signup and view all the answers

    What are the two main types of molecules that are interwoven in the extracellular matrix?

    <p>Collagen fibers and elastin fibers</p> Signup and view all the answers

    The arrangement of collagen and elastin fibers in the extracellular matrix affects the tissue's flexibility and resilience.

    <p>True</p> Signup and view all the answers

    Study Notes

    Biochemistry Study Notes

    • Sheet number: 20
    • Document Year: 2024
    • Written by: Duha Alnader & Wedad Mustafa
    • Edited by: Reem Ghnemat
    • Doctor: Dr. NafezaButarboush

    Fibrous Proteins

    • Structure-Function Relationship: Fibrous proteins have a strong, solid structure for support. They have a specific type of secondary structure that repeats, allowing for compression and expulsion of water, creating a strong structure. They may also have tertiary and quaternary structures.
    • Biological Functions: Enzymes catalyze reactions. Transport molecules include hemoglobin and lipoproteins. Contractile proteins like myosin and actin, along with structural proteins such as collagen and keratin, are involved in movement and structure. Defense proteins include antibodies (i.e. immunoglobulins). Signaling molecules like hormones are involved in communication, along with receptors and toxins (e.g., diphtheria & enterotoxins).
    • Types: Fibrous proteins have a uniform secondary structure only. Globular proteins have three-dimensional compact structures.
    • Examples: Collagen, elastin, and keratin are fibrous proteins. Myoglobin, hemoglobin, and immunoglobulins are globular proteins.

    Extracellular Matrix

    • Composition: The extracellular space is filled with an intricate network of macromolecules including proteins and polysaccharides. Collagen is synthesized by cells and released into the extracellular fluid (ECF), providing structural support and tissue straightening.
    • Collagen Properties: Collagen accounts for 40% of proteins in the body. It is a family of fibrous proteins with 25 types found in all multicellular animals. Type I collagen is the most common, found in bones and cartilages. Types differ in amino acid composition but share similar structural features. The main function of collagen is to provide structural support in tissues. It is stiff.
    • Structure of Collagen: It is a left-handed, triple-stranded, helical protein (tropocollagen). The collagen helix is more extended than the typical α-helix. Every 3 amino acids, a glycine is present. Glycine is the most frequent amino acid in collagen and breaks up the α-helix. Collagen has high amounts of glycine (33%), and proline (13%), and hydroxyproline (9%) & hydroxylysine.

    Structure of Collagen

    • Properties: Left-handed, triple-stranded, helical protein where three polypeptide chains (a-chains) are wound around one another. Compared to α-helices, collagen helices are more extended (3.3 residues per turn). The basic unit is tropocollagen. Glycine (a breaker of alpha-helices) is present every 3rd amino acid in the sequence. Collagen differs in length (5.4A) and number of amino acids per turn (3.6A) from α-helices.
    • Composition: Rich in glycine (33%), proline (13%) and hydroxyproline (9%). The modified form of proline is hydroxyproline, which creates kinks that disrupt the helical structure.

    Functional purpose of amino acids:

    • Glycine: Packs the three α-chains together to form the final collagen superhelix. It causes the formation of the final triple helical structure.
    • Proline: Creates kinks and stabilizes the helical conformation of each α chain.

    Hydroxylysine (modified Lysine)

    • Lysine can form an aldehyde, or remain as is.
    • Hydroxylysine acts as an attachment site for polysaccharides, making the polypeptide chain a glycoprotein
    • Two enzymes hydroxylase and oxidase are involved in forming modified forms (crosslinks) of lysine.

    Oxidation of lysine

    • Some lysines are oxidized to aldehyde (allysine)
    • Covalent aldol linkages form between hydroxylysines or other modified lysines creating covalent bonds between polypeptide chains.

    Function of Cross-Linking

    • Purpose: Cross-linking strengthens collagen fibers.
    • Formation: The formation of cross-linking in collagen involves the modification of lysine residues. Hydroxylysine is first formed and then converted to an aldehyde (oxidation). This covalent bond formation stabilizes the side-by-side packing of collagen molecules, creating stronger fibers.

    Formation of collagen fibers

    • Following release of procollagen, 5 molecules connect through aldehyde bonds to form microfibrils.

    • Microfibrils combine forming larger collagen fibers which are stabilized by cross-links between lysine residues

    Scurvy (acquired disease):

    • Cause: A dietary deficiency of vitamin C (ascorbic acid).
    • Mechanism: Vitamin C is a coenzyme that is necessary for the proper hydroxylation of proline and lysine residues in collagen. Without this hydroxylation process, the triple helix structure of collagen cannot form. Defective collagen is rapidly degraded.
    • Symptoms: Blood vessel fragility, spontaneous bleeding, bruising, and teeth loosening.

    Elastins

    • Properties: Prevents tearing of tissues during stretching. Has weak bonds between small polypeptides and primarily non-polar interactions.
    • Resilience vs. Flexibility: Important for tissues requiring both strength and elasticity, like skin, blood vessels, and lungs. Requires elasticity for recoil from stretching.
    • Composition: Rich in proline, glycine, and lysine. Has allysine but a lack of lysyl hydroxylase. Non-glycosylated.
    • Cross-linking: Cross-links occur between allysine residues.
    • Structure: Two segment types alternate along the chain: hydrophobic segments for elasticity, and alanine/lysine rich helical segments.

    Keratins

    • Structure: Unusual content of cysteine (forming disulfide bonds), is found in nails, hair, horns, and skin. α-keratin tends to have higher cysteine content/disulfide bonds, leading to greater hardness.
    • α-Keratin: The protein of hair, fingernails, and animal skin. Has high cysteine content. Right-handed α-helix.
    • Structure: Repeated amino acid sequences and biological functions.
    • Cross-linking: Three allysine and one unaltered lysyl side chains form desmosine.

    Keratins structure

    • Types of Keratin: Two types α-helix and β-sheet.
    • Structure: Helical arrangement. Protofibrils, microfibrils, and macrofibrils. Disulfide bonds between keratin molecules make keratin stronger.
    • Hardening: Disulfide cross-links in keratin can be hardened further.

    Hair design

    • Temporary wave: Water molecules weaken the hydrogen bonds in the hair, allowing it to be shaped.
    • Permanent wave: A reducing substance breaks the disulfide bonds, allowing the hair to be reshaped. An oxidizing agent then reforms the bonds in the new position.

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    Description

    Explore the essential aspects of fibrous proteins in this biochemistry quiz. Understand their structure-function relationship, biological roles, and various types. This quiz is based on study notes that provide deeper insights into the fascinating world of fibrous proteins.

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