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Collagen and Elastin

Fatima G. 7 questions

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  1. 1 • Alpha Keratin: skin and hair
    • [blank_start]Elastin[blank_end]: Tissue that undergoes stretching
    • [blank_start]Proteoglycans[blank_end]: components of the extracellular matric
    • Tubulin: muscle and most cells
    • Adhesive Glycoproteins ([blank_start]fibronectin[blank_end] & [blank_start]laminin[blank_end]): form a mesh of fibers that bind cells and other molecules to components of the extracellular matrix
    • Collagen Overview:
    ○ Primary structural protein in the body: most abundant in strong, tough connective tissues: tendons, cartilage, bones, cornea of the eye
    ○ The most prevalent protein - approx. 30% of ALL proteins
    ○ Approximately 28 distinct types identified: characterized by different [blank_start]alpha[blank_end] chains; each type found in particular locations of the body
    ○ Type 1, 2 and 3 are the abundant of the collagens with type1 being the most abundant protein in mammals
    • Type [blank_start]1[blank_end]: skin, bone, tendon, blood vessels, cornea
    • Type [blank_start]2[blank_end]: cartilage, vitreous body
    Type [blank_start]3[blank_end]: blood vessels, skin, muscle
    1. AProteoglycans
    2. BElastin
    3. Claminin
    4. Dfibronectin
    5. Ealpha
    6. F1
    7. G2
    8. H3
  2. 2 ○ Each single collagen chain is a long Gly and Pro rich [blank_start]left[blank_end] handed helix individually
    • Proline and hydroxyproline confer rigidity
    ○ Three collagen chains intertwine into a [blank_start]right[blank_end]-handed super-helical [blank_start]triple[blank_end] helix ([blank_start]left[blank_end] handed Gly and Pro to form right handed)
    ○ [blank_start]Glycine[blank_end] occurs at every third position of the triple helical portion of the alpha chain
    ○ Triple helix made up of 3 polypeptide chain subunits ([blank_start]alpha[blank_end] chains)
    ○ The triple helix has higher tensile strength than a steel wire of equal cross section
    ○ Many triple-helices assemble into a collagen [blank_start]fibril[blank_end]
    ○ Gly- X- Y repeats; X is often a proline and usually [blank_start]hydroxyproline[blank_end]
    ○ Glycine is small enough to fit in the triple helix
    • Glycine deficiency affects collagen structure because glycine holds the collagen structure with its [blank_start]hydrophobic[blank_end] bonds
    ○ Triple helix forms intra and inter disulfide bonds
    • Formation of [blank_start]disulfide[blank_end] bonds and further enhance the stability of the folded conformation of a peptide
    ○ [blank_start]Intrapolypeptide[blank_end] disulfide bonds involves oxidation of the cysteinal sulfhydryl groups and requires oxygen
    [blank_start]Interpolypetide[blank_end] disulfide bonds stabilize the quaternary structure of certain oligomeric proteins
    1. Aleft
    2. Bleft
    3. Cright
    4. Dtriple
    5. Ealpha
    6. FGlycine
    7. Ghydroxyproline
    8. Hfibril
    9. Ihydrophobic
    10. Jdisulfide
    11. KIntrapolypeptide
    12. LInterpolypetide
  3. 3 • Post-Translational Modifications of Polypeptide Chains - hydroxylation reactions
    ○ [blank_start]Hydroxylation[blank_end] of Proline and lysine residues in collagen. Proline and lysine within chains are hydroxylated by reactions that require molecular oxygen , iron (Fe+) and the reducing agent vitamin C and [blank_start]cofactors[blank_end] (ascorbate, ascorbic acid), Fe+ is required to [blank_start]activate[blank_end] oxygen
    • Hydroxyproline is formed by posttranslational hydroxylation of peptide-bound proline residues catalyzed by [blank_start]prolyl hydroxylase[blank_end]
    • Hydroxylation forms H-bonds for inter and intra strands (stabilize the triple helix) formed between glycine and other AA
    • Defective hydroxylation can cause devastating effects due H-bonds and [blank_start]disaccharides[blank_end] won't be able to me made
    • Hydroxyproline and [blank_start]succinate[blank_end] complete the hydroxylation reaction
    ○ Hydroxylysine
    • [blank_start]Lysine[blank_end] and alpha [blank_start]ketoglutarate[blank_end] start this reaction
    • The cofactors here are oxygen, iron and [blank_start]ascorbate[blank_end] as well
    • Hydroxylysine and [blank_start]succinate[blank_end] are the final products that complete the reaction
    • Hydroxylysine are sites of attachment of disaccharide groups
    Some hydroxylysines can be further modified by addition of [blank_start]galactose[blank_end] and galactosyl-glucose through an O-[blank_start]glycosidic[blank_end] linkage, a [blank_start]glycosylation[blank_end] site that is unique to collagen
    1. Acofactors
    2. BHydroxylation
    3. Cactivate
    4. Dprolyl hydroxylase
    5. Edisaccharides
    6. Fsuccinate
    7. Gketoglutarate
    8. HLysine
    9. Iascorbate
    10. Jsuccinate
    11. Kglycosidic
    12. Lglycosylation
    13. Mgalactose
  4. 4 • Collagen forms Long [blank_start]Rod[blank_end]-Like Structures
    ○ These are fibers in tissues
    ○ Assembled into [blank_start]lateral[blank_end] association of triple helical units called fibrils, which in turn into fibrils and then into thicker fibers
    ○ Collagen is further stabilized by covalent [blank_start]cross-links[blank_end] that form [blank_start]lysyl oxidase[blank_end] (copper dependent) that [blank_start]deaminates[blank_end] the epsilion amino groups of certain lysine and hydroxylysine residues yielding reactive aldehydes
    Aldehydes can form [blank_start]aldol[blank_end] condensation products with lysine or [blank_start]hydroxylysine[blank_end] to form [blank_start]Schiff bases[blank_end]
    1. ARod
    2. Bcross-links
    3. Clysyl oxidase
    4. Ddeaminates
    5. Ehydroxylysine
    6. Faldol
    7. GSchiff bases
    8. Hlateral
  5. 5 • Lathyrism
    ○ Lathyrism is a paralyzing [blank_start]dietary[blank_end] disease that arises from regular consumption of seeds of Lathyrus odoratus, the sweet pea.
    ○ The seeds contain ß-aminoproprionitrile which inactivates [blank_start]lysyl oxidase[blank_end] - results in [blank_start]decreased[blank_end] crosslinking of collagen. Without these crosslinks, collagen is extremely fragile.
    • Penicillamine is another collagen cross-linking inhibitor used in chelation therapy. It also causes lathyrism because it chelates copper ions that are needed for [blank_start]lysyl oxidase[blank_end] activity.
    Penicillamine is used in the treatment of Wilson’s disease which is a copper overload disease.
    1. Adietary
    2. Blysyl oxidase
    3. Cdecreased
    4. Dlysyl oxidase
  6. 6 • Elastin
    ○ Connective tissue protein responsible for properties of extensibility and elastic recoil
    ○ Major protein found in elastic tissues
    ○ Variants arise by alternative [blank_start]splicing[blank_end]
    ○ Once cross-linked in extracellular form, elastin is highly [blank_start]insoluble[blank_end], extremely stable and has very low turnover rate
    ○ Elastic fibers, which are composed of elastin and [blank_start]glycoprotein[blank_end] microfibrils, allow tissue to expand and contract.
    ○ Elastin has a highly cross-linked, insoluble, amorphous structure
    Elastin is synthesized from the precursor [blank_start]tropoelastin[blank_end]
    1. Asplicing
    2. Binsoluble
    3. Ctropoelastin
    4. Dglycoprotein
  7. 7Collagen is degraded by collagenases [and other matrix metalloproteinases (MMPs)]:

    1. Tissue Collagenase
    ○ Function in the growth and remodeling of tissues
    2. Bacterial Collagenase
    ○ Clostridium histolyticum collagenase ([blank_start]gangrene[blank_end])
    ○ Breaks down connective tissue barriers
    ○ Allows the bacteria to spread
    3. Elastin is degraded by [blank_start]elastase[blank_end].
    ○ is a [blank_start]serine[blank_end] protease
    ○ will hydrolyze elastin but not collagen
    ○ will hydrolyze other proteins
    ○ functions in tissue upkeep and remodeling
    • A genetic defect leads to a1-[blank_start]antitrypsin[blank_end] deficiency
    ○ Emphysema results from an imbalance between a1-antitrypsin and elastase, resulting in increased degradation of extracellular matrix components
    ○ [blank_start]Emphysema[blank_end] - accompanied by a marked loss of elastin in the lungs
    ○ Cigarette smoke increases the number of neutrophils and macrophages into the lungs – [blank_start]decreases[blank_end] a1-antitrypsin, [blank_start]increases[blank_end] elastase; increases risk of emphysema
    Deficiency can also lead to scarring or [blank_start]cirrhosis[blank_end] of the liver
    1. Aelastase
    2. Bserine
    3. Cgangrene
    4. Dantitrypsin
    5. EEmphysema
    6. Fdecreases
    7. Gcirrhosis
    8. Hincreases

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Description
Biochemistry Quiz on Collagen and Elastin, created by Fatima G. on 21/08/2019.
Author
Fatima G.
Language
English
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