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FTM Exam 2 > Lecture 27: Fibrous Proteins, Proteoglycans and Glycoproteins > Flashcards

Lecture 27: Fibrous Proteins, Proteoglycans and Glycoproteins Flashcards

1
Q

Fibrous proteins: Types and function

A

Types

1) Collagen fibers
2) Elastin fibers

Function:
-Structural support of surrounding cells

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2
Q

Proteoglycans

A
  • Contain Glycoaminoglycins (GAGS) > Proteins
  • Formed intracellularly by O-glycosylation at the core protein (in the golgi) and released into ECM

Function:
Fills the extracellular space and attract water

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3
Q

Collagen’s

function

A

Function:

-Forming of fibrils and of networks

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4
Q

Collagen:

Type I

Type III

A

Type I: Skin, bones, tendons, blood vessels, cornea

Type III: Blood vessels, fetal skin

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5
Q

Collagen in tendons (what do they look like)

A

Bundled in long and cross-linked parallel fibers.

neat looking

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6
Q

Collagen in bones

A

-Provides the overall structure and strength
and the flexibility to resist mechanical sheer

-Calcium phosphate around fibrils

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7
Q

Collagen Structure and Amino acid composition

A

Structure:

  • Triple-helix of three Alpha-chains (1000 amino acids long)
  • Rigid rope-like structure
  • Covalently cross linked

Amino acid composition:
1) Glycine= 3rd positon

2) Proline and hydroxylproline (Hyp) have kinks = tight winding (Hydroxyl proline (OH) stabilizes collagen and needs vitamin C to function)
3) Hydrogen bonds stabilize the structure (Non covalent)

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8
Q

Scurvy

A
  • Due to vitamin C deficiency
  • Decreased stability and tensile strength of collagen

Symptoms:
-Bleeding gums, hemorrhages and poor wound healing

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9
Q

Collagen Synthesis

A

Collagen = insoluble
-Needs to be synthesized as soluble prcollagen before release into the ECM

Steps to synthesis:
1) Nucleus releases collagen genes

RER:

2) Synthesizes collagen as soluble procollagen
3) Postranslational modifications (hydroxylations of some proline and lysine) (NEEDS VITAMIN C)
4) Chaperone proteins connect the correct 3 pro-a-chains

Golgi:
5) Finishing glycosylation and assorting procollagen for release into ECM (Creates triple helix)

ECM:

8)
- Tropocollagen assembles into fibrils with a staggered pattern (Cuts ends)
- Covalent cross-linking in ECM needs LYSYL OXIDASE which modifies lysine residues and (NEEDS COPPER)

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10
Q

Biosynthesis of Collagen Type I

A

1) Two genes are expressed: COL1A1 and COL1A2 which lead to
2) Two pro-a1 chains and one pro-a2 chain: (a12a2) for the triple helix.

Post-translational modifications:
3) Hydroxylation of selected proline and lysine residues (vitamin C)

4) Glycosylation of selected hydroxylysine residues.

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11
Q

Chaperone proteins function

A
  • Form trimers
  • Help form zipper-like triple-helix formation of procollagen from the C- to the N- terminus

(Ex: Hsp 47 aka serpin)

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12
Q

Extracellular cross-linking

A

-Strengthens collagen fibers

Lysyl oxidase:
1) oxidatively removes lysine or hydroxylysine residues

2) Needs copper as cofactor and forms aldehydes = ALLYSINE or HYDROXYALLSINE residue
(Highly reactive, binds covalently to other lysine hydroxyallysine residues)

-aldehyde is highly reactive and forms a covalent bond with other lysine or hydroxylysine residues of another collagen molecule

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13
Q

Ehlers-Danlos syndrome:

Vascular form

Classical form

A
  • Connective tissue disorder
  • Mutation of collagen Type III and V collagen

-Hereditary enzyme deficiency of one of the enzymes
needed for collagen synthesis

Vascular form:

  • Mutation of Type III
  • Fragility of skin and vascular vessel walls
  • Severe: lethal arterial rupture
Classical Form:
-Mutation of Type V collagen
Symptoms:
1) Hypermobility of the joints
2) Hyperextensibility of the skin
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14
Q

Osteogenesis Imperfecta (OI)

A

-Brittle bones disease

Cause:
-Usually inherited by mutation in one allele of the COL1A1 or COL1A2 gene (Collagen type 1 and 2 formation)

Effects on structure:

  • Displacement of glycine in bone collagen
  • Improper formation and stability of the collagen triple-helix
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15
Q

Osteogenesis Imperfecta (OI)

Types

A

Type I:

  • Mildest form
  • Bone fractures in childhood
  • Hearing loss in adulthood
  • blue sclerae

Type II:

  • More severe
  • death in utero or neonatal death bc of respiratory problems (Ex: Underdeveloped lungs/small and fragile ribcage)

Types III and V:
-Can result in scoliosis, bone malformations,
and dentiogenesis imperfecta

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16
Q

Elastin Fibers

A

-Contain elastin and microfibrils

-Allows the flexibility of blood vessels, lungs,
ligaments and skin

17
Q

Elastin structure

A
  1. Hydrophobic region: rich in glycine, valine and proline.

2. Hydrophilic region rich in lysine and alanine.

18
Q

Elastin and Marfan’s syndrome

A
  • deficiency of fibrillin-1 gene (FBN1) on chromosome 15, which leads to abnormal elastic fibers.
  • Elastin gene itself is normal but elastin cannot be efficiently cross-linked and the abnormal fibrillin is found in elastic fibers.

(3 allysine (lysyl oxidase) and one lysine residue are covalently linked in desmosine)

19
Q

Where is Procollagen formed?

A

In fibroblasts, osteoblasts or chondroblast

20
Q

Elastic fibers

A

Components:

1) Elastin
2) Microfibrils

Can be stretched and then reform without an obvious energy source

21
Q

O-glycosylation

A

1) The first sugar is linked in the RER.
2) Enzymes, Glycosyl transferase bound in the Golgi membrane recognize the structures and link the correct additional sugars directly to the growing glycoproteins. The different oligosaccharides are often branched.
3) The first sugar is linked to the OH-group of a SERINE, THREOINE, or hydroxylysine residues
- Used for the glycosylation of proteoglycans, mucins, glycoproteins and blood group substances.

22
Q

N-glycosylation

A

1) Formation of a mannose-rich oligosaccharide
bound to the lipid dolichol pyrophosphate.

2) This mannose-rich precursor is linked in one step
only to the nitrogen of an ASPARAGINE side chain.

3) All proteins receive the same oligosaccharide
and only later the sugars are individually modified
in the RER and Golgi dependent on the protein.

3) Complex glycoproteins or high-mannose
glycoproteins are formed in the Golgi.

4) Golgi: Transport for release into blood, cell membrane, or into lysosomes.

*Transport into lysosomes need the mannose 6-P
marker and if deficient, it leads to I-cell disease.

23
Q

Elastin Synthesis

A

1) Tropoelastin is secreted from fibroblasts into the ECM as a highly soluble linear polypeptide
2) The protein fibrillin-1 acts as a scaffold for the extracellular tropoelastin which has a globular shape and needs to be cross-linked in order to become the insoluble elastin.

3) Lysyl oxidase acts on lysine residues of collagen and of elastin. In elastin lysyl oxidase forms about 40 allysine residues which form covalent bonds with other
lysine or allysine residues and form desmosine which is only found in elastin

24
Q

What do Desmosine and isodesmosine do?

A

Allows elastin to stretch and bend in any direction

3 allysine (lysyl oxidase) and one lysine residue are covalently linked in desmosine

25
Q

I-Cell Disease

A
  • Lysosomal disease
  • Mucolipidosis Type II

Cause:
-Deficiency of the ability to phosphorylate mannose, results in a lack of lysosomal enzymes (N-linked glycoproteins) in the lysosomes and instead are secreted in the urine/plasma

-Molecules won’t be degraded and will accumulate forming “inclusion bodies”

Symptoms:

1) Skeletal abnormalities
2) Restricted joint movement
3) Coarse facial features
4) Severe psychomotor impairment
- Can lead to death at early age

26
Q

Glycoproteins

A

Proteins > sugars (Usually branched)

-O and N glycosylation

27
Q

Blood types Structures

A

-O-linked
(R= protein/lipid)

Types:
1) O: Has NO sugar linked to Gal of the H substance (zero)

2) A: Has GaINA linked to the Gal of the H substance
3) B: Has Galactose linked to the Gal of the H substance
4) AB: Mixture of A and B

28
Q

Mucins

A
  • Type of glycoprotein
  • Contain Carbohydrates > Glycoproteins
  • Rich in SERINE and THREONINE = O-linkages
  • Needed for mucus (mucin + water) in organs = LUBRICATION AND PROTECTION

Ex: Salivary mucin
-Contains one N-aceytlglucosamine linked to serine and threoine which binds to Sialic acid (NANA) = NEG charges

29
Q

How infection begins:

E-Coli

Helicobacter Pylori

A

E-Coli:
-Attaches to mannose residues in plasma membrane of human cheek

Helicobacter Pylori:
-Attaches to gastric surface = ulcers when comes into contact with blood group antigen of gastric epithelium

30
Q

GAGS

Structure/function

A

Full name: Glycosaminoglycans

Structure:

  • Negative charged unbranched sugar chains
  • Sulfated
  • Composed of repeating disarccharides (Position 1= acidic sugar, position 2= amino sugar)

Functions:

1) Lubricant
2) Flexible support of ECM (gel-like matrix)
3) Molecular sieve
4) Shock absorber (Squeezes out water= compression, absorbing water= relaxation)

31
Q

Proteoglycans

A
  • Made up of mostly GAGS
  • Formed intracellularly by the Golgi using O-glycosylation of core proteins: a TRIHEXIDE is bound to SERINE, then GAGS are added
  • Released extracellular matrix
32
Q

Chondroitins

What is it/what are they made up of?

A
  • Most abundant GAGS in the body
  • Sulfated at position 4, 6

Make up:

1) Cartilage
2) Bone
3) Ligaments
4) Aorta

33
Q

Where are keratan sulfates and dermanten sulfates found?

A 
-Types of 
Keratan Sulfates (KS):
-Sulfated galactose in position 1
1) Cartilage
2) Cornea

Dermanten Sulfates:

1) Skin
2) Blood vessels
3) Heart valves

34
Q

Differences between Heparin and Heparan

A

Heparin:

  • Contains iduronyl sulfates
  • Negatively charged
  • Not extracellular
  • Contains mast cells that line arteries, lungs, spleen, liver
  • Coagulant: Stops blood clotting

Herparan sulfate:

  • Contains sulfated glucuronic acid or iduronic acid
  • In Basement membrane
  • Cell to cell communication
  • Cell to cell recognition
35
Q

Hyaluronic acid

Characteristics, Where are they found, Function

A
  • Special GAG
  • Not sulfated
  • Not covalently attached to a protein
  • Synthesized directly into extracellular space
  • Provides central strand in proteoglycan aggregates
  • Connected to core proteins by link proteins

Where:

  • Vitreous humor of the Eye
  • Synovial fluid of the joints
  • Cartilage
  • Loose Connective tissue

Function:

  • Facilitates cell migration
    1) Wound repair
    2) Embryogenesis
    3) Morphogenesis
36
Q

Glycocalyx and virus/bacteria

A

Consists of:

1) glycoproteins
2) glycolipids

Virus:
-Bind to glycoproteins on cells

Bacterial toxins:
-Bind to a surface glycolipid before entering the cell

37
Q

GAGS linkage region

A
  • Trihexoside = linker region

- Bound to the serine side chain and GAGs are added

FTM Exam 2 (25 decks)

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