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Glycobiology in Human Disease I Flashcards

1
Q

Lysosomes contain digestive enzymes that are active at the acidic pH of this organelle, and most of these enzymes are soluble and localized in the

A

Lysosomal lumen

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2
Q

The digestive enzymes in lysosomes are special because they are destined for

A

Intracellular organelles

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3
Q

To do so, they require special processing within the

A

Golgi apparatus

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4
Q

Similar to all other secretory proteins, lysosomal enzymes are synthesized in the

A

ER (then transported to golgi)

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5
Q

Within the Golgi complex they undergo a variety of post-translational modifications, of which one is

A

Addition of terminal mannose-6P

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6
Q

The attachment of terminal mannose-6-phosphate groups to some of the oligosaccharide side chains forms a

A

Glycoprotein

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7
Q

The phosphorylated mannose residues serve as an “address label” that is recognized by specific receptors found on the inner surface of the

A

Golgi membrane

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8
Q

Bind these receptors and are thereby segregated from the numerous other secretory proteins within the Golgi

A

Lysosomal Enzymes

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9
Q

Subsequently, small transport vesicles containing the receptor-bound enzymes are pinched off from the Golgi and proceed to fuse with the

A

Lysosome

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10
Q

Molecules are composed of a protein molecule linked to one or more carbohydrates

A

Glycoproteins

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11
Q

Carbohydrates are O-linked, if they are linked to the protein via a

A

Serine or threonine amino acid

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12
Q

Carbohydrates are N-linked if they are linked to the protein via an

A

Asparagine

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13
Q

The mechanism of synthesis of O-linked glycoproteins is similar to that of

A

Glycosaminoglycans

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14
Q

As the polypeptide is being synthesized, it is extruded into the lumen of the ER. The carbohydrate substrates are

A

UDP-derivates of sugars

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15
Q

The mechanism of N-linked glycoprotein biosynthesis is distinct from that of O-linked biosynthesis. In this case, the carbohydrate substrates are not

A

UDP-derivatives

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16
Q

In the N-linked glycoprotein synthesis, the carbohydrate substrates are not UDP-derivatives, but are instead

A

Dolichol pyrophosphate derivatives

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17
Q

In N-linked glycoproteins, sugars are added individually directly to

A

Dolichol (not the protein)

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18
Q

In N-linked glycoproteins, sugars are added individually directly to dolichol by

A

Glycosyltransferases

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19
Q

The oligosaccharide is then transferred from dolichol to the

A

Asparagine side chain of the protein

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20
Q

The N-linked oligosaccharide is then processed by removal of specific sugar residues – back to

A

Mannose residues

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21
Q

Act as biological labels, including those specifying cell surface recognition and cell surface antigenicity

A

Glycoproteins

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22
Q

Enhance protein solubility (due to polarity of the carbohydrate

A

Glycoproteins

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23
Q

Glycoproteins are resistant to

A

Proteases

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24
Q

The terminus of glycoproteins can also affect intracellular protein targeting. For example, terminal mannose-6-phosphate residues target enzymes for transport to the

A

Lysosome

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25
Q

Mannose6-phosphate receptors on the internal Golgi surface bind mannose-6-phosphate and direct vesicle transport to the

A

Lysosome

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26
Q

A rare but serious disease marked by skeletal abnormalities and psychomotor problems

A

I-cell disease

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27
Q

In I-cell disease, how many acid hydrolases are missing from the lysosome?

A

8

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28
Q

This abnormality, however, is a consequence of a single

A

Gene defect

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29
Q

This abnormality, however, is a consequence of a single gene defect. It turns out that the gene encodes a

A

UMP transferase

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30
Q

This UMP transferase catalyzes phosphate transfer to

A

Mannose-6-OH

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31
Q

As a consequence, acid hydrolases that are normally targeted to the lysosome by mannose-6phosphate are misdirected, resulting in toxic accumulation of

A

Glycosaminoglycans and glycolipids

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32
Q

I-Cell disease can be classified as a toxic accumulation of

A

Glycosaminoglycans and glycolipids

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33
Q

Represent a large group of more than 50 clinically recognized conditions resulting from inborn errors of metabolism affecting the organelle known as the lysosome

A

Lysosomal Storage Disorders (LSDs)

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34
Q

An integral part of the larger endosomal/lysosomal system, and is closely allied with the ubiquitin-proteosomal and autophagosomal systems

A

Lysosome

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35
Q

Consist of the interruption of metabolic pathways involved in the recycling of degradation products of one or several types of macromolecules

A

LSDs

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36
Q

As a consequence of inefficient recycling, imperfectly degraded substances accumulate in cells with cascades of

A

Deleterious repercussions

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37
Q

The histological hallmark of LSDs is

A

Cell vacuolation

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38
Q

With time, cells in most severely affected tissues become progressively clogged with

A

Cytoplasmic inclusions

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39
Q

Over 50 LSDs are known and they have a collective incidence of approximately

A

1 - 7000/8000 births

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40
Q

LSDs are normally

A

Monogenic

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41
Q

LSDs are normally monogenic (i.e. they involve only a single gene), but, for most LSDs, numerous mutations have been described in the

A

Same gene

42
Q

No obvious genotype–phenotype correlation has been found for most

A

LSDs

43
Q

The ever-expanding number of LSDs can be divided into rational categories based on the biochemical nature of the accumulated metabolite, thus creating such subgroups as the

A

Glycogenoses, sphingolipidoses (lipidoses), mucopolysaccharidoses, and mucolipidoses

44
Q

Rich in gangliosides, and hence defective hydrolysis of gangliosides, as occurs in GM1 and GM2 gangliosidoses, results primarily in accumulation within neurons and consequent neurologic symptoms

A

The brain

45
Q

Defective hydrolysis of ganfliosides occurs in

A

GM1 and GM2 gangliosidoses

46
Q

Defective degredation affects virtually every organ because they are widely distributed in the body

A

Mucopolysaccharides

47
Q

Organs rich in phagocytic cells, such as the spleen and liver, are frequently enlarged in several forms of

A

LSDs

48
Q

The most severe LSDs, infantile forms, present with acute

A

Brain involvement

49
Q

These patients die within the

A

First years of life

50
Q

In adult forms, symptoms develop more slowly and disability often arises mainly from

A

Peripheral symptoms

51
Q

Intermediate between infantile and adult forms of LSD

A

Juvenile forms of LSDs

52
Q

Neurological symptoms of LSDs can include seizures, dementia and

A

Brainstem dysfunction

53
Q

Among the peripheral symptoms of LSDs are enlargement of the spleen and liver (hepatosplenomegaly), heart and kidney injury, abnormal bone formation, muscle atrophy and

A

Ocular disease

54
Q

Several diseases are characterized by prominent neurological involvement and minimal peripheral impairment, for example

A

Sanfilippo disease

55
Q

Others have peripheral dysfunction with rare brain involvement, for example

A

Fabry Disease

56
Q

All forms of Pompe disease (or glycogen-storage-disease type II) are characterized by

A

Myopathy

57
Q

?Many of the sphingolipidoses are characterized by

A

Brain disease

58
Q

A family of linear polymers composed of repeating disaccharide subunits. The disaccharide repeating unit consists of an amino sugar for which the amino group is usually acetylated

A

Glycosaminoglycans

59
Q

Made up of repeating disaccharide units, an amino sugar, and an acidic sugar

A

Glycosaminoglycans

60
Q

N-acetylglucosamine and N-acetylgalactosamine are examples of

A

Amino sugars

61
Q

Glucuronic acid and its C5 epimer iduronic acid are examples of

A

Acidic sugars

62
Q

Synthesized by the sequential addition of alternating acidic and amino sugars

A

Glycosaminoglycans

63
Q

The substrates for glycosaminoglycans are not the acidic and amino sugars per se, but are instead

A

UDP derivatives of each monosaccharide

64
Q

In some glycosaminoglycans one or more of the hydroxyl groups of the amino sugar is esterified with

A

Sulfate

65
Q

The combination of these sulfate groups and the carboxylate groups of glucuronic acid gives the glycosaminoglycans a very high density of

A

Negative charge

66
Q

Consequently, glycosaminoglycans are long, thin, hydrated molecules with very high

A

Viscosity

67
Q

Each of the glycosaminoglycans (except hyaluronate) is found covalently attached to extracellular proteins to form

A

Proteoglycan monomers

68
Q

These are enormous aggregates in which the polysaccharide is the principal component, typically 95% or more of mass

A

Proteoglycans

69
Q

The fundamental distinction between proteoglycans and glycoproteins is their

A

Sugar composition

70
Q

The disaccharide repeating unit of proteoglycans, typically 20 – 60 dimers, is covalently attached to protein at a

A

Serine or threonine residue

71
Q

This occurs via a trisaccharide linkage of

A

-xylose-galactose-galactose

72
Q

The core protein of proteoglycans is synthesized in the cytosol and co-translationally translocated into the lumen of the

A

ER

73
Q

Formation of the carbohydrate chain is initiated by transfer of xylose to either a

A

Serine or Threonine

74
Q

This is followed by the addition of two

A

Galactose residues

75
Q

Alternating acidic and amino sugars are then added to the growing chain to reach of length of 20 – 60 disaccharide repeating units, depending upon the type of

A

Proteoglycan

76
Q

Each of these additions is catalyzed by membrane-bound transferases while the nascent proteoglycan traverses the

A

ER

77
Q

Occurs after monosaccharides have been incorporated into the growing carbohydrate chain

A

Sulfation of sugar residues

78
Q

Proteoglycan monomers, in turn, are noncovalently linked to

A

Hyaluronate

79
Q

Composed typically of approximately 50,000 disaccharide repeating units per chain, to form proteoglycan aggregates

A

Hyaluronate

80
Q

One hundred or more proteoglycan monomers can bind a single, extended molecule of

A

Hyaluronate

81
Q

Glycosaminoglycans and proteoglycans function as components of the extracellular matrix of

A

Cartilage and Tendons

82
Q

Contribute tensile strength and elasticity to cartilage and tendons

A

Glycosaminoglycans and proteoglycans

83
Q

Indeed, these structures can cushion compressive forces because glycosaminoglycans have highly hydrated

-spring back after being deformed

A

Polyanions

84
Q

Extracellular proteoglycans are usually interwoven with fibrous proteins such as

A

Collagen and Elastin

85
Q

The association between cells and the proteoglycan of extracellular matrix is mediated by a

  1. ) Membrane protein called
  2. ) Extracellular protein called
A
  1. ) Integrin

2. ) Fibronectin

86
Q

Also comprise the synovial fluid of joints, mucous secretions, and the vitreous humor of the vertebrate eye

A

Proteoglycans

87
Q

Unlike the other glycosaminoglycans, functions within the cell

A

Heparin

88
Q

Heparin is a highly sulfated glycosaminoglycan that binds specifically to

A

Antithrombin

89
Q

Accelerates the sequestration of

A

Antithrombin

90
Q

Thus, Heparin functions as an

A

Anticoagulant

91
Q

Lastly, the disaccharide repeating unit of glycosaminoglycans is also found as a component of the cell wall of certain

A

Gram-positive bacteria

92
Q

Have the disaccharide repeating unit is N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc)

A

Gram-positive bacteria cell membranes

93
Q

A component of human tears, kills bacteria by hydrolyzing the glycosidic bond between GlcNAc and MurNAc

A

Lysozyme

94
Q

Several antibiotics exert their effects by targeting the peptidoglycan components of the wall. For example,

A

Penicillin

95
Q

Targets peptidoglycan

A

Penicillin

96
Q

Interferes with peptidoglycan biosynthesis by inhibiting a transpeptidase that catalyzes formation of the cross-linking polypeptide

A

Penicillin

97
Q

Glycosaminoglycans are degraded in the

A

Lysosome

98
Q

Glycosaminoglycans are broken down by an array of hydrolytic enzymes. Degradation is sequential, beginning with the last group added during

A

Biosynthesis

99
Q

Hereditary disorders characterized by accumulation of glycosaminoglycans in various tissues

A

Mucopolysaccharidoses

100
Q

Accumulation of glycosaminoglycans in various tissues is due to deficiency for specific lysosomal hydrolases in a

A

Mucopolysaccharidoses

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