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Block 3 Week 3 Meg > Schegg: Carb Metabolism III > Flashcards

Schegg: Carb Metabolism III Flashcards

1
Q

What are complex polysaccharides?

A

an oligosaccharide with more than one type of sugar residue

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2
Q

Types of complex polysaccharides

A 
glycoproteins
GPI anchors
glycosylated lipids
GAGs
proteoglycans
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3
Q

Formation of complex polysaccharides dependent on two important classes of enzymes

A
  1. glycosyltransferases

2. glycosidases

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4
Q

These transfer a saccharide from a donor to an acceptor

donor-glycose + acceptor –> glycose-acceptor + donor

A

glycosyltransferases

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5
Q

Glycosyltransferases are very specific for these four things:

A
  1. sugar transferred
  2. acceptor
  3. the site
  4. anomeric linkage formed
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6
Q

These remove specific sugar residues

Also very specific for the bond hydrolyzed

A

glycosidases

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7
Q

Proteins which contain one or more saccharide bound covalently to protein

A

glycoproteins

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8
Q

About what percent of all eukaryotic proteins are glycosylated?

A

50%

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9
Q

Glycoproteins are all synthesized on the rER via the (blank) pathway

A

secretory

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10
Q

How much of a glycoprotein is sugar?

A

Quite variable!

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11
Q

What do the carbohydrate (sugar) portions of glycoproteins look like?

A

Usually less than 12-15 residues
Branched
Heterogeneic

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12
Q

What is the distribution of carbohydrates on glycoproteins?

A

Sometimes evenly distributed across the protein, sometimes in a defined area

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13
Q

Glycoproteins are important for four things

A
  1. cell membranes
  2. mucus constituents
  3. secreted hormones
  4. plasma proteins
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14
Q

T/F: Cell surface glycans are the first molecules encountered by anything that approaches the cell

A

True

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15
Q

Two basic types of glycoproteins

A
  1. N-linked to Asn

2. O linked to Ser or Thr

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16
Q

N-linked glycoproteins have complex structures, but all have (blank) as first sugar residue

A

GlcNAc

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17
Q

The final structure of N-linked glycoproteins can be one of three types

A

high-mannose
hybrid
complex

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18
Q

The common core from N-linked oligosaccharides is assembled on (blank) as a lipid-linked polysaccharide

A

dolichol

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19
Q

N-linked glycoproteins begin on the cytoplasmic side of the ER, accept GlcNAc, get glycosylated, and then are flipped into the (blank), where they are then transferred to a (blank) on a protein being synthesized.

A

ER lumen; Asparagine

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20
Q

After glucoses are removed in the ER, N-linked glycoproteins are moved in vesicles to the (blank) and then one of two things happens. They are either (blank) or sent to (blank).

A

golgi; secreted or in membranes; lysosomes

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21
Q

In (blank) glycoproteins, the protein is synthesized, folded, and moved to the golgi before saccharide units are added.

A

O-linked

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22
Q

Product formed in O-linked glycosylation depends on what?

A

number and type of glycosyltransferases in a cell

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23
Q

In (blank), saccharides are also O-linked to 5-OH Lys

A

collagen

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24
Q

O-linked highly glycosylated glycoproteins that are secreted or membrane-bound
They can form gels that lubricate, provide chemical barriers and hold water

A

Mucins

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25
Q

The oligosaccharide chains of mucin are often sulfated and contain (blank)

A

sialic acid

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26
Q

Disorders of N-linked glycosylation

A

Type 1: most common, involves early steps in the synthesis of N-linked glycoproteins
Type 2: enzymatic defects in N-glycan processing

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27
Q

Most common disorder of N-linked glycosylation

-involves early steps in the synthesis of N-linked glycoproteins

A

Type 1

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28
Q

enzymatic defects in N-glycan processing enzymes

A

Type 2

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29
Q

The most common defect in N-linked glycoprotein synthesis is a deficit in (blank)

A

phosphomannosemutase II

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30
Q
  • enzymatic defects in O-mannosylation and O-fucosylation
    example: Walker-Warburg syndrome deficit in O-mannosyltransferase I causes α-dystroglycanopathies (congenital muscular dystrophy)
A

Disorders of O-linked glycosylation

31
Q

T/F: There are also disorders with combined N- and O-glycosylation defects

A

True

32
Q

Out of the 40 known CDGs, how many are autosomal recessive? What are the symptoms?

A

38; psychomotor retardation, malfunction of organ systems

33
Q

There are also disorders of glycoprotein (blank)

A

degradation

34
Q

If glycoproteins cannot be degraded, what happens?

A

incompletely degraded compounds accumulate in tissues and urine–>lysosomal storage diseases

35
Q

Deficit in GlcNAc-P glycosyltransferase, the enzyme that marks lysosomal proteins for their destination
These proteins are secreted from the cell and are found in plasma and other body fluids

A

I-cell disease

36
Q

Some glycoproteins are anchored to the extracellular side of plasma membranes via (blank)

A

GPI (Glycosylphosphatidylinositol)

37
Q

GPI contains a core tetrasaccharide plus additional saccharides. GPI anchors proteins and concentrates them in (blank)

A

lipid rafts

38
Q

GPI synthesis begins on the (blank) side of the ER. A GlcNAc is added, 3 mannose sugars, an ethanolamine, and a protein. The protein ends up on the exterior of the plasma membrane.

A

cytoplasmic

39
Q

Glycosyltransferases also synthesize glycolipids. These are mainly (blank)

A

sphingolipids

40
Q

3 components of a sphingolipid

A

sphingosine
fatty acid
X (H, single monosaccharide, or more complex oligosaccharide)

41
Q

4 classes of sphingolipids

A

cerebrosides
sulfatides
globosides
gangliosides

42
Q

Which class of spingolipids account for 15% of lipids in white matter

A

sulfatides

43
Q

Globosides and gangliosides are synthesized by a series of specific (blank)

A

glycosyltransferases

44
Q

What’s this?

UDP-Gal + glucocerebroside → lactosyl ceramide (β (1→4))

A

First step in the synthesis of globosides and gangliosides

45
Q

Disorders of glycolipid degradation mainly affect the (blank). What’s the most common one?

A

nervous system; Tay-Sachs

46
Q

Sphingolipids are degraded by lysosomal enzymes, so a deficiency in lysosomal glycosidases results in (blank)

A

sphingolipid storage disease

47
Q

If there is a problem in the pathway for the breakdown of GM1, globoside, and sphingomyelin to ceramide, what can occur?

A

mental retardation, severe mental and motor deterioration

48
Q

Autosomal recessive deficiency in hexosaminidase A
A milky halo occurs around the fovea of the eye due build up of ganglioside in ganglion cells. The fovea remains red because there are no ganglion cells in the fovea.

A

Tay-Sachs disease

49
Q

A, B, and O antigens on the surface of RBCs are (blank). They are erythrocyte surface (blank)

A

complex polysaccharides; sphingolipids

50
Q

the acceptor for a glycosyltransferase coded for by the ABO gene (on chromosome 9). There are several allelic forms of this gene

A

H antigen

51
Q

(blank) codes for N-acetylgalactosamine glycosyltransferase. The GalNAc is added to the terminal Gal in an α 1,3 linkage

A

The A allele

52
Q

(blank) codes for galactosyltransferase. The Gal is added to the terminal Gal in an α 1,3 linkage

A

The B allele

53
Q

(blank) codes for an inactive protein. Therefore, the O group has neither of these monosaccharides at terminus of the antigen

A

The O allele

54
Q

The H gene in epithelial and secretory tissues that produces the H antigen is called (blank)

A

FUT2

55
Q

Antigens are (blank) or (blank), not synthesized by RBCs

A

glycoproteins; sphingolipids

56
Q

Antigens are produced in epithelial and secretory tissues, but are detected in blood. Why?

A

the glycosylated sphingolipids circulate in plasma and absorb to the surface of RBCs

57
Q

Long and unbranched heteropolysaccharides
Composed of disaccharide repeating units
Often have sulfate groups
Highly charged

A

Glycosaminoglycans

58
Q

The charge patterns on (blank) provide for specific recognition by a variety of protein ligands that bind.

A

GAGs

59
Q

May be attached to extracellular protein to form proteoglycans

A

GAGs

60
Q

GAGs are found in extracellular spaces in (blank)

A

ground substance

61
Q

Physical properties of GAGs

A 
not easily compressed
negatively charged (allows them to absorb water)
maintain fluid and electrolyte levels
62
Q

A non-sulfated GAG

A

hyaluronate (hyaluronan)

63
Q

(blank) is a GAG used as an anti-coagulant for patients to reduce clotting post-surgery

A

heparin

64
Q

What does heparin do reduce clotting?

A

speeds up the formation of the antithrombin III complex

65
Q

GAGs are assembled using (blank) and sulfation occurs as the chain grows

A

glycosyltransferases

66
Q

(blank) defect diseases can impair the formation of GAGs, and lead to short stature and bowed limbs

A

sulfation

67
Q

large molecules with a central protein core and extensions of glycosaminoglycans
principle component of the ground substance
negatively charged

A

proteoglycans

68
Q

Example of a proteoglycan with several different GAGs attached to a core protein

A

aggrecan

69
Q

Proteoglycans are degraded through sequential actions of lysosomal enzymes. Deficiencies in these enzymes cause a variety of (blank).

A

mucopolysaccharidoses

70
Q

Hurler and Hunter syndrome

A

defects in degradation of proteoglycans

71
Q

Both proteoglycan and glycoprotein synthesis is controlled at the level of (blank) synthesis

A

hexosamine

72
Q

Main regulatory step in hexosamine synthesis?

A

F-6-P-glutamine transaminase

73
Q

Needed for sulfation of GAGs

A

PAPs

74
Q

Sulfation defect diseases can be caused by defects in (blank) synthetase

A

PAPs

Block 3 Week 3 Meg (9 decks)

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