Schegg: Carb Metabolism III Flashcards Preview

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Flashcards in Schegg: Carb Metabolism III Deck (74)
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1

What are complex polysaccharides?

an oligosaccharide with more than one type of sugar residue

2

Types of complex polysaccharides

glycoproteins
GPI anchors
glycosylated lipids
GAGs
proteoglycans

3

Formation of complex polysaccharides dependent on two important classes of enzymes

1. glycosyltransferases
2. glycosidases

4

These transfer a saccharide from a donor to an acceptor
donor-glycose + acceptor --> glycose-acceptor + donor

glycosyltransferases

5

Glycosyltransferases are very specific for these four things:

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

6

These remove specific sugar residues
Also very specific for the bond hydrolyzed

glycosidases

7

Proteins which contain one or more saccharide bound covalently to protein

glycoproteins

8

About what percent of all eukaryotic proteins are glycosylated?

50%

9

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

secretory

10

How much of a glycoprotein is sugar?

Quite variable!

11

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

Usually less than 12-15 residues
Branched
Heterogeneic

12

What is the distribution of carbohydrates on glycoproteins?

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

13

Glycoproteins are important for four things

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

14

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

True

15

Two basic types of glycoproteins

1. N-linked to Asn
2. O linked to Ser or Thr

16

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

GlcNAc

17

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

high-mannose
hybrid
complex

18

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

dolichol

19

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.

ER lumen; Asparagine

20

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).

golgi; secreted or in membranes; lysosomes

21

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

O-linked

22

Product formed in O-linked glycosylation depends on what?

number and type of glycosyltransferases in a cell

23

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

collagen

24

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

Mucins

25

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

sialic acid

26

Disorders of N-linked glycosylation

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

27

Most common disorder of N-linked glycosylation
-involves early steps in the synthesis of N-linked glycoproteins

Type 1

28

enzymatic defects in N-glycan processing enzymes

Type 2

29

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

phosphomannosemutase II

30

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

Disorders of O-linked glycosylation