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Flashcards in Schegg Carb Deck (63)
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1

What are complex polysaccharides?

oligosaccharides w/ more than one type of sugar residue
ex:
Glycoproteins
GPI anchors
Glycosylated Lipids
GAGs
Proteoglycans

2

What are GPI anchors?

these anchor soluble proteins to the exterior of the plasma membrane

3

GAGs with proteins are called what?

proteoglycans

4

2 important classes of enzymes form complex polysaccharides. What are they?

1. Glycosyltransferases
2. Glycosidases

5

What is dolichol phosphate?

a lipid
an isoprenoid compound w/ 16-20 isoprene units embedded in the ER membrane

6

How do glycosyltransferases work?

they transfer saccharides from a donor to an acceptor
*different families of this enzyme based off of the donor, acceptor, sugar transferred, site where it is transferred etc.

7

A cyclized sugar is considered alpha if the OH is above/below the plane. & beta if the OH is above/below the plane.

Alpha--OH below the plane
Beta--OH above the plane

8

How do glycosidases work?

they remove specific sugar residues/break bonds
usu in the lysosome
if involved in synthesis-->in the Golgi apparatus

9

What are glycoproteins? How are they synthesized? What is their destination?

They are proteins with saccharides covalently bonded to them.
**synthesized by RER via secretory pathway
**Destination: secretion, membrane, lysosome

10

What's the deal with the carbs on glycoproteins?

the amount attached is very variable
usu 12-15 residues
branched
heterogeneity
evenly distributed to crazily distributed

11

What is an example of a glycoprotein that has sugars unevenly distributed on the protein?

Glycophorin A
the sugars are mainly clustered on the portion that is outside the cell

12

What are some examples of glycoproteins?

Glycophorin A
IgG
Human ovarian cyst glycoprotein
Human gastric glycoprotein
FSH
LH
Immunoglobulins

13

What are 4 things that make glycoproteins super important?

Their function in the cell membrane--they mediate a lot of things & touch a lot of things...
Mucus constituents
Secreted Hormones
Plasma Proteins

14

What are the 2 basic types of glycoproteins?

The N-linked to asparagine
The O-linked to serine or threonine

15

What is always the first sugar residue of a glycoprotein?

N-acetyl glucosamine

16

What are the 3 types of glycoproteins that can be formed?

High Mannose Type
Hybrid
Complex

17

What is the common core of all N-linked oligosaccharides?

N-acetyl glucosamine
NAG
Mannose
Mannose
Mannose

18

Explain how you get an N-linked glycoprotein via Dolichol phosphate.

Dolichol phosphate accepts GlcNAc on the cytoplasmic side.
It is glycosylated on the cytoplasmic side
Flippase on the ER flips it into the ER for more synthesis.
Glycosyl transferases in the ER add 4 more mannoses & 3 glucoses
A glycosyl transferase in the ER also transfers the unit onto asparagine.
The asparagine is being made by a ribosome that is attached to the ER.
then the protein folds & a glucosidase takes away the 3 extra glucoses.

19

After the 3 glucoses have been removed on the N-linked glycoprotein in the ER...what happens next?

It is packaged into a Clathrin-coated vesicle & it moves to the Golgi apparatus. Cis-->trans direction.
Could go thru the Golgi & exit to be secreted or put into the membrane-->will meet more glycosidases & transferases
OR could be phosphorylated & put into lysosomes.

20

In collagen-->what are saccharides O-linked to?

5-OH lysine

21

What must O-linked glycoproteins be attached to?

serine or threonine
**this is so it can be accepted by GalNAc transferase.

22

How are O-linked glycoproteins made?

The protein is synthesized in the ER w/o any glycosylation.
Once it moves to the Golgi a bunch of glycosidyl transferases go at it.

23

Describe the structure of mucin & its fcn.

Mucin is secreted or membrane-bound. Its fcn is to provide a gel barrier.
It has a core protein with lots of serine & threonine.
It has a bunch of oligosaccharide chains off of that that are sulfated & have sialic acid/NANA, which is negatively charged.
The neg. charges repel each other--helps w/ function.

24

Which conditions are there a lot of mucins in?

cancers
asthma
bronchitis
COPD
Cystic Fibrosis

25

What are disorders of glycoprotein synthesis called?

Congenital Disorders of Glycosylation

26

Which steps are affected in N-linked congenital disorders of glycosylation-->Type I?

Type I:
the early steps are affected...the steps before the ER
Deficiency in phosphomannosemutase II is the most common disorder

27

Which steps are affected in N-linked congenital disorders of glycosylation-->Type II?

Type II:
defects in the enzymes in the Golgi that process the glycoproteins

28

What's the deal with disorders of O-linked glycosylation?

These are defects in O-mannosylation & O-fucosylation

29

What is Walker Warburg Syndrome?

This is a Congenital Disorder of Glycosylation
O-linked
O-mannosyltransferase I is deficient
**causes congenital muscular dystrophy

30

Congenital Disorders of Glycosylation that are N & O-linked involve what?

a deficiency of the sialic acid transporter