Lecture 9 Glycoproteins/Carbs

Question 1

Glycoproteins

Answer 1

Proteins that contain short glycan chains Usually 3 to 15 sugars (up to 20) Oligosaccharides are highly branched Do not have a repeating unit Contain much smaller amounts of sugar than protein
- usually 10 – 15% carbohydrate by weight

Question 2

Most:

cell surface proteins secreted proteins ER proteins golgi proteins

Answer 2

are glycoproteins

Question 3

carbohydrates on glycoproteins function

Answer 3

Assist in protein folding to correct conformation Enhance protein solubility Stabilize the protein against denaturation Protect the protein from proteolytic degradation Target the protein to specific subcellular locations Serve as recognition signals for carbohydrate
binding proteins (lectins)

Question 4

Oligosaccharides on glycoproteins usually contain

Answer 4

Amino sugars
N-acetylglucosamine N-acetlygalactosamine
Neutral sugars galactose mannose fucose
Acidic sugar
sialic acid (N-acetylneuraminic acid)

Question 5

Proteoglycans

Answer 5

Contain as much as 50 – 60% sugars Sugar chains are long, unbranched polymers Chains may contain hundreds of monosaccharides Usually have a repeating disaccharide unit.

Question 6

All N-linked glycoproteins have

Answer 6

branched oligosaccharide chains with a common core of 3 mannose and 2 GlcNAc residues

The high-mannose type is a precursor for other types

Question 7

N-linked

Answer 7

A glycoprotein may have a single N-linked oligosaccharide or it may have several. These oligosaccarides may have all identical structure or different. Multiple different structures may be found at the same site on glycoprotein due to processing.

Question 8

O-linked

Answer 8

Number of O-linked structure can vary. Some proteins have both N-linked and O-linked.

Question 9

N-linked vs O-linked w/regards to LDL

Answer 9

N-linked oligos are not involved in LDL binding

N-linked oligos help protein fold properly in the ER O-linked oligos help keep protein in its native state

Question 10

All sugar interconversions involve

Answer 10

sugar phosphates or sugar nucleotides…

Normal cells can use glucose to make all other sugars needed

Question 11

Mucins

Answer 11

Secreted by epithelial cells lining the respiratory, gastrointestinal and genitourinary tracts
Very large molecules – mole wt over 1,000,000 As much as 80% of weight is carbohydrate About 1/3 of aa’s are serine or theonine – most are substituted with O-linked oligosaccharides

Question 12

Mucins charge

Answer 12

Negative charges on sialic acid repel each other and prevent protein from folding

Question 13

Mucins surface

Answer 13

The protein solution is very viscous –
forming a protective barrier on the epithelial surface providing lubrication between surfaces facilitating transport processes
Some oligosaccharides participate in interaction and binding to various bacterial cell surfaces

Question 14

Endothelial cell surface

Answer 14

Lectins on surface recognize carbohydrate signals on leukocytes.

Question 15

N-linked oligosaccharide assembly

Answer 15

begins in the endoplasmic reticulum

Question 16

N-linked oligo processing continues

Answer 16

in the golgi

Processing of O-linked oligosaccharides also occurs in the golgi

Question 17

Oligosaccharides

Answer 17

Made directly on polypeptide

Question 18

Functions of oligosaccharides

Answer 18

N-linked oligos have an important role in protein folding High-mannose oligos target some proteins to specific sites in the cell Increase the solubility and stability of proteins Involved in chemical recognition interactions

Question 19

Bacterial capsule

Answer 19

Blocks phagocytosis Aid in bacterial adhesion to host tissues Prevent drying out of bacteria.

Different bacteria have different repeating units
- often 4 monosaccharide units

Question 20

Many, but not all, oral streptococci synthesise extracellular polysaccharides (EPS) by

Answer 20

polymerising the fructose or glucose moiety of sucrose.

Question 21

Fructose polymers are either

Answer 21

β-2,1 linked like the storage compound inulin which is found in some vegetables or β-2,6 linked.

Question 22

Some β-2,1 polymers are

Answer 22

cross linked with β-2,6 bonds and some β-2,6 polymers are cross-linked with β-2,6 bonds.

Question 23

Some β-2,6 polymers are

Answer 23

highly branched with short chains.

Question 24

Fructose polymers function as

Answer 24

energy storage and turn over rapidly in plaque.

Question 25

Glucans are polymers of

Answer 25

glucose and are divided into those with predominantly an α-1,6 or an α-1,3 bonded backbone.

Question 26

Glucans with α-1,6 backbones are generally

Answer 26

water soluble, those with α-1,3 backbones are insoluble

Question 27

Water insoluble glucan is also called

Answer 27

mutan and water soluble glucan is also called dextran.

Question 28

Dextrans are responsible for

Answer 28

cell aggregation and mutans are thought to be involved in adhesion to surfaces.

Question 29

Murein biosynth

Answer 29

Peptidoglycan for bacteria. This can be inhibited by antibiotic, making it impossible to grow - penicillin.

Penicillin only works on cells that are not growing.