Lecture 27 + DLA 21

Question 1

What amino acid is able to be N-glycosylated?

Answer 1

Asparagine in the rER

Question 2

How does N-glycosylation occur?

Answer 2

1. protein synthesis occurs and the peptide chain is taken to the rER
2. A branched oligosaccharide is synthesized on dolichol pyrophsphate
3. The oligosaccharide is transferred from the dolichol to the amide N of the aparagine
4. Trimming of the carbo chain occurs while it is moving through the rER
5. Goes to golgi were more trimming and additions occur (monosaccharides)

Question 3

What are the different fates of N-glycosylated proteins?

Answer 3

can be transported to lysosomes, secreted into the blood, or placed in the cell membrane

Question 4

How are N-glycoslyated proteins moved from the golgi to the lysosome?

Answer 4

1. It needs to have a mannose 6-P marker that is formed by a phosphotransferase.
2. Mannose 6-P receptors are found in the trans-golgi , which bind to the protein and package them into vesicles for transport.

Question 5

What happen when if their is a deficiency in the mannose 6-P marker?

Answer 5

I-cell disease

these proteins will accumulate

Question 6

What are proteoglycans?

Answer 6

contain mainly GAG’s which are special sugars

O-glycoslyation of the core protein

Question 7

What are glycoproteins?

Answer 7

contain mainly protein and a small amount of sugars which are normally branched

O and N linked

Question 8

O- linked sugars are bound to what AA’s

Answer 8

serine, theronine, or hydroxy lysine

Question 9

How are proteins O-linked glycosylated?

Answer 9

1. the protein is synthesized on the rER and extrudes into the lumen
2. The first sugar is enzymatically linked onto a serine, theronine, or hydroxylysine.
3. sugars are add in the golgi by glycosyl transferases

Question 10

Why is O-linked glycosylation used?

Answer 10

1. synthesis of proteoglycans
2. glycocalyx components
3. blood group components
4. mucins

Question 11

Type O blood?

Answer 11

No sugar linked to Gal of the H substance

Question 12

Type A blood?

Answer 12

has GalNAc linked to Gal of the H substance

Question 13

Type B blood?

Answer 13

Has galactose linked to the Gal of the H substance

Question 14

Type AB blood?

Answer 14

A mix of type A and type B structures

GalNAc and galactose

Question 15

What kind of proteins are mucins?

Answer 15

they are a glycoprotein

rich in O-linked

Question 16

What do salivary mucins mainly contain?

Answer 16

contains only one N-acetylglucosamine

this sugar binds NANA, thus a negative charge

Question 17

How is one way viruses can invade a cell?

Answer 17

they can bind to glycoproteins, which is the first step to infection

Question 18

How is one way bacteria can invade a cell?

Answer 18

they can bind to surface glycoproteins before entering the cell

Question 19

E.coli and glycoproteins?

Answer 19

E.coli can attach to a mannose residues that are taken into the cell membrane. first step of infection.

Question 20

How does H.pylori invade cells?

Answer 20

This bacterium leads to ulcers by interaction with a specific blood group antigen of the gastric epithelium.

Question 21

What are glycosaminoglycans (GAGs)?

Answer 21

are long, unbranched chains of negatively charged sugars and are often sulfated.

Question 22

What are proteoglycans?

Answer 22

they mainly contain GAGs and they are part of the extracellular matrix

Question 23

GAGs are repeated sequences of what sugars?

Answer 23

position 1 = glucuronic acid or iduronic acid

position 2 = glucosamine or galactosamine

Question 24

characteristics of GAGs?

Answer 24

1. they have strong negative charges from the carboxyl and sulfate groups
2. bind large amounts of water, thus producing gel like matrix that is part of the ECM
3. can compress and relax using water

Question 25

Functions of GAGs?

Answer 25

1. flexible support for the ECM
2. molecular sieve
3. lubricants
4. shock absorber

Question 26

What is the most abundant GAG? where is it found?

Answer 26

Chondroitins

found in:

1. bone
2. cartilage
3. ligaments
4. aorta

Question 27

explain keratin sulfates?

Answer 27

are special as they contain a sulfated galactose in position-1. They are the most heterogenous regarding their sugars.

found in cartilage and cornea

Question 28

where are dermatan sulfates found?

Answer 28

skin, blood vessels, and heart valves

Question 29

What is heparan sulfate used for?

Answer 29

is found in the basement membranes or on cell surfaces used for cell-cell recognition.

contains: sulfated glucuronic acid or iduronic acid

Question 30

What does heparin do?

Answer 30

It is released from intracellular granules and acts as anticoagulant by ending the blood clotting by facilitating inhibition of thrombin

Question 31

Why is hyaluronic acid a special GAG?

Answer 31

1. it is not sulfated
2. not covalently attached to a protein
3. Synthesized step by step directly into the extracellular space
4. Provides extracellularly the central strand in proteoglycan aggregates
5. Hyaluronic acid is connected to the core proteins via link proteins

Question 32

What is the function of hyaluronic acid?

Answer 32

1. vitreous humor in the eye
2. synovial fluid of the joints
3. cartilage
4. loose connective tissues
5. neural tube closure during devlopment
6. morphogenesis
7. wound repair