L 23

Question 1

How are N linked oligosaccharids added in the ER?

Answer 1

by block transfer as it travels from the ER to the golgi

Question 2

Where does the O linked glycosylation occur?

Answer 2

In the golgi

1. occurs on the OH group of Ser or Thr
2. Occurs on completed polypeptide chains
3. occurs by the serial addition of single monosaccharide units

Question 3

N linked glycosylation occurs where?

Answer 3

in the ER and golgi

1. occurs on NH2 group of Asn in the N-X-S/T sequence motif
2. occurs cotranslationally at the ER part
3. occurs by block transfer of a 14 residue core oligosaccharide in the Er, then trimmed and modified further in the Er and golgi but always retain same 5 residue core pentasaccharide

Question 4

Where are the sugars being added on to oligosaccharides from?

Answer 4

they are added from nucleotide sugar donors.

activating the sugar provides the NRG to form glycosidic bond

Question 5

during synthesis of o linked oligosaccharide, most glycosidic bonds require what?

Answer 5

a specific glycosyltransferase

there’s hundreds in the human genome

Question 6

N linked oligosaccharides are synthesized on what?

Answer 6

dolichol

it’s synthesized in a way that’s similar to cholesterol pathway

Question 7

What’s interesting about the formation of core oligosaccharide on dolichol phosphate?

Answer 7

it starts in the cytosol and is completed in the ER lumen

Question 8

What are some functions of glycosylation? 3

Answer 8

1. recognition - sperm-egg, white blood cell adhesion during inflammation response, bacterial and viral invasion of cells
2. Targeting - lysosome targeting signal is mannose 6 phosphate
3. antigens -ABO group

Question 9

What does EPO stand for?

Answer 9

erythropoeitin

Question 10

What exactly is erythropoietin?

Answer 10

a glycoprotein hormone secreted from the kidneys

40% carbohydrate by weight

Question 11

What does EPO stimulate?

Answer 11

It stimulates the production of red blood cells

Question 12

What can EPO be used to treat?

Answer 12

To treat anemia, esp during chemotherpay and depended on avilability ofrecombinant human EPO

Question 13

How is I cell disease caused?

Answer 13

Caused by defect in lysosomal targeting

• many hydrolytic enzymes fail to be targeted to lysosomes and secreted from cells
• average lifespan is about 8 years
• skeletal abnormalities, psychomotor retardation