Biochemistry Lecture 13 - Carbohydrates

Question 1

Does an alpha sugar have it’s anomeric hydroxyl group above or below the plane?

Answer 1

Below the plane.

Question 2

Are stereoisomeric sugars metabolized differently?

Answer 2

Yes, they are recognized by different enzymes.

Question 3

What is one specific carbon atom that can form glycosidic linkages?

Answer 3

The anomeric carbon.

Question 4

What is the storage polysaccharide in humans?

Answer 4

Glycogen.

Question 5

What type of linkages are found in glycogen?

Answer 5

1,4 linkages with occasional 1,6 branches.

Question 6

What linkages form amylose and amylopectin and what is the difference between those two?

Answer 6

They both have alpha (1 -> 4) linkages but amylopectin has alpha (1 -> 6) branches every ~12 residues.

Question 7

What sugar is glycogen made of and what are the linkages?

Answer 7

Glucose linkages via alpha (1 -> 4) linkages.

Question 8

What are glycosaminoglycans?

Answer 8

They are repeating disaccharides in a linear chain (up to 500 residues) that are negatively charged with sulfate.

Question 9

What makes up maltose?

Answer 9

Two glucose

Question 10

What makes up lactose?

Answer 10

Glucose + galactose.

Question 11

What makes up sucrose?

Answer 11

Glucose + fructose.

Question 12

What is the polysaccharide that cannot be digested? What sugar is it made of? What are the links?

Answer 12

Cellulose = glucose with beta (1,4) linkages.

Question 13

Is heparin a GAG?

Answer 13

Yup

Question 14

What is the difference between glycosylation and glycation?

Answer 14

Glycosylation is enzyme-catalzyed and requires activation of the anomeric oxygen with a UDP group (nucleotide). It is done for polysaccharide bond formation (glycosidic linkage) and also for addition to proteins. Glycation is not enzyme catalyzed and is damaging.

Question 15

What is HbA1C and what is its clinical significance?

Answer 15

If glucose is high in blood for extended periods, it will glycate with Hb, generating HbA1C. Clinically the ratio of Hb to HbA1C can give a history of glucose levels in the past 2-3 months.

Question 16

Where do enzymatically-glycosylated O-linked glycoproteins usually end up? What is the exception?

Answer 16

Secreted, on the ectoplasmic side of a cell, or in the ER lumen. Except O-GlcNac

Question 17

What AA residue can participate in N-linked glycosylation?

Answer 17

Asparagine.

Question 18

What AA residues can participate in O-linked glycosylation?

Answer 18

Serine or threonine

Question 19

Can protein glycosylation lead to complex structures?

Answer 19

For sho.

Question 20

In polysaccharide chain synthesis, what does the enzyme need to recognize and bind?

Answer 20

1. The given sugar-UDP

2. A given acceptor for the sugar

Question 21

What are the enzymes called involved in each step of glycosylation?

Answer 21

Transferases.

Question 22

How many transferases are required per step in O-linkages formation.

Answer 22

One is required for each step in O-linkage formation.

Question 23

Described how and where N-linked sugars are synthesized.

Answer 23

They are also done one at a time on a LIPID called dolichol phosphate. The lipid is associated with the ER membrane. The 14-residue polysaccharide is then transferred to the protein as a unit.

Question 24

Can further glycoprotein/proteoglycan processing occur throughout the secretory pathway?

Answer 24

Yes, it does!

Question 25

Many LSD/CDGs are a result of a deficiency of what enzymes?

Answer 25

Endo and exoglycosidases.

Question 26

What two things make up a proteoglycan? How big can they be? What major component do they make up?

Answer 26

A core protein O-linked to a GAG. Can get as big as bacteria. Major component of basement membrane.

Question 27

What types of proteoglycans make up the basement membrane?

Answer 27

Type IV collagen, heparan sulfate, laminin.

Question 28

What proteoglycan acts as a shock absorber? How?

Answer 28

Aggrecan is polar so it attracts water, acting like a sponge in the knee.

Question 29

Are glycoproteins crucial for biological recognition?

Answer 29

Yes.

Question 30

What does the filtering in Bowman’s capsule?

Answer 30

Proteoglycans - the GAG parts do the filtering.

Question 31

What determines the blood groups?

Answer 31

Sugar residues on the ends of glycoproteins and glycolipids on cell surface.

Question 32

Name five functions of glycosylation of proteins.

Answer 32

1. Assist in protein folding in ER
2. Intracellular protein folding and transport
3. First line of defense in innate immunity.
4. Determines half-life of serum proteins
5. Direct cellular trafficking in vascular system.

Question 33

What is defective in I Cell disease?

Answer 33

The M6P receptor that tells the golgi where to send proteins.

Question 34

Name the structures responsible for leukocyte trafficking/binding.

Answer 34

Both leukocytes and endothelial cells have proteins on the cell surface called selectins. Both have sugars on cell surface. The sugars on the cells bind to the other cells’ lectin domains on the protein (called a selectin). Damage from infection or tissue damage expose these elements, so the leukocytes get bogged down and aggregate where they are needed.

Question 35

What do people who are deficient in leukocyte adhesion suffer from?

Answer 35

Leukocyte adhesion deficiency II, a defect in fucosylation (glycosylation of fructoses). These folks get repeated infections.

Question 36

Is O-Glc-Nac (O-linked N-acetylglucosamine) a glycoprotein that is secreted, faces extracellularly, or remains in the ER lumen?

Answer 36

No, it is the only o-linked glycoprotein that is not found in these hydrophilic environments.