Carbs and Posttranslational Modifications

Question 1

What is a glycosidic linkage?

Answer 1

Formations of bond between anomeric carbon of one monosaccharide and hydroxyl of another

Question 2

What monosaccharides form lactose? Is it a reducing sugar?

Answer 2

Galactose linked by beta(1,4) linkage to glucose

Reducing sugar

Question 3

What monosaccharides make up maltose? Is it a reducing sugar?

Answer 3

2 glucose linked by alpha(1,4) linkage.

Reducing sugar

Question 4

What monosaccharides make up sucrose? Is it a reducing sugar?

Answer 4

Glucose connected to fructose by alpha,beta(1,2) linkage.

Non reducing

Question 5

What are homoglycans? Name 4 examples

Answer 5

Polyners of one type of sugar/modified sugar

Chitin, starch, glycogen, cellulose

Question 6

What sugar makes up chitin?

Answer 6

Beta(1,4) linked N-acetyl-beta-D-glucosamine

Question 7

What is the structure of starch

Answer 7

Consists of amylose and amylopectin

Amylose - alpha 1,4 links; linear polymer with left hand helix

Amylopectin - alpha 1,4 and 1,6 links resulting in branching

Question 8

What is the structure of glycogen?

Answer 8

Similar to amylopectin, but more branching

Question 9

What is the structure of cellulose

Answer 9

beta 1,4 glycosidic bonds

intermolecular H bonds between chains of cellulose

Question 10

What are heteroglycans?

Answer 10

High MW polymers with multiple types of sugars

Question 11

What are N linked oligosaccharides?

Answer 11

Linked via beta glycosidic bond between N-acetyl glucosamine anomeric carbon and side chain amide nitrogen of asparagine

Question 12

What are O linked oligosaccharides?

Answer 12

Similar linkage to N linked, but to OH of Ser/Thr

Question 13

Which has more carbohydrates– N/O glycans or proteoglycans? Which has more protein?

Answer 13

N/O glycans - more protein

Proteo - more carb

Question 14

What is the glycocalyx?

Answer 14

Carbohydrate groups attached to the glycoprotein, proteoglycan, and glycolipid components of cell surface

Question 15

What are lectins?

Answer 15

Carb binding proteins that translate the “sugar code”/glycocalyx

NOT antibodies

Question 16

Which type of protein modification has highest coding capacity?

Answer 16

Glycosylation

Question 17

When does posttranslational modification occur?

Answer 17

After polypeptide formation

Question 18

What posttranslational modifications occur in prokaryotes?

Answer 18

Proteolytic processing- removal of formylmethionine and signal peptide sequence

Methylation, phosphorylation, lipidation
e.g methylation affects histidine kinase

Question 19

What posttranslational modifications occur in eukaryotes?

Answer 19

Proteolytic cleavage- removal of N terminal methionine and signal peptides, activates proteins

Glycosylation, lipidation, phosphorylation, methylation, hydroxylation, carboxylation

Question 20

What is glycosylation?

Answer 20

Attach oligosaccharidr to asparagine (N) or serine/threonine

Usually in ER

Question 21

What happens to proteins in the ER?

Answer 21

They are checked for misfolding and proper sugar labeling.

Chaperones try to fix misfolding–if this does not work, proteins are degraded.

Question 22

What is lipidation? How does it occur?

Answer 22

Lipophilic modification (lipidation) of proteins, including acylation and prenylation, occurs via covalent attachment of fatty acids.

Examples: farnesyl, geranylgeranyl, myristoyl, palmitoyl attachment

Question 23

What is phosphorylation? What purpose does it serve?

Answer 23

Adding phosphates to Serine, Tyrosine, Threonines. Aka, to large polar AAs.

Plays roles in metabolic regulation and signal transduction.

Question 24

What is methylation? What purpose does it serve?

Answer 24

Methylation occurs at aspartate, lysine, histidine and arginine and it may regulate the protein turnover or cellular function

Methylation of lysine/arginine in histones is central to epigenetic gene expression

Question 25

What is hydroxylation?

Answer 25

Addition of OH groups to proline and lysine–part of collagen structural integrity

Question 26

What is carboxylation necessary for?

Answer 26

Carboxylation of glutamate side chain is necessary for blood clotting.