Carbohydrates

Question 1

What is a Carbohydrate?

Answer 1

Saccharide and sugar, not encoded by DNA

Question 2

What are glycoconjugates?

Answer 2

Macromolecules that contain at least one monosaccharide covalently bound to proteins or lipids

Question 3

What is the glycocalyx?

Answer 3

A dense layer of glycoproteins attached to the ECM surrounding all cells

Question 4

How does the body get carbohydrates?

Answer 4

Diet or neoglucogenesis (metabolism)

Carbohydrates are NOT encoded by DNA

Question 5

Basic structure of a monosaccharide

Answer 5

Cn(H2O)n with 3 < n < 9

Question 6

Order of naming monosaccharides

Answer 6

configuration-carbonyl group-###-ose

Ex: D-aldo-pentose

Question 7

What is an asymmetric center

Answer 7

Chiral carbon. A carbon attached to 4 different groups, making it a chiral center. All monosaccharides have at least ONE. Position of asymmetric carbon farthest from the carbonyl group gives the monosaccharide “D” or “L” configuration.

Question 8

What are steroisomers?

Answer 8

Two molecules that share the same formula but differ in 3D orientation of atoms in space.

Question 9

What are epimers?

Answer 9

Two molecules with the same formula but differ in 3D orientation of ONLY ONE of their asymmetric (chiral) centers.

Question 10

Structure of glucose monosaccharide (not cyclic)

Question 11

Structure of fructose monosaccharide (not cyclic)

Question 12

What group/type of bond is formed during the formation of a cyclic monosaccharade?

Answer 12

Hemiacetal - attempt to draw

Question 13

Structure of D-hexo-furanose (cyclic fructose)

Question 14

Structure of D-hexo-furanose (cyclic D-glucose)

Question 15

Structure of D-hexo-pyranose (cyclic D-glucose)

Question 16

What is a special characteristic of pyranose structures?

Answer 16

They have chair conformations (2 major ones)

Question 17

What is an anomer and how are they represented in nomenclature?

Answer 17

A pair of near-identical stereoisomers that differ at only the anomeric carbon, the carbon that bears the aldehyde or ketone functional group in the sugar’s open-chain form. Beta- is up (similar to left –> up) while alpha- is down (similar to right –> down). They are C1 in aldose and C2 in ketose

Question 18

Which modification makes a saccharide no longer a sugar and why?

Answer 18

Reduction (-itol) because it gets rid of the carbonyl group, a key characteristic of a sugar.

Question 19

Structure of Sucrose?

Answer 19

Glucose a(1-2)b fructose

Question 20

Structure of Cellobiose?

Answer 20

Glucose b(1-4) glucose

Question 21

Structure of Maltose?

Answer 21

Glucose a(1-4) glucose

Question 22

Structure of Lactose?

Answer 22

Galactose b(1-4) glucose

Question 23

Structure of Glycogen?

Answer 23

[Glc a1-4]n / [Glc a1-6]n

Question 24

Describe N-Glycans (structure and purpose)

Answer 24

Core: Asn-[GlcNac]2-[Man]3

On receptors, antibodies, and hormones

Question 25

Describe O-Glycans (structure and purpose)

Answer 25

Core: GalNac linked to O of Ser/Thr + X
X = 1/2 GlcNac, Gal, Gal + Glcnac, Sia
Mucins and blood type

Question 26

Describe Proteoglycans (structure and purpose)

Answer 26

Sugar>Protein
Long polysaccharides with repeating, modified disaccharides
O/N linked to protein for attachment
Present in ECM - signaling, structure

Question 27

Describe Glycosphingolipids (structure and purpose)

Answer 27

Lipid-linked to sphingosine

Makes up lipid rafts and in ECM/membrane

Question 28

What is a sphingosine + Glc?

Answer 28

Cerebroside

Question 29

What is a sphingosine + 4 glycan core?

Answer 29

Ganglioside

Question 30

Describe GPI (structure and purpose)

Answer 30

Phospholipid tail + Inositol + GlcNH2 + 3 Mannose + Phospho-Ethanolamine + protein
Anchors proteins that lack transmembrane domains to the membrane

Question 31

Describe O-Glcnacylation (purpose)

Answer 31

Intracellular, signals levels of Glucose

O-linked to Ser/Thr