Introduction to Carbohydrates

Question 1

Give a brief overview of carbs - functions

Answer 1

significant source of dietary cals. (55-60%)
storage form of energy (as glycogen in liver and muscle)
structural component (proteoglycans, GAGs)
source of dietary fiber (cellulose, pectin)
glucose in blood is a major source of energy
components of cell membrane (glycoproteins, glycolipids)

Question 2

where is glucose in blood especially a major source of energy?

Answer 2

in the brain (in resting and active states) and in cells that lack mitochondria - RBCs, WBCs, retina

Question 3

Which form (enantiomer) of sugar are predominant in humans?

Answer 3

D-form of sugar is predom in humans.

Note: L-form was predom in amino acids

Question 4

how are carbohydrates classified?

Answer 4

based on the number of monomeric units or the number of monosaccharides

Question 5

what are isomers?

Answer 5

compounds that have the same chemical formula but different structural formulas

Question 6

where are the aldehyde groups located and the keto groups located?

Answer 6

C1 and C2 respectively

Question 7

how is sugar detects in urine?

Answer 7

presence of monosaccharide in urine based on the reducing property of the aldehyde or keto group in the monosaccharide.
use Benedicts test or the (new, modified) Clinitest

Question 8

what is the most common clinical condition where there will be a presence of sugar in urine/

Answer 8

diabetes mellitus - glucose found in urine when BG is grater than 170-180mg%

they have dipsticks specific for glucose now!

Question 9

what population is fructosuria and galatosemia common in?

Answer 9

smaller children

Question 10

what is pyranose and furanose?

Answer 10

pyranose - 6 membered ring - 5C, 1O

furanose - 5 membered ring - 4C, 1O

Question 11

which anomeric form is perferred in solution?

Answer 11

beta-form glucose

Question 12

what are the C4 epimers?

Answer 12

glucose and galactose

Question 13

what are the C2 epimers?

Answer 13

glucose and mannose

Question 14

what is sorbitol?

Answer 14

formed from glucose in the nerve tissue, retina, and lens of eye when BGL increase
sorbitol is responsible for some of the chronic complications of DM

Question 15

what is galatitol?

Answer 15

formed from galactose in the lens in children with untreated galactosemia

Question 16

when should lactose be avoided in diet

Answer 16

in patients with lactose intolerance and galactosemia

Question 17

when should sucrose be avoided in diet?

Answer 17

when children have hereditary fructose intolerance

Question 18

what are polysaccharides classified into?

Answer 18

homo - starch and glycogen

and hetero polysaccharides

Question 19

where do enzymes of glycogen metabolism act?

Answer 19

on the ends of the beaches - remove and add glucose from the ends of the glycogen molecule

Question 20

what is O-link glycosylation

Answer 20

on the OH group of serine and threonine
often found as EC proteins or membrane bound proteins
glycan group always face EC side

Question 21

what are N-linked glycosylation?

Answer 21

glycosylation on the asparagine residue (not gln)

either 2 types - high mannose, complex

Question 22

What does it mean to be a reducing agent?

Answer 22

Monosaccharides are reducing sugars as they can open their ring structure and react with their functional group (aldehyde or keto group) and reduce a specific chromogenic agent.

Question 23

Can humans form sugar alcohol from fructose?

Answer 23

No, fructose is a ketose and it is not a substrate for aldose reductase.
Aldose reductase forms sugar alcohols from aldoses [glucose (sorbitol), galactose (galactitol) and mannose (mannitol)]