Carbohydrates Structure-gunction

Question 1

What are the overall Functions of carbohydrates?

Answer 1

• Energy in diet (45-65%)
• Storage form: Glycogen in liver and muscle
• Dietary fiber: Cellulose
• Glucose in blood (Brain; RBCs, WBCs, tissues of eye) • Connective tissue/ cell membrane
• D-forms of sugars

Question 2

What are reducing sugars?

Answer 2

• Free aldehyde or keto group

• Reducing sugars in urine
– Convert cupric ions to cuprous ions

• Aldoses vs Ketoses

Question 3

Compare glucose to fructose

Answer 3

Glucose- aldohexose

Fructose- ketohexose

• Phosphohexoseisomerase(glycolysis) • Reducingsugars

Question 4

What is galactose?

Answer 4

• C-4 epimer of glucose
• Aldohexose
• Epimerases (galactose metabolism) • Avoid galactose: Galactosemia

Question 5

What is the clinical significance of sugars in urine ?

Answer 5

• Sugars NOT found in urine • Reducing property
– Benedicts test or Clinitest

• Dipstick test

• Sugars in urine:
– Glucose: Diabetes mellitus
– Fructose
– Galactose
– Lactose intolerance (no sugar in urine)

Question 6

What are polyols. (Sugar alcohols)?

Answer 6

• Sorbitol: Sugar alcohol from glucose
– Diabetes mellitus

• Galactitol formed from galactose
– Galactosemia

• Inositol present in IP3 (second messenger)

Question 7

What is glucuronic acid?

Answer 7

• Oxidation of C-6 of glucose
• Negatively charged
• UDP-glucuronic acid: Conjugation reactions (bilirubin)

Question 8

What are the classifications of carbohydrates ?

Answer 8

• Monosaccharides: Monomers
• Based on number of monomers: 
– Monosaccharides
– Disaccharides
– Oligosaccharides
– Polysaccharides

Question 9

What is lactose?

Answer 9

• Galactose + Glucose

• β1→4 glycosidic linkage
• Reducing sugar
• Intestinal lactase (brush border disaccharidase)
• NOT found in urine in lactose intolerance
• Avoid Lactose: Lactose intolerance and galactosemia

Question 10

Whst is sucrose?

Answer 10

• Glucose + Fructose
• Fructose : glucose = 1
• Non-reducing sugar: C1 and C2 not free
• Intestinal sucrase (brush border disaccharidase)
• Avoid: Hereditary fructose intolerance
• Refined sugars

Question 11

What Is the sinificance of high fructose corn syrup?

Answer 11

• Fructose (55%) and glucose (42%)
• Fructose: glucose ratio is greater than 1
• Mixture of monosaccharides
• Sweetener in soft drinks, ……

Question 12

What is maltose?

Answer 12

• Two glucose units
• α1→4 glycosidic link
• Reducing sugar
• Intermediate product of starch digestion by amylase
• Intestinal maltase (brush border disaccharidase

Question 13

What are polysaccharides?

Answer 13

• Homopolysaccharides
– Starch, glycogen and cellulose (glucose units)
• Heteropolysaccharides
– Glycosaminoglycans/ Mucopolysaccharides

Question 14

What is the significance of glycogen?

Answer 14

• Liver and muscle as glycogen granules
• Glucose units
• Linear chain α1→4 glycosidic links
• Branch point α1→6 glycosidic links
• Branch has 8-10 units

• Glycogenin: Core protein

• Glycogen storage disorders – Liver or muscle
– Abnormal structure

Question 15

How are glycigen granukes made in the liver?

Answer 15

• Enzymes act on ends of branches

* Remove or add glucose

Question 16

What Are the components of starch?

Answer 16

• Two components:
– Amylose (linear unbranched)
– Amylopectin (branched)
• Fewer longer branches

• Glucose units
• Linear chain α1→4 glycosidic links
• Branch point: Amylopectin α1→6 links • Main dietary polysaccharide
• Salivary and pancreatic amylase

Question 17

What is cellulose?

Answer 17

• Undigestible carbohydrate
• Unbranched homopolysaccharide

• Glucose units β1→4 links
– Cannot be cleaved by digestive enzymes in the human gut

• Lactase hydrolyzes β1→4 links only in lactose and NOT in cellulose!!