Nutrition Carbohydrates - Skildum

Question 1

What percentage of glucose is in an average western diet?

Answer 1

0%

Question 2

What are the main dietary carbohydrates?

Answer 2

The main dietary carbohydrates are:
fructose
lactose (Gal + Glu)
sucrose (Fru + Glu)
amylose (a1,4 bonds)
amylopectin (a1,6 & a1,4 branches)

Question 3

Sucrose and lactose are examples of what?

Answer 3

Disaccharides

Question 4

What structure is amylopectin similar to?

Answer 4

Glycogen

Question 5

What is the mechanism of salivary amylase in the mouth?

Answer 5

Converts starch to maltose, maltotriose, a-dextrins

Question 6

Monosaccharides and disaccharides pass through the stomach relatively unchanged. (T/F)

Answer 6

True

Question 7

Where is amylase activity highest and what does it cut?

Answer 7

Amylase activity is highest in the duodenum.

Amylase is an endoglycosidase. It cuts a-1,4 bonds in polysaccharides.

Question 8

These are all what?

1. Glucoamylase
2. Sucrase / Isolmaltase complex
3. Trehalase
4. b-glycosidase complex

Answer 8

Disaccharidases of the brush border

Question 9

Glucoamylase / maltase is an endo or exoglycosidase?

What does it cleave?

Answer 9

Glucoamylase / maltase is an exoglycosidase.
It cleaves a-1,4 bonds of maltose to form two molecules of glucose.
It cuts glucose off the non-reducing ends of starch.
It can also cut maltotriose.

Question 10

Where is Glucoamylase / maltase highest in concentration?

Answer 10

Ileum

Question 11

The Sucrase – Isomaltase complex has what two extracellular domains with different substrate specificities?

Where is it most heavily concentrated?

Answer 11

The Sucrase – Isomaltase complex has two extracellular domains with different substrate specificities.
Sucrase cuts sucrose into glucose and fructose
Isomaltase cuts the a-1,6 bond in isomaltose.

Jejunum

Question 12

B-glycosidase complex is a glycophosphatidylinositol (GPI) glycan anchored protein with two catalytic domains. What are they and their function?

Answer 12

C-glycosidase complex is a glycophosphatidylinositol (GPI) glycan anchored protein with two catalytic domains.

1. ) Glucosyl ceramide domain: Cuts glucose and galactose from glucosylceramide and galatosylceramide
2. ) Lactase domain: Splits the 1,4 bond in lactose to make galactose and glucose. (Site of lactose intolerance if damaged).

Question 13

What is a prominent Na cotransporter on the brush border?

Answer 13

Na-Glucose-Galactose

Question 14

What can also be a substrate for fermentation by gut bacteria?

Answer 14

Amylose and amylopectin can also be a substrate for fermentation by gut bacteria.

Question 15

What bacterial substrate, produced by bacteria, can be used as fuel by colonocytes?

Answer 15

Short chain fatty acids (acetate, propionate, and butyrate) produced by bacteria are used as fuel by colonocytes.

Question 16

Metabolic fates of these carbohydrates?

Glycolysis:  
Glycogenogenesis:  
Fatty acid synthesis:  
Cholesterol synthesis:  
Amino acid synthesis:  
Glycosylation of proteins, lipids:

Answer 16

Metabolic fates of carbohydrates:

Glycolysis: All tissues

Glycogenogenesis: All tissues

Fatty acid synthesis: Liver

Cholesterol synthesis: Liver

Amino acid synthesis: Mainly liver, but most tissues

Glycosylation of proteins, lipids: All tissues

Question 17

What is the only significant monosaccharide in our ingestable diet?

Answer 17

Fructose

It is also produced by sucrase acting on sucrose to produce glucose and fructose.

High fructose corn syrup is a mixture of 55% fructose, 45% glucose.

Question 18

What is the relationship between glucose and fructose and satiety?

Answer 18

Fructose does not trigger the satiety response in the same way that glucose does.

Increased consumption of fructose may result in increased consumption of overall calories because it doesn’t make you feel full.