Carbohydrates Skildum Flashcards
Carbs account for 50 % of the calories in the western diet. Glucose is the main carbohydrate circulating in our blood and used for fuel by our cells. What fraction of the total calories in a Western diet are from glucose?
0 % because it is a monosaccharide! We eat it in the form of starch, maltose, lactose etc..In monosaccharide and disaccharide form
Lactose is composed of what?
Galactose and Glucose
Sucrose is composed of what?
Fructose and Glucose
Which dietary carbohydrate’s structure most resembles glycogen?
Amylopectin
Type of bonds in amylose?
alpha 1,4 bonds between glucose
Amylopectin bonds?
alpha 1,6 and alpha 1,4 branches
What are the 3 dietary disaccharides?
Lactose
Sucrose
Trehalose
When are fructose and disaccharides changed in the body?
Not until they reach the brush border enzymes!
When is starch changed in the body, how?
Starch is acted on my salivary amylase and turned into maltose, maltoriose, and alpha-dextrins.
These are then acted on by pancreatic amylase and turned into maltose, malotriose, and limit dextrans.
These are acted on by brush border enzymes.
What is amylase?
An endoglycosidase. It cuts alpha-1,4 bonds in polysaccharides.
*Can only make starch, not free glucose
Where is amylase activity highest?
Duodenum.
What are the 4 disaccharidases of the brush border (they live on microvilli!)?
- Glucoamylase
- Sucrase/Isolmaltase complex
- Trehalase
- Beta-glycosidase complex
What is Glucoamylase (maltase)?
An exoglycosidase…it cleaves alpha-1,4 bonds of maltose to form 2 molecules of glucose. It cuts glucose off at the non-reducing ends of starch. So it CAN MAKE A FREE MOLECULE OF GLUCOSE
Where is glucoamylase activity highest?
Ileum
What does the sucrase-Isomaltase complex do?
Has 2 extracellular domains with different substrate specificities:
Sucrase cuts sucrose into glucose and fructose.
Isomaltase cuts the alpha-1,6 bond in isomaltose.
Where is sucrase-isomaltase activity highest?
Jejunum
Trehalase has a single substrate specificty for what?
*So this is not a very important one: no pathologies associated.
Trehalose
Why is Beta-glycosidase different?
It is a glycophosphatidylinositol (GPI) glycan anchored protein
What are the two domains of Beta-glycosidase?
Glucosyl ceramide domain: cuts glucose and galactose from glucosylceramide and galactosylceramide
Lactase domain: Splits the 1,4 bond in lactose to make galactose and glucose This one is more important as far as abundance in our diet
Where is Beta-glycosidase activity highest?
Jejunum
What happens if the lactase domain of Beta-glycosidase is lost?
Lactose intolerance!
When can carbohydrates enter intestinal epithelial cell?
When carb concentration in lumen exceeded that of the blood, they can enter cell through facilitated diffusion.
If the concentration of the lumen is lower than in the blood, the cell must expend energy to get the monosaccharides inside. **Na/K+ ATPase
What are produced by bacteria that are used as fuel by coloncytes?
Short chain fatty acids!
What are used as a substrate for fermentation by gut bacteria?
Amylose and amylopectin
