Carbohydrates

Question 1

Main dietary carbohydrates

Answer 1

Fructose
Lactose (Gal + Glu)
Sucrose (Fru + Glu)
Amylose (a 1,4 bonds)
Amylopectin ( a 1,6 and a 1,4 branches)

Question 2

Lactose =

Answer 2

Gal + Glu (b-1,4)

Question 3

Sucrose =

Answer 3

Fru + Glu (a 1,2)

Question 4

Trehalose =

Answer 4

Glu + Glu

found in mushrooms

Question 5

Starches first broken down by

Answer 5

salivary amylase

Question 6

salivary amylase produces

Answer 6

maltose, maltotriose, alpha-dextrins

Question 7

pancreatic amylase produces

Answer 7

maltose
maltotriose
limit dextrans (4-9 residues long, with 1,6 link)

Question 8

brush border enzymes can absorb

Answer 8

fructose, disaccharides
maltose
maltotriose
limit dextrans

Question 9

amylases do/do not produce free glucose

Answer 9

do NOT (smaller oligosaccharides)

Question 10

where does amylase cut

Answer 10

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

Question 11

amylase activity highest in

Answer 11

Amylase activity is highest in the duodenum.

Question 12

disaccharidases of brush border

Answer 12

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

Question 13

Glucoamylase/maltase cuts where

Answer 13

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 (get free glucose) until sterically constrained by 1,6 bond.

Question 14

glucoamylase activity highest in

Answer 14

ileum

Question 15

The Sucrase – Isomaltase complex has two extracellular domains with different substrate specificities.
Where do they cut?

Answer 15

Sucrase cuts sucrose into glucose and fructose

Isomaltose cuts the a-1,6 bond in isomaltose.

Question 16

Sucrase-isomaltase activity is highest in

Answer 16

jejunum

Question 17

trehalase catalytic site substrte

Answer 17

trehalose

Question 18

trehalose

Answer 18

Trehalose: Two glucose units bonded through the number 1 carbons.
Found in insects, algae, mushrooms and other fungi.

Question 19

b-glycosidase complex catalytic domains

Answer 19

Glucosyl ceramide domain

Lactase domain

Question 20

b-glycosidase activity highest in

Answer 20

jejunum

Question 21

b-glycosidase Glucosyl ceramide domain action

Answer 21

Cuts glucose and galactose from glucosylceramide and galatosylceramide

Question 22

b-glycosidase Lactase domain

Answer 22

Splits the β-1,4 bond in lactose to make galactose and glucose.

Question 23

How do monosaccharides get into epithelium cell?

Answer 23

When carbohydrate concentration in the lumen exceed that of the blood, they can enter the cell through facilitated diffusion.
When the concentration in the lumen is lower than in the blood, the cell must expend energy get the monosaccharides inside.

Question 24

How are amylose and amylopectin digested also

Answer 24

Amylose and amylopectin can also be a substrate for fermentation by gut bacteria.
Short chain fatty acids (acetate, propionate, and butyrate) produced by bacteria are used as fuel by colonocytes.

Question 25

Pathology of lactose intolerance

Answer 25

Without lactase, bacteria ferment lactose to lactic acid. Water enters the lumen of the gut to balance difference in proton concentration, causing diarrhea.

Question 26

metabolic fates of carbohydrates

Answer 26

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