Week 1.3 - Carbohydrate digestion and absorption

Question 1

Why do we store nutrients as macromolecules?

Answer 1

breakdown of nutrients causes osmotic pressure, and if osmotic pressure is too high, we will lose a lot of water quickly

Question 2

What form do monosaccharide hexoses come in?

Answer 2

aldoses or ketoses depending on whether they have an aldehyde group or a ketone group

Question 3

What does the suffix -oses mean?

Answer 3

has many hydroxyl (-OH) groups

Question 4

What is the most common form glucose is found in?

Answer 4

beta D glucose

Question 5

What is beta vs alpha glucose?

Answer 5

beta has -OH on top of carbon 1 and alpha has it on bottom

Question 6

What is D vs L glucose?

Answer 6

D has most -OH groups on right white L has most on left

Question 7

What are the ketoses and aldoses hexoses?

Answer 7

glucose and galactose are aldoses.
fructose is ketoses.

Question 8

What are the disaccharides and their constituents?

Answer 8

glu+glu=maltose
glu+fru=sucrose
glu+galac=lactose

Question 9

How does lactose intolerance cause its symptoms?

Answer 9

no lactase means lactose cant be digested. bacteria begin to work on it, producing gas and irritation. osmotic pressure from lactose causes water to enter lumen from blood.

Question 10

What is glycogen and where is it found?

Answer 10

main storage of glucose in humans and animals, found in liver and muscle

Question 11

What is starch and its forms?

Answer 11

storage of glucose in plants.
has alpha glycosidic bonds
can be unbranched or branched - amylose and amylopectin

Question 12

What is amylase?

Answer 12

enzyme used to breakdown starch and glycogen to glucose. found in saliva. cant break down cellulose.

Question 13

What can and cant break down cellulose and why?

Answer 13

amylase cant as cellulose has beta glycosidic bonds. amylase only breaks alpha glycosidic bonds. bacteria can break down cellulose for energy, using enzyme called cellulase

Question 14

What is cellulose?

Answer 14

beta 1-4 glycosidic bonds - unbranched. found in plant cell wall and undigestable by humans.

Question 15

What is cellulose used for in humans?

Answer 15

dietary fibre to help prevent constipation.

Question 16

What is the structure of the enterocytes?

Answer 16

• apical membrane with microvilli
• epithelial cells
• baso-lateral membrane
• tight junctions between epithelial cells

Question 17

What are the mechanisms of transport through the duodenal epithelium?

Answer 17

• trans-cellular through epithelial cell
• paracellular through tight junctions
• Vectoral transport - uses specific carriers

Question 18

How are specific carriers produced?

Answer 18

• nucleus transcribes DNA to RNA,
• goes to endoplasmic reticulum where mRNA
• produces amino acids, become protein
• golgi apparatus
• vesicle to apical membrane

Question 19

How does glucose transport through the epithelium of small intestine?

Answer 19

• NaK pump creates gradient
• SGLT1 on apical membrane brings glucose in with 2 Na+ down gradient
• Once in, GLUT2 allows glucose out via secondary active transport

Question 20

What is the brush-border membrane?

Answer 20

the apical membrane of epithelium with microvilli - resembles brush brittles

Question 21

Where can GLUT1 be found?

Answer 21

mostly in kidney tubules

Question 22

Why does Na+ movement direct water movement?

Answer 22

It is one of the most osmotically active molecules, so drags water out with it - lumen to blood.

Question 23

How do fructose and galactose transport out of the small intestine lumen?

Answer 23

galactose can go through same mechanism as glucose

fructose has different transporters at proximal duodenum - in through GLUT5 and out through GLUT2 (same) passively down conc. gradient

Question 24

What is different about the fructose enter mechanism?

Answer 24

it is not Na+ dependent. water doesn’t move out with fructose. GLUT5 uses passive absorption