TOPIC 7 CARBOHYDRATES OBJs

Question 1

1. Identify the major sites of digestion and absorption in humans

Answer 1

a. Mouth (limited)
b. Stomach (some)
c. Small intestine (bulk)

Question 2

Wheres does the bulk of carbohydrate digestion and absorption occur

Answer 2

Small intestine

Question 3

Ceullose source, subunit and bonds

Answer 3

plant
B-glucose
1-4

Question 4

Starch source, subunit, bonds

Answer 4

Amylose
Plant
a-glucose
1-4

Amylopectin
a-glucose
1.4 , 1,6

Question 5

Glycogen source, subunit, bonds

Answer 5

Animal
a-glucose
1,4 and 1,6

Question 6

Carbohydrate digestion occurs by break of the ____ by enzymes called _________

Answer 6

glycosidic bonds

endoglycosidases

Question 7

Digestion of glycogen, starch and cellulose in humans

Answer 7

The mouth
- α-amylase, secreted from the parotid salivary glands, acts on starch and glycogen
- Breaks α -1-4 glycosidic bonds
- Digestion is limited – amount of time spent there

The stomach
o Salivary amylase is inactivated due to low pH
o No digestion here!
o Oligosaccharides pass into small intestine

The small intestine
o Pancreas releases pancreatic α-amylase
o Digests the oligosaccharides into disaccharides

Cellulose?
o Cellulose (β1-4) cannot be broken down in most animal guts
o In humans, cellulose passed out via the faeces undigested, as we lack the enzyme capable of breaking the bond

Question 8

What are sucrose, lactose, maltose and isomaltose

Answer 8

disaccharides

Question 9

Carbohydrates from starch and glycogen breakdown digests into

Answer 9

disaccharides

Question 10

what can be absobed by small intestine

Answer 10

monosaccharide

Question 11

Mastose goes to ________ by what enzyme

Answer 11

2 glucose by maltase

Question 12

isomaltose goes to _____ by what enzyme

Answer 12

2 glucose by isomaltase

Question 13

Sucrose goes to _____ by what enzyme

Answer 13

glucose and fructose by sucrase

Question 14

lactose goes to _____ by what enzyme

Answer 14

galactose and glucose by lactase

Question 15

disacchardies are associated with

Answer 15

brush border epithelial cells of small intestine

Question 16

4. Explain how glucose, fructose and galactose are absorbed in the small intestine

Answer 16

• SGLT-1 – absorbs glucose and galactose
• GLUT-5 – facilitated transporter, uptake of fructose
• All three are transported into circulation through GLUT-2

Question 17

5. Distinguish between the roles of glycogen in animal skeletal muscle and liver cells

Answer 17

• In skeletal muscle cells, glycogen acts as an energy store for strenuous exercise or ‘fight or flight’ response
• In liver cells, glycogen is primarily a store of glucose to provide to body cells when blood glucose is low

Question 18

6. Identify the reducing and non-reducing ends of a glycogen molecule and relate the non-reducing end to the sites of glycogen synthesis and degradation

Answer 18

• Enzymes act on non-reducing ends for synthesis and degradation
• Having many means can be rapid

Question 19

7. Define the roles of the branching and debranching enzymes and glycogenin

Answer 19

• Branching enzymes: forms the α-1,6 bonds
• Debranching enzymes: breaks or makes the α-1,6 bonds
• Glycogenin: can initiate glycogenesis when no glycogen molecules are available

Question 20

8. Explain the importance of branching in glycogen

Answer 20

• Two main roles:
  1. Increases solubility of glycogen
  2. Creates more non-reducing ends, which are the reactive sites upon which phosphorylase and glycogen synthase act.
• Therefore, increases the rate synthesis and degradation

Question 21

What is glycogen

Answer 21

• Glycogen is a polymer of glucoses bonded by glycosidic bonds (have branches too which make it easier to add and take)
• Glycogenesis high in fed state
• Liver and skeletal muscles

Question 22

Glycogenesis

Answer 22

glycogen synthesis

Question 23

4 steps of glycogenesis

Answer 23

1) Attaching uridine diphosphate (UDP) to glucose
- Phosphoglucomutase
- UDP-glucose phosphorylase
2) Creating glycogen,
- Glycogen synthase catalyzes the bonding of the glucose of one UDP-glucose to another, forming an alpha 1,4 glycosidic bond
- Glycogenin
3) Adding branches to glycogen molecule or polymer
- Branching enzyme
- Glycogen synthase

Question 24

Glycogenolysis

Answer 24

Glycogen degradation

Question 25

Glycogenolysis steps

Answer 25

1) Starts with the branches - **Glycogen phosphorylase** cleaves alpha 1,4 glycosidic bonds, and catalyzes transfer of a phosphate to the free glucose – releasing 1 glucose-1-phosphate molecule at a time, does this until 4 glucose made - **Debranching enzyme** cleaves 1,6 bonds and they are added back to 1,4 linear one, extending it & can also cleave the 1,6 releasing a free glucose - 2) Conversion to **glucose-6-phosphate **by **phosphoglucomutase ** Liver: o Has glucose-6-phosphatase, which removes the phosphate and released into the blood Skeletal muscle: o DOES NOT have glucose-6-phosphatase, so it sends glucose-6-phosphate into glycolysis to release energy

Question 26

10. Explain the cAMP-dependent pathway by which adrenaline and glucagon trigger the breakdown of glycogen

Answer 26

- They bind to G-coupled protein receptor which activates adenylyl cyclase which converts ATP to cAMP - cAMP activates protein kinase A, which adds a phosphate to glycogen phosphorylase kinase , activating phosphorylase, increasing glycogen breakdown and decreasing glycogen synthesis by glycogen synthase

Question 27

Glycogen synthase

Answer 27

Makes glycogen Insulin increases this because its increasing the stores

Question 28

Glycogen phosphorylase

Answer 28

Removes phosphates Glucagon increases this to release glucose

Question 29

To access stored energy from macromolecules they need to be

Answer 29

digested and absorbed

Question 30

plant carbohydrates

Answer 30

starch and cellulose

Question 31

animal carbohydrates

Answer 31

glycogen, disac lactose and succrose

Question 32

glycogen is a

Answer 32

major glucose storage in liver

Question 33

Digestion of carbohydrate in mouth

Answer 33

a-amylase secreted from parotid salivary glands acts on starch and glycogen, breaking the a 1-4 glycosidic bonds, results in oligosaccharide - amylose, amylopectin or glycogen

Question 34

what is oligosacharide

Answer 34

small chain of glucose joined together

Question 35

Carbohydrate digestion in stomach

Answer 35

none

Question 36

Carbohydrate digestion in small intestine

Answer 36

Pancreas releases pancreatic a-amylase oligosaccharides are digested to disaccharides also by cleaving a-1-4 glycosidic bonds - maltose and isomaltose result

Question 37

What about cellulose

Answer 37

cellulose (b1-4) cannot be broken down by body enzymes

Question 38

disaccharidases act where

Answer 38

small intestine

Question 39

disaccharidases are associated with the

Answer 39

brush border epithelial cells

Question 40

how do monosaccharides occur

Answer 40

disaccharidases cleave disaccharides into monosaccharides and now they can be absorbed

Question 41

monosaccharides

Answer 41

glucose fructose galactose

Question 42

how is glucose absorbed

Answer 42

Na+/glucose symporter

Question 43

Na+/glucose symporter is an example of

Answer 43

secondary active transport

Question 44

glucose transport in humans is by _____ systems

Answer 44

GLUT

Question 45

what does the body do with excess glucose

Answer 45

stored as glycogen or fat

Question 46

Glycogen storage occurs in what state and where

Answer 46

fed state liver and skeletal muscle

Question 47

what triggers glycogen breakdown

Answer 47

adrenaline (fight or flight) or low blood glucose (glucagon)