Lecture 4

Question 1

Differences Between Monosaccharides, Disaccharides, and Polysaccharides, with Examples:

Answer 1

• Monosaccharides: The simplest form of carbohydrates (single sugar units). Examples include glucose, fructose, and galactose.
• Disaccharides: Formed by linking two monosaccharides through a glycosidic bond. Examples include maltose (glucose + glucose), sucrose (glucose + fructose), and lactose (glucose + galactose).
• Polysaccharides: Long chains of monosaccharides linked together. Examples include starch, glycogen, and cellulose.

Question 2

How Saccharide Derivatives Increase Chemical Diversity:

Answer 2

• Saccharide derivatives, such as glycoproteins, add diversity to molecules by combining carbohydrates with proteins, which can alter their function. This is important for processes like immune recognition and determining blood group types.

Question 3

Digestive Enzymes Involved in Carbohydrate Metabolism:

Answer 3

• Salivary Amylase: Breaks down starch into maltose and glucose in the mouth.
• Pancreatic Amylase: Further digests carbohydrates in the small intestine.
• Brush Border Enzymes: These include lactase, which breaks down lactose into glucose and galactose in the small intestine.

Question 4

Enzymatic Hydrolysis in Carbohydrate Metabolism:

Answer 4

• Enzymatic hydrolysis is the process where complex carbohydrates are broken down into simpler sugars by the addition of water, catalyzed by enzymes. For example, amylase breaks down starch into disaccharides, and disaccharidases in the small intestine convert disaccharides into monosaccharides.

Question 5

Role of Digestive Organs in Carbohydrate Metabolism:

Answer 5

• Mouth: Begins carbohydrate digestion with salivary amylase.
• Stomach: No significant carbohydrate digestion due to the acidic environment, which inhibits amylase activity.
• Small Intestine: Main site of carbohydrate digestion and absorption, where pancreatic amylase and brush border enzymes act.
• Pancreas: Secretes pancreatic amylase into the small intestine.
• Liver: Processes absorbed monosaccharides and helps regulate blood glucose levels.

Question 6

Process of Monosaccharide Absorption:

Answer 6

• Glucose and Galactose are absorbed into enterocytes of the small intestine via sodium-glucose cotransporter (SGLT), a sodium-dependent active transport mechanism.
• Fructose enters the cells via facilitated diffusion through GLUT-5.
• All monosaccharides exit the enterocytes and enter the bloodstream via GLUT-2 by passive facilitated diffusion.

Question 7

Carbohydrates as One of the Key Biomolecules: Monomers, Structure, and Function:

Answer 7

• Monomers: The monomers of carbohydrates are monosaccharides, such as glucose, fructose, and galactose.
• Structure: Carbohydrates are composed of carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio (general formula: (CH2O)n). Monosaccharides can link together to form disaccharides and polysaccharides through glycosidic bonds.
• Function: Carbohydrates serve as a primary energy source for cells, provide structural components (e.g., cellulose in plants), and are involved in cell-cell recognition and signaling processes.

Question 8

Formula for Carbohydrates:

Answer 8

• The general formula for carbohydrates is (CH2O)n, where “n” represents the number of carbon atoms. For example, glucose, a common monosaccharide, has the formula C6H12O6.

Question 9

Process of Carbohydrate Chemical Digestion and Organs Involved:

Answer 9

• Mouth: Carbohydrate digestion begins in the mouth, where salivary amylase breaks down starch into shorter chains of sugars.
• Stomach: Carbohydrate digestion temporarily halts in the stomach due to the acidic environment, which inhibits amylase activity.
• Small Intestine: The primary site of carbohydrate digestion. Pancreatic amylase continues breaking down starch into disaccharides. Brush border enzymes in the small intestine (e.g., lactase) further break down disaccharides into monosaccharides.

Question 10

Carbohydrate Absorption and Metabolism:

Answer 10

• Absorption: Monosaccharides (e.g., glucose, galactose, fructose) are absorbed by the enterocytes in the small intestine. Glucose and galactose are absorbed via sodium-glucose cotransporter (SGLT) using active transport, while fructose is absorbed through facilitated diffusion via GLUT-5.
• Metabolism: After absorption, monosaccharides enter the bloodstream and are transported to the liver via the hepatic portal vein. The liver plays a central role in regulating blood glucose levels by storing glucose as glycogen or releasing it into the bloodstream when needed. The metabolism of glucose provides energy to cells through cellular respiration.

Question 11

What is the ratio of the three key chemical elements in forming larger saccharides?

Answer 11

1:2:1, C(1), H(2), O(1)

Question 12

Which of the following is not a monosaccharide?

a. Glucose
b. Sucrose
c. Galactose
d. Fructose

Answer 12

B

Question 13

When monosaccharides are linked together to form polysaccharides, what type of chemical bond is used?

a. Ionic bond
b. Peptide bond
c. Phosphodiester bond
d. Glycosidic bond

Answer 13

D

Question 14

4. Which organ is responsible for the secretion of insulin or glucagon to regulate blood glucose homeostasis?

a. liver
b. pancreas
c. kidney
d. brain

Answer 14

B

Question 15

Which of the following are major sites for glycogen storage

a. Adipose tissue
b. Bones
c. Muscle and liver
d. Kidney and liver

Answer 15

C

Question 16

What role does insulin normally have in regard to glucose and cells?

a. It causes glucose to be released from cells so ATP can be produced outside of the cell
b. It unlocks cells so that they can take up glucose to make ATP to use as energy (or store as excess glycogen)
c. It causes protein to be taken into cells, which is then converted to glucose once inside the cell
d. It stimulates the breakdown of fats for ATP to be produced more efficiently.

Answer 16

B

Question 17

Describe the digestion and absorption of carbohydrates in the digestive tract, beginning in the mouth. Include of types of enzymes involved at each organ, and the end molecules produced.

Answer 17

Mouth – chemical digestion from salivary amylase
Stomach – chemical digestion continues from mouth
Small intestine – chemical digestion with brush border enzymes and pancreatic amylase
End molecules = disaccharides and monosaccharides

Question 18

8. How does carbohydrate metabolism differ from carbohydrate digestion?

Answer 18

Metabolism: Set of metabolic pathways which break down molecules into smaller units and release energy.
Digestion: Process by which body breaks down food so it can be absorbed by the blood stream.

Question 19

9. Where does carbohydrate digestion begin? Describe the biochemical process involved, including:
   Name and role of appropriate enzyme involved
   Composition and role of saliva

Answer 19

Mechanical and biochemical digestion begins in the mouth
Name and role of appropriate enzyme involved
Biochemical: starts chemical digestion of carbohydrates with amylase, breakin down long carbohydrate molecules into shorter chains.
Composition and role of saliva
- 99.5% water +electrolytes and proteins
- The water and mucus moisten food, flushes away food particles and act as a solvent
- Amylase
- Lysozyme: an antibacterial enzyme
- Bicarbonate buffer to neutralize acids.

Question 20

10. What is Enzymatic hydrolysis in carbohydrate metabolism? Provide an example including the enzyme involved.

Answer 20

Enzymatic hydrolysis is a chemical process where a molecule is cleaved into 2 parts by the addition of a water molecule by the catalytic actions of enzymes.
Example: Sucrose is broken down to glucose and fructose.

Question 21

11. What role does the stomach do in carbohydrate digestion and metabolism?

Answer 21

• HCl inhibits amylase, halting biochemical digestion
• The stomach has 3 muscle layers which churn and mix food
• The end product is chyme

Question 22

12. Describe how the small intestine, liver, pancreas, and the large intestine contribute to the digestion and metabolism of carbohydrates.

Answer 22

The small intestine:
- Pancreatic amylase is secreted from the pancreas into the duodenum of the small intestine to digest carbohydrates
- The small intestine contains villi which are covered in small intestinal epithelia! absorptive cells, enterocytes
- Enterocytes also have small projections called microvilli which make up the brush border
- The large surface area and transport mechanisms of enterocytes in the small intestine allow for absorption
- Pancreatic amylase breaks down polysaccharides, such as starch and glycogen, to disaccharides, maltose, sucrose and lactose
- Disaccharidases in the brush border of the small intestine breakdown disaccharides into monosaccharides
- Glucose or galactose are absorbed into the enterocytes
The liver:
- Maintaining glucose concentrations in a normal range
- Converting excess glucose into glycogen and store it
- When there is bodily demand for glucose, the liver converts glycogen back into glucose
The pancreas:
- Pancreatic amylase is secreted from the pancreas into the small intestine
- Pancreatic amylase breaks down polysaccharides to disaccharides
The large intestine:
- Indigestible polysaccharides like cellulose are unable to be digested so either form indigestible fibre or are broken down by the gut microbiome.

Question 23

13. Describe the process of monosaccharide absorption of glucose, galactose, fructose, and how they enter the capillary.

Answer 23

• Glucose or galactose are absorbed into the enterocytes with sodium and energy-dependent secondary active transport through a symporter called the sodium cotransporter symport (SGLT)
• Fructose passively enters the cell through a protein called glucose transporter 5 (GLUT-5)
• The monosaccharides then exit the cell at the basal membrane by passive facilitated diffusion via a protein called GLUT-2 and enter the capillary by simple passive.