BS120: Carbs 2

Question 1

What is a Glycosidic bond?

and how are they named

Answer 1

A covalent bond formed by condensation of the hydroxyl group of the anomeric carbon of a monosaccharide and a second compound.

glycosidic bonds are named according to:
1. position of OH of anomeric carbon in first sugar (alpha or beta)
2. number of connecting carbons (ex. 1-4)

Question 2

What are the two types of Glycosidic bonds?

Answer 2

it is classified based on the second group, being either:
* O-glycosidic bond
* N-glycosidic bond

Question 3

What is an O-glycosidic bond?

with example

Answer 3

• a glycosidic bond where the second group is a hydroxyl (OH)
• all sugar-sugar bonds are O-glycosidic bonds
  examples:
  1. sugar to sugar attachment (ex. maltose)
  2. attachment of sugar to hydroxide amino acid (ser, thr)

Question 4

What is an N-glycosidic bond?

Answer 4

• when the second group is an amine (NH).
  examples include:
  1. ribose linked to adenine in nucleotides (ATP)
  2. sugar linked to CONH amino acids (Asn)

Question 5

What are Reducing Sugars?

and their properties

Answer 5

Sugars that have a free carbonyl (aldehyde or ketone) group.
- can donate e-
- can reduce Benedict’s Reagent
- can undergo mutorotation

Question 6

What are Non-Reducing Sugars?

and their properties

Answer 6

Sugars that do not have a free carbonyl (aldehyde or ketone) group.
- can’t donate e-
- cannot reduce Benedict’s Reagent
- cannot undergo mutorotation

Question 7

Which disaccharide is NOT a reducing sugar?

Answer 7

Sucrose because both carbonyl groups are involved in glycosidic bonds, leaving no free carbonyl group.

All other disac. are reducing sugars.

Question 8

Define disaccharides

Answer 8

carbohydrates formed by condensation of 2 monosaccharides by glycosidic bond.

Question 9

What are some examples of disaccharides

Answer 9

1. maltose
2. isomaltose
3. lactose
4. sucrose

Question 10

What is are the sugar units in maltose and what is the glycosidic bond type in Maltose?

Answer 10

it is made of two α-D-Glucose molecules with a [α 1-4] glycosidic bond.

Question 11

What are the properties and importance of maltose?

Answer 11

• it is a reducing sugar and can undergo mutorotation
• it is digested (hydrolyzed) by maltase enzyme
• it is derived from the digestion of starch & glycogen

Question 12

What is isomaltose?

Answer 12

it has the same sugar units as maltose, except the glycosidic bond is [α 1-6].
- digested by isomaltase enzyme
- also derived from the digestion of starch & glycogen

Question 13

What is Lactose also known as and what is its importance?

Answer 13

Milk sugar.
- in humans, it is digested by lactase
- it is the least sweet sugar
- synthesized by lactating mammary gland

Question 14

What are the sugar units and the glycosidic bond type in Lactose?

Answer 14

sugar units: β-D-Galactose + α-D-Glucose
bond: β 1-4.

Question 15

What is another name for Sucrose and what is its importance?

Answer 15

• aka table sugar, Cane sugar.
• OH of anomeric carbon in both sugars is not free
• not a reducing sugar, so it has no mutorotation digested by sucrase (invertase)
• present in cane & various fruits
• used as a sweetening agent

Question 16

What are the sugar units & glycosidic bond found in Sucrose?

Answer 16

sugar units: α-D-Glucose + β-D-Fructose
bond: α 1-2.

Question 17

What does hydrolysis of sucrase (invertase) produce?

Answer 17

Forms honey, invert sugar.

Question 18

What is honey & why is it called invert sugar?

Answer 18

A mixture of glucose & fructose. Honey is called invert sugar because it has the opposite properties of sucrose.

Question 19

What is the main storage form of glucose in plants?

Answer 19

Starch.

Question 20

What is the repeating sugar unit in Glycogen?

Answer 20

α-D-Glucose.

Question 21

What is the primary function of Cellulose?

Answer 21

It is the supporting tissue of plants.

Question 22

What type of glycosidic bond is found in Cellulose?

Answer 22

β 1-4.

Question 23

What are the two types of Polysaccharides?

Answer 23

• Homopolysaccharides
• Heteropolysaccharides

Question 24

What is a Homopolysaccharide?

Answer 24

A polysaccharide that consists of the same monosaccharide units.

Question 25

What is a Heteropolysaccharide?

Answer 25

A polysaccharide that consists of more than one type of monosaccharide units.

Question 26

What are Glycosaminoglycans also known as?

Answer 26

Mucopolysaccharides.

Question 27

What is the digestive enzyme for carbohydrates?

Answer 27

Glycosidases.

Question 28

Where does carbohydrate digestion begin?

Answer 28

In the mouth.

Question 29

What halts carbohydrate digestion temporarily?

Answer 29

The high acidity of the stomach.

Question 30

What is the end product of carbohydrate digestion?

Answer 30

Monosaccharide units.

Question 31

What is the main sugar unit formed during carbohydrate digestion?

Answer 31

Glucose.

Question 32

Fill in the blank: All ________ are Reducing Sugars.

Answer 32

[Monosaccharides]

Question 33

Fill in the blank: Sucrose has no free ________ groups.

Answer 33

[Carbonyl]

Question 34

True or False: Glycogen is more branched than starch.

Answer 34

True.

Question 35

What is the importance of GAGs in the human body?

Answer 35

They are essential components of the extracellular matrix and connective tissue.

Question 36

What two components make up Starch?

Answer 36

* Amylose * Amylopectin

Question 37

What is the primary source of Starch?

Answer 37

Potatoes and cereals (rice, corn, wheat).

Question 38

What is the role of salivary α-Amylase?

Answer 38

Salivary α-Amylase initiates the digestion of carbohydrates in the mouth

Question 39

What limits the digestion time in the mouth?

Answer 39

The gastric hydrochloric acid inhibits the action of salivary amylase

Question 40

Where does digestion end in the digestive system?

Answer 40

Digestion ends in the small intestine

Question 41

What are the two main sections of the small intestine where digestion occurs?

Answer 41

Duodenum & Jejunum

Question 42

What does the pancreas secrete in the duodenum?

Answer 42

Pancreatic α-Amylase

Question 43

At what pH is pancreatic α-Amylase activated?

Answer 43

pH 6.7

Question 44

What ion activates pancreatic α-Amylase?

Answer 44

Chlorine Ion (Clˉ)

Question 45

What type of enzyme is pancreatic α-Amylase?

Answer 45

α-Endoglycosidase

Question 46

What does pancreatic α-Amylase hydrolyze?

Answer 46

Internal α 1-4 bonds inside polysaccharides

Question 47

What does pancreatic α-Amylase not hydrolyze?

Answer 47

α 1-6 bonds of polysaccharides

Question 48

What are the products of polysaccharide hydrolysis by pancreatic α-Amylase?

Answer 48

Maltose, Isomaltose, Dextrins & Branched or Unbranched Oligosaccharides

Question 49

What do the cells of the brush border in the jejunum secrete?

Answer 49

Disaccharidases (α-Glucosidases)

Question 50

Name the disaccharidases secreted in the jejunum.

Answer 50

* Maltase * Isomaltase * Lactase * Sucrase

Question 51

What do disaccharidases hydrolyze disaccharides into?

Answer 51

Monosaccharides

Question 52

What does maltase hydrolyze?

Answer 52

Maltose to Glucose + Glucose

Question 53

What does isomaltase hydrolyze?

Answer 53

Isomaltose to Glucose + Glucose

Question 54

What does lactase hydrolyze?

Answer 54

Lactose to Galactose + Glucose

Question 55

What does sucrase hydrolyze?

Answer 55

Sucrose to Glucose + Fructose

Question 56

What are dextrins?

Answer 56

Partially hydrolyzed starch by the action of acids or enzymes

Question 57

What is absorption in the context of digestion?

Answer 57

Transportation from lumen to the intestinal cell & from intestinal cell to the blood

Question 58

Where are monosaccharides absorbed in the small intestine?

Answer 58

At the jejunum

Question 59

Into what circulation are monosaccharides absorbed?

Answer 59

Portal circulation

Question 60

What is the fate of glucose after absorption?

Answer 60

Transported into cells as a source of energy

Question 61

What happens to fructose and galactose after absorption?

Answer 61

Transported to the liver for conversion into glucose

Question 62

What are the two carrier mediated mechanisms for monosaccharide absorption?

Answer 62

* Sodium independent glucose transporters (GLUT) * Sodium dependent glucose transporters (SGLT)

Question 63

How do glucose and galactose enter intestinal cells?

Answer 63

Actively by SGLT-1

Question 64

How does fructose enter intestinal cells?

Answer 64

Passively by GLUT-5

Question 65

How do glucose and galactose enter the blood?

Answer 65

Passively by GLUT-2

Question 66

What characterizes passive transport of monosaccharides?

Answer 66

Does not need energy and moves from high to low concentration

Question 67

What characterizes active transport of monosaccharides?

Answer 67

Needs energy and moves from low to high concentration

Question 68

What is the transporter for sodium independent glucose transport?

Answer 68

Na+ Independent Glucose Transporter (GLUT 1-14)

Question 69

What is the transporter for sodium dependent glucose transport?

Answer 69

Na+ dependent Glucose Co-transporter (SGLT-1)

Question 70

What is the role of GLUT2?

Answer 70

Facilitated diffusion in intestinal epithelial cells, liver cells, beta cells of pancreas & kidney

Question 71

What is GLUT4 known for?

Answer 71

Major glucose transporter in skeletal muscle and adipose tissue, controlled by insulin

Question 72

What is the mechanism of secondary active transport for glucose absorption?

Answer 72

Coupled with Sodium-Potassium Pump using ATP