BS120: Carbs 2 Flashcards
What is a Glycosidic bond?
and how are they named
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)
What are the two types of Glycosidic bonds?
it is classified based on the second group, being either:
* O-glycosidic bond
* N-glycosidic bond
What is an O-glycosidic bond?
with example
- 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)
What is an N-glycosidic bond?
- 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)
What are Reducing Sugars?
and their properties
Sugars that have a free carbonyl (aldehyde or ketone) group.
- can donate e-
- can reduce Benedict’s Reagent
- can undergo mutorotation
What are Non-Reducing Sugars?
and their properties
Sugars that do not have a free carbonyl (aldehyde or ketone) group.
- can’t donate e-
- cannot reduce Benedict’s Reagent
- cannot undergo mutorotation
Which disaccharide is NOT a reducing sugar?
Sucrose because both carbonyl groups are involved in glycosidic bonds, leaving no free carbonyl group.
All other disac. are reducing sugars.
Define disaccharides
carbohydrates formed by condensation of 2 monosaccharides by glycosidic bond.
What are some examples of disaccharides
- maltose
- isomaltose
- lactose
- sucrose
What is are the sugar units in maltose and what is the glycosidic bond type in Maltose?
it is made of two α-D-Glucose molecules with a [α 1-4] glycosidic bond.
What are the properties and importance of maltose?
- 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
What is isomaltose?
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
What is Lactose also known as and what is its importance?
Milk sugar.
- in humans, it is digested by lactase
- it is the least sweet sugar
- synthesized by lactating mammary gland
What are the sugar units and the glycosidic bond type in Lactose?
sugar units: β-D-Galactose + α-D-Glucose
bond: β 1-4.
What is another name for Sucrose and what is its importance?
- 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
What are the sugar units & glycosidic bond found in Sucrose?
sugar units: α-D-Glucose + β-D-Fructose
bond: α 1-2.
What does hydrolysis of sucrase (invertase) produce?
Forms honey, invert sugar.
What is honey & why is it called invert sugar?
A mixture of glucose & fructose. Honey is called invert sugar because it has the opposite properties of sucrose.
What is the main storage form of glucose in plants?
Starch.
What is the repeating sugar unit in Glycogen?
α-D-Glucose.
What is the primary function of Cellulose?
It is the supporting tissue of plants.
What type of glycosidic bond is found in Cellulose?
β 1-4.
What are the two types of Polysaccharides?
- Homopolysaccharides
- Heteropolysaccharides
What is a Homopolysaccharide?
A polysaccharide that consists of the same monosaccharide units.
What is a Heteropolysaccharide?
A polysaccharide that consists of more than one type of monosaccharide units.
What are Glycosaminoglycans also known as?
Mucopolysaccharides.
What is the digestive enzyme for carbohydrates?
Glycosidases.
Where does carbohydrate digestion begin?
In the mouth.
What halts carbohydrate digestion temporarily?
The high acidity of the stomach.
What is the end product of carbohydrate digestion?
Monosaccharide units.
What is the main sugar unit formed during carbohydrate digestion?
Glucose.
Fill in the blank: All ________ are Reducing Sugars.
[Monosaccharides]
Fill in the blank: Sucrose has no free ________ groups.
[Carbonyl]
True or False: Glycogen is more branched than starch.
True.
What is the importance of GAGs in the human body?
They are essential components of the extracellular matrix and connective tissue.
What two components make up Starch?
- Amylose
- Amylopectin
What is the primary source of Starch?
Potatoes and cereals (rice, corn, wheat).
What is the role of salivary α-Amylase?
Salivary α-Amylase initiates the digestion of carbohydrates in the mouth
What limits the digestion time in the mouth?
The gastric hydrochloric acid inhibits the action of salivary amylase
Where does digestion end in the digestive system?
Digestion ends in the small intestine
What are the two main sections of the small intestine where digestion occurs?
Duodenum & Jejunum
What does the pancreas secrete in the duodenum?
Pancreatic α-Amylase
At what pH is pancreatic α-Amylase activated?
pH 6.7
What ion activates pancreatic α-Amylase?
Chlorine Ion (Clˉ)
What type of enzyme is pancreatic α-Amylase?
α-Endoglycosidase
What does pancreatic α-Amylase hydrolyze?
Internal α 1-4 bonds inside polysaccharides
What does pancreatic α-Amylase not hydrolyze?
α 1-6 bonds of polysaccharides
What are the products of polysaccharide hydrolysis by pancreatic α-Amylase?
Maltose, Isomaltose, Dextrins & Branched or Unbranched Oligosaccharides
What do the cells of the brush border in the jejunum secrete?
Disaccharidases (α-Glucosidases)
Name the disaccharidases secreted in the jejunum.
- Maltase
- Isomaltase
- Lactase
- Sucrase
What do disaccharidases hydrolyze disaccharides into?
Monosaccharides
What does maltase hydrolyze?
Maltose to Glucose + Glucose
What does isomaltase hydrolyze?
Isomaltose to Glucose + Glucose
What does lactase hydrolyze?
Lactose to Galactose + Glucose
What does sucrase hydrolyze?
Sucrose to Glucose + Fructose
What are dextrins?
Partially hydrolyzed starch by the action of acids or enzymes
What is absorption in the context of digestion?
Transportation from lumen to the intestinal cell & from intestinal cell to the blood
Where are monosaccharides absorbed in the small intestine?
At the jejunum
Into what circulation are monosaccharides absorbed?
Portal circulation
What is the fate of glucose after absorption?
Transported into cells as a source of energy
What happens to fructose and galactose after absorption?
Transported to the liver for conversion into glucose
What are the two carrier mediated mechanisms for monosaccharide absorption?
- Sodium independent glucose transporters (GLUT)
- Sodium dependent glucose transporters (SGLT)
How do glucose and galactose enter intestinal cells?
Actively by SGLT-1
How does fructose enter intestinal cells?
Passively by GLUT-5
How do glucose and galactose enter the blood?
Passively by GLUT-2
What characterizes passive transport of monosaccharides?
Does not need energy and moves from high to low concentration
What characterizes active transport of monosaccharides?
Needs energy and moves from low to high concentration
What is the transporter for sodium independent glucose transport?
Na+ Independent Glucose Transporter (GLUT 1-14)
What is the transporter for sodium dependent glucose transport?
Na+ dependent Glucose Co-transporter (SGLT-1)
What is the role of GLUT2?
Facilitated diffusion in intestinal epithelial cells, liver cells, beta cells of pancreas & kidney
What is GLUT4 known for?
Major glucose transporter in skeletal muscle and adipose tissue, controlled by insulin
What is the mechanism of secondary active transport for glucose absorption?
Coupled with Sodium-Potassium Pump using ATP
