L2: Disaccharides and Polysaccharides

Question 1

what do disaccharides consist of?

Answer 1

two monosaccharides

Question 2

what are non-reducing diasaccharides?

Answer 2

Non-reducing disaccharides: two aldehyde/or ketone groups are involved in the linkage (anomeric C not free) e.g. sucrose (reduction happens to fehling solution)

Question 3

what are reducing disaccharides?

Answer 3

if one of aldehyde/or ketone groups is free (free anomeric C) e.g. Lactose and Maltose.
Classification:

Question 4

what are the most abundant disaccharides? “MLS”

Answer 4

sucrose, lactose and maltose.

Question 5

what are other names of maltose?

Answer 5

(malt sugar, maltose syrup)

Question 6

Maltose(malt sugar, maltose syrup)

Answer 6

2 alpha Dextro glucose - alpha 1 4 glycosidic bond
(reducing)

Question 7

isomaltose

Answer 7

It is formed of two α-glucose but linked together by α 1-6 glycosidic bonds. It is a reducing sugar.

Question 8

cellobiose

Answer 8

It is formed of two units β-glucose linked together by a β1-4 glycosidic bond.

Question 9

sucrose(cane sugar, beet sugar, table sugar)

Answer 9

Formed of α-glucose and β-fructose linked by an α-1- β-2 glycosidic bond (involving the anomeric Cs). (non-reducing)

Question 10

lactose(milk sugar)

Answer 10

It is formed from β-galactose and β-glucose via a β (1-4) link with free anomeric C. It is a reducing sugar.

Question 11

starch hydrolysis

Answer 11

starch is hydrolyzed by pancreatic and salivary amylase giving maltose which is hydrolyzed by maltase giving two glucose units.

starch is also be hydrolyzed by acids giving dextrins which are hydrolyzed by alpha dextrinase giving smaller units.

Question 12

dextran hydrolysis

Answer 12

dextran is hydrolyzed into isomaltose

Question 13

cellulose hydrolysis

Answer 13

is ts hydrolyzed by acids into cellobiose.

Question 14

sucrose hydrolysis

Answer 14

it is hydrolyzed by sucrase into alpha glucose and beta fructose.

Question 15

lactose hydrolysis

Answer 15

it is hydrolyzed by intestinal lactase into beta glucose and beta galactose

Question 16

what are the characteristics of lactose sugar?

Answer 16

• It is the principal carbohydrate in milk and is of critical nutritional importance to mammals in the early stages of their lives.

• It may appear in the urine in late pregnancy and during lactation

• Low levels of lactase enzyme lead to undigested lactose that undergoes bacterial fermentation in the colon with the generation of large amounts of CO2, H2, and irritating organic acids.

• These products cause painful digestive upsets known as lactose intolerance.

Question 17

what are oligosaccharides?

Answer 17

• Oligosaccharides consist of 3-10 monosaccharide units joined together by glycoside bonds. E.g. Maltotriose.

Question 18

what is the existence and significance of oligosaccharides?

Answer 18

• Oligosaccharides are important as constituents of the glycolipids and glycoproteins of the cell membrane.

• Many secreted proteins, such as antibodies and coagulation factors also contain oligosaccharide units.

Question 19

what are polysaccharides?

Answer 19

• Polysaccharides, also called glycans, consist of more than 10 monosaccharide units and/or their derivatives joined together by glycosidic linkage.

Question 20

what are polysaccharides classified according to?

Answer 20

according to structure and function

Question 21

how are polysaccharides classified structurally?

Answer 21

1. Homopolysaccharides (homoglycans): contain only one type of monosaccharide. E.g. starch, glycogen, dextran, dextrin, cellulose, inulin.
2. Heteropolysaccharides (heteroglycans): contain more than one type of monosaccharides. E.g. glycosaminoglycans (GAGs, mucopolysaccharides), agar.

Question 22

How are polysaccharides classified functionally?

Answer 22

Polysaccharides are classified according to their function into storage and structural polysaccharides.

• Storage polysaccharides: starch, glycogen, dextran, and inulin.

• Structural polysaccharides: cellulose and agar.

Question 23

starch

Answer 23

It is a glucosan (a-D glucose units) consists of 2 layers:
► An inner linear nonbranching layer called amylose.
► An outer highly branched layer is called amylopectin. The branch points occur about once every thirty linkages.

-Main storage of polysaccharides in plants.

Question 24

Glycogen(animal starch)

Answer 24

-Glucosan

►It is a highly branched molecule (branches every 10 glucose units; more branched than amylopectin). It yields a red-violet color with iodine.

-Main storage of polysaccharides in humans and animals

-It is present mainly in the liver 10% and in the skeletal muscles 1-2% and breaks down to glucose when fasting which helps in maintaining glucose levels in the blood.

Question 25

dextran

Answer 25

-It is formed of α-glucose units (glucosan).

-It is a storage polysaccharide in yeasts and
bacteria

-Bacterial dextrans are used in laboratories as the support medium for chromatography of macromolecules and as replacement therapy in blood loss.

-Dental plaque is due to dextran synthesized from sucrose by oral bacteria.

Question 26

cellulose

Answer 26

-It is formed of β-D-glucose units.

-It is the most abundant natural polymer found in the world. It is the structural component of the cell walls of nearly all plants.

-Cellulose is extremely resistant to hydrolysis whether by acid or by the digestive tract amylases. So, it can stimulate peristaltic movement and prevent constipation.

-The bacteria that live in the gut of ruminant animals secrete cellulase enzyme (β- glucosidase) which is effective in the hydrolysis of cellulose.

Question 27

inulin

Answer 27

-It is formed of fructose (fructosan).

-Hydrolyzed by the enzyme inulinase in plants. It has no dietary importance in human beings as inulinase is absent in human

-It is used in the inulin clearance test to determine the rate of glomerular filtration. It can be used as a diet for diabetics.

Question 28

alpha dextrin

Answer 28

Starch is partially hydrolyzed by acids or enzymes into dextrins and it is hydrolyzed by alpha dextrinase

-It is used as mucilage.

Question 29

what are the examples of heteropolysaccharides?

Answer 29

agar

GAGS (glycosaminoglycans - mucopolysaccharides)

Question 30

Agar

Answer 30

• A polysaccharide isolated from marine red algae.

• Composed of agarose and agaropectin

• Agarose gel is used in gel chromatography and gel electrophoresis.

• Nutrient agar is used in the preparation of culture media in microbiology

Question 31

GAGS

Answer 31

• GAGs are long linear unbranched chains composed of a repeating disaccharide unit (acidic sugar-amino sugar) .

• The amino sugar: (D-glucosamine or D-galactosamine) and the amino group is usually acetylated (sometimes sulphated).

• The acid sugar: either glucuronic or L-iduronic

Question 32

chondroitin sulfate

Answer 32

-glucuronic acid
-N-galactosamine (acetylated)
-sulphated
-cartilage, tendons, ligaments, bone, heart valves, aorta.
-Most abundant GAG
-protective and supportive.

Question 33

keratan sulphate

Answer 33

-no uronic acid
-N-glucosamine (acetylated) and galactose -6- sulfate
-Sulfated
-cornea, bone,cartilage
-aggregated with chondroitin sulfate
-protective and supportive

Question 34

dermatan sulphate

Answer 34

-L-iduronic acid
-N-galactosamine (acetylated)
-Sulfated
-skin, blood vessels, heart valves
-protective and supportive.
Usually replaces hyaluronic acid in aged skin and blood vessels

Question 35

heparin

Answer 35

-glucuronic and iduronic acid
-Glucosamine (non-acetylated)
-More Sulfated
-Intracellular granules of mast cells lining the arteries of the lungs, liver and skin
-Anticoagulant

Question 36

heparan sulphate

Answer 36

-glucuronic or iduronic acid
-Glucosamine (acetylated)
-Less Sulfated
-Extracellular GAG, basement membranes of cell surface
-components of the cell surface.

Question 37

hyaluronic acid

Answer 37

-glucuronic acid
-Glucosamine (acetylated)
-Non sulfated
-synovial fluid of joints, vitreous humor
of eye, skin ECM of loose connective tissue
-shock absorbing, lubricant.

Question 38

what are proteoglycans?

Answer 38

• All of the GAGs except hyaluronic acid and heparin are found covalently attached to a protein, forming proteoglycan monomers.

•A proteoglycan monomer found in cartilage consists of a core protein to which the linear carbohydrate chains are covalently attached.