[2.1-2.2] CARBOHYDRATES INTRODUCTION, MONOSACCHARIDES

Carbohydrates Cn(H2O)n

are structurally *polyhydroxylated ketones or aldehydes

*polyhydroxyl groups for

reactivity and better solubility in water

carbohydrates can exist as

monosaccharides

oligo- and polysaccharides

Monosaccharides

One distinct carbohydrate molecule

Oligo- and Polysaccharides

Repeating structures of the monosaccharide units

Oligosaccharides

are usually composed of 3-9 or 3-10 sugar units (monomers)

Polysaccharides

can extend up to 1000 units (Ex. cellulose, starch)

BIOSYNTHESIS OF MONOSACCHARIDES

is derived from photosynthesis, consisting of the:

Light-dependent reaction

Light-independent (aka Carbon Fixation or Calvin-Benson cycle) reactions

BIOSYNTHESIS OF MONOSACCHARIDES is derived from photosynthesis, consisting of the:

Light-dependent reaction

Light-independent (aka Carbon Fixation or Calvin-Benson cycle) reactions

photosynthesis equation

6 CO2 + 12 H2O → C6H12O6 + 6 O2 + 6 H2O

Photosynthesis

is an anabolic process occurring in the chloroplast

Anabolic

simple molecules combine to create complex molecules; requires energy

Light-Dependent reaction is also called as

photochemical rxns or c3 rxns because the first stable product is a 3-carbon sugar (3-phosphoglyceraldehyde or 3-PGAL) which can be converted to glucose

Light-Dependent reaction

Produces ATP, NADPH (reduced form)

Light-Dependent reaction

Occurs in the thylakoid membranes of chloroplast; they contain chlorophyll, a pigment that absorbs light energy from sunlight.

Light-Independent is Also called

carbon fixation or Calvin-Benson cycle, where carbon dioxide is fixed to become sugar (glucose)

Light-Independent

Produces glucose

Light-Independent

Occurs in the stroma of chloroplast

Formation of OLIGO- AND POLYSACCHARIDES usually involves the:

-Formation of UDP-monosaccharide from uridine triphosphate + the monosaccharide

-Followed by reaction with a preexisting oligo- or polysaccharide several (up to thousands of) times.

The monosaccharide must first be attached to UDP (Uridine Diphosphate) before

forming oligo- or polysaccharides

UDP

is a carrier of monosaccharides and their derivatives

chloroplast

-major photosynthetic organelle

-composed of 4 layers of membranes

thylakoid membrane

-membrane inside chloroplast

-color green because it contains photosynthetic pigments

granum

grp of thylakoid membranes

major photosynthetic pigments

Chlorophyll A: bluish green

Chlorophyll B: yellow green/ light green

accessory photosynthetic pigments

Carotene: orange

Xanthophyll: yellow

SUCROSE is synthesized in the

cytosol

SUCROSE is synthesized in the cytosol by:

Sucrose-6-phosphate synthase

Sucrose-6-phosphate phosphatase

Sucrose

(commonly known as table sugar) is one of the most important disaccharides in plants

Sucrose is used as __

preservative, sweetening agent, etc.

Sucrose is made up of

glucose + fructose, where fructose imparts the sweetness

GLYCOGEN

is a highly branched polymer of glucose; it is the storage form of glucose in mammalian bodies

GLYCOGEN

Found in the liver and muscle tissues

GLYCOSIDIC BONDS OF GLYCOGEN

α(1→4) Linkage- straight

α(1→6) Linkage-branched

2 kinds of starch

amylose (straight)

amylopectin (branched; similar to glycogen)

Glycogen is more branched than amylopectin

Amylopectin: every 20-24 sugars

Glycogen: every 8-12 sugars

UDP-glucose is added at

nonreducing end

"reducing end"

refers to a single specific point on the molecule where a free anomeric carbon (C1) of a glucose unit is available for chemical reactions,

"non-reducing ends"

are all the other branch tips where the glucose units are linked to other sugars, making that C1 carbon unavailable for further reactions.

MONOSACCHARIDES

Smallest unit; cannot be further hydrolyzed

MONOSACCHARIDES are classified by

functional group (aldose vs ketose)

number of carbon

D- or L- ISOMERISM depends on the

PENULTIMATE (2nd to the last) carbon

D- right

L- left

MONOSACCHARIDES

-Crystalline, water-soluble (due to OH groups), and sweet

-3-9 carbon atoms (the most important ones are hexoses)

2 carbons

Diose

Hydroxyacetaldehyde

-aldose

-never free in nature

3 carbons

triose

Glyceraldehyde (aldose)

(DHA)

Dihydroxyacetone (ketose)

4 carbons

tetrose

Erythrose, Threose

Erythrulose

5 carbons

pentose

Ribose, Arabinose

Ribulose

5 carbons

pentose

Ribose, Arabinose

Ribulose

6 carbons

hexose

Glucose, Galactose

Fructose

7 carbons

heptose

Sedoheptulose

8 carbons

Octose

D-glycero-

D-mannoctulose

D-glycero-

D-mannoctulose

Found in avocado pulp and Sedum

Ribose & Arabinose (oligosaccharides)

Common pentoses that is in both furanose and pyranose form in plants and bacteria

Glucose, Galactose, and Fructose (monosaccharides)

Absorbed in the intestinal tract and they are taken up in the liver where they can be utilized as an immediate source of energy

LINEAR CONFIGURATION:

Fischer Projection

L-Glucose

Less Active

Not naturally-occuring; synthesized artificially

D-Glucose

More Active

Most common naturally occuring simple sugar

CYCLIC CONFIGURATION:

Haworth Projection

Pyranose

6-member ring

Ex. glucopyranose

Pyranose

More stable than furanose because more conformation-isomeres are possible:

-2 "chair"

-2 "half-chair"

-1 "boat"

-2 "twist"

Furanose

5-member ring

Ex. ribofuranose

Furanose

Less stable than pyranose because it only exhibits the following conformations:

-"envelope"

-"half-chair" conformations

Furanose

Unstable but may be stabilized on glycoside formation

Anomeric Carbon

Spotted by finding a carbon with 2 oxygens

α Alpha:

anomeric OH down

β Beta:

anomeric OH up

D-ribose:

present in RNA; present as furanose when part of the nucleic acid

Anomers:

cyclic monosaccharides which differs in the configuration of C-1 (aldoses) or C-2 (ketoses)

Ribulose, Xylulose, and Sedoheptulose:

Ketoses

L-Rhamnose

Penultimate carbon @ left

C5 is a methyl group

Hemamelose:

C2 is a hydroxymethyl

Galactose:

C4 epimer of Glucose

Mannose:

C2 epimer of Glucose

GLUCOSE

synonyms

Dextrose, blood sugar, grape sugar, physiologic sugar, corn sugar

GLUCOSE

chemical nature

Aldohexose (C₆H₁₂O₆)

GLUCOSE

sources

Enzymatic hydrolysis of starch

GLUCOSE

uses

sweetening agent

BENEDICT'S TEST FOR REDUCING SUGAR

green (traceable)- 0.5-1g

yelow (low)- 1-1.5g

orange (moderate- 1.5-2

red (high)- .>2

BENEDICT'S TEST FOR REDUCING SUGAR

Copper sulfate (CuSO₄):

Oxidizing agent, responsible for the color change in the reaction

BENEDICT'S TEST FOR REDUCING SUGAR

Sodium carbonate (Na₂CO₃):

Creates an alkaline environment

BENEDICT'S TEST FOR REDUCING SUGAR

Sodium citrate (Na₃C₆H₅O₇):

Prevents the copper ions from precipitating out of solution by forming a complex with them

GLUCOSE DERIVATIVES

liquid glucose

calcium gluconate

calcium gluceptate and levulinate

ferrous gluconate

Liquid Glucose

Thick, syrupy liquid from incomplete hydrolysis of starch

Liquid Glucose

Cough syrup

Vitamins

Calcium Gluconate

Electrolyte replenisher

Calcium Gluconate

Blood calcium level

High blood potassium

Magnesium toxicity

Calcium Gluceptate & Levulinate

Calcium sources from 7C and 5C glucose derivatives

Calcium Gluceptate & Levulinate

Conditions causing hypocalcemia

Ferrous Gluconate

Hematinic, given for iron deficiency anemia

FRUCTOSE

Levulose, fruit sugar

FRUCTOSE

Fruits and honey

Hydrolysis of inulin (see polysaccharides)

*Genus of Bees: Apis

*Honey Bee: Apis mellifera

FRUCTOSE

chemical nature

C₆H₁₂O₆

Ketohexose

In nature, in furanose form

Isolated in crystalline form as pyranose

FRUCTOSE

From isomerization of glucose by Streptomyces through the enzyme glucose isomerase

FRUCTOSE

uses

Food for diabetic patients

For infant feeding formula

For fructose injection

The SWEETEST monosaccharide

GALACTOSE

chemical nature

C₆H₁₂O₆

Aldohexose (C4 epimer of glucose)

Epimers

are carbohydrates which vary in 1 position for the placement of OH

GALACTOSE

source

Milk (as lactose)

Neuronal fibers (as galactoceramides

Milk (as lactose)

Official source of milk: Cow (Bos taurus)

Galactose is convertible to GLUCOSE in the human body (enters glycolysis after 4 steps)

4 STEPS = 4 ENZYMES

Phosphorylatio- Galactokinase

Transfer- UDP-Glc:Gal-1-P uridyltransferase

Epimerization -UDP-galactose-4- epimerase

Mutase - Phosphoglucomutase

Epimerization

(Change in configuration of only one chiral center)