Carbohydrates 1 Flashcards
- serve as the major source of energy and as a reserve food material.
- form part of the structural framework of DNA and RNA molecules.
- are involved in cell-cell interaction.
Carbohydrates
Classification of Carbohydrates
- Monosaccharide
- Oligosaccharides
- Polysaccharides
o Contain single polyhydroxy aldehyde or ketone unit
o They can’t be broken down into simpler substances by hydrolysis (reaction with water) reactions
o Contains 3-7 C atoms
o 5 and 6 carbon species are more common
o Water soluble white crystalline solids
Monosaccharide
o Contains ~2-10 monosaccharide units - covalently bonded to each other
o Disaccharides (contain 2 monosaccharide units) more common - crystalline water soluble substances
o Table sugar (sucrose) and milk sugar (lactose)
o - are common disaccharides
o Upon hydrolysis they produce monosaccharide
o In human body associated with proteins and lipids for structural and regulatory
functions
Oligosaccharides
o Contains many monosaccharide units covalently bonded
o Polymers: May contain 100s of 1000s of monosaccharide units
Polysaccharides
are isomers that have the same molecular and structural formulas but differ in the orientation of atoms in space
Stereoisomers
are stereoisomers whose molecules are non-superimposable mirror images of each other. Molecules with chiral center.
Enantiomers
are stereoisomers whose molecules are not mirror images of each other.
Diastereomers
- a method for giving molecular chirality specifications in two dimensions. A __________ is a two-dimensional structural notation for showing the spatial arrangement of groups about chiral centers in molecules.
Fischer Projection Formula
- The four groups attached to the atom at the chiral center assume a tetrahedral geometry and it is governed by the following conventions
Tetrahedral Arrangements
- Chiral compound that rotates light towards right (clockwise; +)
Dextrorotatory
- Chiral compound that rotates light towards left (counterclockwise; -)
Levorotatory
Blood sugar- Main source of energy
D-glucose
Constituent of sucrose, the common sugar
D-fructose
Constituent of lactose, glycolipids and glycoproteins
D-galactose
Constituent of globulins, mucoproteins, and glycoproteins
D-mannose
o Dominant form of monosaccharides with 5 or more C atoms is cyclic - cyclic forms are in equilibrium with open chain form
o Cyclic forms are formed by the reaction of carbonyl group (C=O) with hydroxyl (-OH) group on carbon 5
Cyclic Hemiacetal Forms of D-glucose
six-atom ring is called a
pyranose
five-atom ring is called
furanose
a two-dimensional structural notation that specifies the
three-dimensional structure of a cyclic form of a monosaccharide.
Hawort Projection Formula
- Oxidation can yield three different types of acidic sugars depending on the type
of oxidizing agent used:
Oxidation to acidic sugars
- The carbonyl group in a monosaccharide (either
an aldose or a ketose) is reduced to a hydroxyl group using hydrogen as the
reducing agent.
Reduction to sugar alcohols
- Cyclic forms of monosaccharides are hemiacetals, they react with alcohols to form acetals
Glycoside formation
- and their N-acetyl derivatives are important building blocks of polysaccharides such as chitin
Amino sugar formation
- of various monosaccharides are stable in aqueous solution
and play important roles in the metabolism of carbohydrates
Phosphate ester formation
- Two monosaccharides can react to form ___________
- One monosaccharide act as a hemiacetal and other as alcohol
Disaccharides
is digested easily by humans because we have enzymes that can break a (1-4) linkages but not b (1-4) linkages of cellobiose. Therefore cellobiose cannot be digested by humans.
Maltose
is made up of b-D-galactose unit and a b-D-glucose unit joined by a b(1-4) glycosidic linkage
Lactose
o Many monosaccharide units bonded with glycosidic linkages
o Two types:
▪ - Linear and branched, homo- and hetero-polysaccharides
Polymers
A storage polysaccharide is a polysaccharide that is a storage form for monosaccharides and is used as an energy source in cells.
Starch
Branched chain polymer - 80 - 85 % of the starch a (14) glycosidic bond for straight chain and a (16) for branch
Amylopectin
▪ Humans and animals storage polysaccharide
▪ Contains only glucose units
Glycogen
▪ Linear homopolysaccharide with b (1 4) glycosidic bond
▪ It serves as dietary fiber in food– readily absorbs water and results in softer stools
Cellulose
▪ Similar to cellulose in both function and structure
▪ Linear polymer with all b (14) glycosidic linkages - it has a N-acetyl amino derivative of glucose
▪ Function is to give rigidity to the exoskeleton s of crabs, lobsters, shrimp, insects, and other arthropods
Chitin
polysaccharides with a repeating disaccharide unit containing an amino sugar and a sugar with a negative charge due to a sulfate or a carboxyl group.
Acidic Polysaccharides
is a lipid molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it.
glycolipid
\is a protein molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it.
glycoprotein
are polyhydroxy aldehydes, polyhydroxy ketones, or compounds that yield such substances upon hydrolysis. Plants contain large quantities of carbohydrates produced via photosynthesis
Carbohydrates
A chiral object is not identical to its mirror image. An achiral object is identical to its mirror image.
Chirality and achirality
The atoms of stereoisomers are connected in the same way but are arranged differently in space. The major causes of The atoms of ________________ in molecules are structural rigidity and the presence of a chiral center.
stereoisomers
are two-dimensional structural
formulas used to depict the three-dimensional shapes of molecules with chiral centers
Fischer projection formulas
re two-dimensional structural
representations used to depict the three-dimensional structure of a cyclic form of a monosaccharide.
Haworth projection formulas
