Carbohydrates Flashcards
Carbohydrates are stored in plants as _____ and in animals as _____
Starch; Glycogen
Ratio of Carbon to Hydrogen to Oxygen in a carbohydrates
1 Carbon to 2 Hydrogens to 1 Oxygen
What are the classifications of carbohydrates?
Monosaccharides, Disaccharides, and Polysaccharides
3 Monosaccharides
Glucose, fructose, galactose
3 Disaccharides
Maltose, lactose, and sucrose
Maltose
Glucose and glucose
Sucrose
Glucose and fructose
Lactose
Glucose and galactose
3 polysaccharides
Starch, glycogen, and cellulose
A monosaccharide with an aldehyde group is referred to as…?
Aldose
A monosaccharide with a ketone is referred to as…?
A ketose
The smallest known monosaccharides are….
Glyceraldehyde and dihydroxyacetone
Aldehyde functional group
Hydrogen, carbonyl, carbon
Ketone functional group
Carbon, carbonyl, carbon
How to name monosaccharides
-either by the functional group: aldehyde or ketone (aldose, ketone) or by the number of Carbon atoms present if 3 carbon atoms...triose if 4 tetrose 5 pentose 6 hexrose
Glyceraldehyde
Three carbon monosaccharide with an aldehyde functional group
Enantiomers
Non super imposable mirror images
Can monosaccharides exist as enaontimores and diasteromers
Yes - both
How are D and L forms assigned?
By the chiral carbon atom furthest from C1
D - designation
Dextrarotary
Rotates plane of light clockwise
+
-OH is on the right
L - designation
Levorotary
Rotates plane of light in an anti clockwise direction
-
OH is on the left
If the rotation value is 0 what does this mean?
The mixture is racemic and is designated as +/-
In very simple carbohydrates what is the most oxidized group
The aldehyde or ketone group, which is always designated/drawn at the top and the carbon is numbered as 1
Fischer projections
- horizontal lines represent bonds projecting out of the page and vertical lines represent bonds projecting into the page
- aldehyde/ketone always at the top
- chiral carbon atom represented at point where both horizontal and vertical lines cross
Epimers
Sugars that are diastereoisomers and differ only in configuration at a single asymmetric center
D-glucose and D-galactose are abundant six carbon _____ while D - fructose is a six carbon ____
Aldoses; ketose
*ketoses have one less asymmetric center than aldoses with the same number of carbon atoms
When a monosaccharide is more than 5 arbors in length what usually happens?
They form a cyclic structure
-this occurs naturally and is due to the aldehyde or ketone group reacting with an -OH at the other end
Hemiacetal
When an aldehyde functional group reacts with the alcohol group
Hemiketal
When a ketone and an alcohol react
How are hemiacetal and hemiketal different?
They are both cyclic ring structures of carbohydrates; one has a hydrogen attached and one does not (b/c it originated from a ketone)
alpha and beta designations of glucose
BUDA
Beta is up, down is alpha
What is a six membered ring called
A pyranose because of its similarity to pyre
Anomeric carbon
Carbon one; to the right of the oxygen
For an aldehexose such as glucose
The same molecule can provide both the aldehyde and the alcohol group needed for the reaction
The C-1 aldehyde in the open chain form of glucose reacts with the C-5 hydroxy group to form an intramolecular hemiacetal
(results in a pyranose)
When glucose is in the cyclic form what is its true name?
d-glucopyranose
How is a 5-membered cyclic hemiketal formed
C-2 keto group in the open chain form can form an intramolecular hemiketal by reacting with the C-5 hydroxyl group to form a 5 membered cyclic hemiketal…which is called fructofuranose because of its similarity to furan
Haworth Projections
Give a simple 2D image of a monosaccharide where the carbon atoms in the ring are not written out
What are the two conformations in solution that glucose can take
Chair and boat
-chair form predominates because al axial positions are occupied by hydrogen atoms - boat form is to favored due to stearic endurance
Fehling’s solution
monosaccharides in solution change from blue to red ppt (both aldehyde & ketone essentially)
Benedict’s reagent
blue-copper containing solution gives a very distinct brick red ppt (copper II oxide)
Tollen’s reagent
diamminesilver I complex forms a silver ppt forming a ‘silver mirror’ on inside of test tube
Which reagents rely on oxidation-reduction reactions
Fehling’s, Beneficts and Tollen’s
All monosaccharides and all common disaccharides (minus sucrose) are _____ sugars
Reducing
What ca an aldehyde group be reduced to?
An alditol
Sodium borohydride
Converts D-glucose to D-glucitol or D-sorbitol
Aldose reductase
In the body this enzyme acts on glucose to form sorbitol
Define the term anomer
Anomers are isomers that differ in the arrangement of bonds around the hemiacetal carbon
Why does cyclisation of D-glucose give 2 isomers, alpha-D-glucose and B-D-glucose?
When carbonyl group of C1 of D-glucose reacts with C-5 hydroxyl group, a new chiral carbon is created (C1). In the alpha-isomer of the cyclic sugar, the C1 hydroxyl group is below the ring; in the beta -isomer, the C1 hydroxyl group is above the ring
When discussing sugars what is meant by an intramolecular hemiacetal
An aldehyde sugar forms an intramolecular hemiacetal when the carbonyl group of the monosaccharide reacts with a hydroxyl group on one of the other carbon atoms
How is glucose used industrially?
To make vitamin C, citric acid, bioethanol, gluconic acid and sorbitol
Sorbitol
Used as a sweetener in chewing um because it still tastes sweet but it prevents bacteria building up and dental plaque
Fructose
- levulose or fruit sugar (sweetest of all simple sugars found in honey and corn syrup)
- Derived from the digestion of table sugar
- can be produced anaerobically be fermentation of yeast/bacteria
- can undergo Maillard reaction with amino acids
- Fructose malabsorption leading to increased fructose in intestine resulting in irritable bowel syndrome
- some plants store fructose as a polymeric form known as inulin
Galactose
- Less sweet than glucose, found in hemicellulose as a polymer called galactan – can be hydrolysed to galactose
- Together with a modified form (N-acetylgalactosamine) is an important component of blood group antigens
- Galactose can be metabolised to glucose by the Leloir Pathway
- Glucose can be converted to galactose in humans by hexogenesis
- Galactosaemia – defects in galactose metabolism (very serious for newborns
What pathway can galactose be metabolized to glucose by?
The leloir pathway
Glucose can be converted to galactose in humans by
Hexogenesis
Galactosaemia
Defects in galactose metabolism
*very serious for newborns
What is the linkage in maltose?
alpha 1,4 glycosidic linkage
*maltose is a reducing sugar that is about half as sweet as glucose and often used in confectionary
What is the linkage in lactose?
Beta-1-4 glycosidic linkage
-reducing sugar and principal sugar found in milk
What is the linkage in sucrose
Alpha 1,2 glycosidic linkage
-NON reducing sugar
Homopolysaccharides
Homoglycans
Composed of a single type of sugar
Heterpolysaccharides
Heteroglycans
Composed of more than 2 types of sugar units
Structural features that define polysaccharides
- Monomeric units
- Sequence of sugar units
- Types of glycosidic bonds linking the monomeric units
- Approximate number of sugar units
- Degree of structural “branching”
Starch
Homopolymer; is the nutritional reservoir in plants that comes in two forms
2 forms of starch
amylose and amylopectin
Amylose
Unbranched chain of alpha-D-glucose units with alpha-1,4 glycosidic bonds
Amylopectin
Has a glucose backbone - branches leading to one reducing and many non reducing ends
-branches are attached to the main chain from the C1 of one alpha-d-glucose to the C6 hydroxy group of alpha d-glucose in the main chain through alpha- 1,6 glycosidic bonds
What bonds are in the main chain of starch
alpha 1,4 glycosidic bonds
Amylose and amylopectin are rapidly hydrolyzed by what enzyme?
Alpha-amylase; secreted by the salivary glands and pancreas
Glycogen
- Storage polysaccharide: represents a major energy store in humans and animals
- Glycogen is a highly branched molecule structurally similar to amylopectin but has more numerous -1,6 glycosidic linkages (thus higher molecular weight)
- As glycogen is similar to starch – sometimes referred to as ‘animal starch’
- Like amylopectin, glycogen consists of a single reducing end and numerous non-reducing ends
What is the most common homopolymer in animal cells?
Glycogen
Where is glycogen found
Liver and muscle
Cellulose
Structural polysaccharide: represents a major structural component of wood and plant fibres
- Cellulose consists of a linear chain of several hundred to thousands of -D-glucose units (typically 3000 units
- D-glucose units are linked by -1,4 glycosidic bonds
- Cellulose is the most abundant polysaccharide
What bond do humans not posses the enzyme to break
Beta 1,4 glycosidic bonds
Chitin
- Structural polysaccharide: homopolysaccharide makes up protective exoskeletons of arthropods (not in humans)
- Structurally chitin is similar to cellulose and functionally it is similar to the protein keratin
- Chitin is composed of the glucose derivative N- acetylglucosamine linked by -1,4
Glycoprotein
Sugars are attached either to amide nitrogen in side chain of asparagine (N-linkage) or to –OH group in side chain of serine or threonine (O-linkage) - known as glycosylation
-N-linked glycoproteins have a common pentasaccharide core (3 mannoses and 2 N-acetylglucosamines
Proteoglycans
Important structural roles: serve as lubricants, structural components in connective tissue, help cells adhere to the extracellular matrix and can bind important factors that help stimulate cell proliferation
-The Proteoglycan aggrecan and the protein collagen are key components of cartilage
Mucins (mucoproteins)
- Protein component extensively glycosylated to serine or threonine residues by N-acetylgalactosamine
- Defining feature is the protein backbone known as the variable number of tandem repeats (VNTR
- synthesized in specialised cells within the bronchus, gastrointestinal tract and urogenital tract
