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4 functions of carbohydrates
- 1. provide energy through oxidation
- 2. supply carbon for synthesis of cellular compounds
- 3. serve as a stored form of chemical energy
- 4.form a part of the structural elements of some cells and tissues
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definitions of carbohydrates
polyhydroxyl aldehydes or ketones, or substances that yield such compounds on hydrolysis
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General formula for carbohydrates
Cx(H2O)y
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Functional groups of carbohydrates
C=O and OH
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Carbohydrates are classified based on:
- size of base carbon chain
- number of sugar units
- location of C=O
- stereochemisty
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monosaccharides
single sugar units
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disaccharides
two sugar units
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oligosaccharides
2 to 10 sugar units
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polysaccharides
more than 10 units
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aldose
has an aldehyde functional group
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ketose
has a ketone functional group
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sterochemistry
study of the spatial arrangment of molecules
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sterisomers
- the same order and types of bonds
- different spatial arrangement
- different properties
- Many biologically important chemicals, like sugar, exist as steroisomers. Your body can tell the difference
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Enantiomers
- designed by D- or L-0 at the start of the name
- they are mirror images that can't be overlapped
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Chiral center
Asymmetric carbon:
- 4 different groups are attached to it
- you must have at least one asymmetric C to have a stereoisomer
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Chiral carbons:
- Note: molecules of all enzymes are chiral. Thus enzymes are very specific
- Its molecules are like left hands rummaging through a box of right handed gloves- nothing fits
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optical activity
ability to rotate plane polarized light
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dextrorotatory
- rotate to right
- use + symbol
- usually D isomers
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leveorotatory
- rotate to left
- use - symbol
- usu. L isomers
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Properties of sugars
- colorless, crystallin solids
- they can form H bonds w/ H2O
- solubility is extensive in water
- soluble to a small extent in ethanol
- any other solvent not soluble in
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Fischer Projection
- These are 2 dimensional structures
- The chiral carbon is represented by the intersection of 2 lines
- In carbohydrates, the carbonyl group is placed at or near the top depending upon whether the sugar is an aldose or ketose
- D- and L- designations are used to indicated the position of teh OH group on the chiral carbon farthest from the carbonyl group
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Maximum number of possible steroisomers
- 2nn= # of chiral carbon centers
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Amino sugars
- contain an amino group in place of an -OH group
- only 3 amino sugars are common in nature
- they are D- glucosamine, D- mannosamine, D- galactosamine
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Glucose
- an aldohexose sugar
- common names include dextrose
- most important sugar in our diet
- most abundant organic compound found in nature
- level in blood can be as high as 10%
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Galactose
- seldom encountered as a free monosaccharide
- in body, galactose is synthesized from glucose in mammory glands for use in lactose (milk sugar)
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Fructose
- ketohexose
- sweetest of all sugars
- also know as levulose (+) and fruit sugar
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ribose
- a component of a variety of complex molecules including RNA and energy rich compounds such as ATP
- compounds 2-deoxy-D-ribose is also important in nucleic acid chemistry
- this monosaccharide is a component of DNA
- the term deoxy means minus as oxygen 2-deoxy-lacks an oxygen on carbon 2
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intramolecular cyclization
- sugars also form rings. from many sugars, its the most common form.
- hemiacetal- form from alcohol & aldehydes
- hemiketal- form from alcohol & ketone
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anomer
- the -OH group that froms can be above or below the ring resulting in two forms
- we use alpha and beta to identify
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mutarotation
the alpha and beta forms are in equilibrium so one or can convert to the other
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Reducing sugars
- aldehyde sugars are readily oxidized and will react with Benedict's reagent
- good test for presense of glucose in urine
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Reducing sugars
aldehyde sugars are readily oxidized and will react with Benedict's reagent
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Oxidation of Monosaccharides
D-glucose--->D-gluconic acid
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Reduction of monosaccharides
- reduction--->polyhydroxy alcohols
- D-glucose--->D-glucitol (sorbitol)
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Sorbitol
- properties similar to trihydroxy alcohol glycerol.
- moisturizing agent in foods and cosmetics
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hydrolysis fo dissaccharides:
sucrose
maltose
lactose
- sucrose+water-->D-glucose+D-fructose
- maltose+water--> D-glucose+D-glucose
- lactose+water-->D-glucose+D-galactose
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Glycosidic bonds
- type is base on the position of the C-1 OH
- alpha glycosidic bond- linkage b/w a C-1 alpha OH and a C-4 OH
- Beta glycosidic bond- linkage b/w a C-1 beta OH and a C-4 OH
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General format for glycosidic bond
- Gen. formal used to describe bond
- OH type (carbon# of 1st sugar-->carbon# of 2nd sugar)
- for disaccharides- the sugar is either alpha or beta based on form of hte remaining C-1 OH
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Beta maltose
named because:
uses:
- not common in nature except in germinating grains
- called beta maltose b/c unreacted C-1 on beta-D-glucose is in the beta postion
- uses: ingredient in infant formulas, production of beer, flavoring
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sucrose
- table sugar
- disaccharide of alpha glucose and beta fructose
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cellobiose
- composed of two molecules of D-glucose
- the difference in the linkage results in cellobiose being unusable (beta 1-4 linkage)
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Lactose
milk sugar- dimer of beta-D-galactose and either the alpha or beta-D-glucose
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polysaccharides
- no fixed size
- used to store excess sugar
- can be used by plants to make cell walls and other sturctures
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