BS 120: Carbs 1 Flashcards
Define carbohydrate
Hydrates of carbon
- polyhydroxy aldehydes/ ketones
General Molecular/ empirical formula:
(CH2O)n
Properties of carbohydrates
- parent compound of all carbohydrates is glycerol, a 3-carbon, trihydric alcohol
- all carbohydrates have carbon, hydrogen, & oxygen
- may contain phosphorus, nitrogen, or sulphur (sugar derivatives)
- have at least 3 carbon atoms
- have a potentially active carbonyl group, being either an aldose or ketose group
What is the difference between aldoses & ketoses?
aldoses are formed by oxidation of glycerol at the end (C1), ketoses are formed by the oxidation of glycerol within the chain (C2).
What are the 4 things carbohydrates are important for?
- energy
- structure & support
- protection
- metabolism
What are the energy-related functions of carbohydrates?
- CHO is source of energy for most organisms (main & preferred source)
- provides 4Kcal/g
- glucose is converted into ATP by cellular respiration in cells
- glucose is an abosulte requirement for RBCs, brain, & fetus
- CHO stores energy as: starch in plants, glycogen in humans
Where is glycogen stored in humans?
liver & muscle
What are the structure-related functions of carbohydrates?
- glycolipids & glycoproteins make: a) cell membrane, b) receptors, & c) blood groups
- GAGs make connective tissue (a. bone, b. cartilage, c. skin
- ribose is a constituent of nucleic acids (DNA & RNA)
- cellulose enter in the structure of plants
- chitin enters the structure of exoskeleton of insects
What are the protection-related functions of carbohydrates?
carbohydrates play a role in:
1. immunity
2. lubrication
3. intercommunication
4. detoxification
What are the metabolism-related functions of carbohydrates?
- CHO provide key intermediates in metabolism
- CHO play a key role in metabolism of amino acids & fatty acids
What is a GAG found in bone tissue?
chondroitin sulfate
What is hyaluronic acid?
it is a GAG used in lubrication
What is glucuronic acid?
It is a sugar acid used in detoxification
Which type of carbohydrate cannot be hydrolyzed into simpler sugars?
based on number of sugar units
monosaccharides
How many sugar units in oligosaccharides & polysaccharides?
oligosaccharides have 3-10, polysaccharides have 100s to 1000s of sugar units.
What are simple sugars?
monosaccharides
What are complex sugars?
Polysaccharides
What are polysaccharides divided into?
homo & hetero polysaccharides
What are sugar units linked by?
Glycosidic bond
What are aldoses?
monosaccharides with an aldehyde functional group.
- (R-CHO)
- carbonyl group is at C1
What are ketoses?
monosaccharides with a ketose functional group.
- (R-CO-R)
- carbonyl group at C2
suffix of aldoses
-ose
suffix of most ketoses
-ulose
Names of aldoses:
- aldotrioses: glyceraldehyde (glycerose)
- aldotetroses: erythrose, threose
- aldopentoses: ribose, arabinose, xylose, lyxose
- aldohexoses: glucose, galactose, mannose
Names of ketoses:
- ketotrioses: dihydroxyacetone
- ketotetroses: erythroulose
- ketopentoses: ribulose, xylulose
- ketohexoses: fructose
- ketoheptoses: sedoheptulose
What is ribose?
- a structural element of nucleotides, nucleic acids, ATP, coenzyme FAD, NAD
- an intermediate of pentose phosphate pathway (PPP)
What else is an intermediate of pentose phosphate pathway (PPP)?
Ribulose
What is glucose?
- aka dextrose/ blood sugar
- most abundant sugar in nature
- found in fruits, fruit juices, & honey
- the most important carbohydrate in mammals
What is the principal metabolic fuel for tissues?
Glucose
What are (nearly all) carbohydrates in food converted into?
they are converted into glucose in the liver
What happens if there is too much glucose in blood?
excess glucose in blood is called hyperglycemia.
How is glucose made?
produced by hydrolysis of: - starch
- glycogen
- maltose
- lactose
What is glucosuria?
When there is glucose present in urine
What is hyperglycemia & glucosuria an indication of?
diabetes mellitus
what causes cataract?
sorbitol, a sugar alcohol obtained by the reduction of glucose
What is called the milk sugar?
galactose
Where is galactose found?
in lactose in milk
How is galactose produced?
via the hydrolysis of lactose
When is galactose synthesized?
in lactating mammary gland
What are some properties of galactose
- constituent of glycolipids & glycoproteins
- can be converted to glucose in liver
- lack of enzymes of metabolism can lead to galactosemia
- galactitol causes cataract
What are 2 sugar alcohols that can cause cataract?
Sorbitol & galactitol
What is fructose?
all its properties
- aka levulose
- the fruit sugar
- the sweetest sugar
- found in fruits, fruit juices, honey
- produced by hydrolysis of sucrose & insulin
- found in seminal fluid
- main nutritional source of energy for spermatozoa
- can be converted to glucose in the liver
- lack of enzymes of metabolism can lead to essential fructosuria
What is the asymmetric carbon?
- aka chiral carbon
- it is a carbon attached to four different groups/ atoms
What are the properties of asymmetric carbon?
allows for the formation of:
1. optical activity
2. stereoisomerism
What monosaccharide contain asymmetric carbons?
all of them except dihydroxyacetone (DHA)
How do you know the number of asymmetric carbons in aldoses?
n-2
n being the number of carbons
How many asymmetric carbons does glucose have?
n= 6
6-2=4
glucose has 4 asymmetric carbons
How do you know the number of asymmetric carbons in ketoses?
n-3
How many asymmetric carbons does fructose have?
3
n=6
n-3= 3
DHA is …
- achiral
- optically inactive
- has no L or D isomers
What is optical activity?
- aka optical isomerism
- the ability (capacity) of compound to rotate polarized plane light (PPL)
Which direction do dextrorotary sugars rotate PPL?
to right, clockwise
Which direction do levorotary sugars rotate PPL?
to the left, anti-clockwise
Which direction does glucose rotate PPL?
to the right, so it is dextrorotary.
- that is why in practice, glucose is called dextrose
Which direction does fructose rotate PPL?
rotates PPL to the left, so it is levorotary
- that’s why in practice, fructose is called levulose
What is a racemic solution?
A solution containing equal amounts (molecular mixture) of optical isomers (D & L isomers) that has no net rotation
- this makes the solution inactive
What is stereoisomerism?
- aka structural isomerism
compound that has the same chemical formula (molecular formula) but differs in arrangement of atom & physical properties
Which monosaccharide lacks stereoisomers?
dihydroxyacetone
What does the number of possible isomers depend on?
the number of asymmetric carbons
- 2^n= number of isomers
- n being the number of asymmetric carbons
How many stereoisomers does glucose have?
2^4= 16
glucose has 16 stereoisomers
What are the 4 types of isomers?
- Aldose-ketose isomers
- L & D isomers
- epimers
- anomers
What are 4 sugars that are isomers?
- glucose, galactose, mannose, & fructose
Why are they isomers?
they have same chemical formula: C6H12O6, but differ in organization of atoms.
- atom bonding in a different order
Define aldose & ketose isomers
isomers that differ in position of potential functional group (carbonyl group)
How many carbons does an aldose need to be a chiral?
3C or more
How many carbons does a ketose need to be a chiral?
4C or more
What property does achiral display?
Achiral means being optically inactive; having no L or D isomers.
List all the examples of aldose & ketose isomers:
- Glycerose & dihydroxyacetone
- erythrose & erythrulose
- ribose & ribulose
- xylose & xylulose
- glucose & fructose
Define L & D isomers
Isomers that differ in orientation of OH & H around the last asymmetric carbon
examples of L & D isomers
- D-glucose & L-glucose
- D-fructose & L-fructose
What is a special type of isomerism?
L & D isomerism
What is the last asymmetric carbon?
it is the carbon adjacent to the terminal alcohol carbon
What is the last asymmetric carbon in glycerose?
C2
What is the last asymmetric carbon in glucose?
C5
Notes about L & D isomers
- D sugars the most common in naturally occurring monosac.
- L & D isomers are mirror images so they are enantiomers
- the direction of rotation of PPL is independent of the stereochemistry of the sugar
- this means that sugars can be designated D(+), D(-), L(-), or L(+)
T/F: the direction of rotation of polarized light depends on the stereochemistry of the sugar.
False, it is not effected by the stereochemistry of the sugar. This means a D isomer can be (-) or (+) in direction of PPL rotation.
Define epimers
isomers that differ in configuration of OH & H around one specific asymmetric carbon
What are 2 examples of epimers?
- Glucose & mannose: epimers at C2
- glucose & galactose: epimers at C4
Are galactose & mannose epimers?
No, they are isomers but not epimers
- differ in more than one carbon (C2 & C4)
Define anomers
isomers that differ in configuration of OH & H around anomeric carbon
What is the anomeric carbon?
the new additional asymmetric carbon created after crystalization
What are the 2 types of anomers?
- alpha anomers
- beta anomers
What are alpha anomers?
- OH is right of anomeric carbon
- OH is down (below) the plane
- OH is trans with C6 [CH2OH]
What are beta anomers?
- OH is left of anomeric carbon
- OH is up (above) the plane
- OH is cis with C6 [CH2OH]
What is an example of anomers?
α glucopyranose & β glucopyranose
What are anomers like in a solution?
- less than 1% of monosaccharides exist in open-chain Fischer structures
- monosac. predominantly exist as closed-chain ring Haworth structures
- cyclization of glucose forms pyranose, a 6-membered ring
- cyclization of fructose forms furanose, a 5-membered ring
- glucopyranose has 5 asymmetric carbons
How does the Haworth structure form in aldoses?
hemiacetal: a reaction between the aldehyde group and one of the alcohols on the same sugar.
- it is a covalent bond between the carbonyl group & the oxygen of a hydroxyl group along the chain
How does the Haworth structure form in aldoses?
hemiketal: reaction between the keto and an alcohol group on the same sugar (1 hydroxyl group)
Which carbon is the anomeric carbon in aldoses?
the anomeric carbon of aldoses, ex. glucose, is C1.
Which carbon is the anomeric carbon in ketoses?
the anomeric carbon of aldoses, ex. fructose, is C2.
Define mutorotation
spontaneous interconversion of sugar anomers (alpha & beta) in a solution to reach equilibrium
What is an example of mutorotation
mixture of glucose at equilibrium:
- 38% alpha
- 62% beta
sugar derivatives
What are the 5 types of sugar derivatives
- sugar acids
- sugar alcohols
- sugar amines
- deoxy-sugars
- sugar esters
What is key about reducing sugars?
All reducing sugars exhibit mutorotation
What are sugar acids?
- they are sugars produced by oxidation, a reaction of sugar with oxygen
- this can only happen to aldoses
- aldoses are easy to oxidize due to the presence of hydrogen atom in aldehydes (CHO), H is alone
- ketones are resistant to oxidation because they lack a hydrogen atom
- oxidation occurs to C1 (carbonyl carbon) or the last OH carbon (or both)
How is aldonic acid produced?
- mild oxidation condition
- oxidation of sugar at C1 (CHO)
Which sugar acid occurs when oxidation occurs at last carbon (CH2OH)?
in uronic acid, when the aldehyde group is protected and the oxidation of the sugar is at the last hydroxyl.
Which sugar acids are rendered when there are strong oxidation conditions?
- saccharic acids
- aldaric acid
- dicarboxylic acid
oxidation in these sugar acids occurs at both the first & last carbons
glucose & galactose oxidation:
oxidation at C1 only
- glucose becomes gluconic acid
- galactose becomes galatonic acid
oxidation at C6 only
- glucose becomes glucouronic acid
- galactose becomes galacturonic acid
oxidation at both carbons (C1 & C6)
- glucose becomes glucosaccharic acid
- galactose becomes mucic acid
What is glucouronic acid?
(oxidation at C6 of glucose) used in:
- detoxification
- making GAGs
- making vitamin C
What are sugar alcohols?
- polyol
- produced by reduction, sugar reacting with hydrogen [H]
- can occur in both aldoses & ketoses
- reduction occurs at carbonyl carbon of aldoses & ketoses
- aldose yields 1 corresponding alcohol.
- ketose forms 2 alcohols because of the appearance of a new asymmetric carbon
examples of sugar alcohols
- glucose: sorbitol (glucitol)
- mannose: mannitol
- galactose: galactitol (dulicitol)
- ribose: ribitol
- fructose: sorbitol & mannitol
What are deoxy-sugars?
- produced by deoxidation, the replacement of OH with O
- occurs in both aldoses & ketoses
- deoxidation occurs to any carbon
What are examples of deoxy-sugars?
- 2-deoxyribose (occurs in DNA)
- 6-deoxygalactose, aka L-fucose (in glycoproteins)
What are sugar amines?
- aka amino sugar
- produced by amination, the replacement of OH with NH2 (amino group)
- occurs to aldoses only
- animation occurs at C2
What are examples of amino sugars?
- glucose: glucosamine
- galactose: galactosamine
- mannose: mannosamine
Sugar amines are usually acetylated. What are some examples?
- glucose: N-acetyl glucosamine [NAGA] [GlcNac]
- galactose: N-acetyl galactosamine [NAGIA] [GalNac]
- mannose: N-acetyl mannosamine [NAMA] [ManNac]
Where are amino sugars found?
they are important components of:
1. glycoproteins
2. gangliosides
3. glycosaminoglycans
4. some antibiotics
- D-glucosamine is part of Hyaluronic acid (in GAGs)
- D-galactosamines, aka chondrosamine, is a part of chondroitin in bones
- amino sugars are important for anitbiotic activity (ex. erythromycin)
