chapter 1 (carbohydrates) Flashcards
(86 cards)
1
Q
what are monosaccharides
A
made up of one monomeric unit (the can’t be hydrolysis) (ex: aldoses, ketoses, trioses)
2
Q
what are oligosaccharides?
A
made up of 2-20 monosaccharides
3
Q
what are polysaccharides?
A
made up of more than 20 monosaccharides
4
Q
A
5
Q
what are glycoproteins?
A
they are linked to proteins or lipids (ex: glycoprotein, proteoglycans, glucolipids, lipoglycans)
6
Q
what are aldoses?
A
polyhydroxy aldehydes (aldehyde +hydroxyl groups on each of its C atoms) (ex: glucose)
7
Q
what are ketoses?
A
polyhydroxy ketones (keto group + hydroxyl group on each of the C atoms)
8
Q
what are trioses?
A
e carbon sugars and they are the smallest monosaccharides (aldotriose -> glyceraldehyde -simplest aldose- and ketotriose -> dihydroxyacetone -the simplest ketose-)
9
Q
glyceraldehyde
A
(aldotriose) has only one chiral center carbon 2 meaning it rotates the plane of polarized light and leads to the presence of stereoisomers (-> 2 stereoisomers)
10
Q
dihydroxyacetone
A
(ketotriose) does not have a chiral center and is not a chiral carbon
11
Q
what is the common factor between D-sugar configuration and that of D-glyceraldehyde?
A
they have the same configuration when it comes to their chiral carbon most distant from the carbonyl group
12
Q
which C is C1 in aldose?
A
the one connected to the aldehyde group
12
Q
which C is C2 in ketoses?
A
the one attached to the carbonyl group
13
Q
how many stereoisomers does aldotetrose have?
A
it has 2 chiral centers so 4 stereoisomers.
14
Q
what is the most abundant monosaccharide?
A
hexose
15
Q
which monosaccharides play an important role in nucleic acid?
A
aldopentoses (DNA is deoxyRIBOnucleic acid)
16
Q
simple monosaccharides
A
they are white crystalline solids that are freely soluble in water and polar solvents but insoluble in inpolar solvents. most (not all) have a sweet taste. sugars are polar due to the many hydroxyl groups.
17
Q
stereoisomers
A
they have the same molecular formula and the same structure but differ in their configuration (the arrangement of their atoms in space)
- geometrical stereoisomers (cis and trans)
- optical stereoisomers (occur in molecules with one or more chiral centers)
18
Q
monosaccharides that contain one or more chiral center
A
(aka show stereoisomerism) all monosaccharides except dihydroxyacetone contain one or more chiral centers.
19
Q
what compound is referred to as the reference or parent compound of stereoisomeric compounds?
A
D- and L- Glyceraldehyde is the parent compound for designating the configuration of stereoisomeric compounds.
this is based on the optical properties of glyceraldehyde (chiral centers lead to rotation of the plane of polarized light).
D- glyceraldehyde caused rotation to the right (dextrorotatory).
L-glyceraldehyde caused rotation to the left (levorotatory).
-> longer aldoses and ketoses can be considered extensions of glyceraldehyde and dihydroxyacetone, respectively, with chiral H-C-OH groups inserted between the carbonyl carbon and the primary alcohol.
20
Q
enantiomers
A
pairs of D and L sugars
21
Q
which rotation dominates in nature?
A
D-sugars dominate nature
(L-sugars are also found however -> L-fructose and L-rhamnose)
22
Q
what are epimers?
A
sugars that differ at only one of several chiral centers. (starting from tetrose)
-> erythrose and threose are epimers.
(NOTE: mannose and galactose are not epimers because they differ at 2 chiral centers)
23
Q
what are anomers?
A
cyclic monosaccharides that differ from each other in the configuration of C1 if they are aldoses and C2 if they are ketoses
-> The carbonyl group is called anomeric carbon which is the mot oxidized carbon
24
monosaccharides in aqueous solutions: (hint: chiral centers)
they act as if they have one more chiral center than is given by the open chain (fisher projection)
-> This extra chiral center is from the carbonyl carbon (be it aldehyde or ketone)
25
α-D-glucose: (hydroxyl group is below plane)
specific rotation [α]^20 = +112.2°
melting point = 146°C
solubility in H2O, g per 100ml= 82.5
relative rate of oxidation by glucose oxidase= 100
26
β-D-glucose: (hydroxyl group is above plane)
specific rotation [α]^20= +18.7°
melting point= 150 °C
solubility in H2O g per 100ml= 178
relative rate of oxidation in glucose oxidase <1.0
27
explain mutarotation of anomers:
when the α and β isomers of D-glucose are dissolved in water, the optical rotation of each gradually changes with time and approaches a final equilibrium value of [α] ^20= +52.7°.
the change is called mutarotation and is due to the formation of an equilibrium mixture of about 1/3 α and 2/3 β D-glucose at 20°C.
(NOTE: the β and α isomers of D-glucose are not open chains but 6-membered ring structures formed by the reaction between the -OH at C5 and the aldehydic at C1)
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what do we call a six-membered ring?
pyranose
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what do you call a 5-membered ring?
furanose
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alcohol + an aldehyde ->
hemiacetal
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alcohol + ketone ->
hemiketal
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d-glucopyranose:
an intermolecular hemiacetal in which -OH group at C5 has reacted with aldehydic C1, rendering it asymmetric.
it can exist in 2 different stereoisomers designated α and β
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nucleotide
S+P+nitrogenous base
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nucleoside
S+ nitrogenous base
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ribo
C5, you will have H up and down if α OH down H up if β OH up and H down
36
fructo ribo (furanose)
D-> CH2OH on C5 up and H on C5 down if α OH on C2 down CH2OH up. if β OH on C2 up CH2OH down
L-> CH2OH on C5 down and H on C5 down if α OH on C2 up and CH2OH down. if β OH on C2 down and CH2OH up
37
gluco pyranose
D-> CH2OH on C5 up and H on C5 down if α OH on C1 down and H up. if β OH on C1 up H down
L-> CH2OH on C5 down and H on C5 down if α OH on C1 up and H down. if β OH on C1 down and H up
38
derivatives:
sugar-phosphate
deoxy sugars (abequose)
amino sugars
sugar alcohols
sugar acids (iduronic acid)
39
phosphate esters
monosaccharides are often converted to phosphate esters by a reaction with ATP.
these are important intermediates in metabolic pathways
40
deoxy sugars
in deoxy sugars a H atom replaces an OH
(examples: β-2-Deoxy-D-ribose and α-L fucose aka α-6-Deoxy-L-galactose)
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β-2-Deoxy-D-ribose
most abundant deoxy sugar
important building block for DNA
42
α-L fucose aka α-6-Deoxy-L-galactose and L-Rhamnose aka 6-deocy-Lmannose
they are important components of bacteria cell wall
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from monosaccharide to sugar alcohol
the carbonyl group (of both aldehyde and ketones) of monosaccharide can be reduced by H2 gas in the presence of metal catalysts to form the corresponding sugar alcohol polyhydroxy alcohol
44
sugar acids
they are carboxylic acids.
produced from aldose:
- oxidation of C1 to yield aldonic acid
- oxidation of the highest numbered carbon to an alduronic acid
45
aldonic acids
D-glucose yields yields D-gluconic acid which in its phosphorylated form is an important intermediate in CHO metabolism
46
uronic acid (usually aldoronic acid but fructuronic acid also exists)
D-glucose yields D-glucuronic acid
uronic acids are very important biologically (examples: D-galacturonic acid and D-mannuronic acid)
47
reducing sugars
if a sugar has a free aldehyde group or a group that can readily convert to an aldehyde group like ketone for example (for example fructose) it will act as a reducing agent in an alkaline solution and will be oxidized to a sugar acid
-> They can be tested using benedict's test or fehling test
-> The reagent designed to test for a reducing sugar includes a mixture of cupric ions (cu2+, blue) in a basic solution that will react with the reducing sugar to form cuprous ions (CU+, red precipitate) if sugar is oxidized it reduces CU2+ to CU+ the color changes from blue to red
(NOTE: sucrose is not a reducing sugar -> no free aldehyde or ketone group)
48
amino sugars
an amino group replaces a monosaccharide OH usually on C2
the amino group is sometimes acetylated (the acetyl group is added in place of an H)
(example: N-acetyl-α-D-glucosamine and N-acetyl-α-D-galactosamine)
49
N-acetyl-α-D-glucosamine
is a major component of chitin a structural polysaccharide found in the exoskeleton of insects and crustaceans
in chitin it is connected via β-(1-4) glycosidic bonds
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N-acetyl-α-D-galactosamine
component of glycolipids and chondroitin sulfate, major polysaccharide of cartilage
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N-acetylmuramic acid
N-acetyl-D-glucosamine and lactic acid
-> important building blocks of the structural polysaccharide found the cell walls of bacteria
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N-acetylneuraminic acid
N-acetyl-α-D-mannosamine and pyruvic acid (sialiac acid)
-> Important building blocks of the structure of the cell coats and membranes of higher animal cells
53
glycosidic bonds:
they are formed by the reaction between the anomeric carbon of a monosaccharide with the hydroxyl group of another monosaccharide to yield disaccharide
(between 2 glucose we call it O-glycosidic bond as it is linked by an O)
54
glucosides:
a glucoside where glucose provides the anomeric carbon
55
explain the hydrolysis of glycosides:
glycosides are hydrolyzed by glycosidases, which differ in their specificity according to the type of glucoside bond (alpha or beta), the structure of the monosaccharide units, and the structure of the alcohol.
56
anomeric carbon:
a C that is an aldehyde or ketone in an open-chain form and becomes a chiral center in the cyclic form
57
glycoside:
a compound formed from a simple sugar and another compound by replacement of a hydroxyl group in the sugar molecule
for example: D-glucose with methanol yields a glycoside.
-> in this acid-catalyzed condensation reaction, the anomeric -OH group of the hemiacetal is replaced by an -OCH3 group, forming methyl glucoside, an acetal (the product of this rection results in both alpha and beta and that is due to mutarotation)
58
disaccharides:
- the most common oligosaccharide in nature
- they consist of two monosaccharides joined by a glycosidic bond
- in the systematic naming of disaccharides we need to specify:
- linking atoms
- configuration of the glycosidic bond
- name of each monosaccharide residue
59
maltose (explaining structure of disaccharide):
- it is present in malt
- it is formed as an intermediate product of the action of amylases on starch
- it contains two D-glucose molecules linked by α(1->4) glycosidic bond
- the second glucose molecule contains a free anomeric -OH group that could exist in an α or β:
- it undergoes mutarotation
- it is a reducing sugar due to the free anomeric carbon
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the link between having an anomeric C and being a reducing sugar
if a chiral center has an OH group off of it, it is a reducing sugar. this is because when the sugar is in the open configuration that alcohol becomes ketone or aldehyde which can reduce other compounds
61
cellobiose:
- repeating disaccharide uni of cellulose
- it contains two D-glucose molecules linked by β(1->4) glycosidic bond
- it undergoes mutarotation
- it is a reducing sugar
62
lactose:
- most abundant carbohydrate in milk (5%milk)
- contains D-glucose and D-galactose linked by a β(1->4) glycosidic bond
- it undergoes mutarotation
- it is reducing sugar
- infants have the intestinal enzyme lactase that hydrolyzes lactose to its component monosaccharides for absorption into the bloodstream
- many adults have low levels of this enzyme and consequently much of the lactose they drink moves through their digestive track to the colon where its bacterial fermentation produces large quantities of CO2 and H2 and irritating organic acids
63
sucrose:
- it is the table sugar and is synthesized only in plants (sugarcanes and sugarbeets)
- contains β-D-fructose and α-D-glucose units linked by an α, β(1->2) glycosidic bond
-unlike most disaccharides and oligosaccharides sucrose contains no anomeric carbon atoms:
- it does not undergo mutarotation
- it is nonreducing sugar
- digested by sucrase or invertase in pancreatic juice and can be followed with a polarimeter (The rate of the reaction in which sucrose is hydrolyzed to glucose and fructose is determined by observing the change in the optical rotation of sucrose as the reaction proceeds. Each sample has a different specific rotation and the rate of inversion can be measured using polarimetry)
- sucrose is much more readily hydrolyzed than other disaccharides
- the hydrolysis of sucrose to D-glucose and D-fructose is often called inversion
- sucrose [α]^20 = +66.5 --> D-glucose [α]^20= +52.5 + D-fructose [α]^20=-92
- the mixture is called the invert sugar (because you start with dextrorotatory and end with levorotatory as a total sum)
64
aglycones
the groups attached to the anomeric sugar carbon
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glycosides
sugar+ non sugar (aglycon)
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digoxin (O-glycoside)
- it is made up of digoxigenin and 3 digitoxose (they are 6-deoxyglucopyranose rings β(1->4) O-glycosidic bond)
- extracted from the leaves of the foxglove plant.
- a potent stimulant of the heart muscle
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polysaccharides
they are also called glycans and differ from each other in the nature of their recurring monosaccharide units, the length of their chains the types of bonds linking the units and their degree of branching
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homoglycans
homopolysaccharides containing only one type of monosaccharides
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heteroglycans
heteropolysaccharides containing residues of more than one type of monosaccharide
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Starch and glucogen (storage homoglycans)
-D- glucose is stored intracellularly in polymeric forms
-polymer of α(1->4) linked subunits of glucose, with α(1->6) linked branches
-plants and fungi-starch
-animals- glucogen (more extensively branched and more compact than starch)
-they are both made of one sugar (α-D-glucose)
(NOTE: it can't be L-glucose)
71
starch
it is a mixture of amylose (unbranched 100-1000 D-glucose residues) and amylopectin (branched 300-6000 D-glucose residues)
the structure of amylose:
- linear polymer
-gives blue color with iodine
-MW up to 50000 Da
-assumes a left-handed helical conformation in water
(NOTE: in free linear polysaccharides :
- reducing end C1
- non-reducing end C4
and number of branching = number of reducing ends -> however always we have one reducing end regardless)
structure of amylopectin:
- branching occurs once every 25 residues and the branch contains 12-25 residues
-gives red-violet color with iodine
-MW up 100 million Da
(branch is α(1->6) glycosidic bond then continue with α(1->4) glycosidic bond
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glycogen
- abundant in the liver (10% of wet weight) and skeletal muscles (1-2%) -much larger than amylopectin (about 50000 D-glucose residues)
- more highly branched than amylopectin; branching occurs once every 8-12 glucose residues
73
starch and glycogen
- they are hydrolyzed by α- and β amylases, both cleave α-(1->4) glycosidic bonds (anywhere)
- α-Amylase is endoglycosidase (an enzyme that releases polysaccharides from glycoproteins or glucolipids) found in saliva and pancreatic juices
- β-Amylase is an exoglysocides (an enzyme that releases particular monosaccharides from non-reducing termini of oligosaccharides and the sugar chains of glycoproteins and glycolipids)
(NOTE: the difference between endo and exo is that exo would remove from carbohydrate monomers one by one whereas endo can cut any glycosidic bond and may cleave after a signature "link oligosaccharide" that links certain carbohydrates to certain proteins
-limit dextrin (a short-chained amylopectin remnant produced by hydrolosis of amylopectin with α amylase -> action is limited because of (1->6) bond)
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cellulose
- linear unbranched polymer of 300-15000 D-glucose units linked by β(1->4) glycosidic bond. MW range 500000 to 2500000 Da
- the most abundant structural polysaccharide in the plant world. it accounts for over 50% of the organic matter in the biosphere
-digested by cellulase (β-glucosidase), which is not secreted by the digestive tract of most mammals. it cannot be used as food
- ruminants (cows and sheep) are exceptions and can use cellulose as food. the bacteria in their rumen form the enzyme cellulase.
-cellulase is only prokaryotic
-present in the cell walls of plants as cellulose microfibrils, linked by strong intra and intercellular Hbonds, giving cellulose its strength and rigidity
75
hemicelluloses:
- (there's many types and they are synthesized in the Golgi apparatus)
-heteropolymers present in most plant cell walls such as xylan, arabinoxylan, and xyloglucan
- they are not structurally related to cellulose and are called cellulose-linked glycan. they have different types of sugars, linkage, and bonds. (they link cellulose fibers)
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pectins
- released by the Golgi apparatus through vesicles -> that make the middle lamella -> cell plat
-they are present in the primary cell walls of plants and the middle lamella.
- there are different types of pectins, including homogalacturonan, rhamnogalacturonan, and others. they bind calcium in plant cells.
- calcium in plant cells in the true form of calcium pectane because of -ve charge
-it is mainly used in food as a gelling agent and stabilizer, among others.
77
structural polysaccharides in bacteria
-bacteria are classified into:
-gramp positive (cell walls contain very little lipid) ex-> streptococcus
-gram-negative (cell walls rich in lipids) eg-> E.coli
-bacteria cell walls are different in having varying levels of peptides, proteins, lipids, and carbohydrates
-they are similar in that the peptide and carbohydrate part are arranged in a common structural framework, a grid-like network of polysaccharide chains covalently cross-linked to each other via small peptide bridges, referred to as peptidoglycans.
78
peptidoglycans
- the polysaccharide (heteroglycan) moiety is composed of repeating disaccharide units consisting of GlcNAc and N-acetylmuramic acid (MurNAc) with β(1->4) glycosidic bond connecting the units. successive units are also attached by β(1->4) linkages.
- the peptide moiety consists of a tetrapeptide and a pentapeptide
- peptidoglycans synthesis: the cross-linking is catalyzed by a transpeptidase, the enzyme that penicillins inhibit (irreversible inhibitor-> antibiotic)
-> Penicillinase, secreted by resistant bacteria converts penicillin to penicillinoic acid.
- penicillin structure resembling -D-Ala-D-Ala.
79
chitin
-linear homopolysaccharide composed of N-acetylglucosamine (GlcNAc) residues in β(1->4) linkage
-the principal component of the hard exoskeleton of many arthropods (insects, lobsters, crabs, etc)
-2nd most abundant polysaccharide in nature (after cellulose)
80
structural polysaccharide in animals -> cell coats
-the cells in the tissues of vertebrates are not surrounded by a rigid cell wall.
-they do have an outercoat that is in some respect comparable to cell walls.
-the major components of cell coats of animals are:
-glycolipids
-glycoproteins
-glycosaminoglycans
81
glycosaminoglycans
- heteropolysaccharide of the extracellular matrix (ECM), unique to animals and bacteria and are not found in plants
- family of linear polymers composed of repeating disaccharide units (-> these sugars can be amino sugars or sugar acids or sugar sulfates)
- they are so named because of the presence of amino sugars (usually the N-acetyl forms of D-glucosamine and D-galactosamine)
- they are also characterized by the presence of negatively charged -COO- (sugar acids) and --OSO3^- groups (sulfate group)
- glycosaminoglycans do not occur in the free state but are associated with proteins to form proteoglycans (the main polymer is carbohydrate 90% and contains proteins whereas glycoproteins carbohydrates =1% and main polymer proteins but with exceptions)
-important glycosaminoglycans in carbohydrates:
1. hyaluronic acid
2. chondroitin sulfate
3. keratan sulfate
(all of which are found in the proteoglycans of connective tissues)
4. heparin
82
hyaluronic acid
-composed of 250-25000 linked disaccharide units
-primary components of the ground substance of connective tissues.
-present in the synovial fluid, a viscous packing around bone joints serving as a lubricant and shock absorber
-present in the vitreous humor of the eye and the umbilical cord.
-certain pathogenic bacteria secrete hyaluronidases as well as snake venoms and insect venoms. (this protects the cells but some pathogenic bacteria can invade)
-> cleave β(1->3) and β(1-> 4) by so doing bacteria have free access around the cell now that the cell coat of connective tissue can be surpassed and invaded.
83
chondroitin sulfate
(if it is N-acetylgalactosamine-4-sulfate it is chondroitin A if it is 6-sulfate it would be chondroitin C)
- similar to hyaluronic acid in having alternating β(1->3) and β(!->4) and the presence of N-acetylamino sugar
- the length of chondroitin sulfate ranged form 15-150 disaccharide units
-chain length and extent of sulfation may be affected by the age of tissue and may be related to disease conditions.
84
keratan sulfate
similar to hyaluronic acid in having alternating β(1->3) and β(1->4) and the presence of N-acetylamino sugar
- GlcNAc is sulfated at C6
-chain length 10-15 disaccharide units (smallest glycosaminoglycan)
- in addition to the disaccharide units it contains a small amount of fucose (deoxy sugar), mannose, scialic acid, and GlcNAc
- 2 sugars derivates before here also 2 but in addition to other sugars making it most heterogenous glycosaminoglycan.
85
heparin
-a natural anticoagulant that binds strongly to antithrombin III(a protein involved in the terminating and clotting process) and inhibits blood clotting
- in contrast to other glycosaminoglycans, it is not a constituent of connective tissue but is found in the mast cells that line arterial walls, especially in the liver lungs, and skin.
- it is administrated intravenously to patients during and after surgery
- it is heterogeneous and made of at least 4 sugar derivatives: D-glucuronic acid, L-iduronic acid, D-glucosamine, N-acetylglusamine
