Chapter 11- Sugars and polysacharrides Flashcards
(222 cards)
1
Q
Oligosacharides
A
few covalently linked monosaccharide units.
2
Q
glucoconjugates
A
glucoproteins and glucolipids collectively
3
Q
simple sugars or monosacharides are what
A
ketone or aldehyde derivatives of straight-chain polyhydroxyl alcohols containing atleast 3 carbons
4
Q
Can these simple sugars such as D-glucose or D-Ribulose be hydrolyzed to form simpler saccharides?
A
NO
5
Q
A ketone
A
O
II
R - C - R’
6
Q
An aldehyde
A
O
II
R - C - H
7
Q
if the carbonyl group is an aldehyde then the sugar is an
A
aldose
8
Q
If the carbonyl group is a ketone then the sugar is called a
A
ketose
9
Q
A three carbon chain sugar is a
A
triose
10
Q
A four carbon chain sugar is a
A
tetrose
11
Q
A five carbon chain sugar is a
A
pentose
12
Q
A six carbon chain sugar is called a
A
hexoses
13
Q
A seven carbon chain sugar is a
A
heptose
14
Q
A glucose is also called _____ because glucose has a _____ derivative with _____ carbon chain
A
glucose is a aldohexoses since glucose is an aldehyde derivative with a six carbon chain
15
Q
A Ribulose is also called ______ because Ribulose has a ______ derivative with _____ carbon chain
A
Ribulose is called a ketopentose since it has a ketose derivative with a five carbon chain.
16
Q
Monosacharides are classified according to ________
A
chemical nature of their carbonyl group and number of carbon atoms
17
Q
All of D-glucose’s carbons but _____ of six are chiral centers and these are carbon ____ and ____.
A
All but two of six of D-Glucose’s carbons are chiral centers and these are carbon 1 and carbon 6.
18
Q
How can you determine the number of stereoisomers of aldoses?
A
n-carbon aldoses have 2^(n-2) stereoisomers
19
Q
How many stereoisomers does Glucose have ?
A
2^(6-2) = 2^4 = 16 stereoisomers
20
Q
Sugars that differ by the configuration of 1 carbon are called
A
epimers of one another.
21
Q
Are D-glucose and D mannose epimers of each other?
A
Yes in respect to carbon 2
22
Q
Are D-glucose and D-galactose epimers of eachother?
A
yes by respect to carbon 4
23
Q
Are D mannose and D galactose epimers of each other?
A
NO because they have two different carbons configurations not one.
24
Q
What is the only aldose that commonly occurs in nature as a monosacharide?
A
D-glucose
25
____ sugars are significantly less abundant than _____ sugars
L sugars are significantly less abundant than D sugars
26
How many achiral centers does ketoses have?
3
27
What is the general equation in determining the number of stereiosmers of a ketose?
2^(n-3)
28
The most common form of ketose is when the ketone is at carbon _____
2
29
Alcohols react with the carbonyl groups of aldehydes to form
hemiacetals
30
Alcohols react with the carbonyl group of ketones to form
hemiketals
31
The hydroxyl in either the aldehyde or ketone can react intramolecularly to form ____ and ____
cylic hemiacetals and cylic hemiketals.
32
The configuration of cylic hemiacetals and cylic hemiketals are represented how?
Haworth projection formulas
33
A sugar with a six membered ring is known as ___
pyranose
34
A sugar with a five membered ring is known as ___
furanose
35
The cylic form of glucose is called ____
glucopyranose
36
The cylic form of fructose is called ____
fructofuranose
37
The cyclization of a monosaccharide renders the former carbonyl carbon asymmetric. The resulting pair of diasteromers are known as ____ and the hemiacetal or hemiketal carbon is referred to as the _____ carbon
anomers and the heiacetal or hemiketal carbon is referred to as the anomeric carbon
38
In the alpha anomer the OH substituent to the anomeric carbon is ____ of the sugar ring from the CH2OH group at the chiral center that designates the D or L configuration.
on the opposite side
39
In the beta anomer the OH substituent to the anomeric carbon is _____ of the sugar ring from the CH2OH group at the chiral center designated D or L
is on the same side
40
How does the specific rotations of alpha glucose and beta glucose differ?
alpha is +112.2 and Beta is +18.7
41
What happens to specific rotation when a pure alpha or pure glucose substance is dissolved in water? what is this phenomena called?
The optical rotation changes slowly until it reaches an equilibrium value of _52.5 degrees. This is called mutarotation.
42
The mutarotation in glucose results in what?
an equilibrium optical rotation of _52.7 degrees and an equilibrium mizture containing 63.6% of thee Beta anomer and 36.4% of the alpha anomer.
43
The optical rotations of separate molecules in solution are ____ of each other so the optical rotation of a solution is ____
The optical rotations of separate molecules in solution are independent of each other so the optical rotation of a solution is the weighted average of the optical rotations of its components.
44
Do Hexoses assume pyranose of furanose form?
They can assume Both
45
Do pentoses assume pyranose or furanose form?
They can assume both
46
What form does glucose assume in aqueous solutions?
almost entirely pyranose form
47
What form does fructose assume in aqueous solutions?
67% pyranose form and 33% furanose form.
48
What form does ribose assume in aqueous solutions?
75% pyranose and 25% furanose.
49
What form does gucose assume in polysacharides?
almost entirely pyranose
50
What form does fructose assume in polysacharides?
almost entirely furanose
51
What form does ribose assume in polysacharides
almost entirely furanose
52
Rings of seven or more can form so why are they rarely observed?
because the greater stabilities of the five- and six- membered rings of these sugars can also form.
53
What makes 3 and 4 membered sugar rings unstable with respect to linear forms?
Internal strain
54
Why can't furanose and pyranose rings be planar
all atoms in ring are tetrahedrally (sp^3) hybridized.
55
In the chair conformation the equatorial position is ____ and the axial position is ___
equaitorial position is outward
| axial position is verical
56
In deciding what chair formation is correct sterics plays a role how?
The least sterically hindered predominate thus typically where the bulky substituents occupy equitorial positions
57
What is the only D-aldohexose in which all non H substituents occupy the equitorial postion
Beta-D- Glucopyranose
58
In acid catalyzed reactions the anomeric hydroxyl of a sugar reversibly condenses with alcohol to form ____
alpha and Beta glycosides.
59
the bond connecting the anomeric carbon to the acetal oxygen is ____
a glycosidic bond.
60
How are polysacharides held together?
glycosidic bonds
61
The hydrolysis of glycosidic bonds is catalyzed by
enzymes known as glycosidases
62
Glycosidases differ in specificity to _____ but are rather insensitive to ____
Differ in specificity to the identity and anomeric configuration of the glycoside but are rather insensitive to the identity of the alcohol residue.
63
Do glycosides undergo mutarotation like monosacharides? Why or why not?
No because because under basic or neutral conditions in the absence of glycosidases the glycosidic bond is stable.
64
Mild oxidation of an aldose results in conversion of aldehyde group to a _______ yielding ___
conversion of aldehyde to carboxylic acid function yielding aldonic acid
65
How are aldonic acids named?
By adding -onic to the root name of its parent aldose such as gluconic acid.
66
What are reducing sugars?
Saccharides bearing anomeric carbon atoms that have not formed glycosides. They facility with which the aldehyde group reduces mild oxidizing agents.
67
What is a classic test that test for the presence of a reducing sugar is ___
the reduction of Ag+ in an ammonia solution (Tollen's reagent) to yield a metallic silver mirror lining on the inside of the reaction vessel.
68
The specific oxidation of the primary alcohol group of aldoses yields _____ which are named how?
uronic acid which are named by appending -uronic acid to the root name of the parent aldose such as D-Glucuronic acid, D-galacturonic acid and D-mannuronic acid.
69
Both aldonic and uronic acids have a strong tendency to internally ____ so as to form _____
to internally esterify so as to form f or 6 membered lactones
70
Ascorbic acid (vitamin C) is a ___ lactone that is synthesized by ____
Y lactone synthesized by plants and almost all animals except primates and guinea pigs.
71
What happens in the prolonged deficiency of ascorbic acid in the diet of humans?
Scurvy which causes an impairment of collagen formation which generally results in a lack of fresh food.
72
Why is ascorbic acid related to scurvy?
Under physiological conditions, ascorbic acid is reversibly oxidized to dehydroascorbic acid which is irreversibly hydrolyzed to the vitamin-inactive diketogulonic acid.
73
Aldoses and ketoses may be reudced under mild conditions by treatment of NaBH4 to yield _____
acyclic polyhydroxyl alcholds called alditols
74
How are alditols named
by adding the suffix -itol to the root name of the parent aldose.
75
the polyhydroxy alcohol myo-inositol is a what component?
a lipid component
76
Xylitol is what?
a polyhydroxy alcohol; it is also a sweetener used in sugarless gum and candy.
77
What are deoxy sugars?
sugars in which an OH group is replaced by H
78
In amino sugars one or more ____ groups are replaced by _____
one or more OH groups are replaced by an often acetylated amino group.
79
The amino sugar derivative N-acetylmuramic acid consists of ____ in an ether linkage to ____
consists of a N-acetyl-D-glucosamine in an ether linkage with D-lactic acid.
80
N-acetylmuramic acid is a prominent component of ____
bacteria cell walls.
81
N-acetylneuraminic acid is dervied from ____ and ____
N-acetylmannosaminic acid and pyruvic acid
82
N-acetylneuraminic acid is an important constituent of ____ and ___
glycoproteins and glycolipids
83
N-acetylneuraminic acid and its derivatives are reffered to as ___
sialic acids.
84
Polysaccharides are also known as what?
glycans
85
A homopolyscharide consists of _____ monosacharide reidues
one type of
86
A heteropolysacharide consists of _____ monosacharide residues
more than one type
87
homopolysacharides can be further classified how?
According to idenity of monomeric units
88
What are glucans?
polymers of glucose
89
What are galactans?
polymers of galactose
90
Heteropolyscharides usually consist of what?
A few types of monosacharides that alternate in a repetitive sequence
91
Do polysacharides branch or are they linear? why ?
Both because glycosidic linakges can be made to any of the hydroxyls of monosacharides. Many polysacharides are linear and those that branch tend to do so in well defined ways.
92
What are Lectins?
sugar binding proteins found in animals and plants used for a variety of signaling, cell-sell recoginition, and adhesion processes as well as targeting newly synthesized proteins to specific cellular locations.
93
Lectins recognize ______ with particular linkages to ________ usually with exquisite specificity
recognizes one or more monosacharides with particular linkages to other sugars in oligosaccharides usually with exquisite specificity.
94
Lectin's protein-carbohydrate interactions typically include _____ which often include ______ water molecules and the packing of ______ against the _____
Lectin's protein-carbohydrate interactions typically include multiple hydrogen bonds which often inclyde bridging water molecules and the packing of hydrophobic sugar faces against aromatic side chains.
95
What is jack bean concanavalin A
A lectin which specifically binds alpha-D-glucose and alpha-D-mannose residues.
96
What is wheat germ aggulitinin?
A lectin which specifically binds Beta-N-acetlymuramic acid and alpha-N- acetylneuraminic acid; also causes cells to clump together.
97
The linkages on monosacharides can be determined by____
methylation analysis or also called permethylation analysis
98
How does methylation analysis work?
Methyl enters at at the anomeric C atom resistant to hydrolysis but glycosidic bonds are not. Consequently if an oligosachharide is exhaustively methylated and then hydrolyzed the free OH groups on the resulting methlyated monosacharide mark the former positions of the glycosidic bonds.
99
methylated monosacharides are often identified how?
gas chromotagraphy.
100
The sequence and anomeric configurations of the monosaccharides in an oligosaccharide can be determined through the use of _____. How?
specific exoglycosidases. These enzymes specifically hydrolyze their corresponding monosacharides from the nonreducing ends of oligosachharides (the end lacking a free anomeric carbon atom).
101
Beta-galactosidase does what?
excises the terminal Beta anomer of galactose
102
Alpha- mannosidase does what?
excises the terminal alpha anomer of mannose.
103
How can it be determined the sequence of a polysaccharide after exoglycosidases are used?
mass spectrometry; the sequence can be deduced from the mass decrements generated by exoglycosidases
104
What do endoglycosidases do?
cleaves glycosidic bonds between nonterminal sugars
105
What is the most abundant disaccharide?
Sucrose
106
To name a polysaccharide systematically one must specify what?
component monosacharides,ring type, anomeric forms and how they are linked together.
107
name Sucrose systematicaly.
O-alpha-D-glucopyranosyl-( 1 -> 2) Beta-D-fructofuranoside
108
the symbol ( 1->2) indicates what?
The glycosidic bond links C1 of the first monosacharide to the C2 of the second monosacharide.
109
Is O-alpha-D-glucopyranosyl-( 1 -> 2) Beta-D-fructofuranoside a reducing sugar?
No because thes e two positions are the anomeric carbon atoms of their respective monosacharides thus sucrose is not a reducing sugar.
110
The hydrolysis of sucrose to D-glucose and D-fructose is accompanied by a change in _______
optical rotation from dextro to levo
111
hydrolyzed sucrose is sometimes called _____ and the enzyme that catalyzes this process is _______ but sometimes called _____
sometimes called invert sugar and the enzyme Beta-D-fructofuranosidase catalyzes this process but sometimes this enzyme is also called invertase.
112
What is the systematic name for lactose? what does this indicate?
O-Beta-D-galactopyranosyl-(1 -->4)- D-glucoopyranose. This indicates that it is a free sugar since it has a free anomeric carbon of its glucose residue.
113
a lack of the enzyme _____ will cause lactose intolerance?
B-D-galactosidase or lactase
114
Maltose has a ____ to ___ disaccharide
glucosyl - glucose disaccharide
115
what is maltose
an enzymatic hydrolysis product of starch; present in plants
116
Cellobiose has a _____ to ____ disaccharide
glucosyl-glucose disaccharide
117
What is cellobiose?
it is a Beta (1 --> 4) isomer of maltose and the repeating disaccharide of cellulose; present in plants
118
What is isomaltose?
it is an alpha (1--->6) isomer of maltose present in plants.
119
What is the primary structural component of plant cell walls?
Cellulose
120
Cellulose is a _____ polymer of up to ___ linked by ____ glycosidic bonds
linear polymer of up to 15,000 D-glucose residues (a glucan) linked by Beta (1--->4) glycosidic bonds.
121
Cellulose's highly _____ structure gives cellulose fibers exceptional strength and makes them _____ despite ____
its highly hydrogen bonded structure gives cellulose fibers exceptional strength and makes them water insoluble despite their hydrophilicity.
122
In plant cell walls, the cellulose fibers are embedded in and ______ by a matrix of ______ that are composed of glucose as well as other monosaccharides.
embedded in and croslinked by a matrix or several polysaccharides that are composed of glucose as well as other monosaccharides.
123
In wood the cell wall contains cellulose but also contains a large proportion of ____. This is a _____ material which does what?
wood contains large proportions of lignin which is a composite material. Composite materials can withstand large stresses because the matrix evenly distributes the stresses among the reinforcing elements.
124
Can vertebrates themselves hydrolyze celluose?
No do not have an enzyme capable of hydrolyzes of B(1 --> 4) linkages.
125
How do herbivores hydrolyze cellulose?
The digestive tract of herbivores contain symbiotic microorganisms that secrete a series of enzymes collectively called cellulase that can hydrolyze cellulose.
126
Is the hydrolyzes of cellulose a fast of slow process? why?
Slow because cellulose is tightly packed and hydrogen bonded glucan chains are not easily accessible to cellulase and do not separate readily even after many of their glycosidic bonds have been hydrolyzed.
127
Do herbivores digest food as fast as carnivores?
No herbivores digestion takes much longer because of cellulose this is why cows have multichambered stomachs and must chew their cud. This is also why the decay of dead plants by fungi, bacteria and other organisms often takes years.
128
Chitin is the principle component of what?
exoskeletons of invertebrates and is a mjor cell wall constituent of most fungi and algae.
129
What is the composition of Chitin
It is a homopolymer of Beta (1 --> 4) linked N-acetyl-D-glucosamine residue.
130
How does the composition of chitin differ from that of Cellulose
only by that each C2-OH group is replaced by an acetoamido function.
131
Starch is what?
a mixture of glucans that plants synthesize as their principle food reserve; energy source
132
Where is starch stored and how?
stored in the cytoplasm of plant cells as insoluable granules composed of alpha amylose and amylopectin.
133
What is starch composed of?
alpha amylose and amylopectin.
134
What is the structure of alpha amylose?
a linear polymer of several thousand glucose residues linked alpha (1--> 4) bonds. These are very structurally different than cellulose even though amylose is an isomer of cellulose.
135
Alpha amylose differs significantly in structure than cellulose even though amylose is an isomer of cellulose. Why is this?
Cellulose's Beta-glycosidic linkages cause each successive glucose residue to flip 180 degrees with respect the preceeding residue so that the polymer assumes an easily packed, fully extended conformation. While in alpha amylose the alpha glycosidic bonds cause it to adopt an irregualr aggregating helically coiled conformation.
136
amylopectin consist mainly of _____ but is a _____ molecule with ____ points every 24 to 30 glucose residues on average.
consist mainly of alpha (1---> 4) linked glucose residues but is a btanched molecule with alpha (1 --->6) branch points every 24 to 30 glucose residues on average.
137
Amylopectin molecules conating up to ____ residues making it ___ occuring in nature
10^6 glucose residues making it among the largest naturally occurring molecules
138
what is the benefit of storing glucose as starch?
It greatly reduces the large intracellular osmotic pressure that would result from glucose's storage in monomeric form because osmotic pressure is proportional to the number of solute molecules in given volume
139
What is the main carbohydrate source in the human diet?
Starch
140
Digetsion of starch begins in the ____ by ___ which randomly hydrolyzes _____ or starch except _____
mouth by the saliva containing alpha amylase which hydrolyzes all the alpha (1 -->4) glucosidic bonds of starch except its outermost bonds and those next to branches.
141
By the time that fully chewed food reaches the stomach, where the acidity inactivates amylase, the average chain length of starch has what?
the average chain length has been reduced from several thousand to a fewer than eight glucose units.
142
After the stomach what happens to the starch?
It goes to the small intestines where starch is further degraded by pancreatic alpha amylase into a mixture of the disaccharide maltose: maltriose and dextrins
143
What are malitroses?
a trisaccharide which contains three alpha (1 ---> 4) linked glucose residues
144
What are oligosacharrides?
carbohydrate with a relatively small amount of monosacharides
145
Dextrins are what?
oligosacharrides
146
oligosaccharides produced in the small intestines contain ____ branches
alpha (1 --->6 branches)
147
the dextrins are hydrolyzed to their component monosaccharides by specific enzymes contained in the ____ mebranes of the ___: an alpha-glucosidase removes ____ residue at a time from oligosaccharides, an _____ which hydrolyzes _____ and ____ bond, a ____ and at least in infants a lactase.
the dextrins are hydrolyzed to their component monosaccharides by specific enzymes contained in the brush border mebranes of the intestinal mucosa: an alpha-glucosidase removes one glucose residue at a time from oligosaccharides, an alpha-dextrinase (or debranching enzyme) which hydrolyzes alpha (1 --->6) and alpha ( 1 --> 4)bond, a sucrose and at least in infants a lactase.
148
What happens to resulting monosaccharides produced in the small intestines?
The resulting monosaccharides are absorbed by the intestines and transported to the bloodstream
149
Glycogen is a _____ polysaccharide that is most prevalent in ____ and ___ where it occurs as _____
storage polysaccharide of animals that is most prevalent in skeletal muscles and liver where it occurs as cytoplasmic granules.
150
The primary structure of glycogen resembles that of amylopectin by glycogen is ______ with branch points occuring at every ____ residues
glycogen is more highly branched than amylopectin with branch points occuring at every 8-14 glucose residues.
151
How is glycogen's degree of polymerazation compared to that of amylopectin
They are similar.
152
Glycogen is degrade for metabolic use how?
Degraded by glycogen phosphorylase which phosphorolytically cleaves glycogen's alpha ( 1 ---> 4) bonds sequentially inward from its non reducing ends to yield glucose-1-phosphate. The alpha (1---> 6 ) branches of glycogen are cleaved by a debranching enzyme.
153
Glycogen's highly branched structure which has many ______ ends, permits what in the time of metabolic need.
Glycogen's highly branched structure which has many non reducing ends permits the rapid mobilization of glucose in the time of metabolic need.
154
Extracellular spaces particularly of connective tissue, tendons, blood vessel wall, cartilage, skin and bone which consist of colalgen and elastin fibers embeded in a gel-like matrix is known as ______
ground substance.
155
Ground substance is composed largely of what?
glycoaminoglycans (GAG ), unbranched polysaccharides of alternating uronic and hexosamine residues.
156
Hyaluronic acid is an important ____ component of ground substance, ___ (which lubricates joint), and the vitreous humor of the ____.
GAG component of ground substance, synovial fluid (fluid that lubricates the joints) and the vitreous humor of the eye.
157
Hyaluronic acid is in the ____ surrounding some bacteria
capsule surrounding some bacteria, usually pathogenic bacteria
158
Hyaluronic acid molecules are composed of 250-25,000 Beta (1--->4) linked disaccharide units that consist of____ and_____ linked by a _____ bond.
Hyaluronic acid molecules are composed of 250-25,000 Beta (1--->4) linked disaccharide units that consist of D glucoronic acid and N-acetyl-D-glucosamine linked by a Beta (1 --->3) bond.
159
The anionic character of ____ residues causes hyaluronic acid to do what?
The anionic character of its glucuronic acids causes hyaluronic acid to bind cations such as K+, Na+, and Ca2+ tightly.
160
Ca2+ hylaluronate forms an extended, l_____helix with ~ ___disaccharide units per turn
Ca2+ hylaluronate forms an extended, left-handed, single-stranded helix with ~ 3 disaccharide units per turn
161
Hyaluronate has a high _____ and numerous mutually repelling _____ groups make hyaluronate an extended, rigid and highly hydrated molecule which in solution, occupies a volume ____ than in its dry state.
Hyaluronate has a high molecular mass and numerous mutually repelling anionic groups make hyaluronate an extended, rigid and highly hydrated molecule which in solution, occupies a volume ~1000 times than in its dry state.
162
Hyaluronate solutions have a viscosity that is _____ dependent. An object under shear stress has ____ and ___ forces applied across its opposite face
Hyaluronate solutions have a viscosity that is shear dependent. An object under shear stress has equal and opposite forces applied across its opposite face
163
At low shear rates, the hyaluronate molecules form ___ that greatly ____; that is the solution is quite ___.
At low shear rates, the hyaluronate molecules form tangled that greatly impede flow; that is the solution is quite viscous.
164
As shear rates increases, the stiff rodlike hyaluronate molecules tend to_____and thus offer ____ resistance to it.
As shear rates increases, the stiff rodlike hyaluronate molecules tend to line up with flow and thus offer less resistance to it.
165
What is a shear rate?
Shear rate is the rate of change of velocity at which one layer of fluid passes over an adjacent layer.
166
The viscoelastic behavior of hyaluronate make hyaluranate excellent biological ___ and ____
shock absorbers and lubricants.
167
Hyaluronic acid and other GAGs are degraded by _____ which hydrolyzes their _____ linkages
degraded by hyaluronidase which hydrolyzes their B (1---> 4) linkages.
168
Hyaluronidase occurs in bacteria which ______
expedites their invasion of animal tissues.
169
Chondroitin-4-sulfate is a ____ and is a major component of ____ and ____
Chondroit-4-sulfate is a GAG and is a major component or cartilage and other connective tissue
170
Dermatan sulfate is A ______ and is prevalent in ____.
GAG and is prevalent in the skin
171
Keratan sulfate is a _____ and is a component of ___________.
Is a GAG and is a component of cartilage, bone, cornea, hair nails and horn.
172
Heparin is the most ______ poly-electrolyte in the mammalian tissues.
negative
173
Heparin is a ____ that occurs exclusively in the _____ of the ____ that line the _____ especially in the _____. It does not constitute connective tissue.
GAG that occurs exclusively in mast cells that line the arterial walls especially in the liver, lungs, and skin.
174
Heparin inhibits ____ and its release through injury is thought to prevent _____ clot formation.
Hepranin inhibits (meaning does not allow) the clotting of the blood and its release through injury is thought to prevent run away clot formation.
175
most proteins are _______ which are what?
Most proteins are glycoproteins which are associated covalently with carbohydrates.
176
Glycoproteins vary in what?
carbohydrate content from <1% to >90% by weight.
177
What are the functions of glycoproteins?
Have functions that span the entire spectrum of protein activities, including those of enzymes, transport proteins, receptors, hormonesm and structural proteins.
178
Glycoprotein's carbohydrate chains are ______ generated and _____ linked to the polypeptide without the rigid guidance of _______ templates
Glycoprotein's carbohydrate chains are enzymatically generated and covalently linked to the polypeptide without the rigid guidance of nucleic acid templates
179
Who do glycoproteins have a variable carbohydrate composition a phenomena known as ____?
Glycoproteins have a variable carbohydrate composition a phenomena called microheterogeneity this is because the processing enzymes are generally not available in sufficient quantities to ensure the synthesis of uniform products.
180
What are proteoglycans?
They are proteins and glycosaminoglycans in ground substances and in cell-surface membranes aggregate covalently and non-covalently to form this diverse group of macromolecules known as proteoglycans.
181
Proteoglycans consists of _____ protein which atleast one ______ chain, most often ____ and/or ____ is covelently linked
Proteoglycans consists of a core protein which atleast one glycosaminoglycan chain, most often keratan sulfate and/or chondroitin sulfate, is covalently linked.
182
What are the major roles of proteoglycans?
- organizers of tissue morphology via interactions with molecules such as collagen
- Selective filters that that regulate the traffic of molecules according to their size and/or charge
- Regulators of other proteins, particularly those involved in signaling.
183
What is aggrecan
A proteoglycan which is major component of cartilage . Aggrecan has proteoglycan subunit "bristles" which ate noncavalently attached to a filamentous hyaluronic acid "backbone".
184
What are the three domains of aggrecan
1) N terminus domain which bind noncovalently to hyaluronic acid
2) A region rich in oligosaccharides
3) A C-terminus rich in chondroitin sulfate.
185
Aggrecan's N-terminus domain forms a globular region that binds noncovalently to hylauronic acid. This attachment is stabilized by ____ which is similar in sequence to aggrecan's N-terminal domain (binding a relatively few carbohydrates that tend to be ______) . Aggrecan's highly extended central domain is colvalently linked to a series of polysacharrides via the ____________________
Aggrecan's N-terminus domain forms a globular region that binds noncovalently to hylauronic acid. This attachment is stabilized by a link protein which is similar in sequence to aggrecan's N-terminal domain (binding a relatively few carbohydrates that tend to be oligosaccharides) . Aggrecan's highly extended central domain is colvalently linked to a series of polysacharrides via the amide N atoms of specific Asn residues.
186
In region two of aggrecan it is rich in ______, many which serve as _____ points for keratan sulfate chains. These oligosaccharides are covalently bonded to side chain ___ atoms of ___ and _____.
In region two of aggrecan it is rich in oligosaccharides, many which serve as anchor points for keratan sulfate chains. These oligosaccharides are covalently bonded to side chain O atoms of Ser and Thr residues.
187
In region three of aggrecan is the C tterminal region which is rich in ______, which are covalently linked to the side chain_____ of ser residues Ser-Gly dipeptides via galactose-galactose-xylose trisaccharides.
In region three of aggrecan is the C tterminal region which is rich in chondroition sulfate chains, which are covalently linked to the side chain O atoms of ser residues Ser-Gly dipeptides via galactose-galactose-xylose trisaccharides
188
Aggrecan's C terminal domain contains ____ which binds certain monosacharride units. Thus aggrecan can probably function to do what?
contains lectinlike modules which bind certain monosaccharide units. Thus aggrecan can probably function to bind together various constituents of the cell surface and the extracellular matrix.
189
Cartiage consists largely of meshwork of _____that is filled in by proteoglycans whose ____and _____ components specfically interact with collage,
Cartiage consists largely of meshwork of collagen fibrils that is filled in by proteoglycans whose chondrioitin sulfate and core protein components specfically interact with collage,
190
The tensile strength of cartilage is from _____ but the resilence of cartilage is from _____
The tensile strength of cartilage is from collagen but the resilence of cartilage is from the highly proteoglycan content.
191
What causes cartilage to be highly hydrated?
The extended brushlike structure of proteoglycans together with the polyanionic character of keratan sulfate and chondroitin sulfate causes this complex to be highly hydrated
192
The application of pressure on cartilage squeezes water away from charged regions until charge-charge repulsion prevent further compression. What happens when pressure is released?
the water returns.
193
How is the cartilage in joints nourished?
It lacks blood vessels instead it is nourished by the flow of water create from compressing and decompressing the cartilage brought about by body movement. This is why long periods of inactivity causes joint cartilage to become fragile and thin.
194
A bacteria's cell wall is responsible for bacterial ______
virulence
195
antigens of a bacteria are components of their _____ which means ___
cell wall and capsules which means injection of preparations of these substances into animals often invokes immunity against them.
196
Peptidoglycan's polysaccharide component consists of alternating __________ and _____
Beta (1--->4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
197
Neighboring parallel peptidoglycan chains are ______ through their ______ side chains.
Neighboring parallel peptidoglycan chains are covalently cross-linked through their tetrapeptide side chains.
198
The NAM's lactic acid residue in peptidoglycan forms an ____ bond with a ________ to form a petidoglycan repeating unit.
The NAM's lactic acid residue in peptidoglycan forms an amide bond with a D-amino acid-containing tetrapeptide to form a petidoglycan repeating unit.
199
The D-amino acids of peptidoglycan renders them resistant to ____
proteases
200
Gram _____ are resistant to lysozyme but Gram ____ are not.
Gram negative bacteria is resistant to lysozyme but gram positive are not.
201
What do lysozymes do to gram Positive bacteria's peptidoglycan?
lysozyme is an ezyme that catalyzes the hydrolysis of Beta (1 --->4) glycosidic linkage between NAM and NAG. Thus treating gram positive with lysozymes degrades it's cell wall resulting in its lysis.
202
Penicillin kills bacteria by _____. How
Inhibiting cell wall biosynthesis. Penicilin does this by specifically binding to an inactivating enzymes that function to cross-link the peptidoglycan strands of bacterial cell walls.
203
Why is penicillin a low human toxicity?
there is no human enzyme that binds penicillin.
204
Can penicillin-treated bacteria with no cell wall still remain intact?
Only in hypertonic medium.
205
Bacteria that are living in hypertonic solution with no cell wall are called protoplast or spheroplast and when they are transferred to normal medium what happens? why
They lyse because they are extremely fragile since they are encased only by their plasma membranes.
206
Most bacteria resistant to penicillin secrete _____. why?
Beta-lactamase because it hydrolytically cleaves the amide bind of penicillin's Beta ring ,inactivating penicillin.
207
What do you treat penicillin resistant bacteria?
treat it with ampicillin and often administered in combination with Beta-lactamase inhibitors such as sulbactum.
208
Teichoic acid is present in ____ bacteria and are polymers of _____ linked by _____
Gram positive bacteria and techoic acid are polymers of ribitol or glycerol linked by phosphodiester bridges.
209
Why is gram negative bacteria less affected by lysozyme and penicillin than gram positive bacteria?
Gram negative bacteria has an outer membrane that acts as a barrier.
210
Negative pathogens contain an O-antigen which plays a role in _____ based on the observation that___
plays role in host recognition since gram negative bacteria that lacked this O antigen were nonpathogenic.
211
Almost all secreted and membrane-associated proteins of eukaryotic cells are ____
glycosylated.
212
What are the two types of attachments oligosaccharides form to glycisylated proteins
N-linked and
| O -linked
213
In vast majority of N-glycosidic (N-linked) attachments, a NAG is ______ to the amide nitrogen of an Asn in the sequence Asn-X-Ser or Asn-X-Thr where X is any amino acid residue except PRO and rarely_____.
In vast majority of N-glycosidic (N-linked) attachments, a NAG is beta-linked to the amide nitrogen of an ASn in the sequence Asn-X-Ser or Asn-X-Thr where X is any amino acid residue except PRo and rarely Asp, Glu, LEu, or Trp
214
In N-glycosidic (N-linked) attachments the oligosaccharides usually have a distinct ____ whose peripheral mannose residues are linked to either ___ or _____. The latter residues may be linked to other ______so that an enormous diversity of N-linked oligosacharides is possible.
In N-glycosidic (N-linked) attachments the oligosaccharides usually have a distinct core whose peripheral mannose residues are linked to either mannose or NAG residues. The latter residues may be linked to other sugar residues so that an enormous diversity of N-linked oligosacharides is possible.
215
The most common O-glycosidic (O-linked) attachment involves the disaccharide core _____________ alpha linked to the OH group of either Ser of Thr.
The most common O-glycosidic (O-linked) attachment involves the disaccharide core Beta-galactosyl- (1--->3)-alpha-N-acetylgalactosamine alpha linked to the OH group of either Ser of Thr.
216
Less commonly, glucose, galactose, mannose and xylose form _______ with ser or Thr
Less commonly, glucose, galactose, mannose and xylose form alpha-O-glycosides with ser or Thr
217
N-linked glycans are ____ common than O linked glycans with only _____ of glycoproteins having both types of attachments.
N-linked glycans are ~ 5 fold more common than O linked glycans with only ~10% of glycoproteins having both types of attachments.
218
What suggest that oligosaccharides extend from the surfaces of proteins rather than participate in their internal structure?
The fact that oligosaccharides tend to attach to protein sequences that form beta bends taken with their hydrophilic character.
219
Cells tend to synthesize a large repertoire of a given N-linked glycoprotein, in which each variant species (glycoform) differs somewhat in _______.
Cells tend to synthesize a large repertoire of a given N-linked glycoprotein, in which each variant species (glycoform) differs somewhat in seqeunce, location and number of covalently attache oligosaccharides.
220
The oligosaccharide______ affect the native enzyme's conformation, substrate specifity, or catalytic properties.
DOES NOT; The oligosaccharide does not affect the native enzyme's conformation, substrate specifity, or catalytic properties
221
oligosaccharides function similarly to ______. How?
molecular chaperone most likely by shielding a hydrophobic patch on the protein surface; thus enzyme with an oligosaccharide typically folds to its native state faster.
222
O-linked polysaccharides are _____-_ into heavily glycosylated segments in which glycosylated Ser and Thr reidues comprise 25-40% of the sequence.
clustered
