Term
| In solution what form does sugar mostly exist? |
|
Definition
Cyclic form
In solution sugars exist mainly in a ring form. |
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Term
| Why do cyclic forms occur? |
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Definition
| Cyclic forms result from the intramolecular reversible reaction of their C=O group with an OH group (usually the OH on the highest numbered chiral carbon). |
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Term
| How many members does the pyranose form of a monosaccharide have? |
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Definition
| The pyranose form of a monosaccharide has a six-memberred ring. |
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Term
| how many members does the furanose form of a monosaccharide have? |
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Definition
| The furanose form of a monosaccharide has a five-membered ring. |
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Term
| Why do sugars exist in a chair-type structure? |
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Definition
In solution, it is the most thermodynamically favourable arrangement.
Most six-membered rings are chair-type structure. |
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Term
| What is the most thermodynamically favourable arrangement for sugars in solution? |
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Definition
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Term
|
Definition
to cause (two things) to be converted into each other.
Mutorotation = interconversion |
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Term
|
Definition
Interconversion = mutorotation
To cause (two things) to be converted into each other. |
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Term
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Definition
| when sugars such as glucose are in the ring form, carbon 1 is chiral and is called the anomeric carbon. |
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Term
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Definition
| the PH group at C-1 is below the plane of the ring. |
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Term
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Definition
| the OH group at C-1 is above the plane of the ring. |
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Term
| Glucose crystallised from ethanoic acid gives... form anomer with a ... degree of rotation of plane polarized light. |
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Definition
| Glucose crystallised from ethanoic acid gives pure ßform anomer with a [ß]D +19˚ degree of rotation of plane polarized light. |
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Term
| Glucose crystallised from methanol gives a pure ...anomer form with ...degree rotation of polarized light. |
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Definition
| Glucose crystallised from methanol gives a pure alpha form anomer with a +113˚ degree rotation of polarized light. |
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Term
| What happens when crysatallised glucose is dissolved in water? |
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Definition
When either the alpha or beta forms are dissolved in water, the rotation gradually changes until it reaches and equilibrium value of 52˚
Due to the slow conversion of pure anomers into a 37alpha:63ß equilibrium mixture. |
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Term
| What is the most stable form of glucose in solution? |
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Definition
| C1 conformation and the ß anomers is preferred for D-glucose in solution. |
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Term
| Functional group of alcohol |
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Definition
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Term
| Functional group of aldehydes |
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Definition
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Term
| Functional group of ketones |
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Definition
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Term
| Name 3 weak oxidising agents suitable for oxidising monosaccarides. |
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Definition
| Tollens, Fehlings and Benedicts solutions. |
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Term
What affect do weak oxidising agents have on monosaccharides?
name one example. |
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Definition
Weak oxidising agents oxidise the carbonyl group end of the monosaccharide.
Ms: Benedicts solution. |
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Term
| What obstacles are experienced in oxidisation of monosaccharided in relation to structure? |
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Definition
| Sugars need a free aldehyde group in order to be reducing. This is not present in the cyclic form. |
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Term
| How come glucose, although cyclic, is a reducing sugar? |
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Definition
| Even though glucose is mainly in the cyclic form, the equilibrium to the open chain form is established quickly enough to allow it to react with the Fehling's, Benedict's and Tollen's reagents. |
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Term
| How come fructose, although not in possession of an aldehyde group, is a reducing sugar? |
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Definition
A ketose (such as fructose) does not possess an aldehyde group but can undergo these reactions because, in alkaline solution, the ketose form is in equilibrium with the aldose form through an enediol intermediate.
CH2OH CHOH HC=O
| | |
C=O <-> C-OH <-> HCOH
| | |
ketose enediol aldose |
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Term
| Name one strong oxidising agent which may be used to oxidise monosaccharides. |
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Definition
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Term
| Explain how strong oxidising agents work on monosaccarides. |
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Definition
| Strong oxidising agents such as dilute nitric acid can oxidise both ends of a monosaccharide at the same time (carbonyl group + terminal primary OH group) to produce a dicarboxylic acid ms: glucaric acid. |
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Term
| Explain how enzyme systems can oxidise monosaccharides. |
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Definition
| Enzyme systems can oxidise the primary alcohol end of and aldose such as glucose, withough oxidising the aldehyde, to give a uronic acid. |
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Term
|
Definition
any of a class of compounds that are derived from sugars by oxidising a -CH2OH group of an acid group (-COOH)
Often components of polysaccharides.
Glucaronic acid is, for example, a component of hyaluronic acid found in the vitrous humour of the eye. |
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Term
| Name the three different types of oxidising agents used to oxidise monosaccharides and their products. |
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Definition
Weak acids - ms: tollens, Fehlings and Benedicts solutions
Glucose + weak acid = gluconic acid
Strong acids - ms: dilute nitric acid
Glucose + strong acid = glucaric acid
Enzyme systems
Glucose + enzyme system = glucaronic acid |
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Term
What reducing agent can be used to reduce monosaccharides?
What will it produce? |
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Definition
Hydrogen
The carbonyl group (CHO) can be reduced to a hydroxyl group (OH) using hydrogen as the reducing agent to produce polyhydroxy alcohol (sugar alcohol).
Glucose + hydrogen = Glucitol |
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Term
| Give 3 uses for the sugar alcohol Glucitol which can be obtained from reducing Glucose. |
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Definition
1. occurs naturally in some fruits and berries and is sold commercially as the bulk sweetener "sorbitol"
2. Sweetner in "tooth friendly" gum.
3. Moisturising agent in food and cosmetics. |
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Term
| How do monosaccharides form inorganic ester? |
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Definition
The hydroxyl group of a monosaccharide can react with the inorganic oxyacids such as phosphoric acid to form inorganic esters.
Acid + alcohol = ester + water |
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Term
| Give an important role of phosphate esters formed from monosaccharides. |
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Definition
They play important roles in carbohydrate metabolism.
ms: alpha-D-glucose 6-phosphate |
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Term
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Definition
a compound formed from a simple sugar and another compound by replacement of a hydroxyl group in the sugar molecule.
Many drugs and poisons derived from plants are glycosides. |
|
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Term
| how are glycosides formed? |
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Definition
| Cyclic forms of monosaccharides react with alcohols or with amines to form glycolsides. |
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Term
| Give examples of naturally occuring glycosides. |
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Definition
Many plant pigments, toxins, flavourings and steroids occur in cells as glycosides.
Ms: salicin - bitter tasting glycoside from willow bark traditionally used to reduce fever.
Ms: Foxgloves (digitalis purpurea) provide the important heart stimulant, digitalin. They become harmful when the glycon portion is stripped off as in the process of digestion. |
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Term
| Give 3 examples of amino sugars common in nature. |
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Definition
| Glucose, mannose and galactose. |
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Term
| How is an amino sugar formed? |
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Definition
| The hydroxyl group on the carbon-2 of the sugar molecule is replaced with an amino group (NH2) |
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Term
| What link do amino sugars have with blood? |
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Definition
| Deriviatives (N-acetyl) of amino sugars (D-glucosamine and D-galactosamine) are present in the biological markers on red blood cells which distinguish blood type. |
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Term
| What blood type has N-acetyl galactosamine? |
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Definition
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Term
| General formula of carbohydrates? |
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Definition
| Cm(H20)n ....ie. hydrates of carbon |
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Term
| How is carbohydrate made? |
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Definition
It is synthesised by
-plants from Co2 and H2O and energy.
-Oxidation by animals, releasing CO2 & H2O + energy. |
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Term
| What are the 3 major groups of carbohydrates? |
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Definition
| Monosaccharides, Oligosaccharides and polysaccharides |
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Term
| Describe the characteristics of monosaccharides and give 3 examples of monosaccharides. |
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Definition
Monosaccharides have 1 sugar unit.
Ms: ribose, glucose, fructose |
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Term
| Describe the characteristics of oligosaccharides and give 3 examples of oligosaccharides. |
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Definition
Oligosaccharides have 2 or more sugar units.
Ms: sucrose, maltose, lactose. |
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Term
| Describe the characteristics of polysaccharides and give 3 examples of polysaccharides |
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Definition
Polysaccharides have many units (100's - 1000's)
Ms: cellulose, starch, glycogen |
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Term
| What are the 2 most common monosaccharides? |
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Definition
| pentoses (5 carbons) and hexoses (6 carbons) |
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Term
| The common nomenclature for monosaccharides ends in what? |
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Definition
| common names are used ending in "ose" |
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Term
| Monosaccharides can be classified into 2 groups of organic compounds what are these? |
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Definition
Classified as aldoses or ketoses depending on whether they contain an aldehyde or a ketone group.
aldehyde Ketone
O \
" C=O
-C-H / |
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|
Term
Aldoses:
definition and give and example |
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Definition
Organic compounds containing an aldehyde group are called aldoses.
Ms: glucose |
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|
Term
Ketoses:
Definition and give an example |
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Definition
Organic compounds containing a ketone group are called ketoses.
Ms: fructose |
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Term
| How many stereoisomers of monosaccharides are possible? |
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Definition
Monosaccharides have chiral carbon atom(s). The number of stereoisomers possible is 2(to the power of)n with n being the number of asymmetric/chiral carbons.
Ms: glucose. Aldohexoses have 2(to the power of)4 =16 stereoisomers, ie. 8 pairs of mirror images. |
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Term
| What is D/L nomenclature based on? |
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Definition
D/L nomenclature is based on orientation of the hydroxyl group on the C-2.
For larger molecules the carbon chain is numbered, starting at the C=O group end and the highest numbered chiral centre (asymmetric carbon) is used to designate D or L. |
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Term
|
Definition
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|
Term
|
Definition
|
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Term
| List the stereoisomers of aldohexoses. |
|
Definition
D/L Allose
D/L Altrose
D/L Glucose
D/L Mannose
D/L Gulose
D/L Idose
D/L Glactose
D/L Talose |
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Term
| List the stereoisomers of ketohexoses. |
|
Definition
D/L Psicose
D/L Sorbose
D/L Fructose
D/L Tagatose |
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Term
| Explain the glycosidic linkage/bond of oligosaccharides. |
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Definition
| The cyclic form of one monosaccharids can react with an alcohol group from another to form a disaccharide. |
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Term
| Give 2 properties of glycosidic bonds. |
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Definition
Glycosidic bonds are...
Stable under normal conditions.
Hydrolysed by acid + heat or specific enzymes. |
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Term
| Where are free oligosaccharides found? |
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Definition
| Free oligosaccharides other than disaccharids, are rarely found in biological systems and are usually associated with proteins or lipids. |
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Term
|
Definition
| Sucrose, lactose, cellobiose, maltose. |
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|
Term
|
Definition
Disaccharide
Main food sweetner.
Digestible by humans. |
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|
Term
|
Definition
Disaccharide
5-8% in milk
Digestible by many humans. |
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Term
| Properties of Cellobiose? |
|
Definition
Disaccharide.
From cellulose hydrolysis.
Does not occur naturally.
Not digestible by humans. |
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Term
|
Definition
Disaccharide.
From starch hydrolysis, used in food fermentations.
Digestible by humans. |
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Term
| On a molecular level what is lactose made of? |
|
Definition
Lactose consiists of a ß-D-galactose and a D-glucose bonded though a ß1-4 glycosidic linkage.
The C1 on the glucose unit is not involved in bonding. |
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|
Term
Why can the disaccharides lactose, cellobiose and maltose possess a free aldehyde group?
What other implications does this have? |
|
Definition
Because the glucose unit in lactose, cellobiose and maltose can exist in the open chain form in solution and therefore these disaccharides possess a free aldehyde group.
This means that they are therefore reducing and can exist in both alpha and beta anomeric forms in solution. |
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Term
| Why are the disaccharides lactose, cellobiose and maltose reducing? |
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Definition
| Because the glucose unit in lactose, cellobiose and maltose can exist in the open chain form in solution and therefore these disaccharides possess a free aldehyde group. This means that they are therefore reducing and can exist in both alpha and beta anomeric forms in solution. |
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Term
| Do the disaccharides lactose, cellobiose and maltose exist in alpha or beta anomeric forms in solution? |
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Definition
| Due to the free aldehyde these disaccharides possess they are reducing and can exist in both alpha and beta anomeric forms in solution. |
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|
Term
| Explain the glycosidic bonding in sucrose. |
|
Definition
The glycosidic bond in sucrose is an alpha, beta (1-2) linkage and involves the anomeric carbons of both its constituent sugar residues. (Its two constituent sugar residues being glucose and fructose!)
The rings of glucose and fructose are effectively locked closed and therefore the disaccharide does not possess a free aldehyde group in solution and sucrose is non reducing. |
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|
Term
| Why is sucrose non reducing? |
|
Definition
| Because through the alpha,beta (1-2) glycosidic linkage between sucrose's two sugar residue constituents- glucose and fructose- the rings are bound tight. The rings are locked together and do not allow the presence of a free aldehyde group in solution. Therefore sucrose is a non reducing sugar. |
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|
Term
| Human enzymes can hydrolyse the linkage in which disaccharides? |
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Definition
| Human enzymes can hydrolyse the linkage in sucrose, lactose and maltose. |
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Term
| Human enzymes can not hydrolyse the linkage in which disaccharides? |
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Definition
| Human enzymes cannot hydrolyse the ß1-4 linkage in cellobiose (a derivative of cellulose). |
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|
Term
| Name two hydrolysing agents used to invert/hydrolyse sugar. |
|
Definition
|
|
Term
| List the general properties of polysaccharides. |
|
Definition
Contain many, often tens of thousands of monosaccharide units joined by glycosidic linkages.
Linear or branched.
May be homogeneous or heterogeneous.
Commonly food reserves and structural components of cells.
Often insoluble an difficult to purify. |
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|
Term
| Nomenclature of polysaccharides: |
|
Definition
Homopolysaccharides replace the "ose" of sugar with "an"
ms: glucan
Heteropolysaccharides use the structural unit of the main chain, prefixed with names of other units.
Ms: galactomannan |
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|
Term
|
Definition
|
|
Term
| List the properties/characteristics of starch. |
|
Definition
starch is the main food reserve in plants. MS: cereals, potatoes, rice etc (present as granules)
Starch is composed of two soluble polysaccharides -amylose + amylopectin.
The proportion of amylose and amylopectin varies depending on plant source.
Most starches (maize, potatoe, rice) contain 20-30% amylose, some cereals contain only 0-5% (waxy mutants) |
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|
Term
|
Definition
It is a polysaccharide.
It is one of two components of starch.
It is linear with all the glucose units linked via alpha(1-4) linkages.
It is approximately 200-2000 glucose units long.
Amylose tends to form a helix.
Amylose forms a blue complex with iodine. |
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|
Term
|
Definition
It is a polysaccharide.
It is one of the two components of starch.
It is branched having a small number of alpha(1-6) linkages at various points along an alpha(1-4) chain.
Its straight alpha(1-4) chain can have up to 100,000 units.
The branching of amylopectin is similar to the veins of a leaf starting with a single strand which branches out every 20-25 units. |
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|
Term
What is glycogen?
Where can it be found?
Explain the structure of glycogen. |
|
Definition
Glycogen is an energy reserve polysaccharide.
It is abundant in the liver and in muscle cells.
Its structure is similar to amylopectin but more highly branched with shorter branches every 12 glucose units.
Its glucose chain may be up to 60,000 units.
Glycogen may be built up and broken down by enzymic reactions. |
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|
Term
| Where can glycogen be found? |
|
Definition
Glycogen is abundant in the liver and in muscle cells.
It is an energy reserve polysaccharide. |
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|
Term
|
Definition
It is a polysaccharide.
It is a structural component of plant cell walls.
It is composed of linear chains of 2000-3000 glucose units, joined but ß(1-4) linkages.
It can only be digested by microbes and the animals which employ them in digestion. |
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Term
| Explain the role of cellulose in plants. |
|
Definition
| Linearity- allows polymers to line up in fibres with a great deal of hydrogen bonding between adjacent chains (strong) and little interaction with water (insoluble). |
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|
Term
Give an example of a heteropolysaccharide.
Give a source, composition, function. |
|
Definition
Alginate:
It is extracted from seaweed and contains ß-D-mannuronic acid and alpha-D-guluronic acid. Its exact composition varies on with its source.
Alginate gels on the addition of calcium ions.
Egg-box structure forms iwth each Ca2+ complezing with 4 Guluronic acid (COO-) units. |
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