Carbohydrates 1 Flashcards
What are Carbohydrates?
Aldehyde or ketone compounds with hydrocylngroups e.g.
Polyhydroxyl aldehydes
Polyhydroxyl ketones
Compounds that can be hydrolyzed to PHA or PHK
List the biological functions of Carbohydrates?
- Fuel source
- Energy storage
- Structural materials
- Intermediate metabolism
- Recognition
How do Carbohydrates contribute as a fuel source?
When oxidized, they are an important source of energy
How do Carbohydrates contribute to energy storage?
Starch in plants
Glycogen in liver and muscle of animals
Give examples where carbohydrates are used as structural material
- DNA and RNA,
- Cell walls of bacteria and plants
- Chitin in exoskeleton
Give an example of a carbohydrate that is an intermediate of metabolism
Sedoheptulose-7-P
How do carbohydrates play a role in recognition?
Glycoproteins and glyycolipids act as markers for cellular recognition, blood group determination, cell adhesion, cell migration, immune response, blood clotting
List the 4 classifications of Carbohydrates
Monosaccharides
Disaccharides
Oligosaccharides
Polysaccharides
Describe the characteristics of monosaccharides
Cannot be hydrolyzed into simple sugars
Describe the classification of disaccharides
Their hydrolysis yields 2 monosaccharides(sugars)
Describe the characteristics of oligosaccharides
Hydrolysis produces more than 2 but less than 10 monosaccharides
Describe the characteristics of polysaccharides
On hydrolysis produces many monosaccharide units
Give some examples of monosaccharides
Glucose, mannose, galactose, fructose and ribose
Give some examples of disaccharides
Sucrose, lactose, maltose, cellubiose and gentiobiose
Give some examples of oligosaccharides
Raffinose and stachyose
Give some examples of polysaccharides
Glycogen, starch and cellulose
Describe the formula of monosaccharides
- General formula: CnH2nOn where n ranges from 3 to 9
- formula may deviate( deoxyribose, sugar acids etc.) deoxyribose ( C5H9O4)
How are monosaccharides found?
Found as free sugars and as part of many biologically important molecules
What are the 3 criteria for the classification of monosaccharides ?
- Number of carbon atoms present in the molecules
- Whether the sugar contain an aldehyde or ketone
- The stereochemical configuration of the asymmetric carbon atom farthest from the carbonyl carbon
How are ketones named?
By inserting ‘ul’ to the name of the aldose
Erythrose-> erythrulose
Ribose-> ribulose
Xylose-> xylulose
Exception: ketohexoses -> fructose
What is the structural difference between ketones and aldosterone
Ketones has one less asymmetrical C than aldose
Why do all monosaccharides except DHA have optically active isomeric forms?
All monosaccharides except DHA contain one or more asymmetric C chiral center
A chiral/asymmetrical carbon atom is the source of optical isomerism
Describe the difference in the configurations in glyceraldehyde
- The form of glyceraldehyde that caused the rotation of plane polarized light to the right(dextrorotatory)was designated D
- the form that caused rotation to the left(levatorotary) was designated L
What configuration are most naturally occurring sugars?
D configuration
Convention for designating D and L ISO’s,eras was originally based on what?
Optical properties of glyceraldehyde
What are 2 ways to define configuration of a molecule/stereochemistry?
- D and L
- (+ and -)
What is C1 and where is it in glyceraldehyde?
C1 is at the top of the Fischer projection(aldehyde group)
What are enantiomers?
Isomers that are perfect mirror images
D and L isomers are mirror images but non-superimposable
What are diastereoisomers?
- Stereoisomers with more than one chiral carbon
- not mirror images
- non-superimposable
What are epimers?
Stereoisomers that differ in configuration at a single asymmetric C
Give examples of epimers
D-erythrose and D threose differ at C2
Glucose and galactose at carbon 4
Give the results of reactions of aldehydes and alcohols
- Aldehydes react with alcohol once to form a hemiacetal
- hemiacetals react with alcohols to form acetals
Why are hemiacetals rarely isolated?
Because they are not as stable as acetals
When are cyclic hemiacetals particularly stable
cyclic hemiacetals are particularly stable if they result in five or six membered rings
When are cyclic hemiacetals successfully isolated?
If both aldehyde and hydroxyl group are part of the same molecule
In what form do pentoses and ketones exist in aqueous solution?
Mainly as ring structures
How are hemiacetals or hemiketoses formed?
Intramolecular reaction between carbonyl group and an OH
I.e. Reaction of an aldehyde or ketone with an alcohol
Product is a hemiacetals or hemiketone
What are hemiacetals with five membered rings?
Furanoses
What six membered rings that are hemiacetals called?
Pyranoses
What happens chirally when hemiacetals are formed?
A new asymmetric C at C-1 or C-2 is created
What are aldohexoses?
E.g. glucose form a 6- membered pyranoses ring. C1 to C5
Give an example of aldopentoses
E.g. ribose- 5 - membered furanose ring
Give an example ketohexoses
Fructose-5-member furanose ring
How can aldohexoses exist?
As furanoses which are much less stable than pyranoses which they can also exist as
What is the shape of of pyranoses and furanose rings?
They are non-planar
What is the effect of C—C bond in rings?
It leads to many possible shapes
There is an infinite amount of shapes known as conformers
What are the 2 classes of conformations
Chair and boat conformations
Where are boat conformations seen?
Seen in so,e hexose derivatives with bulky groups
What did Emil Fischer discover
Discover structure of monosaccharides
Describe the Fischer projection
- 2D representation of a 3D molecule projected onto a piece of paper
- Written vertically; functional group at the top, horizontal bonds project out of the plane of the paper
- Vertical bonds project behind the plane
What is the purpose of the Haworth formula?
Denotes HOW you go from a linear form to a ring form
Shows the stereochemistry of cyclic forms of monosaccharides
How does the Haworth formula work?
Work clockwise so that the hemiacetals/kettle bond is formed at C1(making itvanomeric)
The groups on the left are up
How does Haworth formula affect the carbonyl C?
The new isomers at the carbonyl C are another’s
What are anomers?
Anomers differ only in the configuration at the anomeric C atom alpha and beta isomers- - OH below and above resp.
What are the reactions of monosaccharides?
- Mutarotation
- Complete oxidation to carbon dioxide and water( via burning or respiration)
- reactions due to carbonyl group
- reaction due to alcohol group
What is mutarotation?
Change in optical rotation
Ocurrs via the open chain as intermediate
The alpha and beta forms can inter convert in solution-> the equilibrium mixture I.e. mutarotation
How does mutarotation occur in open chains and furanose forms?
Only a small % in the open chain and furanose forms
What are the alpha and beta proportions in glucose in solutions?
Glucose in solution- 33% alpha and 66%. Beta
What sugar derivative is produced by reduction of a sugar?
Sugar alcohol (sorbitol, inositol, galactitol)
What sugar derivative is produced by addition of a sugar to another bimolecule?
Glycoprotein, glycolipids
What sugar derivative is produced by a hydroxyl group being replaced with amino group ?
Amino sugar -NH2
What sugar derivatives are produced by oxidation of a C atom to a carbonyl group?
Sugar acid(glucuronic acid)
What is a deoxy sugar( derivative of a sugar)?
H atom instead of an OH group e.g. L-fructose(L-6-Deoxygal)
What sugar derivative is formed from the phosphorylation of a hydroxyl ?
Sugar phosphate
What sugar derivatives have glycosidic bonds?
Glycosides
- N-glycosidic bond
- O-glycosidic bond
What reactions do monosaccharides undergo due to their carbonyl group?
Reduction to polyols, oxidation to acids, reducing sugars
What reactions of monosaccharides are due to the alcohol group?
Esterification, formation of acetals called glycosides
What are the most common reagents to reduce aldose or ketoses to their corresponding polyalcohols, called sugar alcohols or alditols?
Sodium borohydride
Or
Catalytic hydrogenation using a nickel catalyst
What are names for polyalcohols?
Sugar alcohols or alditols
How are alditols named?
By adding the suffix -itol to the root name of the sugar
E.g. glycerol, myo-inositol and d-ribitol
What are sugar acids?
Monosaccharides that have had an -OH group oxidized to a carboxyl group
How are amino sugars formed?
The OH at C-2 is substituted by an amino group
Amino group is often acetylated
Where are amino sugars usually present?
Many structural polysaccharides such as chitin, GAG and bacterial cell walls
Describe the mechanism behind phosphate sugar synthesis
Phosphoric acid can react with hydroxyl group of monosaccharides, forming esters called phosphate sugars
Describe phosphate sugars at neutral pH
Very stable at neutral pH- negative charge due to the phosphate
Phosphorylation activates the sugar for….
Reaction
Phosphate sugars/sugar esters are components of…
Nucleotides
These sugar esters/phosphate sugars are important intermediates in…
CHO metabolism
How are phenylhydrazines formed by aldehyde and ketones?
Ketones/aldehyde lose carbonyl oxygen and phenylhydrazine loses both hydrogens to form phenylhydrazone and water
How do sugars form the simple phenylhydrazone derivatives?
Sugars do not form the simple the simple hydrazine derivatives
Explain osazone formation
Two molecules of phenylhydrazine condense with each molecule of sugar to give osazone
Both C1 and C2 are converted to phenylhydrazones, losing carbonyl oxygen and hydrogen and oxygen
Formation of glycosides is an example of__________ _________. Which is a reaction between a hemiacetals and another ________ ________
Acetal formation
Hydroxyl group
Glycoside are formed when…
Anomeric (hemiketals or hemiacetals) hydroxyl group of a monosaccharide undergoes
condensation with the hydroxyl group with another molecule, with elimination of water
Glycosides are named after the sugar that provides the ______________ ___________ . Thus if glucose
Hemiacetal group
If glucose provides the hemiacetal group- it is glycosides
If galactose provides the hemiacetal group- it is galactoside
Give 3 examples of reducing sugars?
Glucose, maltose and lactose
Give 2 examples of non-reducing sugars
Sucrose and trehalose
Give the main characteristic of reducing sugars
Can reduce oxidizing agents( chemicals containing Fe3+ or Cu2+) because of their free anomeric carbon
Why can anomeric carbons of non-reducing sugars not reduce oxidizing agents?
Anomeric carbons of non-reducing sugars have been locked up in the formation of glycosidic bonds
What is the reaction of hemiacetal and hemiacetal with alcohol?
Hemiacetal + alcohol = acetal + water
What kind of reaction is glycoside/ acetal formation?
Condensation reaction
List non-carbohydrate targets of glycosides to bond to
Nuclei acids(purine/pyridine bases)
Proteins(form glycoproteins)
Lipids(form glycolipids)
Steroids(via aromatic rings)
What kind of glycosidic bond linkage is formed between a carbohydrate and NH2 group of a non-carbohydrate?
N-glycosidic linkage
What kind of glycosidic bond linkage is formed by a carbohydrate and OH of a non-carbohydrate?
O-glycosidic bond
What kind of glycosidic bonds form between two carbohydrates?
O-glycosidic
Glycosidic bonds are…
Covalent and stable, except in the presence of strong acids
What are the reducing end and terminal end in glycisidic bond formation?
Reducing end- where the anomeric carbon is and where the glycosidic bond is formed to extend the molecule
Terminal end- opposite ends of the reducing end
How are glycosidic bonds named?
- Named according to the numbers on the carbons which are connected
- a-bond if the anomeric carbon has an alpha configuration
- beta-bond if the anomeric carbons has a beta configuration
Lactose has a glycosidic bond on the C1 carbon of beta glucose and C4 of glucose. Name the glycosidic bond
Beta (1-4) glycosidic bond
What keeps oligosaccharides locked in ring structure?
Formation of glycosidic bond
How many residues does an oligosaccharides have?
2-10 residues
Describe how many reducing ends does an oligosaccharides have?
One reducing end and thus one free anomeric carbon
Name the anomers of maltose
Alpha and beta maltose
How is maltose formed?
Formed by the digestion of alpha-amylase during digestion of starch
What are the molecules and glycolic bond of maltose?
Glycosidic alpha 1-4 bond
2 glucose molecules
Is maltose is a reducing sugar?
One glucose is a free anomeric C
What is the biochem name if table sugar?
Sucrose
What are the molecules and glycosidic bond that make up sucrose?
Contains alpha-D-glucose and beta-D- fructose
Glycosidic bond is alpha 1-2 beta bond
Both anomeric carbon atoms involved in glycosidic bond
What synthesizes sucrose?
Synthesized by plants
Not by animals
Is a sucrose sugar reducing or non-reducing?
Non-reducing sugar
What are the molecules involved in lactose?
Beta-D-galactose and alpha-D-glucose
Describe the glycosidic link of lactose
Beta-(1-4) alpha glycosidic bond h( can be either beta or alpha, this the alpha anomer but galactose MUST be beta)
Where do lactose naturally occur?
Only in milk- Milk sugar
Is lactose a reducing sugar?
Yes, it has a free anomeric carbon
What is a homopolysaccharide?
A single type of monomer e.g. cellulose
What is a heteropolysaccharide. ?
More than one type of monomer- contains two components e.g. hyaluronic acid
What is the purpose of starch?
Storage of CHO in plants-heavily hydrated
Describe the components of starch
A homopolysaccharide of glucose with 2 components
- unbrancged polymer-amylose(10-30%)
- branched polymer- amylopectin(70-90%)
Contrast amylopectin and amylose
Unbranched polymer- amylose
Branched polymer- amylopectin
What is the molecular weight of amylose chains?
10^3 is to 10^6
What is the glycosidic bond of amylose?
Alpha. 1-4
How much residues per turn does amylose have?
6 residues per turn
What happens to amylose in solution?
In solution, amylose adopts a helical conformation
Explain a detection test for amylose
Add iodine to amylose. Iodine fits into helix interior
Forms a blue color.
What color does amylopectin produce with iodine and why?
A red violet color due to iodine not fitting into tightly coiled conformation nor micelles
Describe the glycosidic bond linkages in amylopectin
Consists of linear chains with alpha (1-4) but with branches 25-30 residues
Branched portions are alpha (1-6) glycosidic bonds
Describe the glycosidic bonds in glycogen
Same as amylopectin alpha- (1-4) and alpha (1-6) bonds
How does branching of glycogen contrast to that of amylopectin?
Glycogen is more branched with branches at every 8-14 residues and not 25 -30 residues
What is the purpose of glycogen?
Storage form of CHO in animals in the form of granules containing enzymes of metabolism
Glycogen branched chains possesses one reducing and several non-reducing ends. Where does enzymatic degradation and lengthening occur?
Occur at the non-reducing ends
What is the most abundant polymer in the universe?
Homopolysaccharide
Cellulose is resistant to….
Acid hydrolysis and digestive enzymes
Describe the structure and glycosidic bonds of cellulose
Linear homopolysaccharide of glucose. Beta (1-4) glycisiduc binds
Are the properties of cellulose and amylose similar
Very different
Describe the reaction of iodine and cellulose
Negative reaction
Is cellulose soluble in water
Insoluble in water
Describe the structure of chitin
Resembles cellulose I.e. unbranched beta (1-4) polysaccharide of a N-acetylglysamine-an amino sugar at C2
Is chitin digestible as a digested chain?
Undigestible
What is the main component of insects and crustaceans?
Chitin
Give the examples of heteropolysaccharides
Heparin, hyaluronic acid and chondroitins
Describe glycisaminoglycans
Linear chains of repeating disaccharides
One unit is usually an alduronic acid(sugar with carboxylate group)
One unit is usually an amino sugar which may be acetylated forming GlcNac or GalNac
What heteropolysaccharide is a components of Extracellular matrix ( ECM)?
Glucosaminoglycans
One or more of the components of the glycisamines may contain….
A sulfate
Give the structure of hyaluronic acid
A polymer of disaccharides composed of D-glucuronic acid and N-acetylglucosamine
Describe the glycosidic bonds of hyaluronic acid
Alternating beta 1-4 and beta 1-3 bonds glycosidic bonds
What are the functions hyaluronic acid?
Functions as a lubricant in synovial fluid
Where is hyaluronic acid found?
In cartilage, tendons, virteous humor of the eye, arterial walls
CT Virteous humor I see arterial humor
What is the molecular weight of hyaluronic acid?
50,000 repeats - molecular unit over 10^6
Where is chondroitins found?
Tendons, cartilage and connective tissue ( CT connective tissue)
Describe the monomers in chondroitins
Glucoronate and N-acetylgalactosamine
Describe the glycosidic bonds of chondroitins
Alternating beta (1-3) and beta (1-4) glycosidic bonds
What is the molecular weight of chondroitins?
Lower molecular weight- about 60 repeat units
Where is sulfate located on chondroitin sulfates?
C4 and or C6
