Topic 8 - Carbohydrates Flashcards
Describe the structure and chemical reactivity of alcohol functional group
Is an -OH group attached to a saturated C atom. -due to -OH group, can H bond -are polar -
Describe the structure and chemical reactivity of the aldehyde & ketone functional groups
carbonyl functional group is a carbon double bonded to an oxygen
-can undergo oxidation reactions
-can undergo keto-enol tautomerism. This refers to the equilibrium between the two possible tautomers. The interconversion of the two forms involves the movement of a proton and the shifting of bonding electrons. This equilibrium affords the compounds more reactivity
Describe the structure and function of ether functional group
- inability to form H bonds w/ each other
- slightly polar
- subject to reacting w/ strong acids due to two lone pairs of electrons on O atom
Describe the structure and chemical reactivity of the anhydride functional group
List the major functions of Carbohydrates
Energy storage e.g. starch (plants) glycogen (animals)
Structural e.g. cellulose, chitin
Extenders of protein function e.g. when combined w/ proteins, CHD increase H2O binding capacity
**Informational molecules **e.g. bar codes on proteins, secind messengers in signal transduction
Define Carbohydrates and give their formula
A CHD is a compound w/ 3 or more C atoms which as an aldehyde or keto functional group & two or more hydroxyl groups
Cn(H2O)n
- Produced from CO2 and H2O during photosynthesis in plants
- Can be covalently linked w/ proteins to form glycoproteins & proteoglycans
What is a mono/di/trisaccharide?
Mono: A simple CHD; consists of only one sugar unit. Cannot be hydrolysed to smaller CHD molecule
Di: complex CHD; 2 sugar units
Tri: complex CHD; 3 sugar units
What is a oligosaccharide?
A complex CHD
consists or two or more sugar units
What is a polysaccharide?
consists of many sugar units (more than 20); it is a CHD polymer (complex)
(monosaccharides)
How many carbons does a….
triose have?
tetrose?
pentose?
hexose?
triose =3
tetrose =4
pentose =5
hexose =6
What two groups can monosaccharides be divided into?
aldehydes and ketones
- name beginning w/ “aldo” =terminal carbonyl group is aldehyde
- name beginning w/ “keto” =NON-terminal carbonyl group is ketone
(monosaccharides)
Trioses are either aldo trioses or ketotrioses and so on up to aldohexoses and ketohexoses
What are stereoisomers?
are different compounds that have the same structure, but differ only in the arrangement of the atoms in 3D space.
All monosaccharides, except dihydroxyacetone, contain at least 1 chiral C and therefore occur as stereoisomers.
T or F?
True
Molecules w/ one chiral C have 1 type of stereoisomer. Name and describe this stereoisomer.
Enantiomers (pair)
-is one of two stereoisomers that are mirror images of each other that are “non-superposable”
How do we know if a monosaccharide is a D series or L series
- A monosaccharide is a member of the D-series, if the hydroxyl group on the chiral carbon farthest from carbon 1 is on the right.
- A monosaccharide is a member of the L-series, if the hydroxyl group on the chiral carbon farthest from carbon 1 is on the left.
What are diastereomers?
Any pair of stereoisomers that are NOT enantiomers (not mirror images) and differ in 1 or more chiral centres
What are epimers?
Non mirror image isomers that differ only in the configuration around one chiral atom
**not epimers if they differ by more than one chiral atom
Stereoisomer nomenclatural summary
What is the formula used to determine the number of isomers of aldo and keto sugar families?
2n
where n is the number of chiral centres
e.g. Aldotetroses (with 4C) have two chiral centres.
Thus 22 equals 4 stereoisomers.
What kind of pentose is Ribose?
aldo-pentose
What kind of hexose is glucose?
aldo-hexose
What kind of hexose is fructose?
keto-hexose of glucose
Please read over practice (clicker) Q’s in lecture
:)
do it!!!!!!!!!
Monosaccharides with a 5+ C atoms occur predominantly as what?
How is this formed?
cyclic structures
-formed by aldehyde or ketone groups reacts w/ a hydroxyl group along the chain, forming a covalent bond
Describe how to ID alpha and beta forms of simple CHD’s
The middle step where the OH migrates down
=>this can cause rotation, so the molecule either becomes stuck as
alpha (OH below ring)
beta (OH above ring)
What is an anomer?
Compounds that differ in configuration only aroun the C atom that may yield a carbonyl group (ketone or aldehyde) on rearrangement.
Number of cyclic stereoisomers
(see answer)
- Therefore, from the 16 (24) aldohexose stereoisomers, there are an additional 32 cyclic isomers
- i.e. 16 pairs of anomers
- Plus 16 LINEAR isomers
- = 48 total aldohexose isomers
What are conformers?
How do they differ from configurational isomers? (enantiomers, diastereomers, anomers)
Molecules w/ the same stereochemical configuration, but differ in 3D conformation
-differ from configurational as they can interconvert w/out breaking & reforming bonds
What is mutarotation?
alpha and beta anomers interconvert in solution
Monosaccharides are reducing agents.
-read description in answer
•Because of rapid interconversion between 99% ring form and 1% linear form, 100% of glucose molecules in solution can be rapidly oxidised in the reactive (aldehyde) linear form
For info on Disaccharides (glycosidic bonds) see lecture.
What do dissacharides consist of?
How is the bond formed?
two monosaccharides joinded covalently by an O-glycosidic bond.
a glycosidic bond can form b/w the hemiacetal group of one monosaccharide and the alcohol group of another
What does Maltose consist of?
Two D-glucose units joined by a alpha 1-4 glycosidic bond.
-wavy lines indicate it can Beta OG group can freely interconvert with alpha-D-glucose via mutarotation
What does Lactose consist of?
Composed of D-galactose and D-glucose
-Beta-lactose, contains a beta1-4 glycosidic bond
What does Sucrose consist of?
Disaccharide of glucose & fructose
NON REDUCING SUGAR
glycosidic bond forms b/w C1 of glucose and C2 of fructose
-bond involves the anomeric C of both monosaccharides =locked configuration, no mutarotation (interconversion) or reducing end (will not oxidise)
Are there alpha or beta isomers of sucrose? explain.
No.
All the anomeric carbons are involved in bond formation
What is a homopolysaccharide?
Name the 3 most important ones and give a brief description of their role
Contain only one single type of monosaccharide
- starch (energy store in plants)
- glycogen (energy store in animals)
- cellulose (structural role in plants)
What is a heteropolysaccharide?
Contain two or more different monosaccharides
Which two kinds of homopolysaccharides does starch contain?
Amylose (water soluble, simpler structure)
Amylopection (water insoluble, complex structure)
Describe Amylose
- linear polymer of D-glucose residues
- glucose monomers are linked by an alpha1-4 glycosidic bond
- vary in length, form coiled helical structures
Describe Amylopectin
branched polysaccharide, consisting of glucose residues joined by:
-alpha1-4 linkages
-alpha1-6 linkages
Branches occur every 24-30 residues
Describe Glycogen
Glucose homopolysaccharide
-a1-4linkage
-a1-6 linkages
Is similar to amylopectin, but more highly branched. Branches occur every 8-12 glucose residues
Describe Cellulose
structural homopolysaccharide
water insoluble
similar to amylose, though cellulose is unbranched & linear
BETA1-4 linkages (amylose alpha)
parallel cellulose chains linked together by H bonding
SUMMARY OF STRUCTURES AND BOND LINKAGES
(amylose, amylopectin, glycogen, cellulose)
