Second Half I F24: Lecture Slides 34 - 57 Flashcards
What are sugars considered to be?
The most abundant biomolecule on earth.
What are sugars important in?
Energy Metabolism
What are sugars essential components of?
Nucleic Acids
What are Monosaccharides?
Consist of a single sugar unit (Glucose)
What are Oligosaccharides?
Short chains of Monosaccharide Units (Sucrose)
What are Polysaccharides?
Polymers of 20 or more sugar units (Glycogen, cellulose)
What are the 4 chemical properties of Monosaccharides?
- Very water soluble
- Poorly soluble or insoluble in organic solvents such as ether or hexane.
- Colourless
- Sweet to Taste
What is the approx. chemical formula of Monosaccharides?
(CH2O)n
What are the two organic functional groups that combine to make a monosaccharide?
A carbonyl (C = O) group , which can either be an aldehyde or ketone and at least two carbons bearing hydroxyl (alcohol) C - OH groups
What do the simplest carbon atoms contain?
Three carbon atoms (Trioses)
What do each of the trioses have?
They have aldoses and ketoses: aldotriose and ketotriose
What is glycerol considered to be?
An aldose
What is acetone considered to be?
A ketoses
What did Emil Fischer study?
He studied the analysis, synthesis and stereochemistry of simple sugars, and he introduced much of the terminology and notation that we use today
What is the Fischer projection formula?
To represent three dimensional sugar structures on paper
In the Fisher projection formula, how are vertical bonds represented?
Behind the plane
In the Fisher projection formula, how are horizontal bonds represented?
Project out of the planar
What is the Perspective Formula?
Solid Wedge-Shaped Bonds Project in front
Dashed bonds point away
What are the carbon atoms in Monosaccharides?
Asymmetric (4 different substituents)
What do all monosaccharides except dihydroxyacetone contain?
One or more chiral carbon atoms
What does chiral carbon atoms give rise to?
The occurrence of optically active isomeric forms (a type of stereoisomer)
What are D Glyceraldehyde and L Glyceraldehyde?
Enantiomers (mirror images)
What are mirror images?
Differ in Configuration at every chiral carbon atom (can’t be superimposed)
What are the chemical properties of Mirror images
Identical (melting point, water-solubility)
What do mirror images differ in?
Optical activity
What is Optical Activity?
The plane of polarization of polarized light is bent in opposite directions when passing through solutions of the two enantiomers
What are Diastereomers?
More then one chiral carbon atoms that have stereoisomers that differ in hardness at some carbon atoms but not others (not mirror images)
Do diastereomers have identical chemical properties?
They do not have identical chemical properties, because the spatial relationships among the atoms making up the molecules are different
When would a sugar be called a “D” sugar?
If the chiral carbon atom furthest away from the carbonyl group has the same configuration as D-glyceraldehyde.
What are “L” sugars?
Those with a configuration similar to L-glyceraldehyde
What configuration are most naturally occurring sugars in?
D-sugars
What are Epimers?
A pair of sugars that are identical expect for one configuration at one carbon atom (at the chiral centre they have one identical structure at one carbon)
What are epimers a special case of?
Diastereomers
What is the formula for figuring out the number of stereoisomers?
2^n (the power is the # of chiral centres)
What is an example of the number of stereoisomers for n chiral centres of aldose?
An aldose have 5 carbons with 3 chiral centres
2^3 = 8 stereoisomers.
What happens to D-ketoses every time a C atom is added?
The number of isomers doubles
What is the general trend with D-Aldoses?
A aldose has one more chiral centre than a ketone, so the number doubles.
What do Aldehydes and Ketones produce when they react with alcohols?
Hemiacetals and Hemiketals
What happens to the original carbonyl carbon upon the formation of hemiacetals and hemiketals?
It becomes chiral
What is the hemiacetal and hemiketal formation?
Intramolecular: the alcohol and the aldehyde (or ketone) are present in the same molecule
What does hemiacetal and hemiketal formation turn sugars into?
Ring structures
What does the OH group at C-5 react with?
The carbonyl carbon of the aldehyde group to form a stable six-membered ring.
What does the OH group reaction render?
A C-1 asymmetric giving rise to two stereoisomers (a and b)
What do these isomeric forms differ in?
Only in their configuration around the hemiacetal or hemiketal carbon
What is the difference in the configuration around the hemiacetal or hemiketal carbon called?
An anomer
What does the electrophilic carbonyl carbon atom react with?
The nucleophilic O of an OH group
What is solid glucose found in?
Either in the alpha or the beta form of the hemiacetal
What happens as it dissolves in water?
It slowly converts into an equilibrium mixture of the alpha, beta and linear forma.
What is the process of it converting into the equilibrium mixture called?
Mutarotation
What happens with time?
A solution of a-D-glucose and b-D-glucose form identical equilibrium mixtures with identical optical properties
What is the approximate composition?
1/3 a-D-Glucose, 2/3 B-D-Glucose, and trace amounts of linear form.
What are the two rings formed when sugars cyclize?
Pyranose (6-membered) or Furanose (5 membered)
What does the size of the ring formed by a particular sugar depend on?
The relative thermodynamic stabilities of the various possible ring structures, and this depends on the particular geometry of the molecule.
