Carbohydrates Flashcards
What are the functions of Carbohydrates?
-Energy source and energy storage
-structural component of cell wall and exoskeletons
-informational molecules in cell-cell signalling
What is the basic nomenclTURE OF CARBS?
Cn(H2O)n
Number of carbon atoms and add -ose e.g triose
What are the functional groups in carbs
-Aldehydes - aldose
-Ketones - ketose
Examples of enantiomers in sugars?
(MIRROR IMAGE)
D and L isomers of a sugar are enantiomers
Are most hexoses in living organisms L or D stereoisomers?
D stereoisomers
Some simple sugars occur in L form, e.g L-arabinose
How to know whether a sugar is L or D?
The -OH that is farthest from the carbon involved in the aldehyde/ketone group is the one to look at
If the -OH is on the right = D
If the -OH is on the left = L
What are diasteromers?
When 2 sugars have ientical molecular formulas, have different arrangement of atoms and are not enantimers (not mirror images)
What are Epimers?
A subgroup of diastereoisomers - sugrs differ at only one chiral center - not mirror images
Why do ring structure of carbohydrates predominate under normal physiological conditions?
They are lower in energy and more stable than open chains
How does this ring formation take place?
-The nucleophilic alcohol attacks the electrophilic carbonyl carbon, allowing formation of a hemiacetal
-As result linear carb forms ring structure
At the completion of ring formation, what is the carbonyl carbon reduced to?
An alcohol
What sugars readily undergo intramolecular cyclization?
Pentoses and hexoses
When does the anomeric carbon occur and where does it occur in and aldose and a ketone?
-The former carbonyl carbon (carbon that takes part in functional group) becomes a new chiral center, this is called the anomeric carbon.
-Occurs at C1 of an aldose and C2 of a ketose
What determines if the anomer is alpha or ß?
The position of the former carbonyl oxygen.
-If the hydroxl group (-OH) is on the opposite (trans) of the ring as the CH2OH then its alpha
(If the CH2OH is up and the OH is below the c1)
-If the hydroxyl group (-OH) is on the same side (cis) of ring as CH2OH then its ß
(If the CH2OH) is up and the OH is above C1)
What are pyranoses?
`6 membered oxygen containing rings
What are furanoses?
5 membered oxygen containing rings
In amino sugars, what is replaced for what?
An NH2 group replaces one of the OH groups in the hexose
How can 2 sugar molecules be joined?
Via an O-glycosidic bond between an anomeric carbon and a hydroxyl carbon.
Glycosidic bond Vs hemiacetal
The glycosidic bond (an acetal) between monomers is more stable and less reactive than the hemiacetal at the second monomer
What is the hemiacetal?
A carbon connected to 2 oxygen atoms where one oxygen is an alcohol (OH) and the other is an ether (O R)
What is sucrose, lactose and maltose made of?
Sucrose - glucose + fructose
Lactose - Glucose + galactose
Maltose - Glucose + glucose
How is a disaccharide formed?
Formed from 2 monosaccharides when an
-OH (alcohol) from one glucose molecule condenses with the intramolecular hemiacetal (C bonded to OH and OR)
-Eliminates H2O and forms a glycosidic bond
What is the condensation of 2 glucose molecules via a 1 - 4 bond called?
alpha-1-4 glycosidic bond
How to tell if a sugar is a reducing sugar or a non reducing sugar?
If the oxygen on anomeric carbon (the carbonyl group) of a sugar is not attached to any other structure, the sugar is a reducing sugar.
(If there is a hemiacetal then theres a reducing end)
