Carbohydrates Flashcards
What are carbohydrates?
Carbon-based molecules rich in OH groups, written as (CH2O)n for many
What are monosaccharides?
Simple sugars/monomers that make up polysaccharides, fuel
Aldehydes or ketones with 2 or more OH groups, smallest are composed of 3C
What are polysaccharides?
Complex carbs of polymers of covalently linked monosaccharides.
The variety and multiplicity of linkages forming polysaccharides allows carbs to
provide cells with a vast assay of 3D structures that can be used for a variety of purposes
How to determine D and L config for monosaccharides?
Look at the asymmetrical C furthest from the aldehyde or ketone.
D = OH on right
What are epimers?
Sugars that differ in config at only one asymmetric centre and are disasteroisomers
How do the predominant form of common sugars (cyclic) form their ring?
Aldehyde reacts with an alcohol to form hemiacetal
What additional asymmetric centre is created when a cyclic hemiacetal is formed?
Anomer (another diasteroisomer)
Where is the OH group for alpha and beta respectively?
Below the plane (alpha), above the plan (beta)
Pyranose rings adopt two classes of conformations:
chair and boat
Monosaccharides commonly react with
alcohols, amines, and phosphates
What is a glycosidic bond?
Formed between the anomeric C atom of glucose and O-atom of an alcohol = O-glycosidic bond, product is glycoside
When are glycosidic bonds predominant?
When carbs are linked together to form long polymers and when they are attached to proteins
What are oligosaccharides?
Built by a linkage of 2 or more monosaccharides by O-glycosidic bonds
Why are there many different glycosidic linkages possible?
Because monosaccharides have multiple OH groups = many possibilities
How are oligosaccharides synthesized?
Through the action of specific enzymes, glycotransferases, which catalyze the formation of glycosidic bonds
What are the common disaccharides?
Sucrose (alpha-D-glucopyranosyl-(1->2)-beta-D-fructofuranose)
Lactose (beta-D-galactopyranosyl-(1->4)-alpha-D-glucopyranose)
Maltose (alpha-D-glucopyranosyl-(1->4)-alpha-D-glucopyranose)
What are glycoproteins?
A carb group covalently attached to a protein
What are the 3 classes of glycoproteins?
- Glycoproteins
- Proteoglycans
- Mucins/Mucoproteins
What are the 1st class of glycoproteins?
Protein constituent is the largest component by weight, component of cell membranes (part in processes i.e cell adhesion and binding of sperm to egg)
What are proteoglycans?
Protein component is conjugated to a particular part of polysaccharide called glycosaminoglycan, carbs are much larger % of weight, function as structural components and lubricants
What are mucins/mucoproteins?
Predominantly carb, key component of mucus = lubricant, N-Acetylgalactoamine is usually caeb bound to protein
In all classes of glycoproteins, sugar are attached to either?
Amide N atom in side chain of Asn or to hydroxyl O atom in side chain of Ser or Thr
This process is called glycosylation
Carb structures are recognition sites for a special class of proteins called?
glycan-binding proteins, which bind specific carb structures on neighbouring cell surfaces
