Carbohydrates & Glycobiology Flashcards
Functions of Carbohydrates (4)
- Energy source
- Energy storage
- Structural component of cell walls and exoskeletons
- Informational molecules in cell - cell signalling (regulates cell - cell communication)
Carbohydrate formula
Cn(H2O)n
What is an aldose
A carbohydrate with aldehyde functionality
What is a ketose
A carbohydrate with ketone functionality
What are enantiomers
Stereoisomers that are non superimposable mirror images
What are diasteromers
Two sugars that have identical molecular formulas, different arrangement of atoms and are not enantimers (mirror images)
What are epimers
Sugars that differ in stereochemistry at only one chiral center. They are not mirror images and are not enantiomers.
What carbohydrate structure predominates under normal physiological conditions and why?
Cyclic/ ring structure. Because they are lower in energy and are more stable than open chain structures.
Alpha anomer of glucose structure
The OH group (hydroxyl grp) is facing the opposite direction than the CH2OH group
Beta anomer of glucose structure
OH (hydroxyl) group is facing the same direction as the CH2OH group.
How is the cyclic structure formed?
The nucleophilic alcohol attacks the electrophilic carbonyl carbon, allowing formation of a hemiacetal. This results in the linear carbohydrate forming a ring structure. The carbonyl carbon is reduced to an alcohol.
After the cyclisation of monosaccharides what does the former carbonyl carbon become?
It becomes a new chiral center, called the anomeric carbon at C1 of an aldose & C2 of a ketose.
What is a pyranose
Six membered oxygen containing ring
What is a furanose
Five membered oxygen containing ring
What occurs to form amino sugars
An NH2 group replaces one of the OH groups in the hexose.
What occurs to form deoxy sugars
Substitution of H for OH produces a deoxy sugar
What occurs to form acidic sugars
Made by oxidation of carbonyl carbon or hydroxyl carbon or both.
What is the O-glycosidic bond formed between
An anomeric carbon and a hydroxyl carbon
Which part of the molecule is reducing
The second molecule, with the hemiacetal is reducing
Which part of the molecule is non reducing
The anomeric carbon involved in the glycosidic bonding is non reducing
What is sucrose made of
Glucose + fructose
What is lactose made of
Glucose + galactose
What is maltose made of
Glucose + glucose
How is a disaccharide formed
- Formed from two monosaccharides
- The OH of one glucose molecule condenses with the hemiacetal of the other glucose molecule
- This happens with the elimination of H2O
- A glycosidic bond is formed
Reducing sugar
Sugar has the ability to participate in oxidation or reduction rxns due to the free oxygen in the OH group at the end of the molecule
Non reducing sugar
Sugar doesn’t have the ability to participate in oxidation or reduction rxns due to the oxygens in the anomeric carbons being bound by the glycosidic bond
What does the product have after an O-glycosidic bond (bond between two anomeric carbons) is formed
The product has two acetal groups and no hemiacetals
What linkages do glucose monomers form to form glycogen
Alpha 1 - 4 linkages
What is glycogen
- A branched homopolysaccharide of glucose
Function of glycogen
It is the main storage polysaccharide in animals
What is starch a mixture of
Two homopolysaccharides of glucose: amylose & amylopectin
Function of starch
It is the main storage polysaccharide in plants
How is cellulose structured
It’s a linear homopolysaccharide of glucose
What linkages are found in cellulose
Glucose monomers form beta 1 - 4 glycosidic linkages
How is chitin structured
It’s a linear homopolysaccharide of N-acetylglucosamine
What linkages are in chitin
N-acetylglucosamine monomers form beta 1-4 linked chains
Structure of amylose (tyoe & repeating unit)
Linear homopolysaccharide of glucose with alpha 1-4 glycosidic bonds
Structure of amylopectin (type & repeating unit)
Branched homopolysaccharide of glucose with alpha 1-4 glycosidic bonds
What are glycosaminoglycans
A special type of polysaccharides that consist of repeating disaccharide units which are modified to contain an amino grp (either N-acetyl-glucosamine or N-acetyl-galactosamine) and some negatively charged grps (uronic acids or galactose and sulfate esters)
Where are glycosaminoglycans found and what is their function
Found in our joints and act as a shock absorber/ buffer/ lubricant
What are proteoglycans
Proteins that are attached to glycosaminoglycans
What are glypicans
protein that is anchored to a lipid membrane
What are syndecans
protein has a single transmembrane domain
4 functions of proteoglycans
- Joint lubricants
- Structural components of connective tissue
- Bind cell to ECM
- Regulate movement of molecules through the matrix
Main components of ECM
- proteoglycan aggregates
- collagen fibres
- elastin (a fibrous protein)
What is a glycoprotein
Carbohydrate attached to a protein via its anomeric carbon to amino acids on the protein
What amino acids commonly form glycoproteins
Ser, Thr, Asn
(Serine, Threonine, Asparagine)
What are glycolipids
Lipids with covalently bound oligosaccharide
