Carbohydrate structure and properties Flashcards
Carbohydrate structure
Molecules with a 1:2:1 ratio of carbon, hydrogen, oxygen- “hydrated carbon”
Empirical formula (CH2O)n
Good energy storage molecules
- C-H covalent bonds
- Examples: starch, sugars, glucose
Combination of two to ten simple sugars =
oligosaccharides
carbon atom attached to four different functional groups is called a __________
Chiral carbon
same chemical formula, different 2D structures
isomers
stereoisomers = cis/trans
isomers, different 3D orientation.
- epimers = D/L (position of OH around C atom). configuration around one specific carbon atom. eg for glyceraldehyde
- anomers = cyclic epimers
enantiomers
non superimposable mirror images
Monosaccharides - defined by number of C they possess
3 = triose = glyceraldehyde 4=tetrose = erythrose 5 = pentose = ribose 6=hexose=glucose 7=heptose= sedoheptose
Monosaccharides - defined by chemical groups they possess
aldoses = aldehydes eg D-glucose
ketones = ketose eg D-fructose
D & L sugars are _________ of one another
enantiomers (non-superimposable mirror images)
Biologically different
Most naturally occurring sugars are D isomers
For sugars with more than one chiral centre, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto group
Predominant form of glucose in solution is
not linear but cyclic
alpha D glucose
Oh down on C1,2,4
beta D glucose
Oh down on C2,4
glucose alterations
glucosamine - precursor of cartilage components
glucitol/sorbitol - Sweetener/ Lower calorific value
glucoronic acid - Present in many mucus secretions / detoxification
In disaccharides the monosaccharides are joined by a _____________ bond.
O-glycosidic bond
This is formed between two –OH groups from each sugar with the elimination of H2O forming leaving – O -
Depending on carbon molecules linked glycosidic bond links you can have 1-2, 1-4 or 1-6 glycosidic bonds.
Depending on their position can also be a (in maltose and sucrose - U bond) or b (in lactose - S bond).
condensation of 2 monosaccharides gives
1 disaccharide with H - O - H bond + 1H2O molecule
starch composition
20-30% amylose (a-1,4 Glycosidic bonds)
70-80% amylopectin (a-1,6 Glycosidic bond approx every 30 units) generates branching
Gives S shape bonding –
Both rapidly broken down by amylase
Cellulose
b-1,4 linked D-glucose molecules
‘S’ shape type bonding –
Major structural component of green plants, trees etc
- Most abundant organic molecule on earth
- Insoluble
Glycogen
Mainly a-1,4 glycosidic bonds.
Approx. every 7-11th glucose a-1,6 glycosidic bond for branching.
Each glycogen granule can contain up to 30,000 glucose residues
In humans the major storage sites are the liver (100g) and skeletal muscle (400g)
Glycoproteins are formed by linking oligosaccharides and proteins as a post translational modification, in a process called __________
glycosylation.
sugars are linked to polymers via:
1. Asparagine (N-linked)
- Threonine or serine (O-linked)
What does glycosylation of proteins do?
It affects:
- proteins function/activity
- protein folding and processing
- cell interaction with macro-molecules
there are 3 classes of glycoproteins:
3 classes of glycoproteins
- Simple glycoproteins (mainly protein)
- Mucins (mainly carbohydrate) components of mucus
- Proteoglycans (mainly carbohydrate)
Some examples of glycoproteins in humans
Structural: Collagen
Lubrication and cell protection: Mucins
Immunogenic: Antibodies, Cell surface receptors
Protein folding: Calnexin, chaperone in the ER
Hormonal: Erythropoietin
Transport: Transferrin
Clotting: Platelet co-factors
What are:
Congenital Disorders of Glycosylation (CDGs)
lead to deficiency or lack of enzymes involved in glycosylation of proteins
symptoms: Developmental delay with multi-organ involvement Hypotonia Failure to thrive Coagulopathy Seizures
Mucins and mucus
Mucus forms a protective layer on epithelial surfaces
- Airways
Traps foreign particles and bacteria - Digestive tract
Lubricates
Protects stomach lining from acidic environment - Reproductive
Cervical mucus prevents infection
Mucus is complicated mixture of :
(95%) Water (1 – 10%) Mucins - mainly Muc 5AC/ Muc 5B in respiratory tract Salts Protein Lipid Carbohydrate nucleic acid secretory IgA
Mucins are a critical component of mucus. Diverse range of mucins: At least 19 different types of mucins in humans
Mucin structure
Basic structure of mucin comprises a protein backbone ( 1 horizontal S )
Protein backbone is highly O-glycosylated ( vertical S’s )
O-Glycans hygroscopic (attracts and retain H2O)
D-domain that allows polymerisation with other mucins via disulfide bonds
Polymerisation via of mucin via disulfide bond (SS) allows formation of hydrated gel lattice
