Biomolecules - Carbohydrates Flashcards
Define Carbohydrates.
Carbohydrates are aldehydes or ketone derivatives of polyhydroxy alcohols or compounds which give rise to these on hydrolysis.
Classification of Carbohydrates:
Monosaccharides – Simple sugars
Disaccharides – 2 monosaccharides
Oligosaccharides – 3 – 10 monosaccharides
Polysaccharides – More than 10 joined together by glycosidic bonds
Significance of asymmetric carbon atom in carbohydrates.
Asymmetric carbon atom – (C*) carbon atom with four different groups attached
Presence of asymmetric carbon atoms lead to formation of isomers. Isomers - 2n (n- no. of chiral centres)
Stereoisomers?
Compounds which are identical in composition but differ in their spatial configuration
Classification of stereoisomers?
- Aldose and ketose
- D and L isomers
- α and β anomers
- Epimers
5- Pyranose and furanose
Aldoses and ketoses?
Aldose - monosaccharide containing one aldehyde group per molecule
Ketose - sugar containing one ketone group per molecule.
D and L isomers?
D and L Glucose?
enantiomers (mirror images)
Naturally occurring monosaccharides belong to D series
When the OH group around the carbon atom adjacent to the terminal primary alcohol carbon (C- 5) is on the;
Right – D series
left – L series
α and β anomers?
Carbon 1 - anomeric carbon atom
α – “OH” is below the plane of the ring
β - “OH” is above the plane of the ring
Epimers?
Epimerization?
Two sugars which differ from one another by only one carbon atom except the anomeric carbon atom.
Epimerization – the conversion of one epimer to another
Pyranose and furanose ring structures?
Six/five membered rings.
D-Fructose?
◦ Found in fruits
◦ Canned, dried or preserved (jams) more than fresh
◦ Common sweeteners (honey, maple syrup) more than fresh (tbs)
◦ High consumption leads to Non-communicable Diseases (NCD) (not natural sources)§
D - Galactose?
D-Galactose
◦ Constituent of milk sugar (lactose) and glycolipids and glycoproteins
◦ Synthesized in the mammary gland
What are the main derivatives of monosaccharides?
- Deoxy sugars
- Amino Sugars
- Sugar Alcohol
- Sugar Acids
What are Deoxysugars?
◦ Hydrogen atom replaces -OH group on C-2
◦ Constituent of nucleic acids
What are Amino sugars?
◦ Hydrogen atom replaces -OH group on C-2 ◦ Constituent of nucleic acids
Biomedical importance of Amino sugars.
- Glucosamines
◦ Constituents of certain mucopolysaccharides /glycosaminoglycans
◦ Constituents of cell walls of fungi and lobster - Galactosamines
◦ Constituents of sulphated mucopolysaccharides - Antibiotics (erythromycin, carbomycin) contain amino sugars.
What are sugar alcohols?
Examples?
◦ When Monosaccharides are reduced to their corresponding alcohols.
Ex:
Glucose -> sorbitol
Galactose -> Galactitol
Mannose -> mannitol
Relationships between sorbitol and cataract?
cataract is a cloudy area in the lens of the eye that leads to a decrease in vision.
Dietary sorbitol is rapidly converted to fructose by sorbitol dehydrogenase and other carbohydrates in the liver.
Diabetes – sorbitol is produced rapidly
Intracellular accumulation of sorbitol leads to osmotic changes resulting in hydropic lens fibers that degenerate and form sugar cataracts
What are Sugar Acids?
Aldoses are oxidized in a way that the aldehyde group remains unaltered but the primary alcohol group is converted to COOH group.
The sugar acid formed in this case is known as an “Uronic acid”.
Ex;
D-Glucose -> D-Glucuronic acid
D-Galactose -> D-Galactouronic acid
What are Glycosides?
Compounds containing a carbohydrate and a non-carbohydrate residue
If the carbohydrate portion is
◦ Glucose -> Glucoside
◦ Galactose -> Galactoside
Importance of Glycosides?
Cardiac glycosides –used to increase the cardiac output and are important in cardiac insufficiency
Oubain – Inhibits Na+-K+ ATPase in cardiac muscle (Inhibitor of Na pump)
Found in certain drugs, spices etc.
Antibiotics (streptomycin)
Glycosidic bonds?
Two monosaccharides joined by a covalent bond is called a glycosidic linkage.
Disaccharides?
Examples?
A bond is created between the C-1 of one sugar and the OH of another carbon
Ex; Maltose, Lactose, Sucrose
Maltose?
The intermediate product formed during the breakdown of starch by the amylase enzyme
Starch -> Maltose -> Glucose
Lactose?
Present in milk (milk sugar) and produced in the lactating mammary gland
Breast milk – the main source of energy for the newborn
Lactose -> Glucose + galactose
Sucrose?
Present in cane sugar, fruits and some vegetables
Sucrose -> Glucose + Fructose
2 types of polysaccharides and examples.
- Homoploysaccharides – Starch, Cellulose, Glycogen
- Heteropolysaccharides – Glycosaminoglycans
Starch?
Storage form of carbohydrate in plants.
Present in cereals (rice, wheat, rye), potatoes, legumes Mixture of amylose and amylopectin
Amylose? [5 points]
15-20%
Glucose joined by α-1,4 glycosidic linkages
Unbranched chain
Forms a helical structure
There are 6 glucopyranose units per turn
Amylopectins?
80-85%
Highly branched structure
Main chain has α-1,4 glycosidic linkages
Each branch point has a α-1,6 glycosidic linkages
Celluose?
Straight chain homoglycan of glucose with β-1,4 linkages with alternating glucose molecules.
Why humans cannot digest cellulose?
Explain.
Dietary fibre (Insoluble dietary fibre)
Dietary fibre is the edible parts of plants that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine.
Glycogen?
Carbohydrate storage form in animals
After a meal glucose will be converted to glycogen (Glycogenesis)
During starvation/fasting glycogen will be broken down to glucose to provide energy (Glycogenolysis)
Main chain has α-1,4 glycosidic linkages and each branch point has a α-1,6 glycosidic linkages.
Reducing sugars and Non reducing sugars?
examples?
Reducing Sugars:
Some monosaccharides and disaccharides have ◦ A reactive carbonyl group or
◦ Anomeric carbon that can be oxidized.
Ex. Glucose, maltose, lactose / Benedicts test
Non-reducing sugars:
Non reducing sugars have both anomeric carbons in a glycosidic bond ( ex . Sucrose)
Heteroglycans?
Different types of sugars are joined by glycosidic linkages
Glycosaminoglycans (GAG)?
Repeating disaccharide units.
Disaccharide units contain either of two amino sugars,
N-acetylgalactosamine (GalNAc) or N- acetylglucosamine (GlcNAc), and a sugar acid (uronic acid)
Glycosaminoglycans (GAG) examples?
- Chondroitin sulphate
- Dermatan sulphate
- Keratan sulphate (type I) 4. Keratan sulphate (type II) 5. Hyaluronate
- Heparin
- Heparan sulphate
Chondroitin sulphate?
Most abundant GAG
Mainly present in adult bone, cartilages and cornea.
It consists of N-acetylgalactosamine, D-glucuronic acid and is sulphated.
Heparin?
Anticoagulant present in liver produced mainly by the mast cells of liver.
Prevents blood clotting by inhibiting the conversion of fibrinogen to fibrin
Glycoproteins?
Proteins with short oligosaccharide chains which are highly branched and generally do not have a repeating sequence.
Carbohydrate content ranges from 1% - 85% by weight.
Carbohydrate chains
◦ May stabilize against denaturation (modifying the structure of proteins)
◦ Protect from proteolytic degradation ◦ Enhance solubility
Functions of glycoproteins?
Integral components of cell membrane
Function as receptors for hormones/molecules in the circulation
Transport molecules of vitamins, minerals – Transferrin, Caeruloplasmin
Immunogenic molecules – Immunoglobulins
Facilitate cell- cell recognition sites – Interaction of sperm with ovulated eggs.
Proteoglycans?
Proteoglycans are proteins with long, linear, unbranched oligosaccharides with a repeating disaccharide unit.
Disaccharide unit is a glycosaminoglycan
Mucopolysaccharidoses?
Genetic disorder
Some lysososmal enzymes that degrade GAGs are inactive Unable to break down proteoglycans
Leads to the accumulation of proteoglycans within cells.
Leads to a variety of disease symptoms, depending on the type of proteoglycan not degraded.
Blood group antigens?
Membranes of red blood cells contain one blood group substance of
Type A
Type B
Type AB (Universal recipient) or
Type O (Universal donor)
ABO substances are complex oligosaccharides Carbohydrate antigens are present on RBC Oligosaccharide portion gives the antigenic property
H substance?
Who has?
What is it?
How is it formed?
◦ Blood group substance in type O individuals.
◦ Precursor of both A and B substances
H substance is formed by addition of the terminal fucose in α,1- 2 linkage onto the terminal Galactose residue.
A substance:
codes for?
enzyme bond?
A allele encodes a glycosyltransferase; GalNAc transferase.
Enzyme bonds N-acetylgalactosamine to D- galactose end of H antigen
B Substance?
B allele encodes a glycosyltransferase; Gal transferase
Above enzyme joins α-D-galactose to D-galactose end of H antigen.
AB type?
Individuals of AB type possess both enzymes
(GalNAc transferase, Gal transferase).
Have both oligosaccharide chains.
