Carbohydrates Flashcards
(33 cards)
1
Q
What are the Biomedical Importance of Carbohydrates?
A
- cheif source of energy- gives 4 cal/g
- part of cell membrane structure
- storage for of energy (glycogen)
- lactose- principle sugar of milk
- serve to libricate skeletal joint
- used as drugs (cardiac glycosides- treats heart failure and certain irregular heartbeats)
- raw materials (paper and textiles)
2
Q
What is the chemistry of Carbohydrates?
A
- organic substances w/ C, H and O in the ratio 1:2:1
- polyhydroxy aldehyde or ketone derivitives
3
Q
What are the Classifications of Carbohydrates?
A
- Monosaccharides
- Disaccharides
- Oligosaccharides
- Polysaccharides
4
Q
What are Monosaccharides?
A
- Simple sugars and cannot be hydrolysed further
- Further classified on the basis of number of carbon atoms and the presence of functional groups
- Trioses (3C- glyceraldehyde and dihydroxy acetone)
- Tetroses (4C- Erythrose)
- Pentoses (5C- Ribose, Xylose, Xylulose)
- Hexoses (6C- Glucose, Galactose, Fructose)
5
Q
What are Disaccharides?
A
- Two molecules of the same or different monosaccharide units
- Give 2 monosaccharide units on hydrolysis (NB: dehydration forms the glycosidic bond)
- Monosaccharide units joined via glycosidic bonds
6
Q
What are some examples of disaccharides?
A
- Maltose from malt (glucose + glucose- alpha 1-4 glycosidic bonds)
- Lactose from milk (galactose + glucose- beta 1-4 glycosidic bonds)
- Sucrose from sugar cane (glucose + fructose- beta 1-2)
- Isomaltose from digestion of amlopectin (glucose + glucose - alpha 1-6 glycosidic bonds)
7
Q
What are Oligosaccharides?
A
- Contains 3-10 molecules of monosaccharide units
- Eg. Maltotriose (glucose + glucose + glucose)
8
Q
What are Polysaccharides?
A
- Contain more than 10 molecules of monosaccharide units
- Two types:
1. Homopolysaccharides
2. Heteropolysaccharides
9
Q
What are Homopolysacharides?
Examples?
A
- Polymer of the same monosaccharide units
examples:
1. Starch (glucose from plant, rice)
2. Dextrin (glucose from starch hydrolysis)
3. Glycogen (glucose from liver, muscle)
4. Cellulose (glucose from plant fibres)
5. Inulin (fructose from dahlia roots)
6. Chitin (N-Acytyl glucosamine from shells of arthropod)
10
Q
What is starch?
A
A mixture of 2 polysaccharides:
1. Amylose and
2. Amylopectin
11
Q
What are the characteristics of Amylose?
A
- 15-20% present in starch
- Unbranched, linear structure
- Molecular weight of 60 kDa
- 250-300 glucose residues joined by alpha 1-4 glycosidic linkages
- On reaction with I2 solution- blue colour forms as I2 molecues are trapped inside the helical structure- dissapears on heating and reappers on cooling
12
Q
What are the characteristics of Amylopectin?
A
- 80-85% present in starch
- Highly branched structure
- Molecular weight of 500 kDa
- glucose residues joined by alpha 1-4 linkages; branched point occurs by alpha-1-6 glycosidic linkages
- On reaction with I2 solution- reddish violet colour
13
Q
What is Glycogen?
A
- polymer of glucose
- stored in liver and muscle
- also called animal starch
- similar to the amylopectin component of starch
- it has more branches than starch (there are 11-18 gucose residues between any branch points)
14
Q
What is Dextrin?
A
These are partially hydrolysed products of starch
15
Q
What is Cellulose?
A
- made up of beta D glucose joined by beta 1-4 glycosidic bonds
- digested by cellulose enzyme in animals which is absent in human body
- acts as a dietary fibre and adds bulk to the food and helps in peristalsis
16
Q
What is Inulin?
A
- consists of a small number of beta D frusctose joined by beta 2-1 glycosidic linkages
- it is used to measure the glomerular filtration rate, a test to assess the funcion of the kidney
17
Q
What are Heteropolysaccharides?
Examples?
A
They are polymers of different monosaccaride unitsnor their derivitives
Examples:
1. Mucopolysaccharides (MPS)
2. blood groups
18
Q
What are Mucopolysaccharides (MPS)?
A
Proteoglycan - protein = MPS (aka glycosaminoglycans)
Made up of
- Hyaluronic acid
- Chondroitin sulfate
- Heparin
- Keratan sulfate
- Heparan sufate
- Dermatan sulfate
19
Q
What are the Biomedical Importances of MPS?
A
- they are the components of ground substances throughout the extracellular space
- they are attached to proteins and form proteoglycans
- Hyaluronic acid acts as a barrier in tissues against the penetration of bacteria
- Haparin acts as an anticoagulant in vitro as well as in vivo. It inhabits thrombin (an enzyme in blood plasma which causes the clotting of blood by converting fibrinogen to fibrin)
20
Q
What is Isomerism in Carbohydrates?
A
- the presence of asymmetric carbon atoms in a compound producing the following effect:
1. Sterioisomerism of the compouns
2. Confers optical activity to the compound
21
Q
What is Sterioisomersim?
A
compounds which are identical in composition and structural formula but differ in spatial configurations
22
Q
What is an Enantiomer?
A
- Molecules/ cmpounds with their structure being mirror images of each other
- D and L-sugars are referred to as enantiomers
- Only D-glucose or D-sugars are utilised by humans
- When sugar has -OH group on right it’s D- isomer
- -OH group on the left it’s L- isomer
23
Q
What is Anomerism?
A
When the sugars are in ring form and not in straight chain form- this occurs when the sugars are in solution
24
Q
What types of righs do sugars form? (Anomersim)
A
- Aldosgars form mainly pyranose ring structure
- Ketosugar form furanose ring structure
- Carbon 1, after ring formation becomes asymmetric- called an anomeric carbon atom
- If the two sugars which differ in the configuration at only C1in case of aldoses and C2 in ketoses are known as anomers- represented as alpha and beta sugars.
E.g. - alpha -D glucose and beta-D-glucose
- alpha-D fructose and beta-D-fructose
25
What is Epimerism?
- the isomers formed due to variations in the configuration of -H and -OH around a single carbon atom in a sugar molecule
- eg. mannose is a 2-epimer of glucose and galactose is a 4-epimer of glucose
26
What is Optical Activity of a Compound (sugar)?
- compounds that have asymmetric carbon atoms that can rotate the beam of plane polarized light
- an isomer which rotates the plane of polarised light to the right is called dextrorotatory (d) of (+) (D-(d)- glucose aka dextrose)
- an isomer which rotates the plane of polarised light to the left is called levorotatory (l) or (-) (D- (l)- fructose)
27
What is a Glycosidic Bond?
- linkage formed between -OH group of anomeric carbon (C1) of one sugar with any -OH group of another sugar (or alcohol)
- this results in the loss of H2O molecule
- involved in the formation of the disaccharide and polysaccharides.
28
What is the name of the most common reduction test used to test for Reducing Sugars and what is the active reagent?
Benedict's Solution Test
- Cu2+ ions (light blue solution)
29
How do Reduction Tests work for Reducing Sugars?
- The presence of a free aldehyde or ketone group cause carbohydrates to be readily oxidised and behave as the reducing agents.
- These sugars have the capacity to reduce cupric ion (Cu2+) to cuprous ion (Cu+). Therefore the reducing sugar like glucose will give positive Benedicts reactions.
- From a light blue solution to a brick red precipitate
30
How do Reduction Tests work for Non-Reducing Sugars?
In case of sucrose (non-reducing sugar), the aldehyde group of glucose and keto group of fructose are linked. It gives positive test when it gets hydrolysed to glucose and fructose.
31
What are the Sugar Derivitives of Biological Importance?
1. Sugar alcohols (Alditols): Reduction form Alcohols
2. Deoxy sugars: important constituent of DNA.
3. Amino sugars: Important constituent of GAGS (Glycosaminoglycans)
Sugar acids: Important constituents of GAGS
4. Glycosides
5. Ascorbic acid (Vit C)
32
What are some Carbohydrates of Clinical Importance?
*D-Sorbitol and D-Dulcitol, when accumulate in large amounts cause strong osmotic effects leading to swelling of cells. Cataract, peripheral neuropathy and nephropathy. *D-Mannitol: Is useful in reducing intracranial tension by forced diuresis. *Xylitol-sweetener
33
