EHSAN ULLAH Biomolecules
Lecture 2
M.PHIL
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Carbohydrates
Carbohydrates
• They are polyhydroxy aldehydes or ketones or which yield such compounds on
hydrolysis. Carbohydrates contain either aldehyde or Ketone as functional
groups attached to one of the carbon atoms. They also contain two or more
hydroxyl groups.
• They are the most abundant organic biomolecules in nature( cellulose).
Carbohydrates are organic compounds that are mainly composed of carbon,
hydrogen and oxygen.
• The name carbohydrates means that they are hydrates of carbon in which
hydrogen and oxygen is present in the same ratio as in water that is 2:1. But now
many carbohydrates are known that contain hydrogen and oxygen in different
proportion.
• Examples of carbohydrates are glucose, sucrose, starch, cellulose etc.
Sources of Carbohydrates
• We know carbohydrates are an important part of any human’s diet. Some
common sources of carbohydrates are:
1. Potatoes
2. Maize
3. Milk
4. Honey
5. Bread
6. Rice
Classifications
• Carbohydrates are classified into three groups, i.e. monosaccharides,
oligosaccharides and polysaccharides.
1.Monosaccharides
• Monosaccharides are simple sugars. They are not hydrolyzed (broken down by
the addition of water) into more simple units.
• They are easily soluble in water. They are sweet in taste.
• They have empirical formula (CH2O)n containing the same ratio of hydrogen
and oxygen as in water, i.e. 2:1.
• They contain either aldehyde or keto group.
• They have carbon backbone that may contain from three to seven carbon
atoms.
• They have names which end in -ose. Those with three carbon atoms are celled
trioses, with four atoms-tetroses, with five atoms- pentoses, and so on.
Glucose (chain form)
• Trioses are the simplest monosaccharides with three carbon atoms.
• Glyceraldehyde is triose with aldehyde group. Ribose is a pentose. It also
contains aldehyde group.
• Ribulose is its ketonic form. Glucose, fructose and galactose are hexoses.
• They have the same empirical formula (C6H12O6) but different structural
formula. Such molecules with the same empirical formula but different structures
are called isomers.
• Glucose is aldehyde while fructose is ketone. Therefore glucose, fructose and
galactose are isomers. They are inter-convertible.
• Ribose and glucose when put in water form ring structures.
• Monosaccharides are white crystalline powders.
• Monosaccharides may be further classified depending on the number of carbon
atoms:
(i)Trioses (C3H6O3): These have three carbon atoms per molecule: Glyceraldehyde,
Dihydroxy acetone.
(ii)Tetroses (C4H6O4): These monosaccharides have four carbon atoms per
molecule. Example: Erythrose, Threose.
(iii) Pentoses (C5H10O5): Ribose, Ribulose, Xylulose, Arabinose, Lyxose.
(iv) Hexoses (C6H12O6): Glucose, Fructose, Galactose, Mannose, Allose, Sorbose,
Idose.
(v) Heptoses (C7H14O7): Sedoheptulose.
Do you know dear students?
• When two monosaccharides join together—Glysodic bond (-C-O-C-) is
formed.
• Pentoses and Hexoses are the most common sugar of the cell.
• Alpha glucose, when the hydroxyl (OH) group is on the opposite side of
the –CH2OH group.
• Beta glucose, when the hydroxyl (OH) group is on the same side as the –
CH2OH group.
• In Deoxyribose sugar one Oxygen is less on C-2.
• Five sided ring, like ribose, are called furanoses.
• Six sided ring, like glucose, are called pyranoses.
• Raffinose is found in Sugarbeet.
• Glycosidic bond is present between sugar unit (-C-O-C-).
SLOs based question
Q1 What are carbohydrates?
• Carbohydrates are biomolecules comprising carbon, hydrogen and oxygen atoms.
They are an important source of energy. They are sugars, starch and fibres found
in fruits and vegetables.
Q2 How are the carbohydrates classified?
• Carbohydrates are classified into the following:
• i) Simple carbohydrates ii)Complex carbohydrates
Q3 How are the carbohydrates important to our body?
• Carbohydrates provide energy to the body. It breaks down into glucose and enters
our bloodstream. The body cells utilize glucose to produce ATP.
Q4 Name a few sources of carbohydrates.
• Carbohydrates are obtained from a variety of sources such as bread, milk,
potatoes, cookies, corn, etc.
Q5 How are the carbohydrates digested?
• Carbohydrates start being digested in the mouth by the action of salivary amylase.
They are not completely broken down in the stomach, but in the intestine.
Q6 What are simple carbohydrates? Give examples.
• Simple carbohydrates are the ones that are quickly broken down by the body to be
converted into energy. Fruits, milk and milk products are the main sources of
simple carbohydrates.
Q7 How are complex carbohydrates different from simple carbohydrates?
• Complex carbohydrates are the ones in which the sugar molecules are strung in
long, complex chains. Peas, beans, vegetables and grains are the important
sources of carbohydrates.
Q8 What are the three types of simple carbohydrates?
• Three types of simple carbohydrates include:
• Monosaccharides
• Disaccharides
• Polysaccharides
Q9 Name some bad carbohydrates that are harmful to the body.
• The bad carbs include:
i) White bread ii) Sugary drinks iii) Pastries iv) Candies v)chocolates
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