biochemistry

1. BIOCHEMISTRY
LECTURE II

2. • Structures of major compounds of the body
• Carbohydrates
• Lipids
• Amino Acids

3. Structures of major compounds of the body
• Although cells are 70-95% water, the rest consists mostly of
Carbon-based compounds.
• Proteins, DNA, Carbohydrates, and Lipids are all composed of
carbon atoms bonded to each other and to atoms of other
elements
• These elements commonly include Hydrogen (H), Oxygen (O),
Nitrogen (N), Sulfur (S), and Phosphorus (P).

4. • Carbon atoms are versatile and can form up to four
bonds (single, double, or triple) and rings.
• Functional groups in organic molecules confer
chemical reactivity and other characteristics.
• Functional groups are specific groups of atoms within
molecules that are responsible for the characteristic
chemical reactions of those molecules

7. Oxidized and Reduced Groups
Oxidation is the loss of electrons and results in the loss of hydrogen atoms together with one
or two electrons or the gain of an oxygen atom or hydroxyl group.
Reduction is the gain of electrons and results in the gain of hydrogen atoms or the loss of an
oxygen atom.

8. Groups That Carry a Charge
• In biomolecules, the major anionic
substituents are carboxylate groups,
phosphate groups, or sulfate groups (the “-
ate” suffix denotes a negative charge)
• Compounds that contain nitrogen are usually
basic and can acquire a positive charge

11. Carbohydrates
CARBOHYDRATES ARE ALDEHYDE OR KETONE DERIVATIVES OF POLYHYDRIC ALCOHOLS.
If the carbonyl group is an aldehyde, the sugar is an aldose
if the carbonyl group is a ketone, the sugar is a ketose.
Carbohydrates include sugars and the polymers of sugars.

12. • Monosaccharides are those carbohydrates that cannot be hydrolyzed into
simpler carbohydrates:
• Disaccharides are condensation products of two monosaccharide units.
• Oligosaccharides are condensation products of two to ten
monosaccharides.
• Polysaccharides are condensation products of more than ten
monosaccharide units.

15. Monosaccharides
• Monosaccharides are the simplest form of carbohydrates which
cannot be broken down to simpler sugar by hydrolysis.
• Chemical composition- Formula Cn(H2O)n- n(3-7)
• Classification of Monosaccharides
• They may be classified on the basis of number of carbon as
trioses, tetroses, pentoses, hexoses, or heptoses, depending upon
the number of carbon atoms; and as aldoses or ketoses depending
upon whether they have an aldehyde or ketone group.

16. • Glucose- Occurs in fruits, like grapes, and honey
• It is white crystalline solid readily soluble in water and sweet in
taste.

17. Fructose
• Most common sugar in fruits, honey. Sweetest among all the
natural sugar.

18. Galactose
• Occurs in combined form as constituent of lactose(is not found
free in nature). It is rarely found in plants.

19. Ribose and deoxyribose
• In DNA : deoxyribose sugar
In RNA: Ribose sugar
•

20. The stereospecificity of D-
glucose is still frequently
denoted in medicine by the
use of its old name,
dextrose. A solution
used for intravenous
infusions in patients is a 5%
(5 g/100 mL) solution of
dextrose.

21. DISACCHARIDES
• These are carbohydrates that yield two
molecules of same or different types of
monosaccharides on hydrolysis.
• The general formulais Cn(H2O)n-1
• LACTOSE
• Lactose is called as milk sugar.
• It is present in milk and is made up of
monosaccharides - glucose and galactose.
• Glucose + Galactose= Lactose

22. MALTOSE SUCROSE
• Maltose is also known as ‘malt
sugar’ and is present
in germinating cereals, malt
etc.
• It is the intermediate product
in the hydrolysis of starch by
amylase in the alimentary
canal.
• It is made up of 2 molecules of
glucose.
• Glucose + Glucose=
Maltose
Sucrose is called as ‘table sugar’ or ‘cane
sugar’.
It is the common sugar and is widely
distributed in all photosynthetic plants.
It does not exist in the body but occurs in
sugarcane, pineapple, sweet potato and
honey.
It is made up of glucose and fructose.
Glucose + Fructose= Sucrose

23. Glycosidic bond
• A glycosidic bond is a type of covalent bond that joins a
carbohydrate molecule to another group, which may or may not
be another carbohydrate.
The subunits of disaccharides and polysaccharides are linked by
glycosidic bonds.
• During this bond formation water is formed and thus is called as
Condensation.

24. POLYSACCHARIDES
• Polysaccharides are long carbohydrates molecules of repeated monomer
units joined together by glycosidic bonds.
• Number of monomers- 10 to thousands.
• High molecular weight and colloidal size.
• Branched or unbranched linear chains
• Sparingly soluble in water.

25. Classification
• Based on Composition
• A. Homopolysaccharides
Formed by one type of monosaccharide.Eg. Glycogen, starch and
cellulose.
• B. Heteropolysaccharides
Formed by more than one type of monosaccharide. Eg.
Mucopolysaccharides, glycoproteins, peptidoglycans.
• Based on functions
• A) Food storage polysaccharides : Starch, Glycogen, Inulin
B) Structural polysaccharide: Cellulose, Chitin
C) Mucopolysaccharides :

26. GLYCOGEN
• Glycogen is the storage homopolysaccharide in
animals.
• It is a more highly branched structure than
amylopectin, with chains of 12–14 α -D-
glucose residues (in α[1 → 4]-glycosidic
linkage), with branching by means of α(1 → 6)-
glycosidic bonds.
• It is mainly stored in the muscles and liver of
mammals.
• Fungi also store food in the form of glycogen.
• The glycogen is converted to glucose as and
when required.Hydrolysis

28. Lipids
• COMPOSITION
• Lipids form a group of organic compounds which are widely distributed in living
organisms.
• Made up of carbon, hydrogen and oxygen but the proportion of oxygen is much less
than 2:1.
• Most lipids are esters formed by condensation of alcohols and fatty acids.
• PROPERTIES
• Insoluble in water.
• Soluble in organic solvents like chloroform, alcohol, acetone etc.
•

30. SIMPLE LIPIDS: NEUTRAL FATS OR TRUE FATS
• Fat molecule is composed of 1 molecule of glycerol and 1-3
molecules of fatty acids.
Glycerol

31. Fatty Acids
• Fatty acids are carboxylic acid with hydrocarbon side chains.
They are the simplest form of lipids , They exist in the body either
as free acids or fatty acyl esters such as triacylglycerol. The fatty
acids are released from these lipids on hydrolysis by lipases.
• Fatty acids may be divided into (1) saturated fatty acids and (2)
unsaturated fatty acid

32. Unsaturated Fatty Acids
• These are fatty acids which contain double bonds.
• They have general formula (CnH2n-1 COOH).
• They are subdivided into
• (a) Monounsaturated fatty acid : These are fatty acids
containing one double bond. (eg) Oleic acid. Oleic acid
• CH3 (CH2)7CH = CH (CH2)7COOH
(b) Polyunsaturated fatty acid : These are fatty acids that
contain more than one double bond. (eg) linoleic acid, linolenic
acid, arachidonic acid.

33. Saturated Fatty Acids
• These are fatty acids which do not contain double bonds.
• They have general formula CnH2n+1 COOH.

34. Essential fatty acid (EFA)
• The fatty acids that cannot be synthesised by the body and
therefore should be supplied in the diet are known as essential
fatty acids.
Chemically they are polyunsaturated fatty acids (PUFA), namely
linoleic acid, linolenic acid and arachidonic acid.

35. Tryglycerides
• Triglycerides are simple lipids in which glycerol backbone
is esterified with three fatty acids
• a reaction of an alcohol with an acid to produce an ester and
water.

37. Simple (Pure) and mixed fats
• If the three hydroxyl groups are esterified with same type of
fatty acid then the lipid is called as simple glyceride.
• If the three hydroxyl groups are esterified with different type of
fatty acids, the lipid is called as mixed glyceride.

38. CONJUGATED LIPIDS
• PHOSPHOLIPIDS
• Phosphoglycerides, are membrane lipids in which two fatty acids are attached in
ester linkage to the first and second carbons of glycerol, and a highly polar or
charged group is attached through a phosphodiester linkage to the third carbon.

39. Special property: amphipathic
Has polar and non-polar ends
Polar hydrophilic- phosphate group attached to glycerol
and a positively charged base.
Non-polar hydrophobic- two long fatty acids.
Due to this nature they arrange as a bilayer.
Phosphatidylcholine is one of the major
phosphoacylglycerols found in
membranes (see Fig. 5.19). The
amine is positively charged at neutral pH,
and the phosphate is negatively charged.
Thus, the molecule is
amphipathic: it contains large polar and
nonpolar regions. Phosphatidylcholine is
also called lecithin

40. Sphingolipids
• Sphingolipids do not have a glycerol backbone; they
are formed from sphingosine
• Sphingosine is derived from serine and a specific fatty
acid, palmitate
• Ceramides are amides formed from sphingosine by
attaching a fatty acid to the amino group. Various
sphingolipids are then formed by attaching different
groups to the hydroxyl group on ceramide

41. LIPOPROTEINS
• Chylomicron (largest; lowest in density due to high lipid/protein
ratio; highest in triacylglycerols as % of weight)
• VLDL (very low density lipoprotein; 2nd highest in triacylglycerols
as % of weight)
• IDL (intermediate density lipoprotein)
• LDL (low density lipoprotein, highest in cholesteryl esters as % of
weight)
• HDL (high density lipoprotein, highest in density due to high
protein/lipid ratio).

42. DERIVED LIPIDS
• This class includes a large variety of highly lipid-like compounds or compounds
derived from the intermediates of lipid metabolism.
These compounds can be classified into two main groups or categories.
A) Terpenes (Isoprenoids)
B) Icosanoids
• This is a large class of derived lipids formed from combinations of two or more units
of a common precursor molecule, named isoprene.
• Isoprene is a five carbon compound derived from condensation of acetyl co-
enzyme A molecule.
• Isoprene units can be linked in terpenes to form a variety of straight chain or cyclic
molecules.
• Terpenes include steroids , sterols, fat soluble vitamins, bile salts, pigment etc

43. STEROID
• Steroids are not formed from fatty acids but
have some lipid like characters.
• They posses 17 carbon nucleus of four fused
hydrocarbon rings.
• Various steroids differ in the number and
position of double bonds between carbon atoms
and in the side group linked to the ring.
• Examples: Steroids include sterols,
like cholesterol, ergosterol, bile salts, sex
hormones and pigments.

45. Cholesterol
Cholesterol is the steroid precursor
in human cells from which all of the steroid hormones are synthesized by modifications to the
ring or C-20 side chain. Although cholesterol is not very water-soluble, it is converted to
amphipathic water-soluble bile salts such as cholic acid. Bile salts line the surfaces of lipid
droplets called micelles in the lumen of the intestine,
where they keep the droplets emulsified in the aqueous environment.
FIGURE

46. Icosanoids
• Prostaglandins :
These are hormones-like
compounds. Prostaglandins
are hydroxy derivatives of 20 carbon
polyunsaturated fatty acids.
• Found in human seminal fluid, uterus,
stomach lungs etc.
• Functions:
Inflammation
• Allergic reaction
• Blood clotting
• Smooth muscle contraction
Thromboxanes :
They are formed in the
blood platelets and are
associated with blood
clotting.
Leucotrienes
These are secreted
by leucocytes and include
contraction of muscle in the
lining of air passages to the
lungs.
Their overproduction causes
asthmatic attacks

47. PROTEIN
• SOURCES OF PROTEIN
Proteins are obtained from
animal and plant sources.
The animal sources of
proteins include milk, egg,
meat, fish, liver etc.
Plant sources of proteins are
pulses, nuts and cereals.

48. AMINO ACIDS
• Amino acids are the simplest units of a protein molecule and
they form the building blocks of protein structure.

49. Thank you!