1. Dr. Salman Ul Islam
Unit#1 BASIC CELL FUNCTIONS
Topic: Chemical composition of the body
Physiology-A
2. Classes of organic molecules
Organic molecules contain carbon backbones.
Every carbon atom will form 4 covalent bonds with other atoms, specifically other carbon
atoms as well as hydrogen, nitrogen, oxygen and sulfur atoms.
By linking together of many smaller molecules, carbon can form very large polymers
(macromolecules) many of which are important to human physiology.
3. 1. Carbohydrates
These important carbon-based molecules are vital to life in that they provide cells with
energy. Carbohydrates are composed of carbon, hydrogen, and oxygen in a set
proportion. Where n is any whole number, the formula is: Cn(H2O)n.
H— C —OH
Carbohydrates are easily soluble in water due to the polar hydroxyl (OH-) groups. Most are
sweet tasting and are also known by the common name: sugar.
4. 1. Carbohydrates
Monosaccharides are the simplest sugars. Glucose (C6H12O6) is the most abundant and is
called blood sugar because it is the major monosaccharide in blood. The common
monosaccharides in the body contain 5 or 6 carbon atoms and are called pentoses and
hexoses, respectively.
Disaccharides are carbohydrates composed of two monosaccharides linked together.
Sucrose is composed of glucose and fructose. Maltose is composed of glucose and
glucose chains. Lactose, milk sugar, is composed of glucose and galactose.
5. 1. Carbohydrates
An oxygen atom links together monosaccharides by the removal of a hydrogen atom from
one end and a hydroxyl group from the other. The hydroxyl group and the hydrogen
combine to form a water molecule. Therefore, hydrolysis of a disaccharide will break the
link formed and disconnect the two monosaccharides.
Polysaccharides are formed when many monosaccharides link together into long chains.
Glycogen in animal cells and starch in plant cells are both composed of thousands of
glucose molecules linked together.
6. 2. Lipids
Fats to the layman.
Lipids are predominantly composed of hydrogen and carbon atoms linked together by
neutral covalent bonds. Lipids are non-polar and are consequently are not very soluble in
water.
There are four main classes of lipids to be aware of in learning about human physiology.
7. 2. Lipids
1. Fatty acids. In chemistry, particularly in
biochemistry, a fatty acid is a carboxylic acid with
an aliphatic chain, which is either saturated or
unsaturated. .
If all the carbon atoms are linked by single covalent
bonds the chain is called a saturated fatty acid.
If the chain is composed of double bonds, the chain
is called an unsaturated fatty acid. Furthermore, if
only one double bond is present in the chain, then it
is a monounsaturated fatty acid, while if there is
more than one double bond present it is called a
polyunsaturated fatty acid.
8. 2. Lipids
2. Triacylglycerols, or triglycerides,
account for most lipids in the body.
They are formed by linking each of
the 3 hydroxyl groups of glycerol
with the carboxyl groups of three
fatty acids, hence the “tri” in the
name.
When a triacylglycerol is hydrolyzed,
the fatty acids are released from the
glycerol and the products can be
metabolized in order to provide
energy for cell functions.
Glycerol
9. 2. Lipids
3. Triacylglycerols have a near
relative called phospholipids.
The only difference is that one of
the hydroxyl groups of the glycerol
is linked to a phosphate. A
phospholipid has a non-polar
region in the fatty acid; thus, the
molecule is amphipathic.
Phospholipids are very important in
building membranes within the
body.
10. 2. Lipids
4. Finally, steroids are composed of 4 interconnected carbon atom rings.
Sex hormones, such as testosterone and estrogen, are examples of steroids, as well as
cholesterol and cortisol.
11. 3. Proteins
Proteins are very large
molecules composed of basic
units called amino acids.
Proteins contain carbon,
hydrogen, oxygen, nitrogen,
and Sulphur.
Proteins are highly complex
molecules that are actively
involved in the most basic and
important aspects of life. These
include metabolism,
movement, defense, cellular
communication, and molecular
recognition.
14. 4. Nucleic Acids
Nucleic acids store, transmit and express genetic
information. Nucleic acids are composed of subunits
called nucleotides.
(A) Each nucleotide is composed of a sugar phosphate
covalently linked to a base—guanine (G) in this figure.
(B) The nucleotides are covalently linked together into
polynucleotide chains, with a sugar–phosphate
backbone from which the bases—adenine, cytosine,
guanine, and thymine (A, C, G, and T)—extend.
(C) A DNA molecule is composed of two
polynucleotide chains (DNA strands) held together by
hydrogen bonds between the paired bases. The arrows
on the DNA strands indicate the polarities of the two
strands, which run antiparallel to each other (with
opposite chemical polarities) in the DNA molecule.
(D) Although the DNA is shown straightened out in
(C) it is wound into a double helix, as shown here.
