2016
Mrs: Rasha Ibrahim
Chemical Basis of life
Chapter
one
Chemical basis of life
Chapter
Biology is closely
one related to chemistry, as chemistry explains the chemical structure of living
organisms and the chemical reactions taking place inside the cells.
Lesson one
Chemical structure of organisms' bodies
(Carbohydrates)
We already know that the structure of our bodies has the following levels:
systems
organs
tissues
cells
Now, let's take a closer look at the cell:
Living cell consists of
Organic molecules
Contain C &H
Biological macromolecules
1- Carbohydrates
monosaccharide
2- Lipids
fatty acid
Inorganic molecules
Do not contain C
salts
3- Proteins
4- Nucleic acids
water
amino acids
nucleotides
Biological macromolecules:
Biological macromolecules are organic polymers containing C. They are formed of smaller
molecules called monomers through a process called polymerization. They are necessary for the
life of living organisms.
Monomers
polymerization
Polymers
Biochemistry: It is the
science concerned with
As we mentioned before that biological macromolecules are
divided into four groups:
Carbohydrates
Lipids
Proteins
Nucleic acids
studying the chemistry of
living organisms
Carbohydrates::
 Are biological macromolecules formed of a number of smaller monomers.
They include sugars, starch & fibers.
They have the general molecular formula (CH2O)n which means that they are formed of C, H
& O in the ratio 1 : 2 : 1
Importance of carbohydrates:
1-Source of energy :
Carbohydrates are considered as the main and fastest source of energy.
2-storage of energy:
-Carbohydrates are used to store energy in living organisms' bodies.
They are,
-Stored in plants in the form of starch.
-Stored in the human body in the form of glycogen in the liver and muscles.
3-carbohydrates and building the cell:
-Carbohydrates are basic component of some cell parts, such as:
-Cellulose in the cell wall of plant cells.
-Also, found in cell membranes and the protoplasm of cells.
Molecular structure of carbohydrates:
Carbohydrates are classified according to molecular structure into:
1-simple sugars
2-complex sugars
Monosaccharides
Disaccharides
1-simple sugars are:
-Soluble in water.
-Have low molecular weight.
-characterized by their sweet taste.
They're either formed of one molecule and called monosaccharide.
Or
Formed of two monosaccharides and called disaccharide.
Monosaccharides :
-Simplest form of sugar, made up of only one molecule.
-Consist of a chain of carbon atoms, each carbon atom is linked to H & O atoms.
-Monosaccharides have 3-6 carbon atoms.
-Examples of monosaccharides are:
Glucose
Fructose
Galactose
Ribose
Disaccharides :
-Two monosaccharides are together to form a disaccharide molecule.
Such as,
Glucose + Fructose
Sucrose (disaccharide)
Glucose + Galactose
Lactose (disaccharide)
Glucose + Glucose
Maltose (disaccharide )
Role of monosaccharides in energy transport inside cells:
Living organisms obtain the energy stored in carbohydrates through the following process:
1- Glucose is oxidized inside the cells (mitochondria).
2-Energy stored in chemical bonds is released and stored in Adenosine Triphosphate
compounds ( ATP ).
4-ATP transfers this energy to other parts of the cell to be used for all the vital processes inside
the cell.
2-Complex sugars:
-They are polysaccharides formed of monosaccharide monomers.
-Examples of polysaccharides:
Starch
cellulose
glycogen
-They are made of glucose molecules linked together.
-Insoluble in water.
- Has high molecular weight.
-Unlike simple sugars, they lack the sweet taste.
How to detect simple sugars in food:
We detect simple sugars in food by using Benedict's reagent which changes from blue to
orange in presence of simple sugars.
How to detect complex sugar (starch):
By using iodine solution which turns dark blue
Compare between simple and complex carbohydrates
second:
Lipids
There are biological macromolecules (polymer) made up of smaller molecules (monmers)
consisting of C, H, & O atoms.
- All lipids are insoluble in polar solvents( water), but are soluble in nonpolar solvents as
benzene & carbon tetrachloride
- Lipids are formed by union of:
- Three fatty acid + Glycerol (an alcohol containing three hydroxide group (OH) ).
Lipids
Simple lipids
Fats
Oils
Waxes
Complex lipids
Lipid derivatives
Phospholipids
Steroids
1- Simple lipids:
-Formed by the reaction of fatty acids with alcohols.
-Simple lipids are classified according to the degree of saturation into:
Lipid
Way of formation
Examples
Stored fats under the skin in
 Solid
some animals that form as
1Fats
 Saturated fatty acid+
thermal insulator
glycerol
Oils covering the feathers of
 Liquid
eater birds to prevent water
2Oils
 Unsaturated fatty acid+
penetration into their bodies
glycerol
Covering the desert plant
 Solid
leaves to keep water inside ,to
 High molecular weight
reduce its loss during
3Waxes
fatty acid +monohydric
alcohol(alcohol containing transpiration
one (OH)2-Complex lipids:
Formed of Carbon, Hydrogen, Oxygen in addition to Phosphorus & Sulfur.
Examples: Phospholipids.
Phospholipids:
-They are found in the cell membranes of both plant and animal cells.
Molecular structure: similar to that of fats except for the PO4-- group which replaces the third
fatty acid.
3-Derivatives lipids: they are lipids derived from simple & complex lipids through the process
of hydrolysis.
Examples: cholesterol and some hormones.
How can we detect lipids in food:
By using Sudan -4 reagent as it dissolves in lipids and turns its color to red.
Importance of lipids:
1-Source of energy: Though carbohydrates are considered as a fast source of energy, yet lipids
provide more energy than that obtained from the same amount of carbohydrates.
2-Building the cells:
-Makes 5% of the organic material forming the cell.
- Have an important role in the structure of cell membranes.
3- Act as thermal insulators: when stored under the skin of animals enabling them to maintain
their body temp. in cold weather.
4- Form a protective coat: for the surfaces of many plants and animals.
5-Some act as hormones e.g. steroids.
Chemical Structure of living organisms
(Protein & Nucleic acid)
Third : Proteins:
They are biological macromolecules (polymers) made up of many smaller molecules (monmers) called
amino acid( a.a).
 Made up of C, H, O and N
 About 20 types of amino acids participate in building of proteins (Glycine – Alaninie – Valine)
Molecular structure of proteins:
-The amino acid is formed of a C atom linked to:
 A basic functional amino group NH2
 An acidic functional carboxyl group
COOH.
 A terminal R group which differs from one amino acid to the other.
 Hydrogen atom (H).
Amino acids:
They are organic compounds made up of (H,O,C,N) atoms and they represent the proteins
building units.
The repeated units of amino acids are linked together to form protein,
Peptide bonds
A bond formed by joining the carboxyl group of one amino acid to the amino group of
another, with the removal of a water molecule.
Dipeptide: two amino acid molecules linked by a peptide bond.
Polypeptide: a chain of amino acids linked together by peptide bonds.
There are a wide and various possibilities to from proteins depending on:
The type , order and number of amino acids in the chain.
Amino acid
Monomer
Dipeptide compound
2linked amino acid
Polypeptide chain
Protein
3-19 linked amino acid
polymer 20 linked a.a
Classification of proteins :
Proteins are classified according to substances involved in their structure into:
1- Simple Protein
2- conjugated proteins
Simple proteins:
Formed of amino acids only.
Examples: albumin found in leaves and seeds of plants and in blood
plasma in humans.
Conjugated proteins :
Proteins consisting of amino acids associated with other elements.
Examples:
1-Nuclear proteins: contain nucleic acids.
2-phosphoproteins: contain phosphorus element e.g casein (milk protein)
3-Thyroxine: hormone secreted by the thyroid gland and contains iodine .
4-Hoemoglobin: contains iron .
Importance of proteins:
1- Essential for body growth.
2- One of the basic components of cell membranes and chromosomes.
3- Forms: -muscles, tendons, ligaments, organs, glands, nails and hair.
(Hooves and horns of animals, and spider webs are formed from proteins.)
4- Involved in the structure of body fluids like blood and lymph.
5- Involved in the structure of enzymes and hormones which stimulates and regulates vital
body processes.
How can we detect proteins:
We detect proteins by using Biuret reagent which changes from blue to purple in presence of
proteins.
Fourth:
Nucleic acids
They are biological macromolecules (polymers) made up of smaller molecules( monomers)
called nucleotides.
Nucleic acids composed of H,O,C,N and P atoms
Nucleotides: The basic building unit of nucleic acid.
Consist of three units:
1-Pentose sugar: (formed of five carbon atoms )
2-Phosphate group (PO4): connected to the
carbon no.5 in the pentose sugar.
3-Nitrogenous base : connected to carbon no.1 of
the sugar molecule
-Adenine ( A )
- Guanine ( G )
-Cytosine (C )
-Uracil ( U )” uracil found in RNA only instead of thymine in DNA”
- Thymine (T )
-The nucleic acids differ according to type the of pentose sugar and nitrogen bases forming
them.
Classification of nucleic acids:
1- Deoxy ribonucleic acid (DNA).
2- Ribonucleic acid (RNA).
The differences between DNA & RNA
P.O.C
Type of sugar
Nitrogenous bases
No. of strands
Location
Importance
Deoxyribonucleic acid(DNA)
Deoxyribose sugar(lack Oxygen
atom)
A – G – T- C
Two strands
Inside the nucleus of the cell,
involved in the structure of
chromosomes.
Carries the genetic information
which responsible for
1- Appearing the distinctive
characteristics of living
organism
2- Organizing the vital
activities of the cell
Ribonucleic acid (RNA)
Ribose sugar
A–G–U–C
Single strand
Transcribed from DNA inside
the nucleus then transferred into
the cytoplasm.
Building (synthesizing )
proteins which responsible for:
1- Appearing the genetic
traits.
2- Organizing the vital
activities of the cell
Lesson three
Chemical Reactions in Organisms' Bodies
Metabolism: Biochemical reactions that occur inside living organisms' bodies that are essential
for growth, obtaining energy and repairing damaged tissues, the stopping of these reactions
causes the death of the living organism.
Metabolism
Metabolism is divided into:
1-Catabolism: the process of breaking down of macromolecules into simple ones to extract the
energy stored in the chemical bonds of these molecules .
 Example: releasing an energy from glucose by oxidation process during cellular
respiration.
2-Anabolism: the process by which small molecules are used to build complex macromolecules
through a series of reactions that consume energy .
 Example: building of proteins from amino acids.
 Photosynthesis in green plants.
Enzymes
Activation energy:
The minimum energy required to
start a chemical reaction.
Chemical reactions require high activation energy to
occur; a catalyst is used to lower the activation energy
required for the reaction to occur inside the cell which
speeds up the reaction. Such catalysts are called
enzymes.
Enzymes:
Biological catalysts made up of protein molecules that speed up chemical reactions inside
the cells.
The enzyme is made up of a combination of a great number of amino acids forming a chain or
more of polypeptide between each others.
Properties of enzymes:
1-Enzymes, like other chemical catalysts, speeds chemical reactions without being consumed in
the reaction.
2-Enzymes are affected by the concentration of hydrogen ions (pH) and temp.
3-Unlike other catalysts, enzymes are highly specific, meaning that each enzyme is specialized
for only one reactant substance called substrate and specialized for only one or few types of
reactions.
4-Enzymes lower the activation energy required to start chemical reactions.
Factors affecting the enzymes actions:
There are several factors that affect the action of enzymes:
1-The concentration of the enzyme.
2-The concentration of the substrate.
3-Tempratrue
4-pH
5-Presence of inhibitors.
We will study the effect of some of these factors on the speed of enzyme action.
The relation between temperature and enzyme action:
-The protein nature of enzymes makes it very sensitive to temperature.
-When compared to other chemical reactions enzymes work in a narrow range of temp.
Enzyme optimal temperature:
It is the temperature at which the enzyme is more
active(37 - 40◦C)
-Each enzyme has different optimum temp. that ranges
from 37 to 40, it is the temp at which the enzyme
becomes more active.
-when the temp. rises above the optimal temp. the enzyme
activity starts to decreases gradually until it reaches a
temp. at which it stops completely due to change in the enzyme natural composition.
Enzyme minimal temperature:
It is the temperature at which the enzyme is less active.
-on the other hand , when the temp. drops below the optimal temp. the enzyme activity
decreases gradually, until it reaches a minimum temp. at which it stops completely at 0 0C, but
on raising the temp. the enzyme is reactivated.
Potential of hydrogen (pH):
The potential of hydrogen is a measure of the concentration of hydrogen ion H+ in the solution
and it determines whether the solution is acidic, alkaline or neutral.
-solutions with pH greater than 7 are called alkalis or bases.
-solutions with pH less than 7 are called acids.
-solutions with pH that equals 7 are called neutral solutions.
The pH of any solution can be determined using pH indicators.
Relation between pH and enzymes activity:
Enzymes are formed of proteins containing an acidic carboxyl group COOH-and an amino basic
group NH2, so, enzymes are affected by changing the pH.
Every enzyme has an optimal pH at which it works with maximum efficiency, if the pH drops
or rises above this optimal pH the activity of the enzyme decreases gradually until it stops
completely.
Examples:
-Pepsin works in acidic pH
-Trypsin works in basic or alkaline pH
-Most enzymes work at a pH of 7.4 .
(due to the amino acid molecules that forming the enzyme contain an acidic carboxyl group and
a basic amino group.)