Chemical And Cellular Basis Of Life - 1

Question 1

Elemental composition of living matter

Answer 1

92 - 20-25 - 25 - 17 - 96 - 4

92 elements naturally occur in earth’s crust.
Of which, about 20-25% elements are essential to continue healthy life and reproduction. (about
25- elements are essential for humans and about
17 for plants).
O,C,H,N make up 96% of living matter.
CaPKS - 4%
make up most of the remaining 4% of the mass of the organism.

Question 2

Humans - Elemental composition

Answer 2

C, H, O, N- accounts for 96.3% of the body mass
accounts for the remaining 3.7% -
1. Ca, Mg, K, Na
2. PiCkleS - P, Cl, S
3. trace elements - VIBEZ - V, I, B, Zn - CSMF - 3,3,2,2 -
Cu, Co, Cr, Se, Si, Sn, Mo, Mn, F, Fe

Question 3

Physical and chemical properties of water important for life

Answer 3

Water is a vital inorganic molecule

1. Vital chemical constituent of living cell
2. Provides a biological medium for all organisms

chemical structure of water molecule. Physical and chemical properties of water molecule provide the ability to render the vitality.
a small,
polar and
angular molecule.

Question 4

Polarity?

Answer 4

δ+ partial positive δ-partial negative

Polarity is an uneven charge distribution within a molecule. In water molecule, oxygen atom is slightly negative and hydrogen atom is slightly positive. Weak attractions between the slightly polar hydrogen atom of one water molecule and the slightly polar oxygen atom of adjacent water molecuole are known as hydrogen bonds. These hydrogen bonds play a major role in maintaining all the properties of water.

Question 5

properties of water arise due to attractions of different water molecules

Answer 5

In liquid form its H bonds are very fragile. H bonds form, break and reform with great frequency.

Question 6

Four major properties of water to maintain life on earth

Answer 6

• Cohesive behavior
• Ability to moderate temperature
• Expansion upon freezing
• Versatility as a solvent

Question 7

Cohesive behavior

Answer 7

Attraction between water molecules due to hydrogen bonding is known as cohesion.

Attraction between water molecules and other substances are known as adhesion.

Both of the above properties of water allow it to act as a transport medium.

Due to cohesion between water molecules, water and dissolved substances such as minerals and nutrients transport through vascular tissues, xylem and phloem against gravity.

Adhesion between water molecules and cell walls also helps in conduction of water and dissolved substances.

Water has a high surface tension.

This ability is given to water molecules, due to cohesion between the water molecules. Therefore, in an aquatic system, upper surface water molecules are attracted by lower surface molecules and it forms a water film.

Small insects e.g. water skaters can walk on the surface of a pond.

Question 8

Ability to moderate temperature

Answer 8

Water can absorb or release a relatively high amount of heat energy by a slight change in its own temperature.

thermal buffer

Due to the high specific heat, water will function as thermal buffer in living system and aquatic bodies during the temperature fluctuations on earth.

Due to the high heat of vaporization, with the minimum loss of water an organism can release much heat energy. Therefore, body surface of an organism maintained as cool surface.

e.g.

Prevent from overheating.

Evaporation of sweat from human skin helps to maintain the body temperature at constant level.

Transpiration in plants keeps the plant body surface as a cool surface and prevent from becoming too warm in the sunlight.

Question 9

Expansion upon freezing

Answer 9

Usual - increase in temperature reduces their density,
a decrease in temperature increases their density.

When the temperature of water falls below 4 ̊C, it begins to freeze and forms a crystalline lattice called ice cubes.

water has the maximum density at 4 ̊C.

Hence, ice floats on the surface of water bodies.

It is an important property of water in polar regions, where, organisms in aquatic bodies can survive during the winter.

Question 10

Versatility as a solvent

Answer 10

Cuz of polarity.

Polar molecules (e.g. Glucose),
non polar ionic (e.g. NaCl),
both polar and ionic (e.g. lysozymes)

can dissolve in water, because water molecules surround each of the solute molecules and form hydrogen bonds with them.

Solubility depends on polarity and not in their ionic nature.

Question 11

Chemical Nature and Functions of Main Organic Compounds of Organisms

Carbohydrates

Answer 11

Most abundant group of organic compound on earth

Major elemental composition is C, H, and O

Hydrates of carbon contain the same proportion of H: O which equals to 2:1 as in water

General formula is Cx(H2O)y

Three major groups of carbohydrates are
monosaccharides,
disaccharides and
polysaccharides

sugars (monosaccharides and disaccharides) and polysaccharides.

Question 12

Monosaccharides

Answer 12

simplest form of carbohydrates having general molecular formula as (CH2O)n

C varies from 3-7

reducing sugars,
water soluble and occur in
crystalline form.

• 3C- Triose e.g. Glyceraldehydes
(Phosphoglyceraldehyde - derivative of Triose)
• 4C- Tetroses.g. Erythrose (rare in nature)
• 5C- Pentoses.g. Ribose, Deoxyribose, Ribulose
(RUBP is a derivative of ribulose)
• 6C- Hexoses e.g. Glucose, Fructose, Galactose

Type of carbonyl (Keto, aldo)group, they are classified as;
a. Aldoses-glucose, galactose b. Ketoses-fructose

In aqueous media some monosaccharides are in ring form

Question 13

Disaccharides

Answer 13

They are sugars formed by joining two monosaccharides by a glycosidic bond

Glycosidic bond is formed by
removal of a water molecule
from two adjacent monosaccharides
by a condensation reaction.

Water molecule is formed
from OH group of one monosaccharide molecule and
H from adjoining monosaccharide molecule.

G + G = Mal
G + Gal = Lact
G + F = Sucr
Condensation

Maltose and lactose are reducing sugars and sucrose is a non reducing sugar.

Question 14

Polysaccharides

Answer 14

macromolecules and biopolymers.

few hundred to a few thousand monosaccharide subunits

non crystalline, water insoluble, and not considered as sugars.

storage components, others contribute to the structure of living organisms

function they are categorized as 
storage polysaccharides and 
structural polysaccharides.

• Storage- Starch, Glycogen
• Structural- Cellulose, Hemicellulose, Pectin

architecture they are categorized as
• Linear forms- Cellulose, Amylose
• Branched forms- Glycogen, Amylopectin, Hemicellulose

Question 15

Polysaccharide
Monomer
Functions

Answer 15

Starch
Glucose
Stored in plants
Glycogen
Glucose
Stored in animals and fungi
Cellulose
Glucose
Component of Cell wall
Inuline
Fructose
Stored in tubers of Dhalia
Pectin
Galacturonic acid
Component of Middle
lamella of plant cell wall
Hemicellulose
Pentose
Component of Plant cell walls
Chitin (nitrogen
containing polysaccharide)
Glucosamine
Component of Fungal cell walls and exoskeleton of Arthropods

Question 16

Functions of carbohydrates?

Answer 16

Monosaccharides - CEB
• Energy source
• Building blocks of 
disaccharides and polysaccharides (disaccharides such as maltose, sucrose and polysaccharides such as starch, glycogen)
• Components of nucleotides (DNA, RNA)

Disaccharides - SLS
• Storage sugar in milk- Lactose
• Translocation in phloem –Sucrose
• Storage sugar in sugarcane- Sucrose

Polysaccharides

a.) Storage polysaccharides-
• starch stores glucose as energy source in plants and chlorophytes
• glycogen stores glucose as energy source in animals and fungi
• inulin stores fructose as energy source in Dahlia tubers

b.) structural polysaccharides-
• Cellulose in the cell walls of plants and chlorophytes
• Pectin in the middle lamella of plant tissues.
• Hemicellulose in cell walls of plants.
• Peptidoglycan in the cell walls of prokaryotes.
• Chitin in the cell walls of fungi and in exoskeleton in Arthropods.

Question 17

Lipids

Answer 17

• Diverse group of
hydrophobic molecules

• Large biological molecules but
not considered as polymers or macromolecules.

• Consist of C, H, O and H:O ratio is not 2:1.
Comparatively more H are present.

• Biologically important types of lipids:
Fats,
Phospholipids and
Steroids.

Question 18

Fats

Answer 18

made up of glycerol and fatty acids;

Glycerol belongs to alcohol group having 3 carbons
where each of them bear single hydroxyl group.

Fatty acids are hydrocarbon chains with long (16-18) carbon skeleton
with a carboxyl group at its one terminal.

Fatty acid molecules bind to each hydroxyl group of glycerol by ester bond. Resulting fat molecules are called as triacylglycerol.

Hydrocarbon chains of fatty acids contribute to the hydrophobic nature of the fats. Based on the nature of hydrocarbon chains of fatty acids, they are categorized as

a) Saturated fats-
fats are made up of saturated fatty acids:
fatty acids with hydrocarbons having no any double bonds.
animal fats
mostly solid at room temperature.
e.g: butter

b) Unsaturated fats-
fats are made up of unsaturated fatty acids-
fatty acids with hydrocarbons having one or more double bonds.
Usually plant fats
mostly liquid in room temperature.
e.g: vegetable oils.
Unsaturated fats may classify based on the nature of their double bonds. a) Cis Unsaturated fat
b) Trans Unsaturated fat

Consumption excess saturated fats and trans unsaturated fats contribute arthrosclerosis.

Question 19

Phospholipids

Answer 19

major components of the cell membranes.

composed of two fatty acids and one phosphate group attached to one glycerol molecule.

phosphate group gives the negative electrical charge to the phospholipid molecule.

additional polar molecule or small charged molecule is also linked to the phosphate group
e.g. choline.

The two ends of the phospholipids show different behavior.
The hydrocarbon tails are hydrophobic while
phosphate group and its attachment (head) are hydrophilic.

Question 20

Functions of Lipids

Answer 20

• food reserve as energy source (triglycerides such as fats and oils)
• maintain the fluidity of plasma membrane (phospholipids, cholestrol)
• act as signaling molecules (eg. Hormones) that travel through the body
• found as components of animal cell membrane (cholesterol)

food reserve
fluidity
signaling molecules
animal cell membrane components

Question 21

Protein

Answer 21

made up of amino acids.

20 amino acids are involved in the formation of proteins.

Elemental composition is C, H,O,N and S.

At the centre of the amino acid is an asymmetric carbon atom except in glycine.

Each amino acid is composed of an
amino group, a
carboxyl group, a
hydrogen atom and a
variable group symbolized by R, which is an alkyl group.
In the case of glycine R is replaced by H atom.
The R group also called the ‘side chain’ differs with each amino acid where as the other groups are in the ‘ back bone’ (including the H atom).

(Thereof R chain is involved in tertiary structure formation)

Amino acids may have one or more carboxyl groups and amino groups.

Amino group has alkaline nature
and carboxyl group has acidic nature.
When both characteristics are found in one molecule they are known as amphoteric molecules.

amino acids are amphoteric.

Two Amino acids undergo condensation reaction by removing a water molecule from both and result a bond known as peptide bond;

Protein is composed of one or more polypeptide chains which are composed of amino acids.

Question 22

Levels of protein structures

Answer 22

There are four levels of structure which play important roles in their functions;

a) Primary
b) Secondary
c) Tertiary
d) Quaternary

Question 23

a) Primary structure

Answer 23

The unique sequence of linearly arranged amino acids linked by peptide bonds is the primary structure of proteins.

Question 24

b). Secondary structure

Answer 24

The primary structure of a single polypeptide chain coils and folds, as a result of intra molecular hydrogen bonds between the oxygen atoms and the hydrogen atoms attached to the nitrogen atoms, of the same poly peptide chain backbone, to form the secondary structure, which is either β pleated or alpha helical.
• Alpha helix- e.g.Keratin.
• β pleated sheet e.g.spider’s silk fiber

Question 25

b) Tertiary structure

Answer 25

Usually the secondary polypeptide chain 
bends and folds extensively forming a 
precise 
compact 
unique, 
functional and 
3D shape resulting from following 
interactions between the side chain/ R-group of amino acids;
• H bonds
• Disulphide bonds
• Ionic bonds
• Van der Waals interactions/ Hydrophobic interactions
e.g.most of the enzymes, myoglobin, albumin

Question 26

c) Quaternary structure

Answer 26

Aggregation of two or more polypeptide chains involve in the
formation of one functional protein.
Separate chains are called protein subunits
which were held together by inter and intra-molecular interactions.
e.g.Haemoglobin, Collagen

Question 27

Denaturation of proteins

Answer 27

Denaturation of protein is the loss of specific chemical three dimensional shape due to the alteration of weak chemical bonds and interactions.

Question 28

Agents affecting the denaturation

Answer 28

1. High temperature and high energy radiation
2. Strong acids, alkaline and high concentrations of salts
3. Heavy metals
4. Organic solvents and detergents

Question 29

Functions of the proteins

Type of protein? Example? Functions?

Answer 29

Catalytic protein Pepsin, Amylase Catalyze biochemical reaction
Structural protein Keratin, Prevent desiccation
Collagen Provide strength and support
Storage Ovalbumin Storage protein in egg
Casein Storage protein in milk
Transport Haemoglobin Transport O2 and CO2
Serum albumin Transport fatty acids
Hormones Insulin Regulate blood glucose level
Glucagon
Contractile/ Motor Actin/Myosin Contraction of muscle fibres
Defensive Immunoglobins Eliminate foreign bodies

Question 30

Nucleic acids

Answer 30

Nucleic acids are
Polymers exist as
polynucleotides made up of
monomers called nucleotides.

C, H, O, N and P

Nucleic acids are 
macromolecules, biopolymers. There are 
two types of Nucleic acids: 
DNA (Deoxyribo nucleic acids) and 
RNA (Ribonucleic acids).

Question 31

Structure of nucleotides

Answer 31

Nucleotides have 3 components; namely
pentose sugar,
nitrogenous base and a
phosphate group

Question 32

A nucleotide without a phosphate group

Answer 32

is called a nucleoside.
e.g. Adenosine, 
Guanosine
Cytidine,
Uridine,
Deoxythymidine

Question 33

Pentose sugar

Answer 33

Pentose sugars are two types; namely
Deoxy ribose and
ribose
(in deoxyribose one oxygen atom is less than in ribose)

Question 34

Nitrogenous bases

Answer 34

There are
two major groups of nitrogenous bases:
1. Purines- larger in size with two rings
2. Pyrimidines- smaller in size with a single ring

In purines there are
two types; namely Adenine, Guanine. In
pyrimidens there are three types, Thyamine, Uracil and Cytocine.
Bases are commonly represented by letters A, G, T, U and C respectively.

Question 35

Phosphate group

Answer 35

It gives the nucleic acids the acidic nature.

Question 36

Formation of nucleic acids?

Answer 36

Millions of nucleotides join by
phospho-di-ester bond to form
polynucleotide chains by
condensation between the
–OH group of the phosphate of one nucleotide with the
–OH attached to 3rd carbon of pentose sugar of the other. These bonds results in a
backbone with a repeating pattern of
sugar-phosphate units.
Nucleic acids are
linear polymers of nucleotides. There are
two kinds of nucleic acids depending on the type of the sugar molecules involved. If the sugar molecule in the nucleotide is
deoxyribose,the nucleic acid is (DNA). If the pentose sugar is
ribose, then the nucleic acid is RNA.

DNA contains Adenine, Thymine, Guanine and Cytosine and

RNA contains Adenine, Guanine, Cytosine and Uracil.

Question 37

Structure of DNA molecule (Watson and Crick model)

Answer 37

DNA molecules have
two anti-parallel polynucleotide chains that
spiral around an imaginary axis, forming a
double helix. The
two sugar-phosphate backbones run in opposite directions from each other, and the arrangement is referred to as
anti-parallel. The
sugar phosphate backbones are on the
outside of the helix, and the
nitrogenous bases are paired in the
interior of the helix. The two strands are held together by
hydrogen bonds between the paired nitrogen bases.

Question 38

Base pair rule?

Answer 38

Always a
purine base, pairs with a
specific,pyrimidine
base,

A=T (2 hydrogen bonds)
G≡C (3 hydrogen bonds)

Hence two chains (strands) are said to be
complementary to each other. These pairs are known as
complementary base pairs.

In this original double helical structure,
one complete turn consists of
ten base pairs as shown in the diagram.

Question 39

Functions of DNA?

Answer 39

• Store and transmit genetic information from one generation to the next generation
• Store the genetic information for protein synthesis

Question 40

Structure of RNA

Answer 40

This is normally a
single stranded nucleic acid composed of
ribo-nucleotides containing bases,
Uracil (U), Cytosine (C ), Guanine (G), Adenine (A).
Complementary base pairing between
two RNA molecules or within the same molecule may occur in some.

Complementary base pairing facilitates
three dimensional shapes essential for their functioning.

Adenine binds with Uracil with two hydrogen bonds and
Guanine binds with Cytosine with three hydrogen bonds.

Question 41

There are three types of RNA present in cells,

Answer 41

1. Messenger RNA (mRNA)
2. Transfer RNA (tRNA)
3. Ribosomal RNA (rRNA)

Question 42

1. Messenger RNA

Answer 42

Messenger RNA is a
linear molecule and is the
least abundant type of RNA in a cells comparatively. There are

two functions;
• Copies the genetic information stored in DNA molecule as a sequence of nitrogenous bases
• Transports genetic information from nucleoplasam to the site of protein synthesis (ribosome) through nucleopores

Question 43

2. Transfer RNA (tRNA)

Answer 43

Smallest RNA molecule.
Linear, but forms
three- looped structure

Function - transportation of amino acids to the site of protein synthesis.

Question 44

3. Ribosomal RNA

Answer 44

It is the
most abundant type of RNA. rRNA has a
complex irregular structure. It
provides the site where polypeptide chains are assembled.

Question 45

Differences between DNA and RNA

Answer 45

1. DNA is double stranded molecule while
   RNA is a single stranded molecule.
2. DNA consists of A, T, G and C and absence of U, while
   RNA consists of A,U, G and C and absence of T
3. Sugar molecule in RNA is ribose, while in
   DNA it is deoxyribose.

Question 46

Nucleotides other than those found in nucleic acids

Answer 46

ATP, NAD+, NADP+, FAD and their functions

Functions of ATP
• Universal energy carrier

B3 Niacin

Functions of NAD+
• Act as a coenzyme
• Act as an electron carrier
• Function as an oxidizing agent during respiration

Functions of NADP+
• Act as coenzymes
• Act as an electron carrier
• NADP+ act as a reducing agent in photosynthesis

B2 Flavin

Functions of FAD
• Act as a coenzyme
• Act as an electron carrier