Unit 1 Biomolecules Bioenergetics B.Pharmacy 2nd Semester 2022 (2021-2022) Previous Year's Question Papers/Notes Download - HK Technical PGIMS

AAM
BIOCHEMISTRY
Unit-I
Biomolecules: Introduction, classification, chemical nature and
biological role of carbohydrate, lipids, nucleic acids, amino acids
and proteins.
Bioenergetics: Concept of free energy, endergonic and exergonic
reaction, Relationship between free energy, enthalpy and
entropy; Redox potential. Energy rich compounds; classification;
biological significances of ATP and cyclic AMP.
Biomolecules:
Introduction, classification, chemical nature
and biological role of carbohydrate, lipids,
nucleic acids, amino acids and protein
Carbohydrates
The term carbohydrate is itself a combination of the “hydrates of
carbon”. They are also known as “Saccharides” which is a
derivation of the Greek word “Sakcharon” meaning sugar. The
definition of carbohydrates in chemistry is as follows:
“Optically active polyhydroxy aldehydes or polyhydroxy ketones or
substances which give these on hydrolysis are termed as
carbohydrates”.
Some of the most common carbohydrates that we come across in our
daily lives are in form of sugars. These sugars can be in form of
Glucose, Sucrose, Fructose, Cellulose, Maltose etc.
General Formula of Carbohydrate
The general formula for carbohydrate is Cx(H2O)y. Although, it
must be remembered that this is just a general formula. There are
various exceptions to this that we will see. Let us take a look at
Acetic Acid which is CH3COOH. Now although this will fit in the
general formula of carbohydrate i.e. Cx(H2O)y, we know that
acetic acid is not a carbohydrate.
Formaldehyde (HCHO) also falls under this category of this
general formula but is also not a carbohydrate. And on the other
hand, Rhamnose (C6H12O6) which is very much a carbohydrate but
does not follow the general formula

Classification of Carbohydrates
The main classification of carbohydrate is done on the basis of
hydrolysis. This classification is as follow:
1. Monosaccharides
Monosaccharide carbohydrates are those carbohydrates that
cannot be hydrolyzed further to give simpler units of
polyhydroxy aldehyde or ketone. If a monosaccharide
contains an aldehyde group then it is called aldose and on the
other hand, if it contains a keto group then it is called a ketose.
Structure of Carbohydrates – Glucose
One of the most important monosaccharides is glucose. The
two commonly used methods for the preparation of glucose
are
• From Sucrose: If sucrose is boiled with dilute acid in an
alcoholic solution then we obtain glucose and fructose.
• From Starch: We can obtain glucose by hydrolysis of
starch and by boiling it with dilute H2SO4 at 393K under
elevated pressure.
• Glucose is also called aldohexose and dextrose and is
abundant on earth.
•
Simple Carbohydrate – Glucose
• Glucose is named as D (+)-glucose, D represents the
configuration whereas (+) represents
the dextrorotatory nature of the molecule.
• The ring structure of glucose can explain many properties
of glucose which cannot be figured by open-chain
structure.
• The two cyclic structures differ in the configuration of the
hydroxyl group at C1 called anomeric carbon. Such
isomers i.e. α and β form are known as anomers.
• The cyclic structure is also called pyranose structure due
to its analogy with pyran.
The cyclic structure of glucose is given below:
Cyclic Structure of Carbohydrates – Glucose
Structure of Carbohydrates – Fructose
It is an important ketohexose. The molecular formula of
fructose is C6H12O6 and contains ketonic functional
group at carbon number 2 and has six carbon atoms in a
straight chain. The ring member of fructose is in analogy to
the compound Furan and is named as furanose. The cyclic
structure of fructose is shown below:
Carbohydrate Classification – Fructose
1.Oligosaccharides: Carbohydrates that on hydrolysis yield two to
ten smaller units or monosaccharides are
oligosaccharides. They are a large category and further divides
into various subcategories.
2.Disaccharides: A further classification of oligosaccharides, these
give two units of the same or different monosaccharides on
hydrolysis. For example, sucrose on hydrolysis gives
one molecule of glucose and fructose each. Whereas maltose on
hydrolysis gives two molecules of only glucose,
3. Trisaccharides: Carbohydrates that on hydrolysis gives three
molecules of monosaccharides, whether same or different. An
example is Raffinose.
4. Tetrasaccharides: And as the name suggests this carbohydrate
on hydrolysis give four molecules of monosaccharides.
Stachyose is an example.
5. Polysaccharides: The final category of carbohydrates. These give
a large number of monosaccharides when they undergo
hydrolysis, These carbohydrates are not sweet in taste and are
also known as non-sugars. Some common examples are starch,
glycogen etc.
Functions of Carbohydrates in Body
1.Carbohydrates provides energy and regulation of blood
glucose.
2.It will prevent the degradation of skeletal muscle and other
tissues such as the heart, liver, and kidneys.
3.It prevent the breakdown of proteins for energy.
4.Carbohydrates also help with fat metabolism. If the body
has enough energy for its immediate needs, it stores extra
energy as fat
LIPIDS
• Lipids are a heterogeneous group of organic compounds
that are insoluble in water and soluble in non-polar
organic solvents.
• They naturally occur in most plants, animals,
microorganisms and are used as cell membrane
components, energy storage molecules, insulation, and
hormones.
Classification of Lipids
Lipids can be classified into two major classes:
• Nonsaponifiable lipids, and
• Saponifiable lipids.
Nonsaponifiable Lipids
A nonsaponifiable lipid cannot be broken up into smaller
molecules by hydrolysis, which includes triglycerides, waxes,
phospholipids, and sphingolipids.
Saponifiable Lipids
A saponifiable lipid contains one or more ester groups
allowing it to undergo hydrolysis in the presence of an acid,
base, or enzymes. Nonsaponifiable lipids include steroids,
prostaglandins, and terpenes
Types of Lipids
Within these two major classes of lipids, there are several
specific types of lipids important to live, including fatty acids,
triglycerides, glycerophospholipids, sphingolipids, and
steroids. These are broadly classified as simple lipids and
complex lipids.
Simple Lipids
Esters of fatty acids with various alcohols.
1.Fats: Esters of fatty acids with glycerol. Oils are fats in the
liquid state.
2.Waxes: Esters of fatty acids with higher molecular weight
monohydric alcohols
Complex Lipids
Esters of fatty acids containing groups in addition to alcohol
and a fatty acid.
1.Phospholipids: Lipids containing, in addition to fatty
acids and alcohol, a phosphoric acid residue. They
frequently have nitrogen-containing bases and other
substituents, eg, in glycerophospholipids the alcohol is
glycerol and in sphingophospholipids the alcohol is
sphingosine.
2.Glycolipids (glycosphingolipids): Lipids containing a
fatty acid, sphingosine, and carbohydrate.
3.Other complex lipids: Lipids such as sulfolipids and
amino lipids. Lipoproteins may also be placed in this
category
Precursor and Derived Lipids
These include fatty acids, glycerol, steroids, other alcohols,
fatty aldehydes, and ketone bodies, hydrocarbons, lipidsoluble vitamins, and hormones. Because they are
uncharged, acylglycerols (glycerides), cholesterol, and
cholesteryl esters are termed neutral lipids. These
compounds are produced by the hydrolysis of simple and
complex lipids.
Some of the different types of lipids are described below in
detail.
Fatty Acid
Fatty acids are carboxylic acids (or organic acid), often with
long aliphatic tails (long chains), either saturated or
unsaturated.
• Saturated fatty acids
When a fatty acid is saturated it is an indication that there are
no carbon-carbon double bonds. The saturated fatty acids
have higher melting points than unsaturated acids of the
corresponding size due to their ability to pack their molecules
together thus leading to a straight rod-like shape.
• Unsaturated fatty acids
If a fatty acid has more than one double bond then this is an
indication that it is an unsaturated fatty acid.
“Most naturally occurring fatty acids contain an even number
of carbon atoms and are unbranched.”
Unsaturated fatty acids, on the other hand, have a cis-double
bond(s) that create a kink in their structure which doesn’t allow
them to group their molecules in straight rod-like shape.
Waxes
Waxes are “esters” (an organic compound made by replacing
the hydrogen with acid by an alkyl or another organic group)
formed from long-chain carboxylic acids and long-alcohols.
Waxes are seen all over in nature. The leaves and fruits of
many plants have waxy coatings, which may protect them
from dehydration and small predators.
The feathers of birds and the fur of some animals have similar
coatings which serve as a water repellent.
Carnauba wax is valued for its toughness and water
resistance(great for car wax).
Phospholipids
Membranes are chiefly made of phospholipids which are
Phosphoacylglycerols.
Triacylglycerols and phosphoacylglycerols are similar
however the terminal OH group of the phosphoacylglycerol is
esterified with phosphoric acid instead of fatty acid which
leads to the formation of phosphatidic acid.
The name phospholipid comes from the fact that
phosphoacylglycerols are lipids that contain a phosphate
group.
Steroids
The chemical messengers in our bodies are known
as hormones which are organic compounds synthesized in
glands and delivered by the bloodstream to certain tissues in
order to stimulate or inhibit the desired process.
Steroids are a type of hormone which is usually recognized by
their tetracyclic skeleton, consisting of three fused sixmembered and one five-membered ring, as shown in the
diagram above. The four rings are designated as A, B, C & D
as noted in blue, and the numbers in red represent the
carbons.
Cholesterol
• Cholesterol is waxy like substance, found only in animal
source foods. Triglycerides, LDL, HDL, VLDL are
different types of cholesterol found in the blood cells.
• Cholesterol is an important lipid found in the cell
membrane. It is a sterol, which means that cholesterol is
a combination of steroid and alcohol. In the human body,
cholesterol is synthesized in the liver.
• These compounds are biosynthesized by all living cells
and are essential for the structural component of the cell
membrane.
• In the cell membrane, the steroid ring structure of
cholesterol provides a rigid hydrophobic structure that
helps boost the rigidity of the cell membrane. Without
cholesterol, the cell membrane would be too fluid.
• It is an important component of cell membranes and is
also the basis for the synthesis of other steroids, including
the sex hormones estradiol and testosterone, as well as
other steroids such as cortisone and vitamin D.
Basic biological functions of lipids include store house of energy,
component of lipid bilayer and role in intracellular and intercellular
signaling events involving lipids such as glycerophospholipids,
sphinogomyelin, phosphatidyl X or inositol derivatives
NUCLEIC ACID
Nucleic acids are naturally occurring chemical compounds
that serve as the primary information-carrying molecules in
cells
Nucleic acid is the polymer of nucleotides .Nucleotides defines as
the compound consisting one pentose sugar,nitrogenous base
and Phosphate .
Classification: Two type -
(a) DNA (2-Deoxy-ribo Nucleic Acid)
(b) RNA (Ribo Nucleic Acid)
Function:
1.DNA transfer the genetic information thruogh genes.
2.RNA synthesis protein according to the information of DNA.
AMINO ACIDS
Amino acid is an organic compound which contains an amino
group (-NH2) and a carboxyl group (-COOH).
CLASSIFICATION
Although there are many ways to classify amino acids, these
molecules can be assorted into 6 main groups, on the basis
of their structure and general chemical characteristics of their
R groups.
Classes of Amino Acids Name of the Amino Acid
Aliphatic Glycine, Alanine, Valine, Leucine, Isoleucine
Hydroxyl or
Sulfur-containing
Serine, Cysteine, Threonine, Methionine
Cyclic Proline
Aromatic Phenylalanine, Tyrosine, Tryptophan
Basic Histidine,Lysine, Arginine
Acidic and
their amide
Aspartate, Glutamate, Asparagine, Glutamine
CHEMICAL NATURE OF AMINO ACIDS
All peptides and polypeptides are polymers of α-amino acids.
There are 20 α-amino acids that are relevant to the make-up
of mammalian proteins (see below). Several other amino
acids are found in the body free or in combined states (e.g.
not associated with peptides or proteins). These non-protein
associated amino acids perform specialized functions such as
citrulline and ornithine in the disposal of waste nitrogen via
the urea cycle. Several of the amino acids found in proteins
also serve functions distinct from the formation of peptides
and proteins, e.g., tyrosine in the formation of thyroid
hormones or glutamate acting as a neurotransmitter.
The α-amino acids in peptides and proteins (excluding
proline) consist of a carboxylic acid (–COOH) and an amino
(–NH2) functional group attached to the same tetrahedral
carbon atom. This carbon is the α-carbon. Distinct R-groups,
that distinguish one amino acid from another, also are
attached to the alpha-carbon (except in the case of glycine
where the R-group is hydrogen). The fourth substitution on
the tetrahedral α-carbon of amino acids is hydrogen.

Biological roles:
1. Amino acids can be metabolized to produce energy. This is
especially important during fasting, when the breakdown of
muscle protein is a major source of energy and biosynthetic
precursors.
2. Some amino acids act as neurotransmitters, and some act as
starting materials for the biosynthesis of neurotransmitters,
hormones, and a wide variety of other important biochemical
compounds.
3. Amino acids are the primary building blocks for proteins.
PROTIENS
Proteins are the most versatile macromolecules in living
systems and serve crucial functions in essentially all biological
processes. They function as catalysts, they transport and
store other molecules such as oxygen, they provide
mechanical support and immune protection, they generate
movement, they transmit nerve impulses, and they control
growth and differentiation.
CLASSIFICATION OF PROTEIN
Four Protein Structure Types
I. Simple proteins
(i) Albumins:
Soluble in water, coagulable by heat and 1 precipitated at high
salt concentrations.
Examples – Serum albumin, egg albumin, lactalbumin (Milk),
leucosin (wheat), legumelin (soyabeans).
(ii) Globulins:
Insoluble in water, soluble in dilute salt 1 solutions and
precipitated by half 1 saturated salt solutions.
Examples – Serum globulin, vitellin (egg yolk), tuberin
(potato), myosinogen (muscle), legumin (peas).
(iii) Glutelins:
Insoluble in water but soluble in dilute 1 acids and alkalis.
Mostly found in plants.
Examples – Glutenin (wheat), oryzenin (rice).
(iv) Prolamines: Insoluble in water and absolute alcohol 1
but soluble in 70 to 80 per cent alcohol.
Examples – Gliadin (wheat), zein (maize)
(v) Protamines:
Basic proteins of low molecular weight. 1 Soluble in water,
dilute acids and alkalis, j Not coagulable by heat.
Examples – Salmine (salmon sperm).
(vi) Histones:
Soluble in water and insoluble in very I dilute ammonium
hydroxide.
Examples – Globin of hemoglobin and thymus histones.
(vii) Scleroproteins:
Insoluble in water, dilute acids and alkalis.
Examples – Keratin (hair, horn, nail, hoof and feathers),
collagen (bone, skin), elastin (ligament).
II. Conjugated Proteins
(i) Nucleoproteins:
Composed of simple basic proteins (protamines or histones)
with nucleic acids, I found in nuclei. Soluble in water.
Examples – Nucleoprotamines and nucleohistones.
(ii) Lipoproteins:
Combination of proteins with lipids, such ‘ as fatty acids,
cholesterol and 1 phospholipids etc.
Examples – Lipoproteins of egg-yolk, milk and cell
membranes, lipoproteins of blood.
(iii) Glycoproteins:
Combination of proteins with carbohydrate
(mucopolysaccharides).
Examples – Mucin (saliva), ovomucoid (egg white),
osseomucoid (bone), tendomucoid (tendon).
(iv) Phosphoproteins:
Contain phosphorus radical as a | prosthetic group.
Examples – Caseinogen (milk), ovovitellin (egg yolk).
(v) Metalloproteins:
Contain metal ions as their prosthetic | groups. The metal ions
generally are Fe, I Co. Mg, Mn, Zn, Cu etc.
Examples – Siderophilin (Fe), ceruloplasmin (Cu).
(vi) Chromoproteins:
Contain porphyrin (with a metal ion) as | their prosthetic
groups.
Examples – Haemoglobin , myoglobin, catalase, peroxidase,
cytochromes.
(vii) Flavoproteins:
Contain riboflavin as their prosthetic 1 groups.
Examples – Flavoproteins of liver and kidney.
III. Derived Protein
A. Primary derivatives
(i) Proteans:
Derived in the early stage of protein hydrolysis by dilute acids,
enzymes or alkalis.
Examples – Fibrin from fibrinogen.
(ii) Metaproteins:
Derived in the later stage of protein hydrolysis by slightly
stronger acids and alkalis.
Examples – Acid and alkali metaproteins.
(iii) Coagulated:
They are denatured proteins formed by the action of heat. Xrays, ultraviolet rays etc.
Cooked proteins, coagulated albumins.
B. Secondary derivatives
(i) Proteoses:
Formed by the action of pepsin or trypsin. Precipitated by
saturated solution of ammonium sulphate, incoagulable by
heat.
Examples – Albumose from albumin, globulose from
globulin.
(ii) Peptones: .
Further stage of cleavage than the proteoses. Soluble in water,
incoagulable by heat and not precipitated by saturated
ammonium sulphate solutions.
(iii) Peptides:
Compounds containing two or more amino acids. They may
be di-, tri-, and porypeptides.
Examples – Glycyl-alanine, leucyl-glutamic acid.
Structure of Proteins
1] Primary Protein Structure
The primary structure is the unique formation and order in which the
amino acids (the building blocks) combine and link to give us a
protein molecule. Protein gets all its properties from its primary
structure.
There are in all twenty amino acids in the human body. All of these
have a carboxyl group and an amino group. But each has a different
variable group known as the “R” group. It is this R group that lends
a particular protein its unique structure.
Every protein is determined by the sequencing of the amino acids.
The formation and ordering of these amino acids in proteins are
extremely specific. If we alter even one amino acid in the chain it
results in a non-functioning protein or what we call a gene mutation.
2] Secondary Protein Structure
After the sequencing of amino acids, we now move on to the
secondary structure. This is when the peptide backbone of the
protein structure will fold onto itself, to give proteins their unique
shape. This folding of the polypeptide chains happens due to the
interaction between the carboxyl groups along with the amine groups
of the peptide chains.
There are two kinds of shapes formed in the secondary structure.
These are
• α-helix: The backbone follows a helical structure. The hydrogen
bonds with the oxygen between the different layers of the helix,
giving it this helical structure.
• β-pleated sheet: here the polypeptide chains are stacked next to
each other and their outer hydrogen molecules form
intramolecular bonds to give it this sheet-like structure
3] Tertiary Structures
This is the structure that gives protein the 3-D shape and formation.
After the amino acids form bonds (secondary structure) and shapes
like helices and sheets, the structure can coil or fold at random. This
is what we call the tertiary structure of proteins. If this structure is
disrupted or disturbed a protein is said to be denatured which means
it is chemically affected and its structure is distorted.
4] Quaternary Structure
Finally, we come to the fourth structure. The spatial arrangement of
two or more peptide chains leads to this structure. It is important to
note it is not necessary for proteins to have quaternary structures.
Primary, secondary and tertiary structures are present in all natural
proteins, but the same is not true for quaternary structure. Hence if a
protein has only the first three structures it is considered to be a
protein.
Biological Importance of Proteins:
i. Proteins are the essence of life processes.
ii. They are the fundamental constituents of all protoplasm
and are involved in the structure of the living cell and in its
function.
iii. Enzymes are made up of proteins.
iv. Many of the hormones are proteins.
v. The cement substances and the reticulum which bind or
hold the cells as tissues or organs are made up partly of
proteins.
vi. They execute their activities in the transport of oxygen and
carbon dioxide by hemoglobin and special enzymes in the red
cells.
vii. They function in the homostatic control of the volume of
the circulating blood and that of the interstitial fluids through
the plasma proteins.
viii. They are involved in blood clotting through thrombin,
fibrinogen and other protein factors.
ix. They act as the defence against infections by means of
protein antibodies.
x. They perform hereditary transmission by nucleoproteins of
the cell nucleus.
Bioenergetics
Defination
- Bioenergetics means study of the transformation of energy
in living organisms.
- The goal of bioenergetics is to describe how living organisms
acquire and transform energy in order to perform
biological work. The study of metabolic pathways is thus
essential to bioenergetics.
- In a living organism, chemical bonds are broken and made
as part of the exchange and transformation of energy.
Energy is available for work (such as mechanical work) or for
other processes (such as chemical synthesis and
anabolic processes in growth), when weak bonds are broken
and stronger bonds are made. The production of
stronger bonds allows release of usable energy.
- Adenosine triphosphate (ATP) is the main "energy currency"
for organisms; the goal of metabolic and catabolic
processes are to synthesize ATP from available starting
materials (from the environment), and to break- down ATP
(into adenosine diphosphate (ADP) and inorganic phosphate)
by utilizing it in biological processes.
- In a cell, the ratio of ATP to ADP concentrations is known as
the "energy charge" of the cell.
- A cell can use this energy charge to relay information about
cellular needs; if there is more ATP than ADP
available, the cell can use ATP to do work, but if there is more
ADP than ATP available, the cell must synthesize
ATP via oxidative phosphorylation.
- Living organisms produce ATP from energy sources via
oxidative phosphorylation. The terminal phosphate bonds
of ATP are relatively weak compared with the stronger bonds
formed when ATP is hydrolyzed (broken down by
water) to adenosine diphosphate and inorganic phosphate.
Here it is the thermodynamically favorable free energy
of hydrolysis that results in energy release; the
phosphoanhydride bond between the terminal phosphate
group and
the rest of the ATP molecule does not itself contain this energy
Types of Bioenergetics Reactions
1. Exergonic Reaction
- Exergonic implies the release of energy from a spontaneous
chemical reaction without any concomitant utilization
of energy.
- The reactions are significant in terms of biology as these reactions
have an ability to perform work and include
most of the catabolic reactions in cellular respiration.
- Most of these reactions involve the breaking of bonds during the
formation of reaction intermediates as is evidently
observed during respiratory pathways. The bonds that are created
during the formation of metabolites are stronger
than the cleaved bonds of the substrate.
- The release of free energy, G, in an exergonic reaction (at constant
pressure and temperature) is denoted as
ΔG = Gproducts – Greactants < 0
2. Endergonic ReactionsEndergonic in turn is the opposite of exergonic in being nonspontaneous and requires an input of free energy.
Most of the anabolic reactions like photosynthesis and DNA and
protein synthesis are endergonic in nature.
- The release of free energy, G, in an exergonic reaction (at constant
pressure and temperature) is denoted as
ΔG = Gproducts – Greactants 0
-
3. Activation Energy
- Activation energy is the energy which must be available to a
chemical system with potential reactants to
result in a chemical reaction. Activation energy may also be defined
as the minimum energy required
starting a chemical reaction.
Bioenergetics Relationship Between Free
Energy, Enthalpy & Entropy
- Every living cell and organism must perform work to stay
alive, to grow and to reproduce. The ability to harvest
energy from nutrients or photons of light and to channel it into
biological work is the miracle of life.
- 1st Law of Thermodynamics: The energy of the universe
remains constant.
- 2nd Law of Thermodynamics: All spontaneous processes
increase the entropy of the universe.
- The important state functions for the study of biological
systems are:
The Gibbs free energy (G) which is equal to the total
amount of energy capable of doing work during a
process at constant temperature and pressure.
o If ∆G is negative, then the process is spontaneous and
termed exergonic.
o If ∆G is positive, then the process is nonspontaneous and
termed endergonic.
o If ∆G is equal to zero, then the process has reached
equilibrium.
The Enthalpy (H) which is the heat content of the system.
Enthalpy is the amount of heat energy transferred
(heat absorbed or emitted) in a chemical process under
constant pressure.
o When ∆H is negative the process produces heat and is
termed exothermic.
o When ∆H is positive the process absorbs heat and is termed
endothermic.
The Entropy (S) is a quantitative expression of the degree
of randomness or disorder of the system. Entropy
measures the amount of heat dispersed or transferred during
a chemical process.
o When ∆S is positive then the disorder of the system has
increased.
o When ∆S is negative then the disorder of the system has
decreased.
- The conditions of biological systems are constant
temperature and pressure. Under such conditions the
relationships between the change in free energy, enthalpy
and entropy can be described by the expression where T
is the temperature of the system in Kelvin. ∆G = ∆H − T∆S
[∆G = Gibbs Free Energy; ∆H = Change in Enthalpy; T =
Temperature in K; ∆S = Change in Entropy]
REDOX POTENTIAL, Eh
Redox potential also called as reduction potential designated
as, Eh. It is a measure of the tendency of a chemical species
to acquire electrons and thereby get reduced. It is an intrinsic
property. A larger value of Eh indicates a greater affinity of
species to accept electrons and get reduced. In biochemistry
numerous enzyme catalyzed reaction are redox reactions.
The ability of an organism to carryout redox reaction depends
upon oxidation-reduction state of environment. Aerobic
organisms are active at positive Eh values, anaerobic
organisms are active at negative Eh values while facultative
organisms adjust their metabolism according to their
environment, that is they can be active either at positive or
negative Eh values.
ENERGY-RICH COMPOUNDS
An energy-rich compound is a compound the hydrolysis of
which has a highly negative biochemical standard free energy
change, ∆G°
Classification of energy-rich compounds:
Majorly there are three types of energy-rich compounds, acid
anhydride, special esters and derivatives of phosphamic acid.
1- Acid anhydride: General structure of an ordinary acid
anhydride is given as:
Acid anhydrides of importance in biochemistry are generally
the ones having one or both of carbon atoms replaced by
phosphorous atoms so that the compound has the structure:
(I) is named the mixed anhydride while (II) include di- and trinucleoside, like ADP, ATP, GDP and GTP.
2- Special esters: The special esters include sulfur esters
(acyl thioesters) and esters of enols.
3- Derivatives of phosphamic acid: These have general
formula of:
According to second law of thermodynamics one cannot
derive useful work from heat in an isothermal system. Since
living cells operate essentially in an isothermal (system that
functions at constant temperature) fashion therefore even if
cells could tolerate the deleterious effects of a large release
of heat they could not derive useable energy from it. The large
energy is thus utilized by their temporary storage forms in
compounds called energy-rich compounds. These are also
called as having “high chemical transfer potentials".
Adenosine triphosphate
Adenosine triphosphate is abbreviated as ATP. It is called as
macroergic compound; a compound that contains phosphatephosphate bond and act as store-house of energy.
Structure of ATP
The hydrolysis of this bond is strongly ‘exergonic’ and
therefore releases large amount of energy.
ATP -----------》ADP + Pi ^G = -30.5 KJ/mol
Production of ATP:
1.By oxidation of fuels
2.Reducing equivalents like NADH and FADH
3.Mitochondria, respiratory chain by proton gradient
generation
4.Phosphorylation of ADP.
Functions of ATP:
1. Formation of other macrogenic compounds, ADP, GTP,
cAMP and AMP.
2. Transportation of macromolecules through active transport
associated with hydrolysis of
3. Cell signaling: It participates in the process of cell signaling
by generating secondary
messengers like cAMP.
4. Muscle contraction: ATP binds to myosin to provide energy
and facilitate its binding to
actin to form a cross-bridge.
5.Synthesis of DNA and RNA.
Cyclic Adenosine Monophosphate (cAMP)
Chemically, it is 3’,5’-adenosine monophosphate. It is a cyclic
nucleoside, synthesized in tissues from ATP.
It is a secondary messenger. Secondary messengers are
molecules that relay signals received at receptors on the cellsurface to the target to the target molecules in the cytosol
and/or nucleus.
Functions of cAMP: The cAMP plays vital role in cell
signaling and result in following actions:
1. Causes glycogenolysis
2. Causes lipolysis
3. Modulates transcription
4. Activates hormone secretion
5. Increases gastric secretion
6. Regulates cell permeability to water.
AAM