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1. MCB 101
MAMUN RASHID CHOWDHURY
Retired Professor, Deptt. Of Biochemistry
and Molecular Biology, Dhaka University
email : kbm.mamun@iub.edu.bd
phone: 8801715021864

2. Living beings are isothermal open system working on the
principle of maximum economy of parts and process, deriving
energy through well-regulated enzyme catalyzed reactions and
are capable of precise replication of their kind.
Living beings are made up of entities organized in a membrane
enclosed environment and in some cases with additional wall.
Almost all living systems maintain a constant temperature like
370C in human beings, except animals which undergo
hibernation during winter, like reptiles etc., the so called cold-
blooded animals.
Being system with definite enclosure, there must be constant
supply of components for activities and removal of unwanted
materials. So the barrier must not be permeable or porus, but
semi-permeable, allowing certain materials to pass through
the membrane as per need, but not everything. The system is
thus in continuous transaction with its surroundings, the
environment.

3. • For continuity of life, living system has to do some form of work or activities using
energy. Some system traps solar energy to utilizable form of chemical energy. But
most living beings use oxidation energy from some energy- rich natural
biomolecules.
• This energy generation is not spontaneous, but enzyme catalyzed, involving a
well-regulated sequence of enzyme activities for any particular pathway so that a
particular product is formed as per need, in addition to energy generation. Thus
the reactions and the organ/organelle which possesses the reaction sequences
work with maximum efficiency, maintaining optimal economy. Living systems do
not encourage waste of any kind.
• For continuity of life, they reproduce like themselves.
Organisation:
Living beings are made up of simple molecules organized in complicated ways to
form complex ones. All start from elements of some kind at certain proportion. After
incinerating an animal, one can get few kilograms or such amount of each of
different elements. Can any human being organize these elements into an animal?
For instance, the following hierarchy can be taken into consideration for
understanding:
elements---- compounds----macromolecules
--------organelles------ cells ----- tissues-------- organs
------- system-------- Individuals.

4. Organization is important from both structural and functional
points as well. Any defect in organization reflects not only in
defective physical make up but also in functional behaviour.
For instance, clogging in blood vessels in heart due to
deposition of LDL-cholesterol, an organization problem, causes
diminished blood flow to the relevant region of the organ,
leading to tissue damage, resulting in myocardial infarction or
heart attack.
At the same time defective function can bring organizational
problem. For instance, if one leg is incapacitated by putting
plaster for a few months because of fracture, on removal of
plaster after bone healing, it will be found that circumference
of this leg is less than that of normal one, because of non-
functional muscle wasting.
So living system is a large well-enclosed
compartment with a number of well-connected
compartments.

5. Metabolism
Living system carries out lots of enzyme-catalyzed chemical
reactions all the time.
The sum total of all the chemical reactions is called
metabolism.
Catabolism is the degradative part where larger molecules are
broken down to smaller precursor molecules with the
generation/release of energy trapped as ATP and metabolic
wastes to be disposed off of the body.
Catabolism can occur in the presence of oxygen (aerobic
metabolism), producing more energy as ATP and CO2 as
metabolic waste or can occur in the absence of oxygen
(anaerobic metabolism), producing less ATP along with
ethanol in bacteria/yeast and lactic acid in animals.

6. • Anabolism is where smaller precursors are used for the
synthesis of desired macromolecules at the expense of
metabolic energy generated .For instance, amino acids
absorbed from dietary protein digestion are used for specific
body protein e.g. hemoglobin synthesis.
• Anabolic and catabolic reactions are not simple reversal of
each other, but they maintain separate and independent
control or regulation, otherwise there would develop futile
cycle of synthesis and degradation.
• These may occur in different compartments in eukaryotes,
e.g. catabolism occurs in mitochondria and anabolism or
biosynthesis occurs in cytosol. Disturbance in this
regulation, however, results in abnormalities. For instance,
intake of more than recommended amount of carbohydrate
causes synthesis and deposition of excess fat leading to
obesity. On the other hand, excess degradation of purine
bases of nucleic acid due to high nucleic acid containing
food intake or excess tissue degradation causes
hyperuricemia, leading to gout.

14. Micro-organisms and their activities are vitally
important to virtually all processes on Earth.
Micro-organisms matter because they affect every
aspect of our lives – they are in us, on us and around us.
Microbiology is the study of all living organisms that are
too small to be visible with the naked eye. This includes
bacteria, archaea, viruses, fungi, prions, protozoa and
algae which are collectively known as 'microbes'.
These microbes play key roles in nutrient cycling,
biodegradation/biodeterioration, climate change, food
spoilage, the cause and control of disease, and
biotechnology.
Thanks to their versatility, microbes can be put to work
in many ways: making life-saving drugs, the
manufacture of biofuels, cleaning up pollution,
fermentation of various food items etc.

15. • Microbiologists study microbes, and some of
the most important discoveries that have
underpinned modern society have resulted
from the research of famous microbiologists,
e.g. Jenner and his vaccine against smallpox,
Fleming and the discovery of penicillin, Marshall
and the identification of the link between
Helicobacter pylori infection and stomach
ulcers, and Zur Hausen and the link between
papilloma virus and cervical cancer.
• Microbiology research has been, and continues
to be, central to meeting many of the current
global aspirations and challenges, such as
maintaining food, water and energy security for
a healthy population on a habitable earth.

17. 1677:Anton Von Leewenhock- Little animals
1796: Edward Jenner- Small Pox vaccine
1862-63 Pasteur- disapproved spontaneous generation and
supported germ theory of diseases
1876: Robert Koch- Proved germ theory of disease using B anthracis
1882: Robert Koch- Koch’s postulates
1885: Pasteur- Rabies vaccination
1892: Ivanovsky- Discovery of virus
1899: Beijerinck- viral dependence on living host cell for reproduction
1900: Walter Reed- mosquito as vector for Yellow fever transmission
1928: A Flemming- discovery of penicillin
1977: Sanger & Gilbert- method for DNA sequencing
1983: Karry Mullins- Polymerase Chain Reaction developed
1995:The Institute of Genomic Research- H influenzae genome sequen.

18. The steps of Koch's postulates used to relate a specific microorganism to a specific
disease. (a) Microorganisms are observed in a sick animal and (b) cultivated in the
lab. (c) The organisms are injected into a healthy animal, and (d) the animal
develops the disease. (e) The organisms are observed in the sick animal and (f)
reisolated in the lab.

19. • In the late 1800s and the first decade of the 1900s, called
Golden Age of Microbiology, using the concept of germ theory
of disease by Pasteur and Koch, many of the etiologic agents of
microbial disease were discovered, leading to the ability to halt
epidemics by interrupting the spread of microorganisms.
• Despite the advances in microbiology, it was rarely possible to
render life-saving therapy to an infected patient. Then, after
World War II, the antibiotics were introduced to medicine and
the incidence of pneumonia, tuberculosis, meningitis, syphilis,
and many other diseases declined with the use of antibiotics.
• Work with viruses could not be effectively performed until
development in the 1940s of the electron and also cultivation
methods for viruses were also introduced, and the knowledge of
viruses developed rapidly.
• With the development of vaccines in the 1950s and 1960s, such
viral diseases as polio, measles, mumps, and rubella came under
control.

20. By applying microbes in a range of controlled settings,
microbiologists can harness their power for beneficial use in areas
as diverse as healthcare, food production and agriculture.
• The essential ongoing work of microbiologists includes making
agriculture more sustainable, cleaning up pollution,
manufacturing biofuels, and processing food and drink.
• With the threat of antibiotic-resistant bacteria and global
pandemics on the rise, microbiologists are also helping to
produce the vital life-saving drugs for survival.
• So, Microbiologists aim to solve a range of problems affecting
our health, the environment, climate and food and agriculture.
These include:
Studying the prevention, diagnosis and control of infections and
specific diseases
• Ensuring food and drink is safe to consume
• Understanding the role that microbes play in climate change
• Developing green technologies
•

22. • .

23. • Bacteria are ubiquitous, mostly free-living large
domain of prokaryotes, with a few µm in length.
• Bacteria are vital in many stages of the nutrient
cycle by recycling nutrients e.g. N₂ cycle of nitrogen
fixation from atmosphere. The nutrient cycle
includes decomposition/putrefaction of dead
bodies.
• In the biological communities surrounding deep
sea hydrothermal vent and cold seeps,
extremophile bacteria provide the nutrients
needed to sustain life by oxidizing dissolved
compounds, e.g. H₂S and CH₄ to energy.
• Bacteria also live in symbiotic and
parasitic relationships with plants and animals.
• Most bacteria have not been characterised and
there are many species that cannot be cultured in
the laboratory, like many marine bacteria.

24. • Humans and most other animals carry millions of bacteria,
mostly in the gut and on the skin.
• Most of the bacteria in and on the body are harmless or
rendered so by the protective effects of the immune system,
though many are beneficial, particularly the ones in the gut.
• However, several species of bacteria are pathogenic, causing
infectious disease, like cholera, respiratory infections etc.
• Antibiotics are used to treat bacterial infections, even in
farming, but uncontrolled use or misuse leads to antibiotic
resistance , a serious medical problem.
• Bacteria are important in sewage treatment & breakdown of
oil spill, in the fermentative production yogurt & cheese; in
the recovery of gold, palladium, copper and other metals in
the mining sector, as well as in biotechnology and the
manufacture of antibiotics and other chemicals.

25. • Size: Bacteria display a wide diversity of shapes and sizes;
are about one-tenth the size of eukaryotic cells and are
typically 0.5–5.0 µm in length, Mycoplasma, the smallest
bacteria measuring only 0.3 micro-metres,
• Shape: Most bacterial species are either spherical,
called cocci (singular coccus, from Greek kókkos, grain,
seed), or rod shaped, called bacilli (sing. bacillus,
from Latin baculus, stick). Some bacteria, called vibrio, are
shaped like slightly curved rods or comma shaped; others
can be spiral shaped, called spirilla or tightly coiled,
spirochaetes.

30. • Bacteria require certain conditions for growth, and
these conditions are not the same for all bacteria.
Factors such as oxygen, pH, temperature, and light
influence microbial growth. Additional factors
include osmotic pressure, atmospheric pressure,
and moisture availability. A bacterial population's
generation time, or time it takes for a population to
double, varies between species and depends on
how well growth requirements are met.
• In nature, bacteria do not experience perfect
environmental conditions for growth. As such, the
species that populate an environment change over
time. In a laboratory, however, optimal conditions
can be met by growing bacteria in a closed culture
environment.

48. • Pure culture, when one type of bacteria is grown; identified through
colony nature on agar media; in mixed culture different types of
colonies are formed.
Colony from pure
culture is used to
prepare pure broth
culture.

49. • The bacterial growth curve represents the number of live cells
in a bacterial population over a period of time.
• Lag Phase: This initial phase is characterized by adaptation to
new growth conditions and with having cellular activities but
not growth. A small amount of bacterial cells, called
inoculum, are placed in a nutrient rich medium that allows
them to synthesize macromolecules necessary for replication.
These cells increase in size, but no cell division occurs in the
phase.
• Exponential (Log) Phase: After the lag phase, bacterial
cells are dividing by binary fission and doubling in numbers
after each generation time(time for being double in number).
Metabolic activity is high as DNA, RNA, Protein and other cell
components necessary for growth are generated for division. It
is in this growth phase that antibiotics and disinfectants are
most effective as these substances typically target bacteria cell
walls or the DNA transcription/RNA translation processes.

50. • Stationary Phase: Eventually, the population growth
experienced in the log phase begins to decline as the
available nutrients become depleted and waste products
start to accumulate. Bacterial cell growth reaches a plateau,
or stationary phase, where the number of dividing cells
equal the number of dying cells. This results in no overall
population growth. Under the less favorable conditions,
competition for nutrients increases and the cells become
less metabolically active. Spore forming bacteria produce
endospores in this phase and Pathogenic bacteria begin to
generate substances (virulence factors) that help them
survive harsh conditions and consequently cause disease.
• Death Phase: As nutrients become less available and
waste products increase, the number of dying cells
continues to rise. In the death phase, the number of living
cells decreases exponentially and population growth
experiences a sharp decline. Spores are able to survive the
harsh conditions of the death phase and become growing
bacteria when placed in an environment that supports life.

61. PURE CULTURE
In nature there are mixed population of bacteria. Isolating and
growing bacteria from natural sources e.g. soil/water, will give a mixed
population of bacteria in the culture, with different characteristics.
Pure culture involves techniques for isolating and growing one species
of bacteria from a mixed culture i.e. a population of cells from a single
cell for studying the characteristics of the concerned organism.
• The techniques of isolation of the pure culture were primarily
developed to find out and characterize the bacteria that was
responsible for causing anthrax, tuberculosis,and such major
diseases.
•
• It is also used for commercial fermentation purposes including
yoghurt, alcohol, citric, lactic acid, and several other beverages for
many years now. The pure culture technique has also contributed to
the development of several vaccines and antibiotics.

62. Isolation methods:
Streak-plate & spread-plate technique: Using inoculating
needle, sample is streaked/spread on agar plate and incubated. If
diluted separate colonies of individual bacterium will developed, to be
transferred to nutrient broth for pure culture.
Pour plate technique: A loopful bacterial suspension is
transferred to liquid & cool agar medium and mixed; serially
transferred to a few agar media ( serial dilution) and mixed every time;
poring on petridishes and incubating overnight would give isolated
colonies to be used for pure culture in nutrient broth.
Enrichment-culture technique: When the specific type of
bacteria is present relatively in smaller number and grow slowly, the
specially designed cultural environment of that bacteria friendly
cultural composition & specific incubation conditions would favour
the growth of designated bacteria and prevent the growth of others.

65. MAINTENANCE /PRESERVATION OF PURE CULTURE
• Once a microorganism has been isolated and grown in
pure culture, it becomes necessary to maintain the
viability and purity of the microorganism by keeping the
pure culture free from contamination. Normally in
laboratories, the pure cultures are transferred aseptically
and periodically onto or into a fresh medium
(subculturing) to allow continuous growth and viability of
microorganisms, without contamination.
• Since repeated sub-culturing is time-consuming, it
becomes difficult to maintain a large number of pure
cultures successfully for a long time. In addition, there is a
risk of mutations as well as contamination.