1
1-define:
 Meisosis:produces daughter cells that have one half the number of chromosomes
as the parent cell.
 Mitosis:produces two daughter cells that are identical to the parent cell.
 Chemotaxis:Flagella gives the bacteria the ability to migrate towards favorable
environment (taxis). Chemical stimuli (chemotaxis), light stimuli (phototaxis)
 Dimorphic fungi:can switch between a yeast phase and a hyphal phase in
response to environmental conditions.
 Gene is a certain segment of DNA that contains the necessary code to make a
protein or RNA molecule.

genome.The sum total of the genetic material residing on chromosomes is
referred.
 Autotrophic (lithotrophic) bacteria:Bacteria which are able to utilize CO2 as the
main source of carbon and ammonium salts as a source of nitrogen.
 Heterotrophic (organotrophic) bacteria: Bacteria which may need complex
organic compounds as a source of carbon.Most bacteria of medical importance
are heterotrophic.
 Auxotrophs :These microorganisms must obtain, at least, one component from
the environment .e.g. amino acids or vitamins Which is considered as growth
factor.
 Osmotolerant.:Some microbes adapt to wide concentrations in solute
 Halophiles.:One common type of osmophile requires high concentrations of salt;
these organisms
 Mesophiles: are organisms able to grow within a temperature range of 20-40°C
(optimum temperature of 37°C). Human pathogens are mesophiles.
 Psychrophiles (cold-loving) are capable of growth at refrigeration temperature
(0-8°C) e.g., Flavobacterium spp.
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 Thermophiles (heat-loving), grow best at high temperature (>60°C) e.g., Bacillus
stearothermophilus.
 Generation time (doubling time); is the time between two successive divisions. It is usually less than one hour for bacteria and so bacterial growth is usually
used as a synonym of multiplication.
2_Compare between eukaryotic and prokaryotic cells ?
Higher Protista (eukaryotic)
Larger
Lower Protista (prokaryotic)
Smaller
Divide by mitosis* and meiosis**
Binary fission
Show true nucleus; i.e. have nuclear Have nuclear material but NO nuclear
material, histones and nuclear membrane. membrane
Ribosome is 80S
Have endoplasmic reticulum
Ribosome is 70S
Endoplasmic reticulum is absent.
Contains mitochondria****.
No mitochondria
Cell wall composed of chitin or cellulose Mucopeptide
or absent.
Cell membrane usually contains sterols
no sterols except in mycoplasma
Doesn't contain mesosome
Contain mesosome
It includes fungi, protozoa, slime molds, Bacteria,
blue
algae except blue green algae
archaebacteria***
green
algae,
3_ What are mitochondria (power house) of the cell? Is it eukaryotic or prokaryotic
organelles?

an eukaryotic cellular organelle consisting of
a smooth outer membrane and a folded inner membrane. The inner
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folds are called “cristae”. The structures are called “power houses
of the cells” because ATP is produced in them. i.e. concerned
with energy conversion “sites of oxidative phosphorylation.
4_What are the different shapes of bacteria? And different arrangement of bacterial
cells?
 Shapes:
 Coccus: spherical (plural: cocci)
 Bacillus: rod-shaped (plural: bacilli)
 Spiral: helical shape, like corkscrew
 Vibrios: curved rods
 Arrangement:
 When cocci divide to reproduce, the cells can remain attached to one another.

Cocci that remain in pairs are called diplococci; or in chainlike patterns
streptococci.
 Those dividing in two planes and remain in groups of four are known as
tetrads.
 Those dividing in three planes and remain attached in cube-like of eight are
called sarcinae.
 Those dividing in multiple planes forming grapelike clusters are called
staphylococci.
 Most bacilli appear as single rods.
 Diplobacilli appear in pairs after division, and streptobacilli occur in chains.
5_What are the function and composition of the following bacterial organelles?
 Glycoclayx( capsule) :
 Protect pathogenic bacteria from phagocytosis.
 Some bacteria use capsule fot nutrrition and glycocalyx protect cell against
dehydration.
 Enable bacteria to attach vairus surface to form biofilm.
 Flagella:
 Responsible for bacterial motility.
 Flagella gives the bacteria the ability to migrate towards favorable
environment (taxis). Chemical stimuli (chemotaxis), light stimuli (phototaxis).
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 Spreading rapidly or swarming over media surface.
 Axial filament :
 is responsible for the locomotion caused by the corkscrew-shaped bacteria
called spirochetes.
 Fimbriae :
 They are responsible for attachment of cells that lead to

biofilms and other thick aggregates of the cells on the surfaces.
 2. It helps the microbe to adhere and colonize mucous membranes.
 Pili :

join (conjugate) bacterial cells allowing the transfer of DNA from one cell to
another. For this reason, they are sometimes also called sex pili.
 Cell wall :
 Responsible for the shape of the cell.
 Protects the cytoplasmic membrane from adverse environmental changes,
especially in hypotonic solutions.
 The site of action of some antibiotics.
 Differentiate major types of bacteria.
 Plasma membrane :
 ) Selective permeability and nutrient uptake (determine what goes in and what
goes out)
 b) Production of energy, site of oxidative phosphorylation enzymes (respiratory
enzymes)
 c) Secrete extra cellular hydrolytic enzymes
 d) Site of polymerizing enzymes for synthesis of cell wall, membrane, and DNA
 Nucleoid:
 carries all the genetic information required for the cell's structures and functions
 Plasmaid:
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 Plasmids carry genetic information for function that are not essential to the life of
organism eg. antibiotic resistance
 Ribsosome :
 Prokaryotic ribosomes are important for manufacturing proteins
 Endospore:





Bacterial endospore is highly resistant to adverse environmental conditions as:
lack of moisture or essential nutrients
toxic chemicals
radiations and high temperature.
because of their heat resistance all sterilization processes have to be designed to
destroy bacterial spores.
6_When do we call glycocalyx “capsule” and when do we call it “slime layer”?
 If the substance is organized and is firmly attached to the cell wall, the
glycocalyx is described as a capsule.
 If the substance is unorganized and loosely attached to the cell wall, the
glycocalyx is described as a slime layer.
7_ What are the different arrangements of flagella?
 There are four arrangements of flagella:

A- Monotrichous: single polar flagellum

B- Lophotrichous: two or more flagella at one pole of the cell

C- Amphitrichous: single flagellum at each end of the cell

D-Peritrichous: flagella distributed over the entire cell

E- Organism without flagella called atricate
8_What is the composition of cell envelope?
 The cell envelope is composed of two basic layers: the cell wall and the cell
membrane.
 Although each envelope layer performs a distinct function, together they act
as a single unit that maintains cell integrity.
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9_Compare between structure of cell envelope of gram positive and gram negative
bacteria.
10_what is the function of outer membrane of gram negative bacteria?
(1) Its strong negative (-ve) charge is an important factor in evading phagocytosis.
(2) The outer membrane also provides a barrier to certain antibiotics (for example,
penicillin), digestive enzymes such as lysozyme.
 When Gram negative bacteria disintegrate, the lipopolysaccharide (LPS) in the
outer most layer forms endotoxin or pyrogen that cause fever and shock
11_What is endotoxin?
that cause fever and shock
12_When bacterial cells treated with or cultured in the presence of certain antibiotics
or enzymes may lose all or a portion of their walls, What is the name of the formed
structures in case of gram positive and gram negative bacteria? What is meant by
L-form?
 Bacterial cells treated with or cultured in the presence of certain antibiotics or
enzymes may lose all or a portion of their walls and form either protoplast or
spheroplast.

In Gram positive it leaves a protoplast, in which the cell wall is completely
removed.
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In Gram negative it leaves a spheroplast, where the special structure remains.
Both protoplast and spheroplast easily rupture in hypotonic solutions
When penicillin or lysozyme is removed, protoplasts or spheroplast forms again
cell wall.
However, certain Gram negative bacteria form stable spheroplast that are known
as L-form bacteria (wall-less bacteria), which are capable of growing and
dividing.
13_What is the difference between eukaryotic and prokaryotic plasma ?
 i- Prokaryotes
 Each phospholipid molecule contains:
- a polar head, composed of a hydrophilic (water-soluble) phosphate group and
glycerol,
- non-polar hydrophobic (water-insoluble) tails composed of fatty acids.
 The polar heads are on the two surfaces of the phospholipid bilayer, and the
non-polar tails are
in the interior of the bilayer.
 ii- Eukaryotes
Eukaryotic plasma membranes contain additional compound i.e. sterols, such as
cholesterol.
Sterols make eukaryotic membrane more rigid than prokaryotic
14_What is the site of oxidative phosphorylation and energy production in bacteria?
what is the site which has selective permeability for nutrient?
 Plasma (cytoplasmic) membrane
15_What is meant by 70 s and 80 s for ribososme?
 Prokaryotic ribosomes have a sedimentation constant of 70S
 while eukaryotic ribosomes have a sedimentation constant 80 S
16_What is meant by sporulation and germination of spores?
 Sporulation:The process of endospore formation (sporulation) within a vegetative
(parent) cell
 Germination:An endospore returns to its vegetative state by a process called
17_Describe the process of sporulation.
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1- a newly replicated bacterial chromosome and a small portion of cytoplasm are
isolated by spore septum.
2-The spore septum becomes a double layered membrane that surrounds the
chromosome and cytoplasm within the original cell.
3-Thick layers of peptidoglycan are laid down between the two membrane layers.
4the resistance of endospores to chemicals
18_Explain the high heat resistance of spores.
 Bacterial endospore is highly resistant to adverse environmental conditions as:
 lack of moisture or essential nutrients

toxic chemicals

radiations and high temperature.
 because of their heat resistance all sterilization processes have to be designed to
destroy bacterial spores.
19_What are the different positions of spores in bacterial cells?
1- in the middle of the cell (central),
2- at end (terminal)
3- in between (subterminal).
In some species the spore is wider than the mother cell (bulging).
20_Why actinomyctes are mold like bacteria?
1. This is a large group of bacteria possessing a characteristically mycelial
vegetative construction similar to that formed in higher fungi.
21_What is the medical importance of actinomyctes?
. Actinomycetes, e.g. Streptomycetes synthesize antibiotics:
streptomycin
1_neomycin
2_chloramphenicol
3_ tetracycline
22_Why rickettsiae are virus like bacteria?
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1-They are visible under light microscope.
2-They are retained by bacterial filters.
3-They can be stained by ordinary stains and are gram-negative.
4-They reproduce by binary fission.
5-They are small cocco-rods having cel
6. They contain both desoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
7. They produce metabolic enzymes.
8. They are sensitive to many wide-spectrum antibiotics (but their growth is enhanced
in the presence of sulphonamides).
9. They are primary parasites of arthropods (e.g. fleas, lice, ticks and mites) from
which they can infect man and animals.
l walls containing peptidoglycan.
23_What is the medical importance of ricketssiae?
rickettsial diseases
-Epidemic and endemic typhus
- Spotted fever
- Q-Fever
24_Why do mycobacteria require special stain by acid fast stain?
 they have a unique lipid in their cell walls known as mycolic acid
25_What is the disease caused by Mycobacterium tuberculosis?
 causes tuberculosis (TB)
26_What is archaebacteria? And how it differs from bacteria?
They differ from bacteria and blue green algae in their wall membrane structure and
pattern of metabolism. They are thought to be the first of the prokaryotic and indeed
the first living organisms to be appear on the earth. -eg. Methanogens
-Most survive under extreme environments
( high temperature, high salt concentrations)
27_What is the difference between mycoplasm and protoplasts?
The genus Mycoplasma and related organisms have no walls or have very little wall
material naturally.
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It is the smallest bacteria
Their plasma membranes are unique among bacteria in having sterols, which are
thought to help protect them from osmotic lysis.
28_How could we stain mycoplasma bacteria?
 They colour poorly with aniline dyes, best by Giemsa’s stain.
29_What is the medical importance of mycoplasma?
 Mycoplasma hominis found associated with non-gonococcal urethritis and
reported to cause mild pharyngitis in human.
 Mycoplasma mycoides, causes pleuropneumonia.
30_What is the difference between cell wall of bacteria, fungi and plant?
 The bacterial cell wall is composed of a macromolecular network called
peptidoglycan or murein.
 The fungal cell walls contain chitin, while cell walls of plants contain cellulose.
31_What is the difference between the two morphological shapes of fungi (Hyphae
and yeast)?
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32_What is meant by vegetative hyphae and reproductive hyphae?
 Vegetative hyphae (mycelia) are responsible for the visible mass of growth that
appears on the surface of a substrate and penetrates it to digest and absorb
nutrients.

reproductive hyphae (aerial) which is responsible for the
production of fungal reproductive bodies called spores.
33_Compare between four orders of fungi.
zygomycota
ascomycota
Basidiomycota deuteromycota
division
Fungi perfecti
Fungi perfecti
Fungi perfecti
Sexual spores
zygospores
Ascopsore
asci
conidia
Asexual spores Sporangiospor
es,
some
conidia
Fungi
imperfecti
in Basidia
and --------basidiospore
conidia
conidia
hypahe
Usually non With
septate.
If septa
septate
the
septa
are
complete
porous the septa are Hyphae
complete
septated
habitat
Free
living Many human
saprobes; some and
plant
are
animal pathogen
parasite
examples
Rhizopus
They
are mushroom
black
bread unicellular
mold
(saccharomyce
s),
or
Some
plant
parasite and
one
human
pathogen
are
Majority are
yeast or molds
saprobe and a
few animal and
plant parasite
Candida
albicans
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multicellular
(such as those
members
of
the
genera
Penicillium
and
Aspergillus).
34_What is fungi imperfecti and fungi perfect ?
 Fungi perfecti:



Zygomycetes : non septate
Basidomycetes : septate
Ascomycetes: septate
 Fungi imperfecti
 Fungi imperfecti :septate
35_State the order of fungi which include the following fungi
a) Baker’s yeast ( sacharomyces cervesiae) : ascomycota
b) Pencillum
: ascomycota
c) Candida albicans
:deuteromycota
d) Mushroom
:Basidiomycota
e) Rhizopus black bread mould
:zygomycota
36_What is the industrial importance of fungi?
1- ferment fruit juices or cereal products, alcohol
23-Irradiation of yeast with ultraviolet light converts ergosterol into Vit D2.
4-Penicillium roqueforti is used in the production of cheese.
5- One of the main uses of fungi in recent years has been in the production of
antibiotics.
37_What is the characteristics of viruses that make it a unique group of biological
organisms differ from other living organisms and so it is not classified either as
eukaryotic or prokaryotic cells?
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 Viruses are unique group of biological entities known to infect every type of cell,
including bacteria, plants, animals and man.

Characteristics
 grow and reproduce only in living cells

Because of their small size they pass through bacterial filters
but can be retained by ultramembrane filters.
 show no independent metabolism and may even be obtainable in crystalline form.
38_What are the different viral shapes?
 Animal viruses are spherical or polyhedral

Plant viruses are rod-shaped or helical

Bacterial viruses (Bacteriophage or phages) are commonly
tadpole-shaped with a polyhedral head with hexagonal faces and a straight tail.
A fully formed viruses that is able to establish an infection in a host cell is often
called a viron.
39_What is the structure of virus?
1_a nucleic acid core:
(either RNA or DNA)
Plant viruses contain RNA only
Bacterial viruses contain DNA
About half of the animal viruses contain DNA and half RNA
2- protective coat (capsid) of identical subunits (capsomeres) made of one kind of
protein.
Together the capsid and the nucleic acid are referred to as nucleocapsid
40_What is meant by naked virus?
 Viruses that consist of only a nucleocapside and lack envelope
41_What is the structure of bacteriophage?
1.
2.
tail.
tadpole-shaped
with a polyhedral head with hexagonal faces and a straight
42_What is the difference between lytic and lysogenic cycles of viral replication?
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1- Lytic ( virulent virus): virus that can only multiply within living cell and kill the
cell by lysis.
2- lysogenic cycle (temperate phage ): Phage that can either multiply via the lytic
cycle or enter a
quiescent state in the bacterial cell.
43_What are the steps of viral replication?
1- adsorption,
2- penetration and uncoating ,
3-synthesis,
4-assembly, and packaging
5-release from the host cell.
44_What is the eclipse phase?
 Eclipse phase begins after a virus has entered a cell, since it becomes
increasingly difficult to detect infective virus.
45_What is meant by cytopathic effect (CPE) ,inclusion bodies, interference?
 cytopathic effect (CPE):are defined as virus induced damage to the cell that alters
its microscopic appearance.
 inclusion bodies:As viruses multiply within the host’s cells, large distinctive
structures called inclusion bodies may appear in the cytoplasm or in the nucleus.
 These bodies stain characteristically they are often of diagnostic importance e.g.
in rabies of the dog the presence of such structure in brain cells justifies
presumptive diagnosis.
 Interference:When organisms are inoculated with certain viruses they become
resistant to a second more virulent virus.
 The infection may be quite unrelated.
46_What is interferon and its function?
 Interferon: This substance has been found to be a protein
 Function:
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 Interferon acts on or in the host cells preventing the synthesis of virus particles
47_Write on cultivation of animal virus in details.
. Animal inoculation:
Experimental animals such as mice are used for the cultivation of some viruses.
Growth of the virus is indicated by
-signs of disease
-death of the inoculated animal
Exceptions
-serum hepatitis: not possible to grow them in experimental animals
48_What is the difference between plasmid and chromosome?
 Chromosome:
1-The majority existing as large complexes of DNA and proteins called
chromosomes.
Each bacterial cell has a single circular chromosome composed of two polynucleotide
chains twisted together in a double helix.

Plasmid:
Extrachromosal DNA. Plasmids are independently replicating, small DNA molecules
found in some bacterial, protozoan, and fungal cells. It is not generally considered
part of the genome.
49_What is the composition of nucleotide ?
The nucleotide consist:
1.
2.
3.
4.
5.
6.
Base
deoxyribose or ribose sugar (5 carbon monosaccharide)
phosphate group
Purine bases: Guanine, Adenine
-Pyrimidine bases,Cytosine, Thymine, Uracil
bases are arranged along a backbone made of
deoxyribose sugar or ribose sugar
groups
and phosphate
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50_Compare between DNA and RNA
DNA
Stores the genetic information of the
organism
Contains four bases: 1-Pyrimidine
bases
Cytosine,
Thymine
2-Purine bases
Guanine, Adenine
RNA
Converts the genetic information into
proteins
Contains four bases: 1-Pyrimidine
bases
Cytosine, Uracil
2-Purine
bases
Guanine, Adenine
DNA is a double helix molecule
(except in some viruses)
Single-stranded (except in some
viruses)
The sugar is deoxy ribose in DNA
The sugar in the RNA is ribose
51_What is the phosphate sugar backbone?

The sugar molecule has OH groups one at carbon number 3 and the other at
carbon number 5. These two sites are points of connection between sugar
molecules forming sugar backbone.

The phosphate molecule is attached to the number 5 carbon
atom of the sugar

The strand of nucleic acid has two ends
5 prime (5') end, which ends with the phosphate group.
3 prime (3') end, which end with number 3 carbon atom of the sugar
 Two neighboring nitrogenous bases are connected to each other by hydrogen
bonds.

The two nitrogenous bases that make hydrogen bond
together are said to be complementary to each other.
52_What is meant by codon?
17
 The message of this transcriped strand is later read as a series of triplets called
codons.
53_What are the different types of RNA and their function?
a.Ribosomal RNA (rRNA)
The procaryotic ribosome (70S) ribosome is a particle composed of tightly
packaged ribosomal RNA (rRNA) and protein, it consists of two subunits of the
ribosome (50S and 30S)
b.Messenger RNA (mRNA)
Is a transcript (copy) of genes in the DNA. The message of this transcriped strand
is later read as a series of triplets called codons.
c.Transfer RNA (tRNA)
It act as a translator that converts RNAs language into protein language.
The bottom loop of the coverleaf expose a triplet , the anticodon, that
complement mRNA’s codons. At the opposite end of the molecule is a binding
site for the amino acid that is specific for that tRNA’s anticodon.
For each of the 20 amino acids, there is at least one specialized type of tRNA to
carry it.
54_What is meant by DNA replication and describe the steps of replication?
 DNA replication, the information in DNA is duplicated prior to cell division so
that after binary fission, both cells will have the same genetic information as the
parental cell.
 Steps:
 1.One DNA strand serves as template
18

 2. A replication fork is formed, where helicase maintains single stranded regions

 3. Primase inserts a primer
 4. DNA polymerase adds nucleotides
55_What is meant by transcription and its steps?
 The second process is the transfer of information contained in the sequence of
nucleotides in DNA into a sequence of amino acids in protein (transcription and
translation).
 Steps:
 1.DNA serves as template

 2.RNA polymerase synthesizes RNA
56_What is meant by translation and its steps?
nitiation of protein synthesis requires the presence of:
-ribosome (30S and 50S subunits)
-tRNA
-mRNA
-mRNA is translated into a sequence of amino acids that make up the protein.
-Codon is in the form of a linear sequence of triplets (one triplet = three bases).
 Translation- steps
1-The ribosome moves along the mRNA exposing a triplet.
2-As each triplet is exposed by the ribosome, a transfer RNA (tRNA) with a
complementary anticodon binds to the triplet (ie. codon) of the mRNA.
3-Attached to the other end of the tRNA is a single amino acid.
4-The amino acid of the second tRNA bonds to the amino acid carried by the first
tRNA.
5-As soon as the bonding between amino acids takes
place, the bonds between the tRNA and amino
acids are broken and leave the ribosome.
57_How does genotypic variation take place?
19
ALTERATIONS IN GENETIC INFORMATION
Genotypic variation is heritable .
Genomes change by a variety of mechanisms.
1. Without gene transfer: mutation
2. With gene transfer: Transformation
Conjugation
Transduction
58_What is meant by mutation?
It results from a change in the nucleotide sequence of DNA that may occur
spontaneously as a replication error (at a rate of once every 106-107 cells), or may be
induced by radiation or chemical agents.
Induced mutation occur by the action of mutagenic agents e.g irradiation, acridine
dyes and alkylating agents
These new properties are irreversible and passed to the offspring.
59_Compare between genotypic and phenotypic variations
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Phenotypic variation
Genotypic variation
It occurs in response to changes in
the environmental conditions without
change in the genetic constitution.
It occurs as a result of a change in
the underlying genetic constitution.
- Reversible (transient).
Irreversible (permanent).
Not-heritable.
- Heritable.
Examples:L-forms of bacteria.Loss
of flagella upon exposure to phenol.
Examples;
It
occurs
through:Mutation.Gene
transfer:Transformation.Transduction
.Conjugation.
60_How gene could be transferred from one bacteria to another one?
 Transformation
 Transduction
 Conjugation
61_What are the types of mutation?
1- Missense mutations
-Result in a change in the amino acid inserted into the polypeptide chain; can lead to
production of inactive enzyme.
Sometimes have little effect on phenotype (silent mutations).
2- Nonsense mutations
- when the alteration in the base sequence of DNA results in the
nonsense codon terminator signal during protein synthesis
formation
of
a
21
3- Frame shift mutations
Adding or deleting single base pair changes reading frame of transcribed mRNA
Can result in misreading of large number of codons
62_What is meant by transformation, conjugation and transduction?

Transformation: free DNA released by lysis from certain bacterial cell, can be
taken up by other cell leading to acquired new character in this cell.
Cells that are capable of accepting gentic material through this means are termed
competent
-eg. DNA from dead capsulated cells of Diplococcus pneumoniae was mixed with
some changes into capsulated.
 Conjugation: It is a transport of genetic material from one cell to another related
cell by sex pili.
 Transduction: hereditary material of one cell is transmitted to
another cell by means of bacteriophage (virus) called temperate phage:
-When phage attacks a bacterial cell (donor), certain fragments of the genetic
material of this cell will be incorporated into the newly formed phage.
63_What is meant by F factor? High fertility factor and low fertility factor

F factor: known as transmissible plasmids that allows the synthesis of a
conjugative pilus
1. F+ cells serve as genetic donors,
2.
F- cells serve as recipients,
 High fertility factor: it may become integrated in the chromosome .

low fertility factor: The F factor may be present in the cytoplasm of the cell
(plasmid)
64_Write in catabolism and anabolism.
In catabolism,
1) The carbon source of nutrients is converted into basic small molecules (building
units) such as acetate, ….etc
22
2) Energy is liberated and trapped by the conversion of adenosine diphosphate
(ADP) in the cell to adenosine triphosphate (ATP).
ADP
Energy
ATP
Products of catabolism are utilized in:
a) Biosynthesis of cell components (macromolecules) in anabolism
b) Cell movement.
c) Cell multiplication and growth.
d) Transport of nutrients.
e) Repair of cell damage.
In anabolism,
1. The building units produced by catabolic processes are converted to activated
monomers (amino acids, nucleotides,...) and coenzymes. This step requires energy
(ATP).
2. The activated monomers are then polymerized into macro-molecules (e.g.
polypeptides, polynucleotides, polysaccharides,...). This step requires energy (ATP).
3. The polymerized molecules are then assembled to form the cell structures. This
step also requires energy.
65_What are the types of metabolic enzymes?
1-Constitutive enzymes: enzymes are synthesized inside the microbial cell in
presence or absence of their substrates.
2- Induced enzymes: enzymes are produced by the organism only in the presence
of the substrate itself (inducers).
The specificity of enzyme is described as “lock and key” fit in which the substrate is
inserted into the active site’s pocket.
66_Write on the classification of bacteria according to the mean by which it obtain its
carbon source.
Autotrophic (lithotrophic) bacteria:
Bacteria which are able to utilize CO2 as the main source of carbon and ammonium
salts as a source of nitrogen.
The energy required for their metabolism is predominantly derived from light or
simple chemical reactions.
Heterotrophic (organotrophic) bacteria:
Bacteria which may need complex organic compounds as a source of carbon.
Most bacteria of medical importance are heterotrophic.
23
67_Write on the classification of bacteria according to oxygen consumption giving
examples
Oxygen is a major component of organic compounds such as carbohydrates, lipids,
nucleic acids, and proteins.
According to O2 requirements, bacteria are classified into:
a) Strict or obligate aerobes require oxygen for growth, e.g., Pseudomonas
aeruginosa and Vibrio cholerae.
b) Strict or obligate anaerobes require complete absence of oxygen, e.g.,
Bacteroid fragilis.
c) Facultative anaerobes generally grow better in presence of oxygen but still are
able to grow in its absence, e.g., Staphylococci, E.coli, …etc.
d) Micro-aerophilic organisms require reduced oxygen level, e.g., Campylobacter and
Helicobacter.
68_How do we cultivate anaerobic bacteria?
-cultivation in oxygen free atmospheres ( by using anaerobic jar)
-growth in culture media containing a reducing agent
Sometimes a combination of both methods is used.
69_How ATP is is generated in bacterial cells?
Cellular respiration: is a process in which molecules are oxidized and ATP is
generated. That take place in catabolism
Oxidation of a molecule is equivalent to removal of hydrogen or electrons.
70_What is the difference between aerobic respiration fermentation?
 aerobic respiration, the final hydrogen or electron recipient in oxidation process
is molecular oxygen (O2).
 the oxidation process is referred to as fermentation
71_What is meant by capnophilic bacteria?
he minute amount of CO2 present in air is sufficient for most bacteria. However,
certain species require higher concentrations (5-10%) of CO2 for growth (capnophilic)
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e.g., Neisseria spp. and Brucella abortus
72_What is meant by halophiles, osmpohiles, osmotolerant?

Halophiles: One common type of osmophile requires high concentrations of salt;
these organisms
 Osmpohiles: Most microbes exist under hypotonic or isotonic conditions.
A few called osmophiles, live in habitats with a high solute concentration.
 Osmotolerant: Some microbes adapt to wide concentrations in solute,
73_Write on the classification of bacteria according to temperature suitable for
growth
 Mesophiles are organisms able to grow within a temperature range of 20-40°C
(optimum temperature of 37°C). Human pathogens are mesophiles.

Psychrophiles (cold-loving) are capable of growth at
refrigeration temperature (0-8°C) e.g., Flavobacterium spp.

Thermophiles (heat-loving), grow best at high temperature
(>60°C) e.g., Bacillus stearothermophilus.
74_Write on bacterial reproduction by binary fission
Bacterial multiplication takes place by simple binary fission:
1- The cell grows in size, usually elongates.
2- The bacterial chromosome acts as a template for the replication of another copy.
3- Each copy is attached to a mesosome on the cytoplasmic membrane.
4- The protoplasm becomes divided into two equal parts by the growth of a
transverse septum from the cytoplasmic membrane and cell wall.
75_How can we maintain the bacteria in the exponential phase?
 Cells can be maintained in exponential phase by transferring them repeatedly into
fresh medium of identical composition while they are still growing exponentially.
Two devices have been invented for carrying out this process automatically:
-chemostat
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-turbidostat
76_What are the different phases of bacterial growth curve?
Lag phase
Exponential
(logarithmic phase)
-The initial number -the number of
of bacterial cells cells increases in
remains constant.
an
exponential
-The
cells, manner
however, consume
nutrients from the
medium with the
result
of
an
increase in their
size prior to the
division.
Stationary phase
Exhaustion
of
nutrients
and
accumulation
of
toxic
products
cause growth to
decrease.
-There is slow loss
of cells through
death which is just
balanced
by
formation of new
cells.
-Secondary
metabolites such as
antibiotics
and
exotoxins
accumulate during
this phase.
Death rate=growth
rate
Decline or death
phase
the death rate
increases and the
number of viable
organisms
decreases markedly