Prokaryotic cell :History,Features,Structure,Bacterial genome, Bacterial Nutrition, Bacterial toxin, Control of Microbial Growth

 PROKARYOTIC CELL

• History of Microbiology
• Features of prokaryotic cell
• Structure of prokaryotic cell
• Bacterial genome
• Bacterial Nutrition
• Horizontal gene transfer and genetic recombination
• Various Bacterial Groups
• Bacterial toxin
• Control of Microbial Growth 

HISTORY OF MICROBIOLOGY

• Microbiology – Study of Microbes

Father of microbiology – Antoni Van Leewnhoek

• Pasteurization(killing of microbes) – Louis Pasteur
• Pioneer in medical microbiology – Robert Koch
• Comparative study of rRNA- Carl Woese

FEATURES OF PROKARYOTIC CELL

• Nucleus is absent
• DNA complex with histone is absent
• One chromosome
• Mitosis and meiosis is absent
• Sterol in plasma membrane
• 70s Ribosome
• Membrane bound organelle absent
• Cell wall made up of peptidoglycan
• Small ribosomal unit (16S)

STRUCTURE OF PROKARYOTIC CELL

Size – 0.2-2 μm in diameter and 0.5-5 μm

Smallest bacteria – genus Mycoplasma(0.3 μm in diameter )

Largest bacteria – Thiomargarita namibiensis and Epulopiscum fishelsoni

Shape – Bacillus (rod ), Coccus (spherical ovoid), Spirilla (helical shaped), Vibro

(comma shaped)

Staining- Gram negative bacteria - pink colour(thin peptidoglycan and thick outer

membrane

Gram positive bacteria – purple colour(thick peptidoglycan)

Cell wall – made of peptidoglycan which consist of NAM(N-muramic acid) &

NAG(N- acetyl glucosoamine) and tetrapeptide(L-alanine,L-lysine,

D- Glutamine, D-alanine)

• Biosynthesis of peptidoglycan

First stage- occur in the cytoplasm and synthesis of UDP- NAM and

UDP-NAG

Second stage- addition of amino acid leads to formation of

NAM-pentapeptide

Third stage- UDP-NAM-Pentapeptide make complex with bactoprenol and

forms lipid I and UDP-NAG is added to lipid I yielding lipid II

Fourth stage- polymerization

• Protoplast- lack of cell wall
• Spheroplast-which retain outer membrane after pencillin treatment
• Outer Membrane- made up of lipopolysaccharide(core-polysaccharide,O-polysaccharide, lipid portion),lipoprotein, proteins and phospholipid andporin(protein) are present

GLYCOCALYX

made up of capsule(tightly bound) & slime layer(loosely bound)

Plasma Membrane- composed of protein and phospholipid and perform

various function including transport , energy transduction

Mesosome – invagination(folding) of plasma membrane

CYTOPLASM

-70S(30S &50S)

Inclusion bodies- Ribosomes and reserves deposits in cytoplasm.

Gas vesicle- structure of protein permeable to gas

Carboxysomes- polyhedral inclusion body contain the CO2 fixation

enzyme

Polyphosphate granules- inorganic phosphate present in cytoplasm

Magnetosomes- magnetic mineral crystal surround by lipid bilayer

(Fe3O4 and Fe3S4)

Surface appendages

3 types-   flagella(locomotion)

                pili(Conjugation)

                fimbriae(attachment)

Structure of flagella – long filament(which lies external to the cell surface), hook(end

of filament), Basal body(hook is anchored which impart motion to the flagellum)

Various membrane of flagella-

 M(Membrane), S(supermembranous), P(Peptidoglycan)

and L(Lipopolysaccharide),C(Cytoplamic) , MS & S is a rotor

Monotrious (one flagellum)

Amphitricous(one flagellum attached at each end)

Lophotricous(cluster of flagella at one end or both ends)

Peritricous(flagella are spread fairly evenly over the whole surface)

ENDOSPORES

Property of gram positive or negative bacteria

BACTERIAL GENOME

Bacterial chromosomes – Nucleoid (consist of proteins)

Plasmid- autonomous self replicating molecules of DNA

• Conjugative plasmid – self transmissible plasmid
• Immobilizable plasmid
• F plasmid
• R plasmid
• col plasmid

BACTERIAL NUTRITION

Carbon Source – Autotroph(CO2) & Heterotroph(Organic Carbon)

Energy Source- Phototroph(light) & Chemotroph(chemical compound)

Electron Source- Lithotroph(Inorganic Compound) & organic Compound)

Nutritional Types of Bacteria

• Photolithoautotropy-(purple and green sulphur bacteria, Blue green bacteria)
• Photoorganoheterotropy-(Purple non sulphur bacteria , Green non sulphur bacteria)
• Chemolithoautotropy-(Sulphur oxidizing bacteria, Hydrogen bacteria , Nitrifying Bacteria)
• Chemoorganoheterotrophy –(Non photosynthetic Bacteria)

HORIZONTAL GENE TRANSFER AND GENETIC
RECOMBINATION

TRANSFORMATION – transfer of DNA molecule from medium to

cytoplasm

TRANSDUCTION – vector transfer from one donar bacteria to receipent

bacteria

General transduction =

CONJUGATION – DNA transfer by pilus formation between two

bacteria . Ex- F+ F- conjugation , Hfr- F- conjugation, F’ F+ conjugation

VARIOUS BACTERIAL GROUPS

Rickettsias (non motile,obligate intracellular parsasite , transmitted by blood

sucking orthopods) ex- typhus fever.rocky mountain spotted fever and Q

fever(Coviella burnetii)

Chlamydiae (non motile, obligate intracellular parsasite , gram negative

bacteria, lack many biosynthetic pathway

Actinomycetes ( aerobic gram positive bacteria) ex- Conidiospores &

sporangiopores )

Spirochetes ( gram negative, chemoheterotrophic bacteria )ex- Treponema

pallidum)

Mycoplasma ( self producing gram negative bacteria)

Cyanobacteria ( gram negative bacteria photosynthetic bacteria)

Archaebacteria( consist of DNA replication , transcription and translation)

ex- Methanogens ,Extremely halophiles,thermophilies

BACTERIAL TOXIN

Toxin- metabolic product that damages the host

CONTROL OF MICROBIAL GROWTH

Bacterial growth (lag phase, log phase, stationary phase,decline phase)

Generation time = t/n

n = logNo-logN/log2

Disinfectants (kill micro-organisms) ex- hypochlorites, copper

sulfate,formaldehyde,phenolic compound, mercuric chloride

Antiseptic( kill or inhibit micro-organism) ex- alcohol ,silver nitrate,iodine

solution

Sterilization(total distruction of elimination of organism)

Physical agent ( radiation, filtration)

Chemical agent( heavy metal , halogen and dyes)

MCQ

1. What is the name of the region where double-stranded single circular DNA is found in the

prokaryotic cell?

(a) Protonucleus (b) Nucleus (c) Nucleoid (d) Nucleoplasm

Answer: (c)

2. In prokaryotic cells, ribosomes are

(a)70 S (b) 80 S (c) 60S + 40S (d) 50S + 40S

Answer: (a)

3. The two domains to which prokaryotes are classified into are:

(a) Bacteria and Protista (b) Bacteria and Archaea (c) Archaea and Eukarya (d) Eukarya and Monera

Answer: (b)

4. When a water sample from a hot thermal vent was tested, it was found to contain a single-celled

organism having a cell wall lacking a nucleus. What is its classification most likely?

(a) Eukarya (b) Fungi (c) Protista (d) Archaea

Answer:

5. Which of these is a characteristic of prokaryotic cells?

(a) Absence of cell organelles (b) Absence of nucleus (c) Presence of 70S ribosomes (d)

All of these

Answer: (d)

6. A difference between eukaryotic and prokaryotic cells is in having

(a) Ribosomes (b) Cell wall (c) Nuclear membrane (d) None of the above

Answer: (c)

7. In prokaryotes, the hair-like outgrowths which attach to the surface of other bacterial cells

are

(a) Flagella (b) Pili (c) Capsule (d) Plasmids

Answer: (b)

8. A component of prokaryotic cells:

(a) Plasma membrane (b) DNA (c) Cytoplasm (d) All of these

Answer: (d)

9. The process of recombination in prokaryotes takes place in this way

(a) Transformation (b) Conjugation (c) Transduction (d) All of the above

Answer: (d)

10. The flagella of a prokaryotic and eukaryotic cell vary in

(a) Mode of functioning and location in the cell (b) Types of movement and placement in the cell

(c) Microtubular organization and function (d) Microtubular organization and type of movement

Answer: (d)

11) the electron acceptor in the anaerobic conditions in prokaryotic

a) glucose, frutose, matltose b) SO4-2 c) antioxidant as vit k d) fatty acid

Answer :(d)

12) which one of the following features is not required in prokaryotic expression vector

a)oriC b) selection marker c)CMV promotor d) ribosome binding site

Answer :(c)