Bacterial Genetics

Dr. Iman Ibrahim

Structure of Bacterial genome1 -Bacterial nucleoid

2 -plasmids or large -The nucleic acids are polymeric macromolecules known forms of life, biological molecules, essential for all

(deoxyribonucleic acid ) - and The nucleic acids includes DNA RNA (ribonucleic acid)

- it is composed of Simple units called nucleotides, connected in long chains

Nucleotides have 3 parts:

1 -5-Carbon sugar (pentose).2 -Nitrogenous base .

3 -A phosphate group ( P ).Dr. Iman Ibrahim

1 -Ribonucleic acids (RNA)

The pentose sugar is Ribose (has a hydroxyl group in the 2nd carbon---OH)

2 -Deoxyribonucleic acids (DNA)

The pentose sugar is Deoxyribose( has just an hydrogen in the same place--- H)

Deoxy = “minus oxygen“

Dr. Iman Ibrahim

DNA Nucleotides Composition (3 parts):

1 -Deoxyribose sugar (no O in 2nd carbon)2 -Phosphate group

3 -One of 4 types of bases (all containing nitrogen) : - Adenine

- Thymine (Only in DNA) - Cytosine - Guanine

RNA Nucleotides

Composition ( 3 parts):1 -Ribose sugar (with O in 2nd carbon)

2 -Phosphate group3 -One of 4 types of bases (all containing nitrogen) :

-Adenine -Uracyl (only in RNA)

-Cytosine -Guanine

Dr. Iman Ibrahim

Dr. Iman Ibrahim

A gene is the molecular unit of heredity of a living organism. It is widely accepted by the scientific community as a name given to some stretches of deoxyribonucleic acids (DNA) and

ribonucleic acids (RNA) that code for a polypeptide

Dr. Iman Ibrahim

AUG The start codon always codes for methionine

stop codon (DNA) TAA or TAG or TGAStop codon (RNA) UAG, UAA, UGA

Dr. Iman Ibrahim

Bacteriophage

-Bacteriophage are bacterial viruses which pass through minute pore filters and live at the expense of reproducing bacteria, it has strict species.

-Phage distributed in nature and found wherever the bacteria are found

Dr. Iman Ibrahim

Structure of phage

Bacteriophage has spermatoid shape

1 -Head : Consisted of protein coat (capsid) and enclosing a core of nucleic acids

2 -Hollow core

3 -Tail : -Helical contractile sheath

-Base plate -Tail pins ( perferator)

Dr. Iman Ibrahim

Uses of phages:1 -Used in diagnosis of unknown bacteria.2 -Used for serotyping of different bacteria

Mechanism of interaction between phage and bacteria

1 -The phage particles come in contact with the bacterial cell

2 -the phage adsorbed on bacteria by its tail3 -the tail penetrate the bacterial cell wall

4 -the contents of the head flow into the bacterial cell 5 -replication of the phage DNA and assembly of the

phage structure6 -Lysis of the bacterial cell and exit of new phages

Dr. Iman Ibrahim

Dr. Iman Ibrahim

Bacterial Variation

Dr. Iman Ibrahim

Variation in bacterial characters occurs by acquiring a new characters or by loss of characters

Bacterial variation

Permanent (Genotypic)

Temporary (Phenotypic)

Dr. Iman Ibrahim

Phenotypic Genotypic Item

Temporary Permanent Action

Extrinsic factors, don’t affect DNA

Extrinsic or Intrinsic factors, affect DNA

causes

reversible Irreversible and constant Nature

The second generation similar to the parent cells

The second generation differ completely than the parent cells

The characters of the second generation

1 -loss of motility of some strains due to subleathal dose of phenol, when we remove the phenol the daughter cells

posses the flagella

1 -attenuation of virulent strains2 -change in sensitivity to

antibiotics3 -biochemical characters

4 -antigenic structure

examples

Dr. Iman Ibrahim

Bacterial variation may be

1 -Phenotypic2 -Genotypic

1 -variation in morphology (mutation) (pleomorphism) : -Short bacilli becomes long

-sporulated or capsulated bacteria loss this characters -flagellated bacteria loss flagella

-pigmented bacteria stop its production

2 -variation in biochemical characters : -bacteria produce indole stop its production

-bacteria ferment sugars stop fermenting -bacteria needs CO2 for growth may grow under aerobic

conditions

3 -variation in cultural characters (Dissociation) : -Change of colonies from smooth form to rough form

Dr. Iman Ibrahim

Rough form Smooth form Item

Saprophytic bacteria Parasitic bacteria Type

Rough, irregular, dull, opaque Glistening, smooth, round colonies

Filamentous, pleomorphism Regular in shape Organism morphology

Pale Deeply stained staining

Non-motile or slow motion Motile in motile species motility

Sediment or supernatant Uniform turbidity Subculture in broth

Weakly antigenic Highly antigenic antigenicity

Low or no virulence Virulent except B.anthracis pathogenicity

Difficult to S-form Easily to R-form change

Suspended spontaneously Easily suspended suspension

In laboratory Fresh materials isolation

Non- capsulated Well developed capsule capsule

Less active Active Biochemical activity

Less sensitive sensitive Effect of phage

Dr. Iman Ibrahim