Education

1. ZERA INTERNATIONAL
COLLEGE OF HEALTH
SCIENCES
DEPARTMENT OF CLINICAL MEDICINE
BIOMEDICAL SCIENCES
UNIT: MICROBIOLOGY
LECTURE 9 : MICROBIAL PHYSIOLOGY & PATHOGENICITY
;BACTERIAL GENETICS
Ms Nsofu BSc,.BMS

2. The genome
 Comprises all the genetic material that an organism possesses
 It includes the sequence of each chromosome plus any DNA in organelles
 The main function of the genetic material is to store information required to produce
an organism
 The DNA molecule does that through its base sequence
Chromosome
 Are the structures that contain the genetic material i.e. they are complexes of DNA
and proteins
 # of chromosomes present in bacteria is only one and is circular in shape( no ends)

3. Gene
 Is the basic unit of heredity, and its a segment of deoxyribonucleic acid (DNA)
that encodes in its nucleotide sequence information for a specific physiologic
property
Replicons
 Is a general term for double-stranded DNA circles (chromosomes, plasmids)
capable of self-replication.

4.  DNA is a polymeric nucleic acid macromolecule composed of three types of units:
Five-carbon sugar (Deoxyribose)
A nitrogen-contain base and
A phosphate group

5.  Both RNA & DNA are polymers
 The chemical structure of the simple monomer units making up these two molecules
is very similar
 The single units are called nucleotides or mononucleotides
 Each mononucleotide has three parts
A 5 carbon sugar or pentose sugar
A nitrogen containing base
Phosphoric acid
 The pentose sugar in RNA is ribose and in DNA is deoxyribose
 Deoxyribose as its name suggests, contains one oxygen atom fewer than ribose

7.  The bases are of two types, purines and pyrimidines.
 In DNA, there are two purine bases, Adenine (A) and Guanine (G), and two
pyrimidines, Thymine (T) and Cytosine (C).
 Nucleotides, each composed of a base, a phosphate and sugar moiety, polymerize into
long polynucleotide chains.

8.  Transcribes and translates DNA-bound genetic instructions for protein synthesis.
 Is generally single stranded.
 Substitutes uracil for the thymine base used by DNA; the complementary base
pairs for RNA are A=U or G=C.

9. Found in three types
1. Messenger RNA (mRNA)
 Is the template that carries DNA gene sequences to ribosomes, the site of protein
synthesis.
2. Ribosomal RNA (rRNA)
 Is a structural component of ribosomes.
 Acts as a substrate for protein synthesis.
3. Transfer RNA (tRNA)
 Carries specific amino acids to the triplet-encoded, mRNA borne message that
translates the message into the amino acid structure of proteins.

10.  Bacteria possess two genetic structures:
1. Chromosome
2. Plasmid
 Both of these structures consist of a single circular DNA double helix twisted
counterclockwise about its helical axis
 Replication of this DNA molecule always starts at a certain point (the origin of
replication) and is “semiconservative,” that is, one strand in each of the two resulting
double strands is conserved.
 Each DNA strand serves as a template for the synthesis of a new strand, producing 2
new DNA molecules, each with one new strand and one old strand.
 This is semiconservative replication

12.  DNA can be transferred from one organism to another and that DNA can be stably
incorporated in the recipient, permanently changing its genetic composition
 Despite the fact that bacteria reproduce exclusively asexually, the sharing of genetic
information within and between related species is common and occurs in at least three
fundamentally different ways
 All three processes involve a one way transfer of DNA from a donor cell to a recipient
cell that can result in the acquisition of new characteristics (e.g., antigens, toxins,
antibiotic resistance)
 The molecule of DNA introduced into the recipient is called the exogenote to
distinguish it from the cell’s own original chromosome, called the endogenote
 The three methods of DNA transfer are Transformation, Transduction and
conjugation

13.  Is the process by which one cell, the donor or male, makes contact with another, the
recipient or female and DNA is transferred directly from the donor to the recipient
 Conjugation is mediated by extrachromosomal genetic elements known as plasmids
(circular pieces of DNA that replicate independently from chromosomal DNA)
 Their genes are not essential for growth
 It is mediated by plasmids which are able to code for the F (sex) Pilli (conjugation pili)
 The F pillus attaches to the surface of the recipient cell
 The F-pillus extends to ensure contact between the two cells

14.  Mostly, the only DNA transferred during conjugation is the plasmid that mediates
the process
 Transfer of chromosomal DNA is rare
 The circular plasmid DNA is nicked at a specific site and one end is passed into
the recipient cell
 The DNA is replicated during transfer so that each cell receives a copy of the
plasmid
 The recipient cell then becomes a potential donor cell

17.  Transduction is the transfer of DNA between cells by bacteriophages ( Phage's)
 Phages are viruses that can infect Bacteria
 All known transducing phages are double stranded DNA viruses
 In simplest terms, a transducing particle might be regarded as bacterial DNA in a
phage coat.
 When this transducing phage infects a bacterial cell, the bacterial genome
contained therein is transferred to the infected host cell

18.  It occurs in two forms:
In generalized transduction, the phage randomly packages host DNA in a
bacteriophage coat and may transfer any gene. The transducing particle contains
only host DNA.
In specialized transduction, the phage favors the transfer of host DNA segments
near the site of integration. Specialized transducing phages contain both viral and
host genes.
 The capacity of phages to make rapid replicas of their DNA makes them valuable
to genetic engineering.

19.  As well as chromosomal genes, transducing phages can also pick up and transfer
plasmid DNA
 Genes can be transduced only between fairly closely related strains since
particular phages only attack a limited range of bacteria.

21.  Involves the release of DNA into the environment by the lysis of some cells, followed
by the direct uptake of the DNA by the recipient cells.
 The foreign DNA is either integrated into the bacterial chromosome through
recombination or is degraded.
 Is the direct uptake and recombination of naked DNA fragments through the cell wall
by competent bacteria.
 Natural occurrence of this process is uncommon.
 Bacteria will normally uptake DNA from media or the environment
 In nature, bacteria even after death release nucleic acids into the environment

22.  Other bacteria can uptake foreign DNA, recombine it and express it
 However a lot of nucleic acid is degraded by nucleases including restriction
endonucleases found in many bacteria
 Transformation occurs in many bacteria including Bacillus, Haemophilus,
Neisseria, Acinetobacter, Streptococcus and Staphyloccocus species.

23. TRANSFORMATION
 Cells are competent for transformation only under certain conditions of growth
 There are mechanisms by which cells can be made artificially competent
 Competency refers to the ability of bacteria to uptake and express DNA
 Artificial methods of bacteria transformation are available such as chemical
transformation, or electrical transformation
 Foreign DNA is incorporated into recipient DNA by recombination (Occurs in closely
related organisms)
 Any gene can be transferred by transformation
 The acquired DNA is normally relatively shorter