Mutations are changes in the nucleotide sequence of DNA. They may occur spontaneously during DNA replication or be induced by mutagens like chemicals, radiation, or viruses. Mutations can be harmful, harmless, or beneficial depending on their location and effects. There are several types of mutations including substitutions, insertions, deletions, and frameshifts which can alter protein functions and cause diseases. Bacteria can develop resistance to antibiotics via mutations selected through antibiotic use.

1. Mutations
Dr. Mohammedazim Bagban
Asst. Professor & Head (Microbiology)
C. U. Shah Institute of Science

2. What Are Mutations?
 Changes in the
nucleotide sequence of
DNA
 May occur in somatic
cells (aren’t passed to
offspring)
 May occur in gametes
(eggs & sperm) and be
passed to offspring

3. Are Mutations Helpful or Harmful?
 Mutations happen regularly
 Almost all mutations are neutral
 Chemicals & UV radiation cause mutations
 Many mutations are repaired by enzymes
 Some type of skin cancers and leukemia
result from somatic mutations
 Some mutations may improve an organism’s
survival (beneficial

4. Types of Mutations
A. Spontaneous mutations
B. Induced mutations

5. Spontaneous Mutations
 Mutations may arise in the cell as a result of naturally
occurring changes (spontaneous mutations) in the DNA
sequence as a result of mismatched base insertion or
slippage errors (leading to small additions or deletions)
by DNA polymerases.
 These spontaneous mutations are minimized by the
proofreading function of the DNA polymerases but,
nevertheless, occur at a frequency of approximately
10-9. Other spontaneous mutations may be due to
lesions that occur when the bond be tween a sugar and
base is broken or when deamination of cytosine forms
uracil.

6. The Lederberg experiment
 In 1952, Esther and Joshua Lederberg performed an experiment that
helped show that many mutations are random, not directed. In this
experiment, they capitalized on the ease with which bacteria can be
grown and maintained. Bacteria grow into isolated colonies on plates.
These colonies can be reproduced from an original plate to new plates
by "stamping" the original plate with a cloth and then stamping empty
plates with the same cloth. Bacteria from each colony are picked up on
the cloth and then deposited on the new plates by the cloth.
 Esther and Joshua hypothesized that antibiotic resistant strains of
bacteria surviving an application of antibiotics had the resistance
before their exposure to the antibiotics, not as a result of the
exposure.

7. The Lederberg experiment

8. The Lederberg experiment

9. Spontaneous Mutations
 Five types exist:
 Transition
 Transversion
 Insertion
 Deletion
 Development of AP sites

10. Transition
 Transition, in genetics and
molecular biology, refers to
a point mutation that
changes a purine
nucleotide to another
purine (A ↔ G), or a
pyrimidine nucleotide to
another pyrimidine (C ↔
T). Transitions can be
caused by oxidative
deamination and
tautomerization.

11. Tranversion
 Transversion, in molecular
biology, refers to a point
mutation in DNA in which a
single (two ring) purine (A or
G) is changed for a (one ring)
pyrimidine (T or C), or vice
versa.[1] A transversion can
be spontaneous, or it can be
caused by ionizing radiation
or alkylating agents. It can
only be reversed by a
spontaneous reversion.

12. Insertion
 In genetics, an insertion (also called
an insertion mutation) is the addition
of one or more nucleotide base pairs
into a DNA sequence. This can often
happen in microsatellite regions due
to the DNA polymerase slipping.
Insertions can be anywhere in size
from one base pair incorrectly
inserted into a DNA sequence to a
section of one chromosome inserted
into another.

13. Deletion
 In genetics, a deletion (also called gene deletion, deficiency, or deletion
mutation) (sign: Δ) is a mutation (a genetic aberration) in which a part of
a chromosome or a sequence of DNA is left out during DNA replication.
Any number of nucleotides can be deleted, from a single base to an entire
piece of chromosome.

14. Inversion
 Chromosome segment breaks off
 Segment flips around backwards
 Segment reattaches

15. Development of AP sites
 In biochemistry and molecular
genetics, an AP site
(apurinic/apyrimidinic site),
also known as an abasic site,
is a location in DNA (also in
RNA but much less likely) that
has neither a purine nor a
pyrimidine base, either
spontaneously or due to DNA
damage.
 AP sites can be formed by
spontaneous depurination, but
also occur as intermediates in
base excision repair.

17. Induced Mutations
 Three types exist:
 Chemical mutagens
 Physical mutagens
 Biological mutagens

18. Chemical Mutagens
 In genetics, a mutagen is a physical or chemical
agent that permanently changes genetic material,
usually DNA, in an organism and thus increases
the frequency of mutations above the natural
background level.
 As many mutations can cause cancer, such
mutagens are therefore carcinogens, although not
all necessarily are. All mutagens have
characteristic mutational signatures with some
chemicals becoming mutagenic through cellular
processes

19. Chemical Mutagens (5-BrU)
 5-Bromouracil (5-BrU, 5BrUra, or br5Ura) is
a brominated derivative of uracil that acts as
an antimetabolite or base analog, substituting
for thymine in DNA, and can induce DNA
mutation in the same way as 2-aminopurine.

20. Chemical Mutagens (5-BrU)
 It is used mainly as an experimental mutagen, but its
deoxyriboside derivative (5-bromo-2-deoxy-uridine) is used to treat
neoplasms.
 5-BrU exists in three tautomeric forms that have different base
pairing properties. The keto form (shown in the infobox) is
complementary to adenine, so it can be incorporated into DNA by
aligning opposite adenine residues during DNA replication (see
below left). Alternatively, the enol (below right) and ion forms are
complementary to guanine. This means that 5-BrU can be present
in DNA either opposite adenine or guanine.
 Thus 5-BrU induces a point mutation via base substitution. This
base pair will change from an A-T to a G-C or from a G-C to an A-
T after a number of replication cycles

21. Chemical Mutagens (MNNG)
 Methylnitronitrosoguanidine (MNNG or
MNG) is a biochemical tool used
experimentally as a carcinogen and
mutagen.
 It acts by adding alkyl groups to the O6
of guanine and O4 of thymine, which
can lead to transition mutations
between GC and AT.
 These changes do not cause a heavy
distortion in the double helix of DNA
and thus are hard to detect by the DNA
mismatch repair system.

22. Chemical Mutagens (AO)
 Acridine orange is an organic
compound that serves as a nucleic
acid-selective fluorescent dye with
cationic properties useful for cell
cycle determination. Acridine orange
is cell-permeable, which allows the
dye to interact with DNA by
intercalation, or RNA via electrostatic
attractions. When bound to DNA,
acridine orange is very similar
spectrally to an organic compound
known as fluorescein.

23. Physical Mutagens (UV rays)
 Physical mutagens include electromagnetic radiation, such as gamma rays, X
rays, and UV light, and particle radiation, such as fast and thermal neutrons,
beta and alpha particles.
 Ultraviolet (UV) is a form of electromagnetic radiation with
wavelength from 10 nm, shorter than that of visible light, but
longer than X-rays. UV radiation is present in sunlight, and
constitutes about 10% of the total electromagnetic radiation
output from the Sun.

24. Physical Mutagens (UV rays)
 The different ultraviolet (UV) wavelength components, UVA
(320-400 nm), UVB (280-320 nm), and UVC (200-280 nm), have
distinct mutagenic properties.
 One step in the discovery of genes and gene products
involved in a biochemical function or a developmental
process is to identify mutations that change a function
or process. Ultraviolet light (UV) is a strong mutagen
(in the wavelength that DNA absorbs, roughly 225-
300 nm) and primarily generates dimers between
adjacent pyrimidine bases on the same DNA strand.
These dimers cause the strand to buckle, disrupting
normal base pairing. This prevents proper replication
and can result in point mutations, deletions, and
chromosomal rearrangements. The effects of
mutagenesis can be reversed by photoreactivation, a
light-dependent DNA repair mechanism.

25. Biological Mutagens (Phage Mu)
 Bacteriophage Mu, also known as mu
phage or mu bacteriophage, is a muvirus
(the first of its kind to be identified) of the
family Myoviridae which has been shown to
cause genetic transposition.
 Phage Mu is nonenveloped, with a head
and a tail. The head has an icosahedral
structure of about 54 nm in width. The
neck is knob-like, and the tail is contractile
with a base plate and six short terminal
fibers. The genome has been fully
sequenced and consists of 36,717
nucleotides, coding for 55 proteins.

26. Biological Mutagens (Phage Mu)

27. Transposable element
 A transposable element (TE, transposon, or jumping gene) is a DNA
sequence that can change its position within a genome, sometimes creating
or reversing mutations and altering the cell's genetic identity and genome
size.Transposition often results in duplication of the same genetic material.
 Transposable elements make up a large fraction of the genome and are
responsible for much of the mass of DNA in a eukaryotic cell. Although TEs
are selfish genetic elements, many are important in genome function and
evolution.

28. Insertion sequence
 Insertion element (also known as an IS, an insertion sequence element, or an
IS element) is a short DNA sequence that acts as a simple transposable
element. Insertion sequences have two major characteristics: they are small
relative to other transposable elements (generally around 700 to 2500 bp in
length) and only code for proteins implicated in the transposition activity
(they are thus different from other transposons, which also carry accessory
genes such as antibiotic resistance genes). These proteins are usually the
transposase which catalyses the enzymatic reaction allowing the IS to move,
and also one regulatory protein which either stimulates or inhibits the
transposition activity. The coding region in an insertion sequence is usually
flanked by inverted repeats.

29. Effects of mutation in protein
coding gene
 Forward Mutations:
 Cells that contain the most common form of DNA sequences
are referred to as wild type. The introduction of genetic changes
in wild type cells leads to forward mutations. Sometimes second
mutations occur in a mutant cell that cancel the phenotypic
effects of a first mutation. These genotypically double mutants
appear phenotypically like wild type cells and are called
reversion mutations.

30. Effects of mutation in protein
coding gene
 Silent Mutation:
 Silent mutations are mutations
in DNA that do not have an
observable effect on the
organism's phenotype. They are
a specific type of neutral
mutation.

31. Effects of mutation in protein
coding gene
 Missense Mutation:
 A missense mutation is when
the change of a single base
pair causes the substitution
of a different amino acid in
the resulting protein. This
amino acid substitution may
have no effect, or it may render
the protein nonfunctional.

32. Effects of mutation in protein
coding gene
 Nonsense Mutation:
 A nonsense mutation is a point
mutation in a sequence of DNA that
results in a premature stop codon, or
a nonsense codon in the transcribed
mRNA, and in a truncated, incomplete,
and usually nonfunctional protein
product. The functional effect of a
nonsense mutation depends on the
location of the stop codon within the
coding DNA.

33. Effects of mutation in protein
coding gene
 Frameshift Mutation:
 A frameshift mutation is a
genetic mutation caused by a
deletion or insertion in a
DNA sequence that shifts the
way the sequence is read. A
DNA sequence is a chain of
many smaller molecules called
nucleotides.

35. Effects of mutation in protein
coding gene
 Suppressor Mutations:
 A suppressor mutation is a second mutation that alleviates or
reverts the phenotypic effects of an already existing mutation in
a process defined synthetic rescue. Genetic suppression
therefore restores the phenotype seen prior to the original
background mutation.
 Two types:
 Intragenic Suppression
 Extragenic Suppression

36. Effects of mutation in protein
coding gene

37. Gene Mutations
 Change in the
nucleotide sequence
of a gene
 May only involve a
single nucleotide
 May be due to
copying errors,
chemicals, viruses,
etc.

38. Types of Gene Mutations
 Include:
 Point Mutations
 Substitutions
 Insertions
 Deletions
 Frameshift

39. Point Mutation
 Change of a single
nucleotide
 Includes the
deletion, insertion,
or substitution of
ONE nucleotide in a
gene

40. Point Mutation
 Sickle Cell
disease is the
result of one
nucleotide
substitution
 Occurs in the
hemoglobin gene

41. Frameshift Mutation
 Inserting or deleting
one or more nucleotides
 Changes the “reading
frame” like changing a
sentence
 Proteins built
incorrectly

42. Frameshift Mutation
 Original:
 The fat cat ate the wee rat.
 Frame Shift (“a” added):
 The fat caa tet hew eer
at.

43. Amino Acid Sequence
Changed

44. Classes of bacterial mutants
 Morphological Mutants:
 Morphological mutants affect the
outward appearance of an individual
organism.
 Mutation results in change in color or
colony appearance of an organism.
 Plate of Serratia marcescens showing growth
of wild type colonies (red) and mutant
colonies (gray).

45. Classes of bacterial mutants
 Conditional Mutants:
 For some mutations to be expressed, the individual needs to be
placed in a specific environment. This is called the restrictive
condition. But if the individual grow in any other environment
(permissive condition), the wild type phenotype is expressed.
These are called conditional mutations. Mutations that only
expressed at a specific temperature (temperature sensitive
mutants), usually elevated, can be considered to be conditional
mutations.

46. Classes of bacterial mutants
 Biochemical (Nutritional) Mutants:
 Nutritional mutations occur when a mutation alters the
nutritional requirements for the progeny of a microorganism.
Often, nutritional mutants are unable to synthesize essential
biochemicals, such as amino acids. Nutritional mutants
(auxotrophs) require growth factors, such as specific amino
acids, that are not needed by the parental or wild type
(prototroph) strain.

47. Classes of bacterial mutants
 Resistant Mutants:
 Some bacteria have developed resistance to antibiotics that
were once commonly used to treat them. For example,
Staphylococcus aureus („golden staph‟ or MRSA) and Neisseria
gonorrhoeae (the cause of gonorrhoea) are now almost always
resistant to benzyl penicillin. In the past, these infections were
usually controlled by penicillin.
 methicillin-resistant Staphylococcus aureus (MRSA)
 vancomycin-resistant Enterococcus (VRE)
 multi-drug-resistant Mycobacterium tuberculosis (MDR-TB)
 carbapenem-resistant Enterobacteriaceae (CRE) gut bacteria