Unit 7 Microbial Genetics

Question 1

Bacterial genome

Answer 1

Total collection of genes carried by a bacterium:
- chromosome
- extra chromosomal material like plasmids or bacteriophages

Question 2

Gene

Answer 2

Sequence of nucleotides that has a biological function

Question 3

Phenotype

Answer 3

Morphological or physiological manifestation of the genotype

Question 4

By what is the phenotype determined

Answer 4

By the interaction of the expression of the genome and the external influence of the environment

NOT every character is encoded genetically

Question 5

Genotype

Answer 5

Specific set of gens of an organism
Inherited
Not all genes are expressed phenotypically

Question 6

Phenotypic variations properties

Answer 6

• High frequency, affecting the entire population exposed to the environmental pressure
• Reversible, returning to the original state when the generating cause disappears
• Not inherited, no change in the DNA

Question 7

Types of phenotypic variations

Answer 7

Morphological : apparition of mucus layer in media with sucrose

Chromogenic : color changes depending on temperature

Enzymatic : capacity to produce enzymes only in the presence of the substrate. E g production of penicillinase in the presence of penicillin

Question 8

Mutation definition
Causes

Answer 8

Persistant change of DNA bases without addition of exogenous DNA

Arise
-spontaneously,
-because of mutagens or
-transposable elements

Question 9

Random facts bacterial mutations

Answer 9

-High speed duplication

-DNA repair system of bacteria
produces higher frequency of errors than any species

-Lots of mutations are incompatible with life
-Some spécificité mutation can provide thé mutant BIOLOGICAL ADVANTAGE

Question 10

Characteristics of mutation

Answer 10

-Low frequency : but can be increased by mutagen agent
- Irreversible
- Inherited
- Spécificité: Affects specific character
- spontaneous mutation

Question 11

Selector agent

Answer 11

Selects a spontaneous mutation by killing the specimens that aren’t resistant to it

Question 12

Exemple of mutations in bacteria

Answer 12

• Alteration of surface components such as capsule or flagella
• Loss of ability to synthesize growth factor( auxotroph)
  -Resistance to antibiotics

Question 13

Types of mutations

Answer 13

Substitution
Deletion
Insertion

Question 14

How is a mutation called when it affects a single base

Answer 14

Point mutation

Question 15

After the translation it can result in three types of mutations

Answer 15

• Non sens ( no protein/ terminal codon )
  -Missense ( altered protein)
• Silent

Question 16

Non sense mutation

Answer 16

Premature terminal codon
No protein

Question 17

Missense

Answer 17

Altered protein

Question 18

Silent mutation

Answer 18

Same protein

Question 19

Frameshift mutations

Answer 19

Insertion or deletion of number of nucleotides that is not a multiple of 3

Question 20

Spontaneous mutation

Answer 20

Random errors in replication

Question 21

Induced mutations
Why
Types

Answer 21

From exposure to known mutagens
- Physical agents : ionizing, UV
- Chemical agents ( substitution or insertion )

Question 22

Chemical agents that cause mutations

Answer 22

Substitutions:
- Nitrous acid ( transforms adenine in hypoxanthine that binds to cytosine)
- 5-bromouracil (replaces thymine and binds to guanine)

Insertion : Acridine orange that is an intercalant agent

Question 23

Transposable elements/transposons

Answer 23

Segment of DNA that has the capacity to “jump” to different locations in the genome. Produce insertions and deletions

Question 24

Transposable elements/Transposon are made of

Answer 24

IR inverted repeat

Transposases, enzymes that cut the DNA

Question 25

Inverted repeat

Answer 25

Small nucleotide sequence located at the ends of the transposon. Inverted

Question 26

Where do transposases cut

Answer 26

( DR )direct repeats Few nucleotides on both ends, not inverted

Question 27

Types of Transposable elements

Answer 27

Insertion sequences Complex Transposon Other

Question 28

DNA repair system made of

Answer 28

Specific enzymes Excision repair system Recombination system SOS repair system

Question 29

What’s a reversion

Answer 29

Reverse mutation returns to the wild type genotype

Question 30

Exemple specific enzyme repair system

Answer 30

Photolyase corrects the damage done by UV radiation

Question 31

Excision repair system

Answer 31

Damage chain gets cut by endonuclease and re-synthesized by polymerase and ligase

Question 32

Recombination system

Answer 32

Damaged chain gets cut, replace by the homologous fragment that is then resynthesized

Question 33

SOS repair system

Answer 33

System of enzymes that repairs severely damaged DNA

Question 34

Genetic transfer

Answer 34

Entry of foreign DNA within the bacteria from the surroundings 3 types Environment : Transformation Another bacteria : Conjugation Bacteriophage : Transduction

Question 35

Exogenous DNA can react in three ways

Answer 35

Degradation Circulation Recombination

Question 36

Degradation

Answer 36

The new DNA is destroyed by endonucleases that recognize it as foreign

Question 37

Circulation

Answer 37

Methylated to avoid the action of endonucleases Then it can replicate independently of bacterial DNA (transmitted to daughter cells) Or don’t replicate and will be lost in successive divisions (abortive process) Plasmid can be both

Question 38

Endonucleases

Answer 38

Enzyme that destroys foreign DNA

Question 39

Recombination

Answer 39

Genetic exchange between bacterial DNA and exogenous DNA ➡️ Mixed genetic information

Question 40

Transformation

Answer 40

The uptake by a cell of a naked DNA molecule of the medium and it’s incorporation into the recipient chromosome in a heritable form Happens after cell lysis, that releases its compounds in the environment

Question 41

Transformation usually occurs between cells that share the same

Answer 41

Ecological niche E g 2 bacteria in colon

Question 42

Bacteria able to take up the DNA from environment

Answer 42

Competent bacteria

Question 43

How to artificially induce transformation

Answer 43

Electrical shock or calcium chloride

Question 44

Conjugation

Answer 44

Transfer of genetic material between two bacteria by direct contact between them Different for gram + or -

Question 45

Conjugation gram-

Answer 45

Transfer of plasmid via sex pilus After the conjugation, the receptor f- can become f+

Question 46

Transduction

Answer 46

Induced by bacteriophages, that inject the viral DNA Virulent phages Attenuated phages

Question 47

Virulent phages

Answer 47

Use the enzymatic machinery to synthesize bacterial phage structures. They create viral progeny breaking the bacteria to get out Lytic cycle

Question 48

Attenuated phages

Answer 48

DNA of the phage is integrated into the cell genome and doesn’t produce lysis Lysogenic cycle

Question 49

Lytic cycle

Answer 49

Results in the destruction of the infected cell

Question 50

Insertion or deletion of a number of nucleotides that’s not a multiple of 3

Answer 50

Frameshift mutation

Question 51

Name cycle attenuated phages

Answer 51

Lysogenic cycle

Question 52

When the bacteria is killed because of bacteriophage

Answer 52

Lytic cycle