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Microbiology and immunology > Bacterial growth and genetics > Flashcards

Bacterial growth and genetics Flashcards

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Biology 101 flashcards
1
Q

How do Bacteria multiply?

A

By Binary fission

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2
Q

What does Binary fission result in?

A

Results in two identical daughter cells

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3
Q

What does the time of division depend on?

A

Environmental and species.

For example
E. coli 37oC with lots of food = 20 mins »(chromosome replication takes 30 min!)

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4
Q

What does Rapid growth allow?

A

Rapid evolution of traits by mutations or recombination

For example - Resistance to chemical ages -antibiotics and biocides.

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5
Q

What is the first step for Bacterial growth?

A

Chromosome replication

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6
Q

In Bacterial growth what follows after Chromosome replication?

A

Septation (Continued growth of the cell) and division into two cells

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7
Q

What are the 4 phases in Bacterial growth and replication?

A

Lag phase

Exponential log phase

Stationary phase

Death phase

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8
Q

Why is the idealised growth curve of bacteria in a culture important experimentally?

A

because at different phases cells exhibit different characteristics.

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9
Q

What are the two types of measuring growth or bacterial number in a sample?

A

Direct or indirect

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10
Q

How does Direct count work?

A

Uses Microscopy
Membrane filtration which is mostly for water
Plate counts

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11
Q

How does indirect count work?

A

Turbidity using spectrophotometry
Biomass
Measuring cell products - CO2

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12
Q

Explain viable count

A

Allows the approximate quantity of organisms that are “Alive” to be counted in a sample.

For example: bacteria and yeasts
Spread plates
Pour plates
Miles and Misera

However doesn’t take into account viable but non-culturable organisms (VBNC’s).

is an approximation only

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13
Q

How does spectroscopy estimate bacterial number?

A

It uses a light source to pass through the bacteria sample and hit a photocell detector. The more light that hits the photocell the less bacteria there is.

However the less light that hits the photocell the higher amount of bacteria

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14
Q

When is Turbidity used?

A

When a growth curve is plotted using plate counts along with the optical density of a sample from a growing culture at 550 – 600 nm, bacterial number can be determined using only turbidity.

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15
Q

How can growth be used to identify an organism?

A

As bacterial cells grow they utilise nutrients or carbon sources in different ways and produce enzymes.

Allows a metabolic fingerprint to be obtained- Characteristic to the organism

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16
Q

How can growth be used to identify an organism- What are the 2 of many systems developed to exploit the differences?

A

Manual –agar plates – biochemical tests

Mechanised – robotic biochemical assays

All rely on differences in cellular biochemistry

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17
Q

List the parts of a bacteria

A 
Capsule
Ribosomes
Cytoplasm
Plasma membrane
Pili
Cell wall 
DNA
Flagellum
18
Q

List the parts of the bacterial chromosome

A 
Double stranded circular DNA molecule
Condensed into the nucleiod
No nuclear membrane
Chromosome is unpaired - Haploid
Encodes all the genes required for essential cell functions
19
Q

Explain Chromosome replication

A

This must happen for cell division

Replication is semi-conservative - each copy made contains one new (daughter) and one old strand (parent).

Replication starts from a specific site the origin of Replication (ori C)

Bi-Directional

Uses a large collection of enzymes- Replisome

20
Q

What phase in the growth curve is of most danger to humans?

A

Exponential phase

21
Q

What is required for each phase in the growth curve?

A

A different subset of genes is required for each phase.

22
Q

How does chromosome vary?

A

it varys significantly between species

23
Q

Explain the recent research into genome sequencing

A

Efficient methods for genome sequencing available only from 1995.

Whole genome “Shot gun” sequencing.

Venter and Smith where the first to sequence Haemophilus influenzae and Mycoplasma genitalium.

24
Q

What are Operons?

A

Functionally linked genes are grouped together. The expression is controlled by a single operator which together is called a Operon.

All genes in a operon are transcribed onto one large messenger RNA molecule. This ensures that all the genes required for a particular metabolic task are expressed and active at the same time.

25
Q

How is gene expression controlled?

A

By proteins which regulate the rate of gene transcription.

Repressors (Negative control - down regulate).

Activators (positive control - up regulate)

Can be specific proteins or products such as levels of catabolites - glucose.

26
Q

What are Regulon’s?

A

A group of operons that is co-regulated

Toxins and Pathogenicity islands.

27
Q

What are plasmids?

A

Extra-chromosomal genetic elements that replicate independently from host chromosome

Not always essential for survival or the bacterium - lab vs host

Thousands of different plasmids exist

  • 300 isolated from strains of E. coli alone
  • Possible to make them in the lab - Plasmid vectors for cloning
28
Q

How do plasmids spread?

A

Spread naturally by conjugation between donor cells and recipient cells (Sex pilus)

29
Q

What is the typical size and shape of a plasmid?

A

Typically circular, DS and <5% size of chromosomes - 1 to 5 x 10^5 bp

30
Q

How do plasmids replicate?

A

Replication is similar to that of the chromosome and starts at origin of replication (Ori V).

31
Q

In research what can plasmids be used for?

A

A typical plasmid that is used as cloning vector genes of interest can be inserted in the multiple cloning site (MCS) and are expressed once introduced to a cell

32
Q

Medical importance of plasmids- How is it involved with Antibiotic resistance?

A

Called R factors

First discovered in Japan in early 1940’s

Usually enzymatic inactivation of the antibiotic
Beta-lactamases - penicillin resistance
Prevent uptake by modifying cell wall

Increase of R plasmids correlates with increasing use of antibiotics

33
Q

Medical importance of plasmids- How is it involved with Virulence factors?

A

Toxins
Enteropathogenic E.coli strains - enterotoxin
S.aureus - enterotoxin B
B. anthracis - PA, LF, EF and capsule.

Adherence factors - pili in E.coli

Siderophores - Iron important for pathogens

34
Q

Explain mutation in a bacterial gene

A

In heritable change within a nucelotide (DNA) sequence.

A bacterial strain carrying such a change is called a mutant.

Call be
Spontaneous- natural radiation, errors during DNA replication
Induced- chemical mutagens

35
Q

Explain the types of mutation

A

Point mutation - affects one base pair

Insertion or deletion of large DNA fragment.
usually due to a transposon
may result in loss of gene function

inversion and duplications

36
Q

Explain what mutations can do

A

Can alter the function of a gene

Replacement of nucleotide resulting in amino acid substitution in a protein (missense).
Premature termination of protein synthesis (nonsense).
Change in expression levels due changed regulation - deletions or insertions.

37
Q

Explain Recombination

A

Genes in two separate bacterial cells brought together in one.

Occurs by transfer of genetic information between bacteria - have a common gene pool

Swap genes through horizontal gene transfer

includes genes of plasmids

Happens through - Transformation, Conjugation and transduction.

38
Q

Explain Transformation

A

Uptake of pure (naked) DNA from medium surrounding cell.

Released into medium from lysed cells

DNA must integrate into chromosome to transform recipient cell - Transformants

Can be induced in the lab - Plasmids

This can also be a way that plasmids are introduced into the cells, this process can happen naturally or can be induced in the lab to create mutants.

39
Q

Explain Transduction

A

DNA transferred cell to cell by Bacteriophages (bacterial viruses).

bacteriophage picks up partially degraded bacterial DNA instead of its own by mistake when making new virus - transducing phage.

Not all bacteriphages can transduce and not all bacteria can be tranducible

40
Q

Explain Conjugation

A

Cell to cell contact allowing transfer of DNA

Plasmids are self- transmissible by conjugation
Encode the sex pilus and other transfer genes (Tra region).

is the major mechanism of transfer of antibiotic resistance genes on R plasmids.

Microbiology and immunology (17 decks)

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