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BI311 > R.O Lecture 1 > Flashcards

R.O Lecture 1 Flashcards

1
Q

Describe Bacteria

A
  • Single cells
  • prokaryotes – DNA not enclosed in cellular compartment
    (i.e. no nucleus)
  • among earliest forms of life to appear on earth
  • probably created atmospheric oxygen that enabled other, more complex
    forms of life to evolve e.g. cyanobacteria
  • more complex cells may have developed as free-living bacteria took up
    residence in other cells, eventually becoming organelles e.g. mitochondria
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2
Q

What are the shapes of bacteria

A
  • 1,000’s species
  • 3 basic shapes:
    rod-shaped ‘bacilli’
    sphere-shaped ‘cocci’
    spiral-shaped

some exist as individuals, others cluster
together to form pairs, chains or other
groupings

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3
Q

Where do bacteria live?

A

live in or in every material and environment on Earth - soil, water and air.

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4
Q

bacterial cells in comparison to human cells.

A

Ten times as many bacteria as human cells in the body
Approx. 50 different species on the human skin

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5
Q

Flagella

A

Flagella allow them to move in response to different stimuli

  • some have flagella to move (also sensory – chemical, temp)
  • some secrete a slime layer and ooze over surfaces like slugs
  • some non-motile
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6
Q

How do bacteria make food?

A
  • some are photosynthetic
  • make own food from sunlight and release oxygen
  • some absorb food from the material they live on
  • *some utilise iron or sulfur - usefully for bioming/bioremediation
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7
Q

Describe the Cell Wall

A

Cell membrane surrounded by cell wall
Composition varies among species
NB for identifying and classifying bacteria

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8
Q

thick cell wall of peptidoglycan

A
  • thick cell wall made of peptidoglycan (carbohydrate polymers cross-linked by proteins)
  • purple colour when stained with dye crystal violet – Gram-positive
    -sensitive to large range of antibiotics as it is completely porous
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9
Q

thin wall of peptidoglycan

A
  • double cell membrane
    -thin inner wall of peptidoglycan, outer membrane of carbohydrates, proteins, and lipids
  • do not stain purple with crystal violet – Gram-negative
  • can be resistant to a lot of antibiotics
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10
Q

What do bacteria have instead of a membrane bound nucleus?

A

*Nucleoid -a tangle of chromosomal DNA with no membrane.

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11
Q

Difference between DNA in bacteria vs eukaryotes

A
  • DNA is not bound to proteins as it is in eukaryotes (i.e. no histones)
  • eukaryotic DNA is organized into linear pieces (chromosomes)
  • bacterial DNA forms loops
  • Bacteria generally contain a single large circular chromosome which contains all
    essential genes.
  • Bacteria can also contain plasmids (multiple, small loops of DNA that can be
    lost/gained; non-essential).
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12
Q

Plasmids

A

Plasmids are molecules of DNA that are found in bacteria separate from the
bacterial chromosome
* they are small (a few thousand base pairs)
* usually carry only one or a few genes
* are circular
* enter bacteria easily
- this occurs in nature
by carrying out a transformation you can
introduce new genes to the bacteria

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13
Q

How does bacteria reproduce?

A

Reproduce asexually by simple binary fission
- preceded by replication of bacterial chromosome in the nucleoid
- have a short generation span

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14
Q

How does a short generation span benefit bacteria?

A

Short generation span helps them adapt to changing environments, can proliferate rapidly

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15
Q

Genetic variation in bacteria

A

A. Introduction of mutation
B. *Transfer of DNA between two individual bacteria:
1. Transformation
2. Transduction
3. Conjugation
Bacteria, having acquired DNA from any of these events, can then undergo fission and pass the
recombined genome to new progeny cells

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16
Q

Transformation

A

*Not all bacteria are capable of transformation
*Transfer of naked DNA from one bacterial cell to another in solution
*happens in nature

17
Q

How are cells made competent (transformation)

A

Competent cells: Bacteria cell walls are made more permeable to DNA by chemicals
(cold Ca2+) or electrical pulses (electroporation).
Heat shock can be used to induce uptake of DNA into chemically competent cells

18
Q

Transduction

A

The transfer of viral, bacterial, or both DNA from one cell to another via bacteriophage
(viruses that infect bacteria)
- used also in Biotechnology

19
Q

Conjugation

A

Transfer of DNA from one bacterial cell to another via a special protein structure called a conjugation/ sex
pilus

20
Q

Who discovered E.Coli

A

E. coli was discovered by Dr. Theodor Escherich in 1885.

21
Q

Describe E.Coli

A
  • Gram-negative bacteria
  • primarily live in the mammalian gut, have been grouped
    with other related bacteria - ‘enteric’ bacteria
  • straight rod shaped cells of about 2 μm long and 0.5 μm
    wide
  • can grow and divide rapidly by binary fission
22
Q

How are the different shapes of E.Coli distinguished

A

distinguished immunologically using serotyping

23
Q

What are the three types of antigen in which the current typing system of E.Coli is based on?

A

The current typing system is based mainly on three types of antigen:
- somatic (O) antigen which corresponds to terminal sugars on the cell surface
lipopolysaccharide (LPS)
- the capsular (K) antigens
- the flagellar (H) antigen
> 170 O antigens, > 100 K antigens, > 50 H antigens

Many strains cause disease

24
Q

Describe E.Coli K-12 strain

A

K-12 strain first isolated in 1922
Commercial derived strains (DH5α, Top10 etc.)
Strain of choice in labs
- easy to grow
- amenable to metabolic studies
- can support the replication of DNA plasmids
- safe: lost its O antigen, risk group 1
- safe: K-12 and strain O157:H7 DNA sequences are 25% different from each other

25
Q

What are the growth conditions for E.Coli K-12?

A

solution of some sugar (glucose), nitrogen, salt and phosphates and grow it aerobically at 37°C

26
Q

What are the modifications made to E.coli K-12 which has led it to becoming an improved strained for recombinant DNA methods?

A
  1. Bacterial restriction modification systems have been removed (recA)
  2. Endonuclease activity has been mutated to increase plasmid yields (endA-)
  3. DNA recombination systems are modified to prevent rearrangements (hsDR-)
27
Q

Bacterial Restriction Modifications have been removed

A

-The EcoK restriction system (hsdR/M/S) encodes proteins that degrade foreign DNA that is not properly methylated
- they will interfere with the replication of foreign DNA in bacterial cells
- the bacteria will degrade foreign DNA the same way viral DNA is degraded as a defence against invasion

28
Q

Endonuclease I activity (endA-)

A
  • Most E. coli K12 strains contain a mutation in the endA gene encoding DNA specific endonuclease I
  • E. coli has a powerful endonuclease on the outside of the cell that degrades DNA.
  • Loss of this endonuclease greatly increases plasmid DNA yields and improves
    the quality of DNA that is isolated
29
Q

recA gene

A
  • recA encodes a well-characterized recombination protein (DNA repair system)
  • Mutations to recA prevent inserted DNA from being rearranged or deleted.
  • recA mutations also enhance the biosafety of E. coli K12 as recA- strains are sensitive to ultraviolet light

BI311 (14 decks)

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