R.O Lecture 1 Flashcards
Describe Bacteria
- 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
What are the shapes of bacteria
- 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
Where do bacteria live?
live in or in every material and environment on Earth - soil, water and air.
bacterial cells in comparison to human cells.
Ten times as many bacteria as human cells in the body
Approx. 50 different species on the human skin
Flagella
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
How do bacteria make food?
- 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
Describe the Cell Wall
Cell membrane surrounded by cell wall
Composition varies among species
NB for identifying and classifying bacteria
thick cell wall of peptidoglycan
- 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
thin wall of peptidoglycan
- 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
What do bacteria have instead of a membrane bound nucleus?
*Nucleoid -a tangle of chromosomal DNA with no membrane.
Difference between DNA in bacteria vs eukaryotes
- 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).
Plasmids
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
How does bacteria reproduce?
Reproduce asexually by simple binary fission
- preceded by replication of bacterial chromosome in the nucleoid
- have a short generation span
How does a short generation span benefit bacteria?
Short generation span helps them adapt to changing environments, can proliferate rapidly
Genetic variation in bacteria
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
Transformation
*Not all bacteria are capable of transformation
*Transfer of naked DNA from one bacterial cell to another in solution
*happens in nature
How are cells made competent (transformation)
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
Transduction
The transfer of viral, bacterial, or both DNA from one cell to another via bacteriophage
(viruses that infect bacteria)
- used also in Biotechnology
Conjugation
Transfer of DNA from one bacterial cell to another via a special protein structure called a conjugation/ sex
pilus
Who discovered E.Coli
E. coli was discovered by Dr. Theodor Escherich in 1885.
Describe E.Coli
- 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
How are the different shapes of E.Coli distinguished
distinguished immunologically using serotyping
What are the three types of antigen in which the current typing system of E.Coli is based on?
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
Describe E.Coli K-12 strain
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
