Microbiology 1 - Diversity and Structure
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What is the oral cavity like at birth?
It is thought that we are born sterile and that the oral cavity is colonised first.
What are the different types basic morphologies of prokaryotes
- - Micrococci - ones
- - Diplococci - twos
- - Streptococci - chains
- - Staphylococci - clusters
- - Sarcina - cuboidal
Vibrios - curved rod
Is morphology related to genetic similarity?
Morphology tends to have more to do with environment. Bacteria can be completely different, but have the same shape
What bother with bacteria since they are so small?
- They are the major causes of diseases in our world - Aids, TB, Malaria. People used to regularly die (and still do) of infection before antibiotics were discovered.
- - Our ecosystem depends on them since they are major contributors to the:
- - Carbon Cycle
- - Nitrogen Cycle
- - Phosphorous Cycle
- - Decomposition Cycle
"The moon is the Earth without microorganisms"
What two main types can we classify cells into?
Eucaryotic and Procaryotic
All animal and plant cells belong to the Eucaryotes (eukaryotes),but there are also many unicellular eucaryotes, such as yeast.
As a general rule, eucaryotic cells are larger than procaryotes (prokaryotes) and are much more complex.
What are some common features of all cells?
- Plasma membrane
- Nucleus / Nucleoid region
Why do procaryotes and eukaryotes share common features?
Because eukaryotes evolved from procaryotes.
At first the earth was anoxic, but they procayotes evolved which were able to produce an oxygen rich environment in which eucaryotes could evolve.
What are some common features of Prokaryotic cells?
- Pili: attachment structures
- Fimbriae: attachment structures
- Flagella(e): not all bacteria:locomotion
- Capsule: not all bacteria:slippery layer
- Cell wall: confers rigidity and shape
- Cell membrane: semi-permeable barrier
- Nucleoid: DNA
- Ribosomes: sites of protein synthesis
- Mesosomes: invagination of membrane
Why do prokaryotic cells need a cell wall?
- There is considerable pressure on the cell membrane of a bacterium, due to the concentration of dissolved solutes inside relative to outside (~2 atmospheres = pressure of a car tyre).
- Therefore, bacteria require cell walls to resist this pressure, and also to confer shape and rigidity to the cell.
- Bacteria have chosen two distinct routes to building a cell wall. This choice divides the bacteria into two groups – Gram positive and Gram negative.
Named after the Danish bacteriologist in 1884, Hans Christian Gram (1853 – 1938)
What is peptigoglycan?
Peptidoglycan is an alternating copolymer of N-acetylglucosamine and N-acetylmuramic acid (joined by β1-4 glycosidic bonds), crosslinked with shord peptide bonds, giving a stong 3D mesh with high tensile strength.
The peptide interbridges are between the peptide side chains of N--acetylmuramic acid
What are bacteria so much more diverse than eukaryotic cells?
- They have a short life cycle - given the right conditions of pH, temperature, water, nutrients and microbes, they will divide by binary fission.
- They reproduce rapidly due to exponential growth which provides more opportunities for mutations (In a single day, one cell of E.coli could produce a super-colony equal in size and weight to the entire planet earth)
- Conjugation -
They can exchange DNA (in forms of plasmids) between related species, which can refer antibiotic resistance
- - Transformtion - Cells can aquire DNA from the environment - from same or different species (Termed "Competent Cells")
- -Does not require close contact, but does require naked DNA (DNA in environment from lysed cells)
- -The DNA can be incorporated into the recipient’s genome by recombination – thus giving it a new genotype – phenotype.
- - Transfection
- - Cells can acquire DNA from infectious bacteriophages (bacterial viruses)
- - When a bacteriophage infects and cell and replicates in that cell it may acquire some of the hosts DNA in the process replication – defective bacteriophage.
- -When this bacteriophage infects another bacterium it will transfer the DNA from the previous bacterium to the new host – in certain circumstances this DNA will become incorporated in the new host, thus adding to its genetic information.
Why is transfer of genetic information important?
This is a fundamental process in the evolution of bacteria and why they are so diverse.
It is also a feature of why they can adapt so quickly to colonize new habitats.
Plays a central role in how they acquire new genotypes and phenotypes – antibiotic resistance.
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