Adaptation and Selection
Genetic variation in bacteria
- Natural selection allows organisms to adjust to suit changing environments in which they live in by adaptation.
- Adaptation increases the long-term reproductive success of a species by helping it survive long enough to breed.
- Adaptation and selection are major factors of evolution.
- Bacteria are one of the most diverse and adaptable group of organisms, due to the ability to develop resistance to anitbiotics etc.
- Changes to an organims DNA can occur in two ways:
- By mutation, which is changing the quantity or structure of the DNA of an organism.
- By sexual reproduction, by recombining the existing DNA of two individuals.
- DNA is also the genetic material of a bacteria.
- Bacteria also increase diversity by changing their DNA, namely by mutations and conjugation.
- Conjugation is the recombination of two individuals DNA, but is not strictly sexual reporduction.
- Mutations are changes in DNA that result in different characteristics.
- Mutations can arise by one or more bases in the DNA sequence either being added, deleted or replaced by others during replication.
- This may then lead to a different amino acid being coded for and so a different sequence of amino acids in the DNA molecule.
- This different amino acid sequence will lead to a different polypeotide, and hence a different protein, or no protein.
- If this protein is an enzyme, it is likely to disrupt the metabolic pathway leading to the production of other substances.
- Changes to DNA are likelt to alter an organism's characteristics.
- This involves DNA from one bacterial cell being passed onto another.
- The process is as follows:
- One cell produces a thin projection that meets the other cell and forms a thin conjunction tube between them.
- The donor cell replicated the plasmid.
- The plasmid is broken to make it linear before it passes along the tube into the replicant cell.
- Contact between cells is brief, so only a portion of the donor's DNA can be transferred.
- This way the recipient cell aquires new characteristics from the donor cell.
- Horizontal gene transmission = when DNA in the form of genes is passed on from one species to another species by conjugation.
- Vertical gene transmission = when genes are passed down from one generation of a species to the next generation of the same species.
- Antibiotics are substances produced by living organisms that can destroy or inhibit the growth of microorganisms.
- They are usually produced by bacteria and sometimes fungi, i.e penicillin.
- Penicillin was the first antibiotic to be used to treat infections.
How antibiotics work
- One way is by preventing bacteria from making normal cell walls.
- In bacterial cells, water constantly enters by osmosis, which would normally cause cells to burst by the process of osmotic lysis; but this is prevented by the cell wall that surrounds the bacteria.
- The cell wall is made out of tough material, which is not easily stretched; therefore as water enters by osmosis, the contents expand and push against the cell wall, which resists…