Flashcards in 16. Adaption And Selection Deck (39):
Through the process of natural selection, organisms adjust to suit the changing environment in which they live.
How does adaption increase the long term reproductive success of a species?
By helping its members to survive long enough to breed.
What are two major factors in evolution?
What is one of the most diverse and adaptable group of living organisms?
Name two ways changes in DNA can occur.
Mutation: changing the quantity or he structure of the DNA of an organism.
The recombination of existing DNA of two individuals - this occurs during sexual reproduction.
Name two ways that DNA can change in bacteria.
By conjugation (not strictly sexual reproduction, even though it recombines the DNA of two individuals).
How do mutations occur?
One of more bases in a DNA sequence may be added, deleted or replaced by others during replication.
Different base sequence=different amino acid sequence=different polypeptide=different protein=(if enzyme) disrupts metabolic pathway leading to the production of other substances, including proteins. Organisms characteristics could change.
What happens in conjugation?
Conjugation occurs when one bacterial cell transfers DNA to another bacterial cell.
Give the five steps in conjugation:
One cell produces a thin projection that meets another cell and forms a thin conjugation tube between two cells.
The donor cell replicates one of its small circular pieces of DNA (plasmid).
The circular DNA is broken to make it linear before it passes along the tube into the recipient cell.
Contact between the cells is brief, leaving only time for a portion of the donor's DNA to be transferred.
In this way the recipient cell acquires new characteristics from the donor cell.
In conjugation DNA in the form of genes can be passed from one species to another species. What is this known as?
Horizontal gene transmission.
What is it called when genes are passed down from one generation of a species to the next generation of the same species?
Vertical gene transmission.
Give an example of the experiments done to prove conjugation.
Strain 1: needs methionine and biotin to grow
Strain 2: needs threonine and leucine to grow
Strains 1 and strains 2 grown together on minimal medium = a few colonies!
The word antibiotic comes from the Greek work...
Most antibiotics are made by:
Bacteria, but a few are made by fungi.
A substance produced by living organisms that can destroy or inhibit the growth of Microorganisms.
Who by and when was penicillin discovered?
By Alexander Fleming in 1928.
What usually happens with osmosis and the bacterial cell wall?
Water constantly enters plant and bacterial cells by osmosis. The cell does not burst because the cell wall is made of tough material which is not easily stretched and so resists expansion and halts entry of further water.
How are antibiotics effective against bacteria?
Antibiotics kil bacteria by preventing them from forming cell walls. They inhibit the synthesis and assembly of important peptide cross-linkages in bacterial cell walls. This weakens the walls making them unable to withstand pressure. Osmotic lysis occurs.
When are antibiotics effective?
When the bacteria are growing. Penicillin works this way.
Why are viruses not killed by antibiotics that work by weakening cell walls?
They enter a host cell
They have a different covering from bacteria and so are not killed by antibiotics.
How does antibiotic resistance occur?
By a chance mutation within the bacteria.
Describe the mutation which causes bacteria to become resistant to penicillin?
The mutation results in the bacteria being able to make a new protein which is an enzyme which can break down antibiotic penicillin before it is able to kill bacteria.
What is the name of the enzyme which breaks down penicillin?
Occur randomly and are very rare but as there are so many bacteria around the total number of mutations is large.
If a bacterium becomes resistant to penicillin, what events proceed?
The penicillin will kill all the normal bacteria without penicillinase but not the mutant type with penicillinase. The mutant type will survive and divide. The bacteria produced from this survivor would be resistant to penicillin.
Which form, the penicillin resistant form or the non-resistant form is selected when exposed to penicillin?
The penicillin resistant form.
How is the gene for penicillinase passed?
By vertical gene transmission. E.g from one generation to the next and by horizontal gene transmission.
When a penicillin resistant bacteria survives and divides what happens eventually?
The penicillin-resistant bacteria gradually predominate in the population. The prequel cry of the allele for penicillin resistance increases in the population.
How can the resistance to penicillin find its way into other bacterial species when a bacteria from one species has the mutation?
By conjugation, this can result in certain bacteria accumulating DNA that gives them resistance to a range of antibiotics: 'superbugs'.
What increases the chance of antibiotic resistance in bacteria?
Using antibiotics more. There is an increased chance that the mutant bacterium will gain an advantage over the normal variety.
What is one problem with antibiotic treatments for TB?
The period for which the antibiotics must be taken is 6-9 months. People stop taking them after they feel better but this is bad because the few bacteria that do remain are the most resistant to the antibiotic.
Why is it an issue in the treatment of TB that the most resistant bacteria survive due to patients not finishing the course of antibiotics?
The resistant strains multiply and spread to others. There is therefore a selection pressure that leads to the development of strains of the bacteria which do not respond to the antibiotics. These strains then interchange genes for resistance by conjunction with other strains. This leads to multiple-antibiotic-resistant strains of bacteria developing.
How have we overcome the problem of multiple-antibiotic-resistant strains of TB.
A 'cocktail' of three or four antibiotics is given to ensure at least one of them will be effective.
Which bacterium is carried by many people in their throats?
Staphylococcus aureus (only causes minor symptoms in healthy individuals).
What is MRSA?
MRSA is the name given to any strain of this bacterium that is resistant to one or more antibiotics.
Where is MRSA particularly prevalent?
Why is MRSA dangerous in hospitals?
People in hospitals tend to be older, sicker and weaker than the general population making them more vulnerable to infection.
Conditions are crowded and transmission is likely through nurses etc touching patients.
Many antibiotics are present. Strains can develop multiple resistance more easily.
Why is MRSA so difficult to treat?
Some strains have developed resistance to almost every known antibiotic.