16. Adaption And Selection Flashcards
How does adaption increase the long term reproductive success of a species?
By helping its members to survive long enough to breed.
Define adaption.
Through the process of natural selection, organisms adjust to suit the changing environment in which they live.
What are two major factors in evolution?
Adaption
Selection
What is one of the most diverse and adaptable group of living organisms?
Bacteria.
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 mutations 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…
‘Against life’
Most antibiotics are made by:
Bacteria, but a few are made by fungi.
Define antibiotic.
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?
Penicillinase
Mutations…
Occur randomly and are very rare but as there are so many bacteria around the total number of mutations is large.
