Chapter 7: Bacterial and Viral Genetic Systems Flashcards
What are the advantages of bacteria for genetic studies?
- Small size
- Easy reproduction (division every 20 min)
- Easy to culture
- Small genome
- Many mutants available
How does the genome of bacteria differ from humans?
Most of the DNA contained within the genome of bacteria has a function (compact and efficient)
What is a minimal medium?
A medium that contains only the nutrients required by prototrophic bacteria
How can bacteria be grown?
- In liquid medium
- On solid medium
What are auxotrophs?
Stains that lack one or more enzymes necessary for synthesizing essential molecules and will grow only on medium supplemented with those essential molecules
How can mutant strains be isolated?
- Based on their nutritional requirements
- A colony that grows only on the supplemented medium has a mutation in a gene that encodes the synthesis of an essential nutrient
Describe the bacterial genome.
- Most possess a circular chromosome, containing a single double-stranded DNA molecule
- Most have a single CIRCULAR chromosome
What are plasmids? Do all bacteria contain plasmids?
- Small, usually circular DNA molecules
- Many, but not all
What is the function of plasmids? Are they essential?
- Plasmids carry genes that are NOT ESSENTIAL to bacterial function
- But may play an important role in the life cycle and growth of their bacterial hosts
What is the significance of the origin of replication within a plasmid?
- DNA replication is initiated at the origin
- Thus, a plasmid can replicate INDEPENDENTLY of its bacterial chromosome
What are episomes? Give an example.
- Plasmids that are capable of replicating freely and are able to integrate into the bacterial chromosomes
- Fertility factor of E. coli
What is the F factor of E. coli?
- Episome
- Regulates the transfer into the bacterial cell, replication, and insertion into the bacterial chromosome
- Genes REQUIRED for CONJUGATION
Without the __________, it is difficult to transfer genetic information from one cell to another?
F factor
Which of the following statements is true of plasmids?
A) They are composed of RNA
B) They normally exist outside of bacterial cells
C) They possess only a single strand of DNA
D) They contain an origin of replication
D) They contain an origin of replication
When does conjugation take place?
When genetic material passes DIRECTLY from one bacterium to another
When does transformation take place?
When a bacterium takes up DNA from the medium in which it is growing
When does transduction take place?
When bacterial viruses (bacteriophages, or phages) carry DNA from one bacterium to another
What happens in conjugation? What needs to occur?
- A plasmid or part of the bacterial chromosome passes from one cell (donor) to the other (recipient)
- A cytoplasmic bridge must form between two bacteria
What may occur following conjugation?
- Crossing-over may take place between the homologous sequences in the transferred DNA and the chromosome of the recipient cell
- Creation of recombinant chromosome
Which exchange process does not involve a donor cell? What does it involve instead?
- Transformation
- Free DNA (DNA fragments or plasmid)