Prokaryote and extrachromosomal Flashcards
(50 cards)
What type of inheritance is shown by extrachromosomal DNA?
Non-Mendelian
Where do maternally inherited diseases map to?
Mitochondrial genome
These diseases therefore tend to affect energy production, and damage tissues that are dependent on energy e.g. nerves and mucle
How would you describe the mitochondrial and chloroplast genomes?
Circular
What is the shorthand for DNA found in mitochondria and cholorplasts?
- Mitochondrial DNA = mtDNA
- Chloroplast DNA = cpDNA
Which parent provides the mitochondrial/chloroplast DNA?
Maternal parent
Vachina
What is heteroplasmy
The possession of normal and mutated mtDNA leading to variable symptoms
The ratio of wild type to mutant mtDNA plays a big role in buffering against harmful mutations, evolution, and the inheritance of mitochondrial conditions
How do mitochondria replicate within cells?
Randomly - they aren’t like nuclear chromosomes
What does three person IVF prevent?
Prevents inheritance of mitochondrial diseases:
- Nucleus is removed from donor egg
- Nucleus is removed from mother’s egg and inserted into the donor egg cell
- Cell is fertilised with father’s sperm
- Healthy zygote produced
What is the endosymbiotic theory?
The theory that once, mitochondria and chloroplasts were free-living bacteria that became part of eukaryotic cells
What is the evidence that supports endosymbiotic theory?
- Own circular DNA
- Replicate independently
- Use bacterial-like (70s) ribosomes
What is homoplasmy?
All mtDNA copies are all the same - e.g. all mutant or all wild type
If they are all mutated, this will likely lead to the death of the organism
What other forms of extrachromosomal inheritance are there?
- Endosymbiotic bacteria e.g. wolbachia
- Infectious prions (cause misfolding of normal proteins)
How do prokaryotes introduce genetic diversity?
Horizontal Gene Transfer (HGT)
What is the name of the chromosomal DNA in prokaryotes?
Nucleoid
What is the mechanism by which bacteria divide?
Binary Fission
Why do prokaryotes need HGT?
- Binary fission copies all mutations, including the harmful ones (these become permanent in the genome)
- Without gene exchange, genetic fitness declines over time
- HGT introduced beneficial mutations over time (e.g. antibacterial resistance), increasing adaptability
What are the three main methods by which prokaryotes perform HGT?
- Conjugation: direct transfer of plasmids by cell-to-cell contact
- Transformation: uptake of free DNA from the environment
- Transduction: gene transfer via bacteriophages (viruses)
Increases genetic variation and adaptability in prokaryote populations
What are the 2 types of bacteria populations/multicellular aggregates that form?
- Biofilms
- Syntrophic consortia
What is the difference between a biofilm and a syntrophic consortia?
- Biofilm: structures microbe communities that adhere to surfaces, surrounded by extracellular polymers
- Syntrophic consortia: mutually beneficial interactions between different microbial species, wherein metabolites are shared
Comapre the sizes of prokaryote chromosomes and plasmids
- Chromosomes are bigger and denser circular genomes
- Plasmids are smaller DNA mols that replicate independently - there can be multiple per cell however
What types of genes do plasmids carry?
Non-essential, but beneficial genes e.g. antibiotic resistance, virulence, metabolism
Explain the process of conjugation
- Donor cell extends a pilus that attaches to a recipient cell
- Rolling circle replication copies one strand of plasmid DNA from the oriT part of the plasmid, which transfers to the recipient
- Recipient synthesises a complementary strand, forming a complimentary strand and a complete plasmid
- Recipient cell becomes a donor and can now transfer the plasmid to others
What is oriT? What does it need to be transcribed?
- oriT = Origin of transfer
- Needs transfer machinery encoded by the plasmid to be transcribed
What do plus and minus mean in the transfer of plasmids?
- Plus = donor cell (has plasmids)
- Minus = recipient cell (plasmids absent)
