Exam 2 Lecture 15 Flashcards
(29 cards)
Silent change in DNA?
A base change that doesn’t result in a change of AA
Missense change?
Single base change that results in a different AA being encoded, can make a protein non-functional or change the function
Nonsense Change?
Base pair change that encodes a new stop codon in the middle of the protein
Translational frameshifts?
Insertion or deletions that make everything downstream change by one or two base pairs and can change the protein code bigtime!!!
How do big changes happen?
Insertion Sequences (IS), Transposons, genomic Island insertions like secretion systems and metabolic cassettes, addition of independent replicating elements, and integration of viral genes or genomes
What is an IS element?
They are typically 700-1500 bp long that encode a protein Tnp that can move DNA elements. Transposase
What are Transposons like Tn5?
Longer sequences than ISs often with several genes in them flanked by IS elements. When they move they either be good such as add antibiotic resistance or be bad and disrupt regular gene function (knock out mutation)
Three main types of HGT (horizontal gene transfer)?
- Transformation
- Conjugation
- Transduction
What was the first description of HGT?
The Griffiths experiment and Streptococcus pneumoniae
Heat killed S cells with capsid and live R cells with out capsid killed rat.
Capsid genes transferred from dead cells to live cells in a process known as transformation
Steps of Transformation?
- dsDNA bind to exterior of competent cell by DNA binding proteins
2 DNA is transported using ATP by DNA competence channal while transforming it into ssDNA
- Rec A mediates recombination of DNA into host DNA using homologous sequences of 20-30 bps
In transformation is the donor living or dead?
Often dead
Can you get big insertions in transformation?
Yes if the genes are flanked by homologous sequences.
Name some bacteria that transformation occurs in?
Bacteria- Bacillus, Pseudomonas, Hemophilus, and Neisseria
Name some archaea that transformation occurs in?
Methanococcus and Thermococcus
Does conjugation happen from live or dead cells?
Live
During conjugation does the donor lose DNA?
No
What is a plasmid?
Extrachromosomal dsDNA that replicates independently from the chromosome
Can have a host range and can be incompatible with each other if in the same host
Plasmid shape and size?
Usually circular, vary in size from 3-200+ kbs
Do Plasmids carry essential genes?
No, but can encode for important functions that can give a significant selective advantage
Plasmid size and copy number (number of copies of the plasmid that the cell carries) relationship?
small size = high copy number
large size = low copy number
low copy number means low initiation of replication
First Plasmid identified?
F (fertility) plasmid in E coli
99kb with several IS/Tn elements and transfer and replication and inc functions
(no antibiotic resistance in F plasmid)
How do conjugative plasmids get transferred?
With conjugative pili
What is a conjugative pili?
A thin protein filament that is polymerized as it is extended from donor cell that makes contact with recipient cell
Steps of Conjugation?
- Pilusis extended from T4SS makes contact and contracts closing distance between two cells
2 Relaxase unwind DNA at OriT and second relaxase is recruited to bubble
3.One strand is nicked at OriT and a relaxase attaches to 5’ end and is passed through T4SS to recipient cell while the other relaxase stay in donor cell continuing to unwind DNA
4 RNA poly III synthesises new strand in donor cell and recipient cell once transfer is complete
Now both are donor
