Lecture 12 Translation and Horizontal Gene Transfer Flashcards
Describe tRNA Molecules
- Convert the language of RNA into that of proteins
- Clover leaf shape
- Two functional regions
- Synthetase enzyme attaches an amino acid here
What are the Three Stages of Translation
- Initiation
- Elongation
- Terminationa
Describe the Initiation step of translation
- ) 16S rRNA in the ribosome hybridizes with Shine-Dalgarno sequence
- ) tRNA with formylmethionine binds start codon in P site
What is the purpose of the Shine-Dalgarno sequence
Aligns mRNA with the ribosome
Describe the Elongation step of translation
- ) tRNA+AA binds A site
- Requires energy - GTP
- Antibiotic tetracycline inhibits binding - ) Peptide bond joins amino acids - catalyzed by 23S rRNA
- ) Ribosome moves 1 codon along mRNA
Describe the Termination step of translation
- Any one of 3 stop codons
- UAA, UAG, and UGA
- no tRNAs with corresponding anticodons
Fig 13.30
What do release factors do?
cleave, release polypeptide
What is a Mutation?
- Heritable change in DNA sequence
- Can generate alleles (alternate forms of genes)
- Can give rise to new phenotypes
What is Vertical gene transfer (Eukarya)
- Sexual reproduction
- New combinations of genes when gametes from parents fuse
How to Bacteria and Archaea create genetic variability.
Horizontal gene transfer a
What are the three mechanisms of Horizontal gene transfer
- Transformation
- Transduction
- Conjugation
Horizontal Gene Transfer
Transformation
What are the examples from lecture?
Uptake of free DNA from environment
Only a few bacterial genera known to be naturally competent
Gram + Streptococcus, Bacillus
What are the two techniques of artificial transformation
- CaCl2 - makes cells more permeable
- Electroporation - pulses high voltage, temporary holes - cell wall, plasma membrane
DNA Transformation
Bacterial RecA protein Integrates DNA by homologous recombination
Membrane-bound protein complexes bring DNA into the cell how?
using a nuclease ?
Fig 16.26
Horizonal Gene Transfer
Conjugation
- DNA transfer by direct cell contact
- Requires pili, plasmids
- Major mode of spreading antibiotic resistance genes
Describe Plasmids
- double-stranded, circular DNA
- Extrachromosomal
- carry genes that confer advantage
- can be transferred by conjugation
- are replicons - have their own ori
What is an episome?
plasmids that exist with or without integrating into chromosome
What is a well-studied example of conjugative plasmid
The F (Fertility) Factor of Escherichia coli
Run through the steps of Conjugation: F+ x F- Mating
- ) Pilus from the donor F+ extends toward the Recipient F-
- ) Pilus Retracts and F factor beings replication
- ) Plasmid-encoded enzyme nicks one strand of F factor , Single strand enters recipient
- ) A new complementary strand made via Rolling circle replication
What is a High Frequency of Recombination (Hfr) cell?
Can transfer integrated F factor and part of chromosome to F- cell
What can happen when there is conjugation across biological domains.
Causes crown gall disease
Tumor-inducing plasmid (Ti)
Piece of Ti, called T DNA, transferred by conjugation from bacterium into plant cell
Piece integrates into plant genome
Agrobacterium tumefaciens
What are the two functions o the T DNA transferred by Agrobacterium?
- ) Directs plant cells to overproduce phytohormones
- Uncontrolled growth forms tumor - ) Stimulates plant cells to make opines a C and N source for bacterium
What does the term “mobile DNA” mean?
refers to segments of DNA that can move from one site to another within other DNA molecules
What is the process that transposable elements move?
Transposition
