Lecture 12 Translation and Horizontal Gene Transfer Flashcards
(25 cards)
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
