Finals - Gene Manipulation Flashcards
why manipulate genes?
- understand their function and interaction with other molecules
- produce drugs, vaccines, hormones, and other important gene products
What does gene manipulation involve?
- nucleic acid hybridization
- rapid sequencing of all the nucleotides in a purified DNA fragment
- cleavage of DNA at specific sites by restriction endonucleases
- DNA cloning
- DNA engineering
use of probes to find a specific sequence of DNA or RNA with great accuracy and sensitivity on the basis of its ability to bind a complementary nucleic acid sequenc
nucleic acid hybridization
determine the boundaries of a gene and the amino acid sequence it encodes
rapid sequencing of all the nucleotides in a purified DNA fragment
greatly facilitates the isolation and manipulation of individual genes
cleavage of DNA at specific sites by restriction endonucleases
a single DNA molecule can be copied to generate many billios of identical molecules
DNA cloning
basic steps in DNA cloning
- isolation of DNA
- cleavage of DNA at particular sequences
- ligation of insert DNA to vector DNA
- introduction of recombinant DNA into compatible host cells
- replication and in some cases expression of recombinant DNA within host cells
- identification of host cells that contain recombinant DNA within host cells
bacteria usually used
E. coli
library of desired genes
genomic and cDNA library
- DNA sequences are altered to make modified versions of genes, which are reinserted back into cells or organisms
- genomic and cDNA library construction
- methods of screening libraries
DNA engineering
methods of screening libraries
- colony and plaque hybridization
- chromosome walking
- DNA footprinting
- molecular scissors that cut DNA into fragments at specific sites in their sequence
- degrades foreign DNA -> defense vs phages
- restriction endonucleases
restriction enzymes
restriction enzymes are aka _
restriction endonucleases
nomenclature = EcoRI
- Eco = 1st letter of genus + 1st and 2nd letter of species
- R = strain of host bacteria
- I - order of discovery
Different classification of restriction enzymes
- Type I
- Type II
- Type III
- Type IV
cut DNA at random far from their recognition sequences
Type I
cut DNA at defiend positions close to or within their recognition sequences
Type II
cut DNA outside of two recognition sequences in opposite orientations
Type III
cut modified DNA (e.g. methylated)
Type IV
mechanism of restriction enzymes
- scan
- bind
- cut
look for a particular pattern of nucleotides
scan
responsible for scanning
enzyme’s recognition sequence
what happens after scanning?
enzyme will bind the DNA molecule
where does the restriction enzyme cut
in each of the two sugar-phosphate backbones of double helix
- the DNA sequence to which a restriction enzyme binds
- may be made up of 4 bases, 6 bases, or 8 bases
- some have similar recognition sequences but different cutting sites
recognition sequence
most common no. of bases of a recognition sequence
6 bases
rare no. of bases of a recognition sequence
8 bases (rare cutters)
have similar recognition sequences but different cutting sites
isoschizomers
eg. of isoschizomers
- SmaI
- XmaI
restriction enzyme that produce blunt ends
- AluI
- HaeIII
restriction enzyme that produce sticky ends
- BamHI
- HindIII
- EcoRI
cleavage is asymmetrical
over-hanging ends are sticky (complementary)
cleavage is symmetrical
ends are blunt
- linear drawing that represents the location of all RE recognition sites within a piece of DNA
- usually the first step in characterizing an unknown DNA, and a prerequisite to manipulating it for other purposes
restriction mapping
Two ways of restriction mapping
- DNA sequence is known
- DNA sequence is unknown
- search for specific enzyme recognition site
- draw map based on distances
DNA sequence in known
- compare pattern of DNA fragments
- single digests show how many sites are present
- double digests show where the sites are relative to one another
DNA sequence is unknown
show how many sites are present
single digests
show where the sites are relative to one another
double digests (cutting with 2 enzymes)
- made by fusing a DNA-binding domain to a nuclease domain
- can target large DNA sites
- can be engineered to bind desired DNA sequences
artificial restriction enzymes
how are artificial restriction enzymes made
fuse a DNA-binding domain to a nuclease domain
artificial restriction enzymes can target large DNA sites up to __ bp
36
e.g. of artificial restriction enzymes
- zinc finger nucleases
- TALENs
- CRISPR
- joins broken phosphodiester linkages in the sugar-phosphate backbone
- common source: T4 bacteriophage
- can ligate sticky-ends more efficiently than blunt-ends
DNA ligase
common source of DNA ligase
T4 bacteriophage
addition of poly(dA) tail or poly (dT) tail to ends of the DNA from each source
modified blunt-end ligation
DNA molecules in which foreign DNA molecule is inserted and which is further capable of replication within host cell to produce multiple clones of the recombinant DNA
cloning vector
Main features of cloning vectors
- origin of replication
- multiple cloning site
- selectable marker(s)
- DNA segment with several RE sites located next to each other
- also called as polylingker
multiple cloning site
multiple cloning site is also called as
polylinker
REs are __ __ anywhere else in the vector plasmid
not present
cutting the vector with and RE that recognize a site in the polylinker…
does not disrupt any of essential features of the vector
- allows selection of host cells with the recombinant vector
- basis if recombinant DNA is formed
selectable marker(s)
- uses selectable marker lacZ
- if ligation and transformation is successful, bacterial colony will be white
- if not, colony will be blue
- transformed cells are grown in the presence of X-gal
blue-white screening
selectable marker of blue-white screening
lacZ
color if ligation and transformation is successful
white
color if ligation and transformation is unsuccessful
blue
lactose/galactose analog
IPTG
in blue-white screening, transformed cells are grown in the presence of __
X-gal
white colony
5-bromo-4-chloro-indoxyl
blue colony
5,5’-dibromo-4,4’-dichloro-indigo
gene in lacZ
beta-galactosidase
types of cloning vectors
- plasmids
- bacteriophage lambda
- naturally occuring extrachromosomal circular ds DNA molecules that carry an origin of replication and replicate autonomously within bacterial cells
- pBR322
plasmids
plasmid and was one of the first widely used E. coli cloning vectors
pBR322
what does pBR322 contain
- ampicillin-resistance gene
- tetracycline-resistance gene
- Col E1 replication origin
- Eco RI site
- linear, double-stranded molecule
- with cos site
- particularly useful for preparing genomic libraries, because they can hold a larger piece of DNA than a plasmid vector
bacteriophage lambda
- single-stranded
- complementary ends/cohesive ends
- can hybridize with each other
cos site in bacteriophage lambda
other types of cloning vectors
- cosmid
- BAC (bacterial artificial chromosome)
- YAC (yeast artificial chromosome)
- MAC (mammalian artificial chromosome)
size limits of insert of plasmid
less than or equal to 10 kb
size limits of insert of phage
5-20 kb
- plasmid containing a bacteriophage λ cos site
- 35-45 kb
- genomic library construction
cosmid
- E.coli F factor plasmid
- 75-300kb
- analysis of large genomes
BAC (bacterial artificial chromosome)
- yeast centromere, telomere, and autonomously replicating sequence
- 100-1000 kb (1Mb)
- analysis of large genomes, YAC transgenic mice
YAC (yeast artificial chromosome)
- mammalian centromere, telomere, and origin of replication
- 100kb to > 1Mb
- under development for use in animal biotechnology and human gene therapy
MAC (mammalian artificial chromosome)
size limits of insert of cosmoid
35-45 kb
size limits of insert of BAC
75-300 kb
size limits of insert of YAC
100kb - 1Mb
size limits of insert of MAC
100 kb to > 1Mb
- cloning vector with regulatory regions for gene expression
- selection is for cells expressing the gene
expression vectors
what are expression vectors
cloning vectors with regulatory regions for gene expression (e.g. strong promoter)
Methods of introducing recombinant DNA to target host cells
- tranformation
- infection of bacterial cells by bacteriophage
- microinjection
- electroporation
- gene gun or bioballistic method
- transfer of cell-free or exogenous DNA into bacterial host cell
- prereq: cells must be competent
transformation
prereq of transformation
cell must be competent
- CaCl2
- uses short electrical high volatege pulses -> transient pores
- the DNA then enters the cell
electroporation
what is produced during the short electrical high voltage pulses
transient pores
parts of a bacteriophage
- protein coat
- DNA
- sheath
- core
- requires the use of a glass micropipette with a diameter that is much smaller than the cell
- the micropipette punctures the plasma membrane, and DNA can be injected through it
microinjection
foreign DNA containing the genes to be transferred is coated onto the surface of minute gold or tungsten particles and bombarded onto the target tissue or cells using a particle gun
gene gun
where is DNA placed during gene gunning
coated onto surface of gold or tungsten particles
size of gold or tungsten particles used
1-3 micrometers