CRISPR - MT3 - Part 1 Flashcards
What is CRISPR? (2)
- It is a technique for finding any place on any genome you wish to find and making any alteration you wish to make
- It is a gene locus in many bacteria
- it is a certain place on the bacterial chromosome that codes for certain proteins and/or has certain functions other than coding
What does CRISPR stand for?
Clustered Regularly Interspaced Short Palindromic Repeats
Locus
Is a fixed position on a chromosome, like the position of a gene or a marker
What is CRISPR the latest example of?
A molecular tool in biology that is derived from a natural structure or process
Plasmid
A genetic structure is a cell that can replicate independently of a chromosome
- easy to manipulate in a test tube
Viruses
An infective agent that consists of nucleic acid molecules in a protein coat, is too small to be seen by light microscopy and is bale to multiply only within the living cells of a host
Restriction enzyme
An enzyme produced by bacteria, having the property of cleaving DNA molecules at or near a specific sequence of bases
DNA ligase
Is a specific type of enzyme, it facilitates the joining of DNA strands together by catalyzing the formation of a phospho-diester
DNA polymerase
Is a type of enzyme that is responsible for forming new copies of DNA, in the form of nucleic acid molecules
What is an example of DNA polymerase?
Taq polymerase
What 3 things are needed when cloning a gene?
- Restriction enzymes
- DNA ligase
- Plasmid vector
What can bacteria be infected with?
Viruses (phages)
What have bacteria evolved?
Defences against viruses
What do bacteria have on them?
A selective pressure on them to develop a defensive mechanism
What do phages encode?
Some functions needed for replication
- a typical virus will make a few of these proteins and then hijack the cell
What do viruses not have?
A selective barrier
What is one kind of innate defence system in bacteria?
Restriction enzymes
- non-acquired, non-specific
What does methylation do?
Prevents cutting of the DNA of the attacked cell
- restriction enzymes font cut the bacterial DNA because they are methylated
What is one kind of adaptive defence system?
CRISPR
- acquired, specific
- changes to individual experience
What happens in the first exposure to a virus?
A bacterial cell can chop up the viral genome into small fragments and insert some of the fragments into the bacterial CRISPR locus
What must the viral genomic fragments be next to?
The sequence 5’-NGG-3’ in the viral genome
- this is the PAM
PAM
Protospacer adjacent motif
What does the CRISPR locus consist of? (2)
- A number of short palindromic repeats
- the viral fragments are interested as non-repetitive spacers between the repeats - Contains genes such as cas or CRISPR-associated genes that encode for proteins, such as nucleases that can cut DNA
What are new viral fragments interested in?
The closest available position to the leader sequence
What do viral sequence represent?
Molecular memories of the viruses they have encountered, just our own memory lymphocytes encodes these memories in us
What happens if the cell encounters the same virus again? (2)
- The CRISPR locus is transcribed to CRISPR derived RNA (crRNA)
- The nearby cas genes are expressed
How can viral DNA find the same sequence in the invading viral genome?
By homologous base pairing
