3.5 - genetic modification and biotechnology Flashcards
define gel electrophoresis
involves separating charged molecules in an electric field, according to their size and charge
how does gel electrophoresis occur
- samples are placed in wells cast in a gel
- the gel is immersed in a conducting fluid and an electric field is applied
- molecules in the sample that are charged will move through the gel
- molecules with negative and positive charges move in opposite directions (proteins may be +vely or -vely charged so can be separated)
- small fragments move faster than large ones so move further in a given time
what does the gel used in gel electrophoresis consist of?
a mesh of filaments that resists the movement of molecules in a sample
why do DNA molecules from eukaryotes need to be broken down before gel electrophoresis?
they are too long to move through the gel
what is the purpose of PCR?
used to make large numbers of copies of DNA
what occurs in PCR?
- DENATURING; temperature raised to 90. Heat denatures the DNA, breaking the hydrogen bonds between the complementary base pairs
- ANNEALING; temperature is reduced to 60 so that primers can form hydrogen bonds with the DNA strand
- temperature is raised to 72 (optimal temperature of tax polymerase) which attaches nucleotides to the strand and forms complementary base pairs with the template DNA strand
- strands double as each cycle goes on
give the stages of DNA profiling
- a sample of DNA is obtained
- sequences in the DNA that vary considerably between individuals are selected and copied by PCR
- the copied DNA is split into fragments using restriction endonuclease
- the fragments are separated using gel electrophoresis
- this produces a pattern if bands that is always the same with DNA taken from one individual (this is the individual’s DNA profile)
- the profiles of different individuals can be compared to see which bands are the same and which are different q
how is DNA profiling used in forensic investigations?
DNA profile of material from the crime scene is compared with the DNA profile of a sample of DNA taken from the suspect or the victim. if the pattern of bands matches exactly it is likely that DNA is from the same person
how is DNA profiling used in paternity investigations?
DNA profiles of the mother, the child, and the man are needed
- DNA profiles of each of the samples are prepared and patterns of bands are compared
- if any bands in the child’s profile do not occur in the profile of the mother or man, another person must be the father
what is genetic modification?
the transfer of genes from one species to another
how is genetic modification possible?
the genetic code is universal, so when genes are transferred between species, the amino acid sequence translated from them is unchanged - the same polypeptide is produced
what has genetic modification been used for?
- to introduce new characteristics to animal species
- to produce many new varieties of crop plant (these are known as GM crops)
what is involved in gene transfer to bacteria?
plasmids, restriction enzymes, DNA ligase
how do plasmids allow gene transfer to bacteria?
- plasmids have genes that encourage their replication in the cytoplasm and transfer from one bacterium to another
- bacteria use plasmids to exchange genes, so naturally absorb them and incorporate them into their main circular DNA molecule
how do restriction enzymes allow gene transfer to bacteria?
- they can be used to cut open plasmids and also to cut out desired genes from larger DNA molecules
- some restriction enzymes can cut the two strands of a DNA molecule at different points, leaving single-stranded sections called sticky ends
- the sticky ends have complementary base sequences so can be used to link together pieces of DNA, by hydrogen bonding between the bases