3.5 - genetic modification and biotechnology

Question 1

define gel electrophoresis

Answer 1

involves separating charged molecules in an electric field, according to their size and charge

Question 1

how does gel electrophoresis occur

Answer 1

• 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

Question 2

what does the gel used in gel electrophoresis consist of?

Answer 2

a mesh of filaments that resists the movement of molecules in a sample

Question 3

why do DNA molecules from eukaryotes need to be broken down before gel electrophoresis?

Answer 3

they are too long to move through the gel

Question 4

what is the purpose of PCR?

Answer 4

used to make large numbers of copies of DNA

Question 5

what occurs in PCR?

Answer 5

1. DENATURING; temperature raised to 90. Heat denatures the DNA, breaking the hydrogen bonds between the complementary base pairs
2. ANNEALING; temperature is reduced to 60 so that primers can form hydrogen bonds with the DNA strand
3. 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
4. strands double as each cycle goes on

Question 6

give the stages of DNA profiling

Answer 6

• 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

Question 7

how is DNA profiling used in forensic investigations?

Answer 7

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

Question 8

how is DNA profiling used in paternity investigations?

Answer 8

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

Question 9

what is genetic modification?

Answer 9

the transfer of genes from one species to another

Question 10

how is genetic modification possible?

Answer 10

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

Question 11

what has genetic modification been used for?

Answer 11

• to introduce new characteristics to animal species
• to produce many new varieties of crop plant (these are known as GM crops)

Question 12

what is involved in gene transfer to bacteria?

Answer 12

plasmids, restriction enzymes, DNA ligase

Question 13

how do plasmids allow gene transfer to bacteria?

Answer 13

• 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

Question 14

how do restriction enzymes allow gene transfer to bacteria?

Answer 14

• 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

Question 15

how does DNA ligase allow gene transfer to bacteria?

Answer 15

when the desired gene has been inserted into a plasmid using sticky ends there are still nicks in each sugar-phosphate backbone of the DNA but DNA ligase can be used to seal the nicks

Question 16

claims about environmental benefits of gm crops

Answer 16

• pest-resistant crop varieties can be produced by transferring a gene for making a toxin to the plants
• use of GM crop varieties reduces the need for plowing and spraying crops, so less fuel is needed for farm machinery
• the shelf-life of fruit and veg can be improved, reducing wastage and area of crops that have to be grown

Question 17

claims about the health benefits of GM crops

Answer 17

• nutritional value of crops can be improved, eg increasing vitamin content
• varieties of crops could be produced lacking allergens or toxins that are naturally present in them
• GM crops could be engineered that produce edible vaccines so by eating the crop a person could be vaccinated against the disease

Question 18

claims about agricultural benefits of GM crops

Answer 18

• varieties resistant to drought, cold and salinity can be produced by gene transfer, expending the range over which crops can be produced and increasing total yields
• a gene for herbicide resistance can be transferred to crop plants allowing all other plants to be killed in the growing crop by spraying with herbicide. with less weed competition crop yields are higher. herbicides that kill all plants can be used to create wee-free conditions for sowing non-GM crops but they cannot be used once a crop is rowing.
• crop varieties can be produced that are resistant to diseases caused by viruses. these diseases currently reduce crop yields significantly and the only current method of control is to reduce transmission by killing insect vectors of the viruses with insecticides.

Question 19

claims made about health risks of GM crops

Answer 19

• proteins produced by transcription and translation of transferred genes could be toxic or cause allergic reactions in humans or livestock that eat GM crops
• antibiotic resistance genes used as markers during gene transfer could spread to pathogenic bacteria
• transferred genes could mutate and cause unexpected problems that were not risk-assessed during development of GM crops