Application of Reproducion & Genetics Flashcards
(66 cards)
1
Q
What was the purpose of the Human Genome Project and the 100K Genome Project?
A
To improve knowledge and understanding of genetic disorders and improve their diagnosis and treatment
2
Q
The Human Genome Project began in 1990 and was completed in 2003. What did it discover?
A
- The order of DNA bases in genomes
- The distribution and sequences of introns and exons
- The loci of individual genes
3
Q
What is ‘Sanger Sequencing’?
A
A DNA sequencing process that involved reading the base sequence of a length of DNA. This method sequenced relatively small sections of DNA at a time
4
Q
What does Next Generation Sequencing allow scientists to do?
A
Can sequence the entire genome in a few hours. Can study variation within the human genome
5
Q
What did the 100k Genome Project enable us to do?
A
- Locate genes responsible for rare diseases and cancers
- Locate mutated genes
- Compare genomes of genetic disorder sufferers with the normal genome
- Develop treatments for genetic disorders
- Undergo effective prenatal diagnosis for genetic disorders
6
Q
What are some ethical issues regarding the screening of DNA?
A
- Ownership of genetic information that could lead to potential discrimination eg health insurance, job applicaitons, social stigmatisation
- There are concerns regarding the possibility of routine screening for adult-onset disorders eg Alzheimer’s. Some people don’t want to know this information and it could cause anxiety
- Concerns over embryo screening and the potential for choosing alleles to ensure specific characteristics - ‘designer babies’
7
Q
What has been done to help control malaria?
A
Chemicals have been used to attack both the vector and the parasite
8
Q
What are 2 methods that could be used to determine how closely related organisms are?
A
DNA hybridisation and amino acid sequence analysis
9
Q
What issue has arisen with the malarial vector?
A
Rapid evolution of insecticide resistance in the Anopheles gambiae mosquito is hampering attempts to eradicate the disease. Pyrethroid resistance is a problem as this is the only insecticide safe for use with the nets that people sleep under
10
Q
What issue has arisen with the malarial parasite?
A
Plasmodium sp. has developed multi-drug resistance. It is hoped that a better understanding of genetic control of Plasmodium infection will allow the development of more effective drugs
11
Q
Using your knowledge of natural selection, describe how the mosquito population in Africa became resistant to insecticides such as Pyrethroid
A
- Mutation in the genome of the mosquito for resistance
- Selection pressure of insecticides means individuals with the resistant alleles had a selective advantage
- These mosquitos survive and reproduce, passing on the resistance alleles to the next generations
- Resistance alleles increase frequency in population
12
Q
Give 3 advantages and 2 disadvantages of chemical control of mosquitos
A
Advantages: quick and easy to apply chemicals, fast result and application does not require a high level of skills
Disadvantages: fear of resistance, can kill beneficial organisms
13
Q
What does the polymerase chain reaction (PCR) allow us to do?
A
It allows the quantity of DNA to be amplified rapidly using a primer which is complementary to the start of the sequence
14
Q
What are the 3 stages involved in PCR?
A
- Separation
- Annealing
- Extension
15
Q
Describe step 1 (separation) in PCR
A
The target DNA molecule is dissolved in a buffer and is heated to 95ºC. This breaks the hydrogen bonds and denatures the DNA causing the two strands to separate, exposing the nitrogenous bases
16
Q
Describe step 2 (annealing) in PCR
A
The sample is cooled to 50-60ºC to allow the short DNA primers to bind to the DNA strands and they form hydrogen bonds with complementary bases
17
Q
Describe step 3 (extension) in PCR
A
Heating to 70ºC allows thermally stable DNA polymerase (Taq) to add complementary nucleotides by forming phosphodiester bonds in the sugar-phosphate backbone. This creates two double stranded molecules
18
Q
State and describe 5 limitations of PCR
A
- Contamination: any DNA that enters the system by mistake will be amplified
- Error rate: Tap polymerase cannot proof-read and correct errors in the base sequence. Each cycle copies and multiplies DNA so these errors accumulate
- Sensitivity to inhibitors: molecules in the sample may act as inhibitors and PCR is very sensitive to them
- Limits on amplification: after about 20 cycles, PCR slows down and plateaus because reagent concentrations become limiting, the enzyme denatures after repeated heating, DNA in high concentration causes the single stranded molecules to base pair with each other rather than with primers
- DNA fragment size: PCR is most efficient at making DNA about 1000-3000 base pairs long as tan polymerase can’t correct its errors. Many genes are much longer than this
19
Q
State 4 advantages of PCR
A
- Rapid
- Easy
- Sensitive
- Doesn’t require living cells
20
Q
What is gel electrophoresis?
A
A method of separating DNA fragments according to size to produce a genetic fingerprint
21
Q
Describe the process of gel electrophoresis
A
- DNA fragments are loaded into wells at one end and a voltage is applied across the gel
- DNA fragments have a negative charge (on the phosphate group) and so are attracted to the positive electrode. Smaller fragments will move further as they move through the pores in the gel more easily
- A DNA ladder can be run alongside the sample. A DNA ladder contains DNA fragments of known length. This can be used to determine the length of DNA in the sample being analysed.
22
Q
What are exons?
A
Regions of DNA that code for proteins
23
Q
What do introns contain?
A
Blocks of repeated nucleotides called short tandem repeats (STRs) that do not code for proteins
24
Q
Why do we separate introns when producing a DNA profile by electrophoresis?
A
There are far more differences between the introns of individuals than between exons
25
Name 6 situations where DNA profiling has been used
- Determining whether twins are monozygotic or fraternal
- Siblings - people who have been adopted may wish to determine blood relatives
- Phylogenetic studies to determine relatedness
- Paternity testing
- Immigration
- Forensic use
26
State 3 applications of genetic engineering
- To make useful products - transfer of genes into bacteria eg to produce human insulin
- Transfer genes into plants and animals so they acquire new characteristics eg disease resistance
- Treating genetic diseases eg by transferring genes into humans so they no longer suffer from cystic fibrosis
27
State the stages involved in the process of producing a new protein using the DNA technology of a gene transfer
1. Identify and isolate DNA fragments from donor organism using restriction enzymes or reverse transcriptase
2. Insert DNA fragments into a vector (recombinant DNA)
3. Transfer the recombinant DNA into a suitable host cell
4. Identify host cells which have taken up and are expressing the recombinant DNA
5. Clone the host cells
28
What is recombinant DNA?
Produced when the donor DNA fragment is spliced into the DNA of another organism
29
Step 1 of genetic engineering is to identify and isolate DNA. In which two ways can the desired gene be isolated?
- Locate it on the donor DNA and cut it out using restriction endonuclease (enzymes that cut DNA at specific base sequences)
- Extract mRNA from a cell actively synthesising the required protein/polypeptide and use reverse transcriptase to produce a single strand of DNA (cDNA) from this mRNA then use DNA polymerase to add free DNA nucleotides to the template strand to produce a double stranded section of cDNA which codes for the desired protein
30
Suggest the source of the reverse transcriptase enzymes used in identifying and isolating DNA
Retrovirus
31
Describe the production of cDNA
1. mRNA is extracted from the donor cells
2. Reverse transcriptase enzymes are used to make a DNA copy of the mRNA
3. The newly synthesised strand of DNA is called cDNA (complementary DNA). Many copies of cDNA are made
4. DNA polymerase enzymes catalyse the addition of free DNA nucleotides. This converts the cDNA into a double strand
5. DNA is copied many times using the PCR
32
State 4 benefits of using reverse transcriptase to produce cDNA
- Overcomes the problem of locating the gene on the DNA
- Avoids restriction enzymes cutting the desired gene into non-functional fragments
- No introns present in cDNA (as these are removed from mRNA)
- No need for post-transcriptional processing to produce funcitonal mRNA
33
What is a common vector used in genetic engineering?
Plasmid (isolated from bacteria)
34
What is a plasmid?
A small ring of DNA that can replicate independently, commonly found in bacteria
35
Describe the steps involved in inserting DNA into a vector (step 2 in genetic engineering)
1. Cut the isolated donor DNA using restriction endonucleases. These cut the DNA between specific base sequences
Many restriction enzymes cut DNA in a staggered pattern and leave overhanging ends with unpaired bases exposed, known as 'sticky ends'
2. The **same** restriction enzymes are then used to cut the plasmid DNA at the same base sequence
3. DNA ligase enzymes are used to splice together the sugar phosphate backbones of donor and vector DNA
4. The new plasmid is now known as recombinant DNA
36
Describe the transfer of recombinant DNA into a host cell (step 3 in genetic engineering)
The recombinant plasmids are mixed with bacterial cells and calcium chloride in the hope that the bacteria will take up the plasmid
37
Describe how we identify host cells which have taken up the recombinant DNA and are expressing it (step 4 in genetic engineering)
Scientists use a marker gene. This is usually a gene which confers antibiotic resistance. Cells which take up the desired gene will also take up the antibiotic resistant gene. If they are grown on a medium containing antibiotics, only the cells containing the plasmids will survive
38
Describe step 5 in genetic engineering (cloning the host cells)
Bacteria are grown on a large scale to produce large amounts of, for example, insulin
39
State 3 advantages of the genetic engineering of bacteria
- Allows the manufacture of medical productions eg insulin to treat diabetes and human clotting factors to treat haemophilia
- Prevention and treatment of disease eg produce vaccines
- Enhancing crop growth - modified bacteria secrete molecules toxic to pests
40
State 3 disadvantages of the genetic engineering of bacteria
- Plasmids are easily transferred. Genes may be exchanged with other bacteria and antibiotic resistance marker genes could be transferred to pathogenic bacteria
- A new microorganism with a new gene may become a threat if released into the environment
- The possible transfer/activation of oncogenes by using fragments of human DNA
41
Describe GM soy beans
Important food source. Used to produce a wide range of products eg flour, protein, oil, bread. They are genetically modified to contain genes for herbicide resistance. They can be sprayed to remove weeds without inhibiting their growth
42
Describe Bt tomatoes
Bacillus thuringiensis is a bacterium that lives in the soil. It contains genes that produce a protein that acts as an insecticide. Tomatoes produce their own insecticide so farmers don't have to, less crop spoilage, higher yiels and lower costs
43
Describe antisense tomatoes
Tomatoes ripen naturally when they produce an enzyme that breask down their cell wall. A second version of this gene was inserted into tomato plant cells to prevent translation and block the production of this enzyme. This means less food spoilage during transport and longer shelf life
44
State 3 benefits of GM crops
- Superior keeping qualities
- Higher crop yield
- Substantial reduction in pesticide use on crops engineered for resistance to fungal pathogens and insect attack
45
State 3 arguments against GM crops
- Pollen from GM plants engineered for herbicide resistance might transfer genes to wild relatives/contaminate organic crops
- There may be adverse health effects of eating a crop that is expressing a new gene and making a new protein
- Reduction in biodiversity such as limited crop varieties and beneficial insects being killed
46
What is gene therapy?
Replacing defective alleles with copies of a new functional DNA sequence
47
What methods can be used in gene therapy to introduce DNA into target cells?
- A virus as a vector
- A plasmid as a vector
- Injection of naked plasmid DNA
48
What are the 2 ways of replacing defective genes?
- **Somatic cell therapy:** targets body cells in affected tissues
- **Germ line therapy:** introduces corrective genes into germ line cells so genetic corrections are inherited
49
What are the problems with somatic cell therapy?
Genetic changes are not inherited in daughter cells and do not appear in future cells
50
Why can germ line therapy be controversial?
As genes interact with each other, potentially influencing genes in the oocyte has unpredictable effects in future generations
51
What are most cases of Duchenne muscular dystrophy caused by?
One or more deletions in the dystrophin gene. These genes have 79 exons - deletions in any of these alter the reading frame of dystrophin mRNA. The ribosome meets a stop codon too soon and the full polypeptide is not translated and functional dystrophin is not synthesised
52
How does the drug **drisapersen** treat DMD?
It acts as a 'molecular patch', binding to the mRNA over the exon with the deletion. That portion of mRNA becomes double stranded to the ribosome can't translate it. This restores the reading frame so a shorter, partially funcitonal dystrophin protein can be made. This type of treatment is called exon skipping
53
What are the drawbacks of gene therapy?
- Only a small proportion of the introduced genes are expressed
- There are a number of potential issues when using a virus as a vector:
- There may be an immune response in the patient
- The virus may invade non-target host cells
- The virus could potentially become pathogenic and cause disease
- The virus may affect other genes such as the formation of oncogenes
54
What is genomics?
The study of the structure, function, evolution and mapping of genomes as exemplified by the Human Genome Project and the 100K projects
55
How should genomics enable healthcare to be improved?
- More accurate diagnosis
- Better prediction of the effect of drugs
- Improved design of drugs
- New and improved treatments for disease
56
What is tissue engineering and its goal?
It uses biochemistry, cell biology, engineering and material science to repair, improve or replace biological tissues. Its goal is to produce 'off the shelf' bio-artificial organs and to regenerate injured tissue in the body
57
What are stem cells?
Undifferentiated cells that have the ability to become many different specialised cell types
58
What can stem cells be used for?
Replacing damaged tissues and organs during tissue engineering
59
Where are embryonic stem cells found?
In 3-5 day old embryos
60
Where are adult stem cells found and what do they do?
Some adult tissues such as bone marrow. They replace cells that are lost through wear and tear, injury or disease, but they cannot form all cell types
61
List some examples of tissues and/or organs that have been created using tissue engineering
Bone, bladder, skin apligraf, artificial meat
62
What is the role of stem cells in tissue engineering?
- Used to regenerate tissues and organs
- To screen new drugs
- To develop model systems to study normal growth and identify the causes of birth defects
- To investigate the events that occur during human development
63
What are the UK requirements for the use of stem cells from embryos?
- Stem cells left over from IVF are deposited in the UK stem cell bank so they are available for other research groups. Donors must give specific consent to embroys created with their gametes being used in stem cell research
- There is no financial reward for any development or discovery made using them
64
What is an argument for the use of embryonic stem cells?
It helps to clarify biological mechanisms
A pre-14 day old embryo is a ball of cells with no possibility of independent existance
65
Discuss and suggests the possible arguments against the use of stem cells
- The moral status of an embryo. An embryo does have moral right, but not to the same degree as a living person
- The rights of a foetus are balances against thr potential benefits people may gain from the research and treatments it produces
- There is a fear that stem cells may lead to humans being cloned, an act that fundamentally devalues human life
66
State 3 advantages of germ-line therapy
1. Present in all cells of the body
2. Doesn't need to be repeated
3. Can be passed on to future generations
