Topic 8 A Level Biology Flashcards
What is a mutation?
- A change in the DNA base sequence.
Where do mutations occur?
- Mutations occur in normal body cells and gametes.
What are the 6 type of mutations?
1) Substitution
2) Deletion
3) Addition
4) Inversion
5) Duplication
6) Translocation
What happens during substitution?
- Where 1 base is substituted for another
What happens during deletion?
- Where 1 base is lost
What happens during addition?
- Where 1 or more base is added
What happens during duplication?
- Where a sequence of bases or whole gene is inserted twice or multiple times.
What happens during inversion?
- Where a base sequence is removed, rotated by 180 degrees and inserted back again.
What happens during translocation?
- Where a base sequence is taken out and inserted at a different position in the genome.
Why aren’t mutations completely harmful? (2 reasons)
1) Some mutations take place within introns.
2) Genetic code is degenerate so the sequence of amino acids coded for may still be the same as the new codon.
Why do mutations cause harm?
- Mutations cause a frame shift meaning all bases shift in one direction so every codon is read differently.
What are mutagenic agents?
- Substances that increase the rate of mutations.
How do mutations work?
- Some chemicals may delete/alter bases.
- Radiation may alter the structure of DNA as problems occur during replication.
What are the 2 properties of stem cells?
- Stem cells can divide and replicate.
- Stem cells can also differentiate.
What are totipotent cells?
- A type of stem cell where division and differentiation can be applied to any type of body cell.
- They only occur for a very limited time in mammalian embryos.
- During development, only part of the DNA is translated, leading to specialisation.
What are pluripotent cells?
- Descendants of totipotent cells that can specialise into any type of body cell except for cells that make up the placenta.
What are multipotent cells?
- Cells that differentiate into a limited number of types of body cell.
What are unipotent cells?
- Cells that differentiate into 1 type of cell.
What is the use of pluripotent stem cells?
- Divide into unlimited numbers and can be used to treat human disorders.
What is the use of unipotent cardiomyocytes?
- Could develop into new heart tissues.
What is the use of induce pluripotent stem cells?
- A type of stem cell that is made by reprogramming adult body cells.
What are the pros of IPS cells?
- There is no destruction of embryos, avoiding ethical issues.
- No risk of rejection
What is Epigenetics?
The heritable changes in gene function without a change to the base sequence of DNA.
What are the 2 factors that cause heritable changes during epigenetics?
1) Increased methylation of DNA
2) Decreased acetylation of associated histones.
How does increased methylation cause heritable changes to DNA?
- Methyl group becomes attached to a DNA which codes for a gene.
- The methyl group attaches at a C-G binding site.
- This changes DNA structure
What is the role of the acetyl groups in DNA?
- DNA is wound around histones to form chromatin.
- If acetyl groups bind to the chromatin, this leads to reduced attraction between DNA and histones.
- This makes it easier for transcriptional machinery to bind to DNA.
What happens when there is a reduction in acetylation?
- Less acetyl groups will bind to the chromatin, leading to more attraction between DNA and histones.
- Therefore, making it harder for transcriptional machinery to bind to DNA.
What is the genome?
- The complete set of genetic material of an organism.
What is recombinant DNA?
- The transfer of DNA fragments from one species to another.
How is it possible for recombinant DNA to be replicated inside another organism?
- Due to the genetic code being universal, the transferred DNA can be translated within the organism that recieves the DNA.
How can we use reverse transcriptase to produce fragments?
1) mRNA for a polypeptide is isolated from a cell.
2) It is mixed with free DNA nucleotides and reverse transcriptase.
3) Reverse transcriptase uses the mRNA as a template to produce complementary DNA, which is a double stranded copy of the required gene.
Why is mRNA useful in recombinant DNA?
- there is lots of the mRNA on each gene.
- mRNA has no introns when matured.
How do we use restriction endonucleases to produce fragments?
- Breaking phosphodiester bonds between DNA bases.
- Binding to recognition sites through complementary pairing.
- Once binded together, there is cutting of the DNA.
What ends to restriction endonucleases form?
- Sticky ends
What are sticky ends?
- Staggered cuts, revealing unpaired base sequences at either end of the fragment.
What are vectors?
- DNA mocleucles that carry DNA fragments into a cell.
What are 2 types of vectors?
- Plasmids
- Bacteriaphages
What enzyme joins sticky ends of the vector and fragments?
- DNA ligase (forms phosphodiester bonds)
What is the gene machine?
- The gene machine determines the amino acid sequence of a specific polypeptide.
- This tells us the mRNA base sequence, from which we can determine the base sequence which acted as a template.
Why is amplification necessary?
- To produce numerous copies to work with.
What are 2 methods of amplification?
- invitro and invivo
What happens during transformation (invivo)
- There is insertion of recombinant DNA into a host cell
How does transformation differ between bacteriophages and plasmids?
- In bacteriophages, they inject their DNA into the bacterium.
- In plasmids, host cells are stimulated to take in the plasmid.
How are cells that take up recombinant DNA identified?
- Marker genes are inserted into the vector together with the required gene.
- Marker genes may code for antibiotic resistance so when cells take up recombinant DNA, they survive, and are seen.
- Flourescent dye can be used.
Why are promoter and terminator regions essential?
- They determine the rate of translation through stop and start codons.
What is PCR?
- PCR is invitro
- widely used to make millions to billions of copies of a specific DNA sample rapidly
How does PCR work?
1) Reaction mixture should contain DNA polymerase, primers, DNA fragments and free DNA nucleotides.
2) Heat to 95 degrees celsius so the DNA denatures and hydrogen bonds break.
3) Cool to 50-60 degrees celsius, allowing the primers to bind to complementary bases at the ends of fragments.
4) Heat again to 72 degrees celsius so that DNA polymerase carries out the extension of the strands (new complementary strands will form). REPEAT
What are DNA primers?
- Primers are short, single stranded DNA base sequences that are complementary to the bases at the start of the desired DNA fragment.
- primers allow DNA polymerase to bind to the DNA fragment.
What are DNA probes?
- Short-single stranded sequence of DNA whose bases are complementary to a specific DNA sequences.
- If DNA sequence is present, then the DNA probe will bind via complementary base pairing.
What are gene probes?
- Probes that test for the presence of a mutated allele.
Why is identification important?
- Helps prevent the worsening of diseases.
How do gene probes get made?
1) Sequence the allele.
2) Produce the probe using a gene machine.
3) PCR will produce many probes.
How are gene probes used?
1) Probe is labelled with flourescent dye.
2) A DNA sample is bound to the bottom of the well.
3) There is incubation of the sample with the probe.
4) Probe binds when there is a complementary DNA sequence.
5) The well is rinsed to wash away any unbound probes (if the target allele is present, the probe will show up).
What are VNTRs?
- Variable Number Tandem Repeats are the same base sequences repeated many times (non-coding)
- In non-coding regions, we find more difference in the DNA between individuals of the same species as mutations in coding regions aren’t inherited.
- The chance of two individuals having the same number of VNTRs is very low.
How does genetic fingerprinting work?
1) Sample of DNA
2) Restriction endonucleases cut out VNTR regions and the PCR amplifies fragments.
3) There must be incubation with a labelled probe.
4) DNa fragments are passed through an electrical current and as DNA is positively charged, it is attracted to the charged opposite ends.
5) Fragments separate into bands.
6) Bands are compared to another genetic fingerprint
What are the uses of genetic fingerprinting?
- Paternity tests
- Closeness
- Genetic variation
- Foresnics
- Medical diagnosis
- Tumour diagnosis
What is the purpose of sequencing projects?
- Read the genomes of a wide range of organisms and are used to determine evolutionary relationships between organisms.
Why are simpler organisms easier for sequencing projects?
- No introns
- Shorter
- No histones
Why is it simpler to determine the proteome from the genome?
- The DNA base sequence determines the sequence of amino acids in a specific polypeptide.
What are the pros of using sequencing projects on simpler organisms?
- Antigens on the surface are detected to help develop vaccines.
Why are complex organisms harder to sequence>
- Introns
- Regulatory genes control the translation of genes.
