Human Bio Ch 10 Flashcards
What does PCR stand for?
Polymerase chain reaction
What is PCR?
A technique used in molecular biology for producing multiple copies of DNA from a sample, used in DNA fingerprinting and in identifying diseases.
What are the 3 main steps of PCR?
- Denaturing: the DNA strands are separated. Temperatures of 94-96 degrees are used to break the hydrogen bonds.
- Annealing: short sections of DNA also known as primers are bound to the separated strands, this is done in temperatures of 50-60 degrees.
- Extension: the short sections of DNA are extended to produce longer strands. DNA polymerase is used to join new complementary nucleotides to the sections originating with the primer. This is done in temperatures of 72 degrees, uses Taq polymerase.
How can restriction enzymes be used in Gel electrophoresis?
When restriction enzymes are added to the DNA, it cuts the strands into different lengths depending on the base sequence of the specific DNA sample. The length of these pieces can be analysed and compared with other DNA samples.
What is gel electrophoresis?
A process used to separate charged molecules based on their size by pushing them through gel. The DNA pieces are placed in wells in a semi-solid gel that is immersed in a solution of an electrolyte. There electrodes at either end with the negative being closest to the DNA and the positive on the other side. When an electric current is passed through the gel the negatively charged DNA moves towards the positive electrode with the smaller DNA pieces moving faster than the longer ones. Results in a pattern of bands, this is known an individual’s DNA profile.
What are the main ways to visualise DNA?
- Ethidium bromide - added to the agar prior to the gel being set, as the DNA moves through the gel it picks up some of the chemical and when finished an ultraviolet light is shone over the gel and the DNA lights up. However, ethidium bromide is a carcinogen and must be handled very carefully.
- Methylene blue dye - bind to the DNA so that the areas containing DNA stain a deeper blue and therefore become visible to the human eye.
- DNA probes - these are short sections of a single strand of DNA with a radioactive or fluorescent molecules that binds to the DNA being tested.
What is DNA sequencing?
The determination of the precise order of nucleotides in a sample of DNA. DNA is synthesised from 4 nucleotides each with a different nitrogenous base.
When DNA forms:
- each nucleotide loses 2 phosphate groups
- the sugar molecule loses a hydrogen atom from the hydroxy group (OH) when is bonds to the phosphate group of an adjacent nucleotide.
Dna sequencing can be used to identify mutations or to compare DNA from different organisms. Useful in identifying inherited disorders. Used for maternity and paternity tests. Can also be used to track evolutionary change.
What is sanger’s method?
The synthetic nucleotides that lack the OH group are added to the growing strands, these are called dideoxyribonucleotides (ddNTPs). These synthetic nucleotides stop elongation of the sequence because there is no OH group for the next nucleotide to attach to. This happens at each of the nucleotides in the DNA sample creating different lengths of DNA. This can be done through gel electrophoresis. Knowing which base was added to create each length allows scientists to determine the order of nucleotides.
What are the ethical considerations surrounding genetic information?
- Autonomy - respect for the right to be self determining and to choose whether or not to be tested and if tested, to know and share that information. Right of an individual to decide their own future.
- Confidentiality - the use of genetic information is treated sensitively and is accessed only by those authorised to access it.
- Equity - the right to fair and equal treatment regardless of genetic information
- Privacy - the right to be ‘left alone’ and to make decisions regarding genetic testing and the resulting information, independent of others.
What is comparative genomics?
The comparison of genome sequences of different species. This can show how species who are more closely related or who have a common ancestor will have similar DNA whereas those who are more distantly related will have more differences in their DNA.
By comparing the sequence of the human genome with genomes of other organisms, researchers are able to identify regions of similarity and difference.
Examination of genomes show that human closest living relatives is the chimpanzee with more than 98% of our DNA being similar.
What are endogenous retroviruses (ERV’s)?
A retrovirus that has become a part of an organism’s genome and exists in every cell of the body.
Retroviruses store their genetic information as RNA, not DNA. Upon entering a cell, a retrovirus copies its RNA genome into DNA in reverse transcription (RNA is copied during the synthesis of DNA). The DNA then becomes inserted into one of the host cells chromosomes. A retrovirus only becomes endogenous if it inserts into a cell whose chromosomes will be inherited by the next generation, an ovum or sperm cell. The offspring of the infected individual will then have a copy of the ERV in the same place.
ERV’s make up 8% of the human genome. Similar ERV’s can show a common ancestor.
What is mitochondrial DNA?
DNA found in the mitochondria of the cells rather than in the nucleus. In the form of small circular molecules, about 5-10 of these molecules in each mitochondrion. Has 37 genes all of which help the mitochondrion to function normally. Contains genes that have the instruction to make enzymes necessary for the reactions of cellular respiration.
Most cells contains large numbers of mitochondria and therefore usually have between 500-1000 copies of mtDNA in each molecule, this makes it a lot easier to find and extract than DNA in the nucleus, meaning smaller samples can be used. In human the mtDNA contains 16500 base pairs representing only a fraction of the total amount of DNA in a cell.
What is the inheritance of mitochondrial DNA?
Both the egg and the sperm have mitochondria, however, whilst the egg has hundreds the sperm only have 100 and used this energy to swim to the egg. When penetration occurs between the sperm and the egg the sperm loses all of its mitochondria. This means that mitochondrial DNA comes only from the egg (maternal side) whilst nuclear DNA comes from both the egg and the sperm.
What evidence can be found from mitochondrial DNA?
Mitochondrial DNA of two people can be used to show how closely related they are through their maternal ancestors. If it very similar or even identical they are likely to be siblings, but if it is different they likely had a common ancestor many years ago. Has allowed scientists to track the ancestry of many species back hundreds of generations. Can also show evidence of evolution.
What is a ubiquitous protein?
One of a group of proteins that appears to be in all species, form bacteria to humans, the small protein called ubiquitin was so named because it is present in all types of cells.
Cytochrome C is an example of a ubiquitous protein as it is an essential step in the production of cellular energy.
Can compare amino acids in a protein in protein sequencing and determine a similarity between different species.
