Unit 3: Topic 6 (Infection, Immunity and Forensics) Flashcards
What are conventional methods for identifying somebody?
- Fingerprints
- Dental Records
- DNA Profiling
What are fingerprints?
- small ridges caused by folds in the epidermis
* they vary in width and length and form distinctive patterns
What are the characteristics of fingerprints?
- they are unique to each individual
- they don’t change over time
- identical twins have different fingerprints
What finger patterns are there?
How are fingerprints left behind?
- plain arch
- tented arch
- whorl
- loop
• sweat and oil secretions leave impressions on any surface touched
How are fresh prints made visible?
- Fine aluminium, iron powder and carbon powder can be used.
- Ninhydrin can be used which reacts with the amino acids in sweat to produce a purple-coloured fingerprint impression.
- Absorbent surfaces can be used.
- Superglue can be used which reacts with water left by the print.
- Magnets and iron flakes can also be used.
What factors affect the method used to obtain fingerprints?
It depends on the surface and the clarity of the print.
When are Dental Records used to identify a body?
They are used when there are no fingerprints on file and when the body’s soft tissue has been damaged.
Teeth are more resistant to burning.
What are DNA Primers?
They are short DNA sequences that are complementary to the DNA adjacent to the STR.
What are DNA primers marked with and why?
They are malted with fluorescent tags to the STR’s visible.
What does STR stand for?
Short Tandem Repeat
What ingredients are needed for PCR?
- your sample of DNA
- DNA polymerase
- DNA primers with fluorescent tags
- a supply of DNA nucleotides
What are the steps involved in PCR?
- The mixture is heated to 95 degrees for 30 seconds which causes the hydrogen bonds to break and the DNA stands to separate.
- The mixture is cooled to 55 degrees for 20 seconds to allow the primers to bind to the DNA strands.
- The mixture is heated to 70 degrees for a minute to allow DNA polymerase to build up the complementary strands of DNA. (DNA Replication)
- It is repeated several times to give an abundance of the original DNA sample.
Why is the mixture heated to 70 degrees in step 3 of PCR?
That is the optimum temperature at which DNA polymerase can work at.
The DNA polymerase used is thermostable because it is extracted from extremophiles (bacteria)
What are DNA primers?
They are short sequences of DNA that are complementary to the DNA bases adjacent to the STR.
How is a DNA profile made?
- obtain the DNA
- create the fragments
- PCR (if needed)
- separate the fragments
- visualise the fragments
What are introns?
How are they removed?
- introns are non-coding regions of DNA as they don’t code for the production of a protein.
- restriction enzymes are used to remove introns in the process of mRNA splicing.
Give me examples of where DNA is obtained.
- cheek cells
- WBC’s from a blood smear
- bone marrow from a skeleton
- sperm cells after a sexual assault
Outline the steps of obtaining DNA
- Tissue is broken down in a buffer.
- A centrifuge is used to separate the DNA from the cell debris.
- The suspension is incubated with protease to breakdown the histones that keep DNA coiled up.
- Ice cold ethanol is added to precipitate out the DNA.
- The DNA is then washed several times in a buffer solution.
What is meant by the term cell debris when obtains DNA?
Cell debris are the cell’s organelles. (Everything about from the DNA)
When obtaining DNA, tissue is broken down in a buffer solution along with salt and detergent. Suggest why these substances are used?
- the buffer maintains the pH so there can’t be any variation
- the salt changes the charge of the solution enabling the DNA to stick together
- the detergent breaks down the phospholipids in the plasma and nuclear membrane
Outline the process of creating fragments
- The DNA sample is treated with a restriction enzyme called restriction endonuclease.
- The enzyme will only cut DNA at specific base sequences (usually 4-6 base pairs long)
- If the restriction sites are either side of a STR sequence then that STR fragment of DNA will remain intact.
If two different DNA samples were cut using the same restriction enzyme, what would you expect to see?
The STR fragments for both DNA samples produced would be identical because each restriction enzyme has a specific restriction site.
The variation will lie in the number of STR fragments produced (but they’ll be the same)
Suggest a function of restriction enzymes
Restriction enzymes are present in bacteria to cut viral DNA into smaller non-infectious fragments.
What are the ingredients needed for PCR?
- DNA sample
- DNA polymerase
- DNA primers with fluorescent markers
- a supply of the four DNA nucleotides (bases)
