T6 Part 1: Forensics Flashcards
Define exons
Parts of DNA that are genes that are expressed
Define introns
Non coding DNA also known as STRs
Define and explain what an STRs
Short tandem repeats
Repeats of a set of base pairs - different people have different repeats within the same STRs as other people.
What part of DNA is used for DNA profiling
Introns/STRs
Name the 2 stages involved in DNA profiling and what the purpose of each is
PCR - to create many copies of the same part of DNA from a sample in case the 1 original sample is damaged
Gel electrophoresis - to separate different DNA fragments to form banding that can be compared
Explain the process of isolating DNA fragments
Endonucleases are enzymes that come from bacteria and are specific to different binding sites on DNA. These enzymes are used to isolate the same STRs in different samples that can be copied and compared. You obtain the same STRs by using the same endonucleases
What is the machine that PCR is called
Thermocycler
What is the polymerase used in PCR and why
Taq polymerase is resistant to high temperatures which are used in the thermocycler
What step must be done before cycling and why
Use detergent to break down phospholipids
Describe step 1 of PCR
95 degrees
High temperature used to break down hydrogen bonds between DNA strand
Describe step 2 of PCR
55 degrees
Primers attach to the start of the STRs
Describe step 3 of PCR
72 degrees celsius
Nucleotides line up opposite strands and Taq polymerase forms phosphodiester bonds to form the new DNA strands
After the first two cycles of PCR how many viable strands are there
0
How many cycles must the thermocycler undergo to have a correct amount of strands; and how many strands will this have produced
30 cycles for over a billion strands
At what rate does the number of strands grow as the number of cycles increases
Doubles every time
Describe the process of electrophoresis
- Fragments of DNA cut with restriction endonucleases
- Fragments are placed in wells in agarose gel
- A 27v current is applied to the gel
- DNA is negatively charged so travels up the gel towards the positive anode.
- Larger fragments move more slowly so move a shorter distance along the gel. Larger fragments produce a thicker band
- Nylon sheet is pressed on top to produce the banding sheet
- Fluorescent markers are added to the DNA fragments
How are DNA profiles produced by electrophoresis used
Banding of different people can be compared to see if they have bands produced at the same points to see if they have the same STR repeats
Name three MAIN factors that can be used to calculate time of death
Body temperature
Rigor mortis
State of decomposition
Explain the role of forensic entomology in determining time of death
Each species of insect has a specific life cycle. Determining the age of the insects present enables the time of death to be determined
Explain the role of succession which occurs as the body decays as a factor to determine time of death
As the body decays, the type of insects colonising the body changes. By analising the community of species present - time of death can be determined
How can body temperature be used to determine time of death
Body temperature begins to decrease after death as heat producing metabolic reactions stop.
The temperature a body is found at (between 37 and ambient) shows how much it has cooled down and this can be used to calculate how long ago the person died
Factors that affect how to use body temp to determine time of death
CLOTHING
POSITION
WATER CONTACT
How can rigor mortis be used to determine time of death
After death muscles begin to contract as ATP is used up and they stay contracted for a period of time. It begins 2-4hrs after death and lasts up to 36 hours
How can state of decomposition be used to determine time of death
Bodies follow a pattern of decay and decomposition. By figuring out the stage of decomposition you can figure out when a person died.
Name some things that happen as a body decays
Putrification
Fluids drain and body dries
Gas and liquid bubbles - liqueifying of tissues
Why do bodies turn green
Sulphaemoglobin
Explain the role of microorganisms in returning carbon back to the atmosphere when someone dies.
Bacteria and fungi secrete organisms that break down organic matter through respiration and this releases carbon dioxide back into the atmosphere.
