forensics - topic 6 Flashcards
describe the order of tests used to identify DNA fragments
- Obtain DNA sample
- Replicate using PCR
- gel electrophoresis of DNA fragments
- analyse results
how many cycles is a standard run of a PCR
20
why is PCR carried out in a thermo cycler?
provides optimal temperature for each stage and controls the timings
what 4 substances does a PCR reaction require?
primers, DNA polymerase, free nucleotides, buffer solution
In PCR, what is the purpose of using primers?
short sequences of single stranded DNA that have complimentary base sequences to the DNA or RNA being copied.
they define the region that is being amplified and show where DNA polymerase should bind
why taq polymerase used in PCR?
- used to build new DNA or RNA strand
- does not denature at high temps in first stage
- optimum temp of taq high enough to prevent annealing of DNA that has not yet been copied
use of free nucleotides in PCR
enable construction of new DNA or RNA strands
use of buffer solution in PCR
Ensures optimum PH for reactions to occur
what are the three mian stages of PCR? + give a brief explanation of each
DENATURATION
heated to 95c breaking H bonds
ANNEALING
50-60c primers can anneal
ELONGATION
72c optimum temp for taq to build complimentary strands to produce new DNA
what is the purpose of adding restriction enzymes post PCR?
breaks up DNA into fragments of different length
which way does DNA move in gel electrophoresis? moves towards
moves towards the anode as negatively charged
which size molecule moves faster in gel electrophoresis and why?
smaller molecules as less friction
what piece of equipment is used to transfer the DNA into the gel in Gel elecetrophoresis
a micropipette
give 3 ways DNA profiling can be useful
- paternity tests
- selective or captive breeding programmes
- cultivation of plants
forensics definiton
the use of science in the investigation of criinal activities
what is the difference between succession in a dead body and in habitats?
in a dead body all species remain none are outcompeted
describe the stages of succession in a dead body
- bacteria found immediately
- ideal conditions for flies to lay eggs and larvae (maggots) to hatch
- favourable conditions for beetles as maggots eat flesh
- when tissue dries out, flies leave
- beetles stay
what is the use of insects in forensics called?
forensic entomology
how can insects show time of death?
the life cycle they are at
what are factors that may affect the progression of insect life cycles?
- drugs present in the body
- humidity
- O2 availability
- temperature
what is the process of the body cooling called?
algor mortis
what is the process of the bodys muscles stiffening called?
rigor mortis
why does temperature drop after death?
metabolic reactions stop so no heat is being produced and body temp will drop until it reaches the teperature of surroundings
why does rigor mortis occur?
- no more oxygen reaches muscle cells
- muscles respire anaerobically
- lactic acid produced
- PH decreases
- enzymes that produce ATP denature
