TOPIC 6 Flashcards
normal body temperature
36.2 degrees celsius to 37.6 degrees celsuis
how long can temp. of body be used to estimate time of death
24hours
factors affecting rate of cooling (at least 4 marks)
body size, humidity, body position, surrounding temp. of environment , clothing
describe rigor mortis process
- muscles starved of oxygen and reactions stop
- respiration in cells becomes anaerobic and lactic acid produced
- pH falls, inhibiting enzymes that stop anaerobic respiration
- ATP no longer produced
- bonds between muscle proteins fixed
- muscles &joints fixed in place
give time length of rigor mortis
- happens about 6-9 hours after death
- whole process wears off after 36 hours
autolysis
enzymes, in body from the digestive tract, and lysosomes break down cells
- process of body decompostion (6 marks)
think acronym and backstory
1.skin&lower abdomen turn green-sulhaemoglobin production(between 36&72 hours
after death)
2. body becomes reddish green then purplish black.
3. gas blisters appear on skin
4.body begins to smell and become bloated(due to gases e.g. CO2, CH4 etc) - 1
week after death
5. gas released and body deflates
6. fluid drains away and soft tissues shrink.
- forensic entomology-any details known to
help with generally graph questions
-succession of species of insect on body along with species present on body allows
stage of succession to be determined&time of death to be estimated
why is everyone’s DNA unique?
because of variety of sections of DNA not used to code for proteins (introns)
- exons
coding regions of DNA
EXPRESSED
introns
non-coding regions of DNA
Short Tandem Repeats (STRs)
- short DNA sequences are repeated many times.
- located within introns
- sequence of repeated bases
why are STRs unique to each individual?
-number of times STRs are repeated on homologous chromosomes at a single locus
varies between individuals
ALTHOUGH … some STRs occur at the same place on both chromosomes of a
homologous pair
Steps of DNA Profiling (5 marks)
think acronym and backstory
- obtain tissue sample
- extract sufficient amount of DNA
- cut DNA into different sized fragments using RESTRICTION ENDONUCLEASES
#only cut DNA at specific base sequences - separate DNA fragments using gel electrophoresis
5.compare sample with reference sample
- why do scientists use PCR?
POLYMERASE CHAIN REACTION
-samples obtained by forensics scientists at crime scene are too small to be
manipulated and experimented with.
- PCR amplifies tiny samples of DNA so they can be used in DNA profiling
what does PCR require
- DNA Fragments
- DNA polymerase
- DNA Primers
- Free Nucleotides
- Thermocycler
describe how small samples of dna can be
amplified
-PCR machine
-DNA polymerase enzyme added
-need for primers/ nucleotides
-heat to 95 degrees celsius, then cool down to 50 degrees celsius&then heat up
DNA to 70 degrees celsius
-cycle needs to be repeated several times to make several copied of DNA
non overlapping genetic code
Each codon is non-overlapping
codon.
The genetic code is formed from the
sequence of bases along the coding
strand of the DNA. We read the
genetic code as a series of three bases(CODON)
degenerate nature of the
genetic code
Because there are 64 possible codons and only 20 amino acids quite
a few amino acids have more than one codon coding for them.
-MORE THAN 3 BASES CODE FOR ONE AMINO ACID
. PCR Process (7 marks)
Polymerase Chain Reaction:
1. Heat sample of DNA to 95°C - H bonds break & it becomes
single-stranded.
2. Add free nucleotides - they will H bond with complimentary
partners in DNA
3. Add RNA Primers - short lengths of single-stranded RNA
that bind to the DNA and stop it annealing
4. Cool to 37°C - allows H bonds to form between nucleotides
5. Add DNA Polymerase
6. Heat to 72°C - optimum temp for thermophilic bacterium (not denatured at
high temp.)
7.REPEAT 20-30 TIMES TO FORM CYCLES
steps in DNA fingerprinting technique?
obtain DNA sample
-amplify DNA sample using PCR
-cut DNA into fragments using restriction endonucleases
-dna fragments separated by gel electrophoresis according to their size
-dna placed on agarose gel, which is submerged in a buffer solution and
connected to electrodes
-dna current applied
-southern blotting used
-dna radioactive probe added to membrane
-x ray film placed next to membrane
-x ray film developed
features of bacteria DEFFO
ribsosomes (70s)
circular DNA
plasmids
cytoplasm
Ribosomes -bacteria
Same function as eukaryotic cells ( site of protein synthesis),
but are smaller (70s rather than 80s)
