explain what are the post transcriptional changes
after transcription introns are removed using enzymes called spliceosomes and some exons are removed or rearranged
state and explain stages of polymerase chain reactions
stage 1; 95 degrees Celsius for 30 seconds to break hydrogen bonds between nucleotides
stage 2; 55 degrees for 20 seconds to allow primers to bind
stage 3; 72 degrees for 1 minute as its optimum temperature for taq polymerase so it catalyzes formation of new complementary strands
stage 4; repeat the cycle many times to amplify DNA
state and explain stages of DNA fingerprinting
1- take sample of cells to obtain DNA
2- amplify DNA using PCR to have a sample big enough for testing
3-restriction enzyme used to cut DNA into smaller fragments
4- fragments are placed on agarose gel then electric current is produced, fragments move towards positive electrode as DNA is slightly negative, lighter bands and more soluble bands move faster. this is called gel electrophoresis
5-label using fluorescent or radioactive material
5-view using uv or x-rays
6-compare size and position of bands with reference
explain how body temperature can be used to estimate time of death
-after death body temperature decreases following a cooling calibration curve
-cooling effect is caused by heat loss by radiation or stoppage of metabolic reactions which release heat
–this continues for 24 hours until the body reaches ambient temperature
-follow the cooling calibration curve to estimate time of death
how to measure Algor mortis
1- use temperature probe to measure core temperature by placing it in liver or rectum
2-several factors affect the cooling curve such as ambient temperature
3-ambient temperature also affects other factors such as rigor mortis
3-track back through cooling calibration curve to estimate time of death
4- measure as soon as possible for more reliable results
5-combine with other factors for more reliable results
What are the limitations of using body temperature to estimate time of death?
as body temperature is affected by many factors such as ambient temperature, clothing, positioning of the body, and amount of body fat
These variables can lead to significant discrepancies in the estimated time of death.
explain how muscle stiffness can be used to estimate time of death
after death muscles of the body undergo 3 phases of muscle stiffness which can be used to estimate time of death.
1-initial relaxation; the first 8 hours after death muscles still undergo anaerobic respiration which releases atp which is needed for muscle relaxation
2-muscle stiffness; from 8-48 hours after death lactic acid is produced from anaerobic respiration which denatures enzymes so respiration stops so no energy for respiration so muscles become stiff
3-final relaxation; after 48 hours lysosomes release hydrolytic enzymes and enzymes from decomposers break down muscle tissue (autolysis) leading to relaxation again
-combine with other factors for more reliable results
explain limitations of using muscle stiffness to investigate time of death
as muscle stiffness is affected by several factors such as; ambient temperature, level of fitness and level of activity before death
explain how stage of decomposition can be used to estimate time of death
1-36 hours after death greenish discoloration of the abdomen is observed
2- from 36 to 72 the discoloration spreads throughout the body
3-after 72 hours deepening of the color occurs and it becomes reddish green then purple black
4- a week after death the body becomes bloated with gases due to respiration of decomposers
5- after a week the body deflates as there will be holes due to decomposition
6-combine with other factors for reliable results
explain the limitations of using stage of decomposition to estimate time of death
as decomposition is affected by many factors, such as;
1-temperature; as temperature increases decomposition is faster as activity of enzymes increases and temp above optimum denatures enzymes
2-humidity; water activates enzymes of decomposers and in dry areas decomposition is either very slow or may completely fail to occur
3-ph ; major changes away from optimum ph causes enzymes of decomposers to denature
