Topic 6-Immunuity, Infections and Forensics

How do microorganisms decompose organic matter?

• They secrete enzymes that decompose the dead organic matter into small molecules that they can respire.

• Methane and carbon dioxide are released when they respire.

• This recycles carbon back into the atmosphere.

Describe how Body Temperature can be used to estimate time of death

• Human body has an internal temperature of 37 degrees.

• After death metabolic reactions slow down and eventually stop, causing body temperature to drop until it matches the temperature of its surroundings -algor mortis.

• Conditions such as air temperature, clothing and body weight affect cooling rate of a body.

Describe how Degree of Muscle Contraction can be used to estimate time of death

• After 4-6 hours muscles begin to contract- rigor mortis.

• Rigor mortis begins when muscle cells become deprived of oxygen.

• Anaerobic respiration occurs producing lactic acid.

• PH of cells decreases due to lactic acid, inhibiting enzymes that produce ATP.

• No ATP means the bonds between myosin and actin become fixed and the body stiffens.

• Rigor mortis occurs faster in higher temperatures because body reactions are faster.

Describe how Forensic Entomology can be used to estimate time of death

• The body is colonised by different insects.

• TOD can be estimated by looking at the type of insect present on the body.

• TOD can be identified by looking at the stage of life cycle the insect is in.

• Different conditions affect an insects life cycle: drugs, humidity, oxygen and temperature.

• At higher temperatures, the faster the metabolic rate and the shorter the life cycle.

Describe how Extent of Decomposition can be used to estimate time of death

• Hours to a few days: Cells and tissues are broken down by the body’s enzymes and bacteria. Skin turns green.

• Few days to a few weeks: microorganisms decompose tissues and organs. Producing gases which cause the body to bloat. The skin blisters and falls off.

• Few weeks: tissues begin to liquefy and seep out into the area around the body.

• Few months to few years: only a skeleton remains.

• Decades to centuries: skeleton begins to disintegrate until there’s nothing left.

• Temperature and oxygen availability affects rate of decomposition.

• Aerobic microorganisms require oxygen, so decomposition could be slower if there’s a lack of oxygen.

Describe how Stage of Succession can be used to estimate time of death

• Immediately after TOD conditions in the body are most favourable for bacteria.

• As bacteria decompose tissues, conditions become more favourable for flies and their larvae.

• When fly larvae feed on dead body they made conditions more favourable for beetles, so beetles move in.

• As the body dries out conditions become less favourable for flies so they leave. Beetles remain as they can decompose dry tissue.

• When no tissue remains, conditions are no longer favourable for most organisms.

Where is a DNA sample of an organism taken from?

• Blood

• Saliva

• Semen

Describe how PCR amplifies the DNA

1. Used to make millions of copies of a specific region of DNA.

2. A reaction mixture is created containing: the DNA sample, free nucleotides, primers and the DNA polymerase.

3. DNA mixture is heated to 95 degrees to break the hydrogen bonds between the 2 strands of DNA.

4. The mixture is cooled to between 50 and 65 degrees, so the primers can anneal to the strands.

5. Reaction mixture is heated to 72 degrees so DNA polymerase can work.

6. DNA polymerase lines up free DNA nucleotides alongside each template strand. New complementary strands are formed.

7. 2 new copies of the fragment DNA are formed and one cycle of PCR is complete.

8. Each PCR cycle doubles the amount of DNA.

What are primers?

Short pieces of DNA that are complementary to the bases at the start of the fragment you want.

What is DNA polymerase?

Enzyme-that creates new DNA strands.

Why is a fluorescent tag added to DNA fragments?

So, they can be viewed under UV light.

What is Gel Electrophoresis used for?

To separate DnA fragments according to their length.

Describe how Gel Electrophoresis works

• DNA is placed in a well in a slab of gel and covered in buffer solution that conducts electricity.

• Electrical current is passed through, DNA fragments are negatively charged so they move towards the anode.

• Short DNA fragments move faster and travel further through the gel, so the DNA fragments separate according to length.

How would you know from DNA profiling that people are related?

More bands on their DNA profiles match.

How can DNA profiling be used on animals and plants?

To prevent inbreeding, which causes health, productivity and reproductive problems.

What does inbreeding do to the gene pool?

It decreases it-leading to increased risk of genetic disorders, leading to health problems.

What is DNA profiling used for?

To identify how closely related individuals are.