Infection and immunity

Notes from the SNAB book

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Topic 6
Fingerprint methods are used to identify a dead body with no identification papers on them.
Fingerprints are small ridges caused by folds in the epidermis of the skin. Sweat and oil leave
impressions on surfaces we touch. Oils are secreted from sebaceous glands (non on
palms/fingers) are and transferred to fingers when touching other parts of our body. There
are 4 types of finger prints: Arch, Tented arch, whorl, loop. This is known as the Henry
Classification. Fingerprints are made visible by using fine aluminium, iron or carbon powders
using superglue using ninhydrin magnets and iron flakes are sometimes used. The police
have a national database of biomedical information called IDENT1. Everyone who is arrested
has their prints taken. Dental records are used if someone has no fingerprints on file or their
body has been burnt. This is because teeth and fillings are more resistant to burning and
decay slowly.
DNA profiling relies on the fact that everyone's DNA is unique (apart from identical twins). The
noncoding blocks on DNA are called introns and the coding blocks are called extrons. In
introns there are sequences of repeated bases known as short tandem repeats (STRs) or
satellites. The same STRs occur at the same place (locus) on both chromosomes of a
homologous pair. The number of repeats on each homologous pair can be different which
causes variation in individuals. E.G.
A DNA profile is made by
cutting up DNA, separating
the fragments and then
comparing it to some
reference (e.g. a suspect, a
relative of the corpse).
To obtain a DNA sample
take any tissue sample
(blood, cheek cells, semen,
bone). Physically break it
down in a buffer solution that
includes salt and a
detergent to disrupt the cell
membranes. The DNA is separated from the rest of the cell debris by filtering or centrifuging.
Protease enzymes remove proteins, and then cold ethanol is added to precipitate out the
DNA. Washing with buffer solution then follows.
Restriction enzymes (restriction endonucleases) will only cut DNA at specific base
sequences. The short tandem repeats remain intact but it will be cut away from the rest of
the genome. They are found in bacteria they protect themselves by changing the bases in
their own sequences that are targeted by their own restriction enzymes.
Polymerase Chain Reaction allows scientists to use tiny amounts of DNA, which is copied
numerous times. It uses DNA Primers which are short DNA sequences complementary to
the DNA adjacent to the STR. The DNA primers are marked with a fluorescent tag. The
forensic sample is placed in a reaction tube with DNA polymerase, DNA primers and
nucleotides .Once in the PCR machine, the tube undergoes a cycle of temperature changes.

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The first separates the double stranded DNA. The second temperature optimises prime
binding to the target DNA sequence in the sample. The polymerase attaches and replication
occurs. The final temperature is the optimum temperature for the heat stable DNA
DNA fragments can be separated by gel electrophoresis according to their size. The gel
(agarose or polyacrylamide) is submerged in a buffer solution and connected to electrodes.…read more

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UV light.
The STR is inherited like genes so are used for identification purposes.
Determining Time of Death
The temperature of the body, the degree of rigor mortis and the state of decomposition
can be used to estimate time of death. In addition, entomological (insect) evidence can
provide further clues about when the person died.
Body Temperature: Core temperature in a human is usually 36.2 to 37.…read more

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Temperature is measured through the rectum or an abdominal stab wound, with a long
thermometer (normal ones are too short and have a lower temperature range).
However, environmental conditions must be noted as they can change the rate at which
the body cools. The cooling of a body follows a sigmoid curve which shows that normal
body temperature lasts for 3060 mins after death. But if the person had a fever or had
hypothermia then the body temperature would not be normal.…read more

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For the commonest bluebottle species found on bodies, Calliphora Vicina, a graph is
seen to determine age. (only used if temperature conditions have stayed constant).
Fly lifecycle... egg: 1 day. Lava: 9 days. Pupa: 612 days.
Other factors e.g. toxins in the body will affect the results ­ cocaine would accelerate
There is succession on a dead body. Normally eggs are laid in wounds or at openings
to the body (mouth or nose) .…read more

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This splitting kills the cell and is
called lysis.
Transmission of TB bacterium
It is carried in the droplets of mucus and saliva released into the air when an infected
person talks, coughs or sneezes. This is known as a droplet infection. The droplets can
stay in the air for several hours and as dust for several weeks making bedclothes
potentially dangerous. Close contact, poor health, poor diet and overcrowding living
conditions increase the risk of developing the disease.…read more

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Plasma fluid, white blood cells and antibodies leak from the blood causing
oedema (swelling) ­ the microbes can now be attacked by intact white blood cells.
Phagocytes are white blood cells that engulf bacteria and other foreign pathogens. They
include both neutrophils and macrophages.
Neutrophils = 70% of WBC ­ leave blood capillaries by squeezing between the cells of
capillary walls.…read more

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Interferon provides nonspecific defence against viruses.
Lymphocytes are white blood cells that help to defend the body against specific
diseases. They circulate in the blood and lymph and gather at the site of infection.
B and T cells (Lymphocytes)
This is the specific immune response.
B cells = secrete antibodies to antigens. Antibodies are known as immunoglobulin's
(acts as labels). B cells are specific. Produced in bone marrow.
T cells + produced in bone marrow but mature in
the thymus gland. They are specific.…read more

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B memory cells ­ long lives, enable body to respond more quickly to the same antigen
in the future.
The process of B cell division is called Clonal Selection. It takes about 1017 days to
produce sufficient antibodies called the primary immune response.
T killer cells bind to the anti. It divides to form a clone (stimulated by cytokines). T killer
cells release enzymes that create pores in the membrane of the infected cell which
allows water and ions into it.…read more

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Activity of immune system is reduced in old and very young ages, also by malnutrition
and poor living conditions.
Most significant factor is AIDS. HIV the virus that causes AIDS directly targets white
blood cells and reduces patient's ability to fight infection.
Bacteria in lungs destroy tissues creating holes and cavities. The lung damage will
eventually kill the sufferer.…read more


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