Topic 6: Immunity, Infection and Forensics Flashcards
How it time of deaths determined?
- extent of decomposition
- stage of succession
- forensic entomology
- body temperature
- degree of muscle contraction
How can the extent of decomposition help determine the time of death?
Time of deaths can be determined as decomposers such as bacteria and fungi in a specific sequence. It can also be be established by visual appearance (skin will become a greenish colour).
1. Green discolouration
2. Gases released from decomposition causing bloating and blistering
3. Tissues liquify, causing gas to be released
4. After a few month only skeleton remains
Why can stage of decomposition not give an accurate representation of time of death?
As it is influenced by wounds to the body and environmental conditions (temperature, humidity and oxygen concentrations).
How does stage of succession indicate time of death?
Time of death can be colonised by different species at different times after death.
1. Colonised by bacteria which decomposes tissue
2. Decomposition by bacteria provided favourable conditions for flies and their larvae
3. Decomposition by flies and larvae produce favourable conditions for beetles.
Why does stage of succession may not give an accurate representation of time of death?
The stages will differ depending on the
- location of the body (soil, coffin, under water)
- environmental conditions (temperature, humidity and oxygen concentration)
How does forensic entomology indicate time of death?
Time of death can be determined because the body is colonised by different species at different times after death, such as flies and beetles which have life cycles that follow a specific sequence.
Why may forensic entomology not give an accurate time of death?
Influenced by
- location of body
- environmental conditions (temperature, humidity, oxygen concentration and drugs)
How can body temperature indicate time of death?
Time of deaths can be determined because body temperature decreases with time after death due to a lack of exothermic chemical reaction. The process of ‘cooling down’ is known as algor mortis
Why may body temperature don’t give an accurate time of death?
Influenced by
- ambient temperature
- position of body
- clothing
- humidity and air movement
Additionally this is useless after 24 hours because the body temperature will equal ambient temperature.
How can degree of muscle contraction indicate time of death?
Time of death can be determined because muscles stiffen between 3-36 hours after death. This is because of the lack of oxygen, causing anaerobic respiration to take place producing lactic acid, and pH to decrease. The decrease in pH denatures respiratory enzymes inhibiting respiration and the production of ATP, causing muscles to contract. This process is called Rigor mortis.
Why may degree of muscle contraction not indicate an accurate time of death?
Influence by
- environmental conditions (temperature, humidity and oxygen concentration)
- size of the Jody
- degree of muscle development
- fitness/active before deaths
- degree of ATP storage
Additionally, useless after 36 hours, ask muscles break down and relax.
What factors should be considered when determining time of death?
Ambient temperature > influences rate of decomposition and forensic entomology. This is because greater temperature will increase the rate of enzyme controlled reactions. Also size of temperature gradient (heat loss).
Location > inside, underground, under water ect influence stage of succession and forensic entomology
Body position > affects the surface areas available for heat exchange, influence the rate of heat loss
Body size > surface area available for Heath exchange, heat loss
Clothing > amount of insulation, influencing heat loss
Humidity > affects amount of evaporation, influences heat loss
Air movement > influences heat loss
What are decomposers?
Decomposers are microorganisms such as bacteria and fungi which are responsible for the decomposition of organic matter and the recycling of carbon.
How do microorganisms decompose organic matter?
Decomposers excrete digestive enzymes which break down organic compounds into smaller ones.
What is the role of microorganisms in the carbon and nutrient cycle?
As microorganisms actively take part in decomposition they are respiring, releasing carbon into the atmosphere. Additionally, the break down of plant matter and animals releases CO2 and methane from its biomass which are released into the atmosphere. The carbon in the atmosphere can then be absorbed by green plants through photosynthesis creating them back into organic substances.
What affects the rate of decomposition?
The rate of decomposition is influenced by
- temperature
- oxygen concentration
A higher temperature up to optimum will increase the kinetic energy of the digestive enzymes causing more enzyme substrate complex’s to form. Beyond optimum the enzymes will become denatured.
What is DNA profiling?
A process that is used to identify and determine genetic relationships between different organisms. (Except identical twins)
How DNA profiling work?
It is possible as every organism profile is unique. It works by analysing the introns in an organism DNA. These introns are sections of DNA that are non coding, numerous and very variable meaning each organisms DNA profile is unique as it will contain a random combination of introns.
What is the polymerase chain reaction?
A process that is used to replicate DNA in order to increase the size of a sample of DNA.
What are the steps in the polymerase chain reaction?
- Denaturing, the reaction mixture is heated to 95oC which breaks the hydrogen bonds that hold the two DNA strands together.
- Annealing, the temperature is decreased to 50-60oc so that the primers can anneal to the ends of the single strands of DNA
- Elongation, the temperature in increased to 72oc as this is the optimum temperature for Taq polymerase to build,d the complementary strands of DNA to produce the new identical double stranded DNA molecules.
Each of these cycles doubles the amount of DNA.
What is required for a PCR reaction?
- DNA or RNA
- primers (shirt sequences of single stranded DNA, identify where DNA polymerase enzymes needs to bind)
- DNA polymerase ( Taq polymerase)
- free nucleotides
- buffer solutions (optimum pH)
What is the process of DNA profiling?
- Source of DNA is obtained (hair, salvia)
- DNA amplified using PCR
- DNA separated into fragments using restriction enzymes
- DNA separated by size/length using gel electrophoresis
- Southern blotting is used
- DNA profiles are analysed and the total number of bands, position of bands and size width of bands.
What is the process of gel electrophoresis?
- DNA is added to wells in a slap or agarose gel using a micropipette
- Agarose gel covered in buffer solution (that can conduct electricity)
- Electrical currents psi lasses through the gel for 20 minutes.
- The electrical current causes the negatively charged DNA to move through the gel towards the anode
- The shorter DNA moves faster and further spreading the DNA into bands
How do restriction enzymes work in gel electrophoresis?
Before gel electrophoresis restriction enzymes cut the DNA into pieces at specific locations (will always cut between sections
of repeats bases)
What is southern blotting?
When an alkaline buffer solution is poured over the slap after gel electrophoresis. A dry nylon filter used to absorb the fragments of stained DNA and produce visible blots.
What can DNA profiles be used for?
- genetic relationship ps between peoples (Paternity test)
- selective or captive breeding programmes
- identify criminals
If two DNA profiles are identical the samples will either be from the same person or identical twins, if they are very similar the samples would be from a closely related organisms that have a common ancestor.
Why may a DNA profile not be accurate?
- can be contaminated /at any stage of the process)
- only a small proportion of DNA is analysed
How does a bacteria cell differ from a eukaryotic cell?
Bacteria are small singled cells prokaryotes they differ from eukaryotic cells as
- prokaryotic cells are slot smaller
- no membrane bound organelle
- smaller ribosomes 70S compared to 80S
- no nucleus instead a DNA loop and plasmids
- peptidoglycan cell wall
- folded cell wall called mesosomes
What is the function of plasmids in prokaryotic cells?
Plasmids are small rings of DNA that can be exchanged between cells.
What is the function of mesosomes in prokaryotic cells?
These are infoldings of the cell surface membrane that contain enzymes required for respiration.
What is the function of pili in a prokaryotic cell?
Small protein tubes that enable the bacteria to attach to other cells of surfaces.
What is the function of a capsule in a bacteria cell?
Sometime called the slime capsule. It helps to retain moisture to prevent the bacteria drying out and adhere to surfaces.
What is the structure of a virus?
Viruses are non-cellular infectious particles that are much smaller than bacteria cells. They have a
- nucleic core acid core (single or double strand of DNA or RNA)
- a protein coat called ‘capsid’
- an outer lipid layer called an envelope (contains specific glycoproteins which make up the antigen)
How do virus differ from a bacteria cell?
- virus’s do not possess a plasma membrane, cytoplasm or ribosomes (any internal structures)
- virus’s cannot reproduce independently whereas bacteria can
How do viruses reproduce?
They bind to host cells and release their nucleic acid into it. The host cells DNA replication mechanisms replicate the viral nucleic acid and replicate the virus protein coat. The new viral particles are then assembled in the host cell and the released by cell lysis (bursting)
How can you compare the structure of prokaryotic cells and viruses?
- bacteria are larger then viruses
- neither contain a nucleus
- bacteria contain DNA whereas viruses can have either RNA or DNA
- bacteria contain circular non linear DNA within nucleoid and plasmids whereas viruses have linear nuclei acid
- neither contains membrane bound organelles
- bacteria has internal structure (ribosomes plasmids p) whereas viruses don’t
- bacteria reproduce independently (binary fission) and viruses can’t
What is Tuberculosis?
TB is an infectious disease caused by the bacteria ‘Mycobacterium Tuberculosis’ which affects the lungs. It suppresses the immune systems, meaning the body is less capable of fighting infections.
How is TB caught?
TB is communicable meaning is it spread by inhalation of infected air droplets. It can also survive in surfaces for months due to its thick waxy cell walls.
What is the sequence of TB infecting the body?
- once inside the lungs TB is recognised as a non-self and is engulfed by phagocytes
- The bacteria is sometimes able to survive and reproduce (binary fission) inside the phagocyte. It can lire dormant due to its thick waxy walls preventing lysosomes breaking it down)
- The dormant TB can become an active infection if the number of bacteria becomes to great of immune systems in weakened by old age, malnutrition or HIV
- This causes extensive damage to the lungs (respiratory failure p) or spread to other parts of the body
What are the symptoms of TB?
- fever, weakness, severe coughing caused by inflammation of the lungs
- fluid or blood in coughing caused by body cells rupturing creating cavities in the lungs
- weight loss
- organ failure (if TB spreads)
- death through organ failure or respiratory failure
How can TB be treated and prevented?
- treated by 3-9 moment of bactericidal antibiotics
- it can prevented by a vaccine
Why is the number of TB infection increasing?
- antibiotic resistance
- increased HIV infections
- increased immigration (from countries with high rates of TB and low rates of immunisation)
What is HIV?
HIV is an infection disease cause by a virus ‘human immunodeficiency virus’. It affects T-helper cells and phagocytic cells suppressing the immune system making he body less capable of fighting of other infections.
How can HIV be transmitted?
Communicable disease that be be sore as by the exchange of bodily fluids.
- sexual intercourse
- blood donation
- sharing used needles (drugs)
- from mother to child across the placenta
- from mother to child through breast milk
How does HIV invade the body and reproduce)
- enters T-helper cells by attaching to a receptor molecule on the cell membrane
- the HIV lipid membrane fuses to the T helper cells membrane allowing HIV to release its viral RNA into the T helper cells
- the viral RNA is used as a template by reverse transcriptase enzymes to procure a complementary strand of DNA
- the HIV then used the hosts cells enzymes to produce more viral components which are assembled to form new viruses
- the new viral HIV are released from the most cells by cell lysis (bursting) and the new HIV
Articles are then able to infect more T helper cells and phagocytic cells
What does the infection of HIV led to?
- the number of T helper cells and phagocytic cells decrease
- infected T helper/phagocytic cells are killed by other T helper cells reducing number further
- this reduced immunity to other diseases as T helper cells can no longer activate other type of T cells, activate B cells and stimulate phagocytic cells (no antibodies produced)
- this makes the immune system vulnerable to opportunistic infections such s TB, pneumonia and Cancer leading to death
What are the symptoms of HIV?
- flu-like symptoms immediately after infections
- patients may begin to suffer from opportunistic diesseases
- may progress to AID when individuals start suffering from constant infections
How can HIV be treated or prevented?
- there is no cure for HIV meaning death due to AID is inevitable, however the life expectancy can be extended used antiretroviral drugs (reverse transcriptase inhibitors and protease inhibitors)
- can be prevented by use of condoms, sterile needles and education
