1
Q
How does body temperature determine time of death?
A
Body Temperature (algor mortis)
- Mammals produce heat from metabolic reactions
- From TOD metabolic reactions slow down and eventually stop
- Body temp falls to temp. of surroundings = algor mortis
- Human bodies cool at a rate of 1.5-2C per hour
- Air temp, clothing and body weight affects cooling rate
2
Q
How does Muscle Contraction determine time of death?
A
Muscle contraction (rigor mortis)
- After 4-6 hours muscles in the dead body start to contract and become stiff
- Occurs when muscle cells become deprived of O2
- Anaerobic respiration occurs = build up of lactic acid
- pH of cells ↓ = ATP-producing enzymes inhibited
- No ATP = bonds b/w myosin and actin can’t detach
- Smaller muscles in the head contract first
- Occurs quicker at higher temperatures
3
Q
How does Forensic Entomology determine time of death?
A
Forensic Entomology
- Body is colonised by dif. insects
- TOD estimated by the type/s of insects on the body
- Flies are first (a few hours after)
- TOD estimated by the stage of life cycle the insect is in
- Blowfly larvae hatch 24 hours after being laid
- Drugs, humidity, O2 and temp. affects life cycles
4
Q
What is decomposition?
A
Decomposition = Immediately, bacteria and enzymes begin to decompose the body
5
Q
Extent of decomposition - Hours→few days
A
Cells and tissues broken down by the body’s enzymes and bacteria. Skin begins to turn green.
6
Q
Extent of decomposition - Few days→few weeks
A
Microorganisms decompose tissues and organs = gases = bloated body. Skin begins to blister and fall off.
7
Q
Extent of decomposition - Few weeks
A
Tissues begin to liquefy and seep into the surrounding area.
8
Q
Extent of decomposition - Few months→few years
A
Only a skeleton remains
9
Q
Extent of decomposition - Decades→centuries
A
Skeleton begins to disintegrate into nothing
10
Q
What is decomposition affected by?
A
- Affected by temp. and O2 availability
11
Q
Stage of succession
A
- Type of organism in a dead body changes over time = succession
- TOD estimates from the stage of succession
- Immediately conditions ideal for bacteria, which decompose tissues
- Conditions then ideal for flies and larvae, which feed on the body
- Conditions then ideal for beetles
- Body dries out, flies leave, beetles stay to decompose dry tissue
- When no tissue remains, conditions ideal for almost nothing
- Similar to plant succession but pioneer species generally remain
- Affected by location, and lots of other things
12
Q
What is the role of microorganisms?
A
They decompose organic matter
- Inc. organisms such as bacteria and fungi
- Important to C cycle
When on/ in a dead organism
- They secrete enzymes to decompose dead organic matter
- Turns it into small molecules they can respire
- CH4 (methane) and CO2 are released
- Recycles C back into the atmosphere
13
Q
What is a DNA profile?
A
DNA profile = genetic fingerprint
- Everyone’s is diff. except for identical twins
- Fingers are coated in oil from sebaceous glands = prints
- Can find prints using aluminium or magnetic powder, or a Ninhydrin spray
14
Q
How do you conduct a DNA profile?
A
- Obtain DNA sample
- PCR amplifies the DNA
- Fluorescent Tag is added
- To view the DNA under UV light - Gel Electrophoresis
- Gel is viewed under UV light
- DNA fragments appear as bands under the light = DNA profile
- Profiles can be compared by looking for similar patterns
15
Q
How are DNA profiles conducted in Forensic Science?
A
Can be used in Forensic Science
- DNA collected from crime scenes and then suspects
1. DNA is isolated from all collected samples
Each sample is amplified
2. PCR products run on an electrophoresis gel
3. DNA is compared to look for matches
4. Matching samples link the person to the crime scene
16
Q
How are DNA profiles used in determining genetic relationships?
A
In humans
- Inherit ~50% of DNA from each parent
∴ more matching bands = more closely related
In plants and animals
- Prevents inbreeding avoiding health, productivity and reproductive problems
- Inbreeding = ↓ gene pool (no. of dif. alleles)
- ↑ risk of genetic disorders and then health problems
- More similar DNA profiles = more closely related
17
Q
What is DNA amplification?
A
Done using Polymerase Chain Reaction (PCR)
- Makes millions of copies of specific regions of DNA
- Used to make sure there’s enough to make a DNA profile
18
Q
How is PCR conducted?
A
- Reaction mixture is set up
- DNA sample, free nucleotides, primers and Taq polymerase
- Primers = short pieces of DNA complementary to bases at start of wanted fragment
- DNA polymerase = enzyme that creates new strands - Heat mixture
- Heat to 95°C
- Break H bonds b/w the two strands of DNA (DNA helicase) - Cool mixture
- Cool to b/w 50 and 65°C
- Primers can bind/ anneal to the strands - Heat mixture
- Heat to 72°C
- Taq polymerase can then work - Taq polymerase gets to work
- Lines up free DNA nucleotides alongside template strand
- Complementary base pairing = complementary strand formed - Cycle complete
- 2 new copies of DNA have been made
- The cycle starts again from stage 2
- Both strands act as template strands
- Each cycle doubles the amount of DNA
19
Q
How to conduct Gel Electrophoresis?
A
- Gel Tray set up
- Solidified Agarose gel in a gel tray w/ a row of wells at one end - Gel Box set up
- End w/ the wells closest to the cathode (-ve electrode) (cats are always -ve)
- Add buffer solution to reservoirs at side of gel tray so surface of gel is covered - Add dye
- Add the same vol. of loading dye into each fragmented DNA sample
- Helps DNA sink to the bottom of the wells and easier to see - Add DNA
- Add set vol. of a DNA sample into a well
- Make sure tip of micropipette is in buffer solution but above the opening of the well
- Don’t pierce the bottom of the well
- Repeat for each DNA sample into each well w/ clean micropipettes - Power Supply set up
- Place lid on gel box
- Connect leads from gel box to power supply
- Turn the power on and set to the required voltage
- Causes an electrical current to pass through the gel
∴ DNA fragments will separate according to length
- Leave for ~30 mins or till dye is ~2cm from end of gel - Staining the DNA
- Remove gel tray from the gel box
- Tip off any excess buffer solution
- Cover surface of the gel w/ staining solution to stain the gel
- Rinse the gel w/ water and DNA fragments will be visible
- DNA = southern blotting
- Protein = western blotting
- RNA = northern blotting
20
Q
What are bacteria?
A
Bacteria
- Single-celled, prokaryotic microorganisms (no nucleus)
- Generally only a few micrometers long
21
Q
What are viruses?
A
- Micro-organisms but aren’t cells
- Are just nucleic acids surrounded by protein
- Smaller than bacteria so less than 1 micrometre long
22
Q
What is HIV?
A
Human Immunodeficiency Virus = HIV
- Spread through infected bodily fluids touching mucosal surfaces or damaged tissues
- Most common transfer is sexual intercourse
- HIV can only reproduce inside infected cells, T helper cells
- It doesn’t have its own equipment, eg. enzymes or ribosomes
- Initial infection period = fast replication = severe flu-like symptoms
- Then HIV replication ↓ = latency period = no symptoms
23
Q
How to replicate HIV?
A
- Attachment proteins attach to receptor molecules on cell membrane of T helper cells
- The capsid is released into the cell
- It uncoats and releases the genetic material
(RNA) into the cell cytoplasm
- It uncoats and releases the genetic material
- Reverse transcriptase makes a complementary strand of DNA from the viral RNA template
- Then double-stranded DNA can be made and inserted into the human DNA
- Host cell enzymes used to make viral proteins from the viral DNA in the human DNA
- Viral proteins are assembled into new viruses
- The new viruses bud from the cell and infect other cells
24
Q
How does HIV turn to AIDS?
A
- Initial symptoms = minor infections of mucous membranes and recurring respiratory infections
E.g nose, ears and genitals
2. T helper cell no.s continue to ↓ = more susceptible to more serious infections
E.g chronic diarrhoea, severe bacterial infections and TB
3. Late stages = v. low no. of T helper cells = range of serious infections
E.g toxoplasmosis of the brain (parasite), candidiasis of respiratory systems (fungal)
Patient will die from these serious infections not AIDS
25
How to treat HIV?
Antiretroviral therapy = combination of drugs everyday
- Doesn’t cure HIV but ↑ life expectancy
- ↓ viral load = ↓ risk of transmission
- Prevents HIV from multiplying
- Reverse transcriptase inhibitors = prevent viral RNA from making DNA
- Protease inhibitors = inhibits proteases
- Proteases cut larger proteins into smaller polypeptides
26
What is TB?
Tuberculosis = TB
- Caused by mycobacterium tuberculosis
- Ppl won’t develop TB straight away b/c immune system seals off infected phagocytes in tubercles
- Bacteria become dormant = no obvious symptoms
- Later, dormant bacteria become reactivated and overcome immune system
- Reactivation more likely in ppl w/ weakened immune systems
27
How do you become infected by TB?
1. Droplets containing mycobacterium tuberculosis are inhaled into the lungs
2. Bacteria engulfed by phagocytes in lungs via phagocytosis
3. The bacteria evade digestion = survive and replicate inside phagocytes
4. Immune systems seals off infected cells in tubercles = latent TB
5. The dormant bacteria will become reactivated
- Can take a few weeks or years
6. Will move to the top of the lungs where there is more oxygen
28
What is the progression of TB?
Initial symptoms = fever, general weakness and severe coughing (b/c of lung inflammation)
Spread to other parts of the lung
- Via airways or lymphatic system
- Damaging the lungs
- Can cause bronchopneumonia
- If untreated can = respiratory failure = death
Spread to other cells in the body
- E.g brain and kidneys
- Via vascular system
- Known as systemic miliary TB
- Causes complications in organs of infected tissue
- If untreated can = organ failure = death
29
What is a pathogen?
Pathogen = any organism that causes a disease
30
What is an infectious disease?
Infectious diseases = any disease caused by a pathogen
31
What is a pathogenic microorganism?
Pathogenic microorganism inc. some bacteria and fung, and all viruses
- They develop in an organism to cause a sequence of symptoms
32
What are the four main routes of infectious diseases?
- Cuts in the skin
- Digestive system via contaminated food or drink
- Respiratory system via inhalation
- Mucosal surfaces, e.g inside the nose, mouth and genitals
33
What are the four main ways the body prevents infection?
Stomach acid = pathogens will be killed by acidic conditions of the stomach
- The ones that survive pass to intestines and invade cells of the gut wall
Skin = physical barrier and blood clots occur
- Damaged skin = pathogens enter blood stream
Gut and skin flora = already covered in billions of harmless microorganisms = flora and compete w/ pathogens for nutrients and space
- Limiting the no. of pathogens living on skin and gut = harder to cause infection
Lysozyme = mucosal surfaces produce secretions containing the enzyme, lysozyme
- It kills the bacteria by damaging the cell walls = bacteria burst open
- It hydrolyses the polysaccharides present
- Attacks gram+ve bacteria better
34
What is the Non-specific Immune Response?
Occurs when foreign antigens are recognised
- Antigens = a section of a protein found on the surface of cells
- Non-specific response occurs first
- Happens the same way for all microorganisms
35
Step 1 - Non-specific Immune Response - Inflammation at the site of infection
- Foreign antigens recognised = molecules triggering inflammation are released
- They cause vasodilation (widening of blood vessels) = ↑ blood flow to site
- They ↑ permeability of blood vessels
- More immune system cells can reach site of infection and move into the blood vessels and infected tissues
- Immune system cells can start to destroy the pathogen
36
Step 2 - Non-specific Immune Response - Interferons are produced
- Virus-infected cells produce antiviral proteins (interferons)
- They prevent the virus spreading to uninfected cells
- Prevent viral replication by inhibiting viral protein production
- Activate cells in specific immune response
- Active mechanisms in non-specific response, e.g promote inflammation
37
Step 3 - Non-specific Immune Response - Phagocytosis and Lysozyme Action
Phagocyte = type of WBC that carries out phagocytosis (pathogen engulfment)
- Found in blood and tissues and first cells to respond to pathogens
- Inc. macrophages
- Will recognise antigens on the pathogen
- Cytoplasm of phagocyte surrounds pathogen and then engulfs it (phagocytosis)
- Pathogen is now in a phagocytic vacuole
A lysosome fuses w/ phagocytic vacuole and releases lysozyme
- Lysozyme breaks down the pathogen
Phagocyte then presents pathogens antigen on its surface
- This activates other immune system cells
- Becomes an antigen-presenting cell
38
What is the lymphatic system?
- Prevents the spread of bacteria
- Uses macrophages in lymph nodes, spleen and liver
- Failure = septic shock or blood poisoning
39
What is the Specific Immune Response?
The specific immune response is antigen-specific
- Produces responses aimed at specific pathogens
40
Step 1 - The Specific Immune Response - Phagocytes activate T cells
T cell = type of WBC and are covered in receptors
- Each T cell has dif. shaped receptors
- Also known as lymphocytes
Receptors bind to complementary antigens on antigen-presenting cell
- This activates the T cell
The activated T cell divides to produce clones of itself
- T helper cells = release cytokines which activate B cells, T killer cells and macrophages
- T killer cells = attach to antigens on pathogen-infected cell and kills it
- T memory cells = antigen-presenting cells in case of a second infection of the same pathogen
41
Step 2 - The Specific Immune Response - T helper cells activate B cells
B cells = a type of WBC and covered w/ antibodies
- Each B cell has dif. shaped antibodies
- The antibodies bind to complementary antigens to form an antigen-antibody complex
- The binding and the T helper cell cytokines activate the B cell
- The B cell divides by mitosis into B effector (plasma) and B memory cells
42
What are antibodies?
Antibodies = proteins that attack cells w/ foreign antigens
43
What are agglutinating pathogens?
- Each antibody has 2 binding sites = bind to two antigens
- Pathogens become clumped together
- Phagocytes bind to antibody and eat a lot of pathogens at once
44
What are neutralising toxins?
- Bind to toxins produced by the pathogens
- Prevents toxins from affecting human cells
- The toxin-antibody complex are phagocytksed
45
What do antibodies do?
- Prevent pathogen binding to human cells
- Antibodies bind to antigens on pathogens blocking cell surface receptors
- Pathogens can’t bind or attach to host cells
46
What are membrane-bound antibodies?
Membrane bound = attached to a membrane of a B cell
47
What are secreted antibodies?
Secreted = free from any attachment
48
Membrane-bound v.s secreted antibodies
- They had dif. heavy chain protein b/c membrane bound ones need an extra section to anchor them to the B cell membrane
- Both heavy chains are coded by a single gene
- Dif. proteins created b/c mRNA is modified before translation
49
Protein modification
mRNA can be used to create dif. proteins by modifying it before translation
Introns = sections on a gene that don’t code for anything
Exons = sections on a gene that code for amino acids
- They exit the nucleus to be coded
- In transcription, introns and exons are copied = pre-mRNA
- Pre-mRNA = mRNA containing both introns and exons
- Introns are removed by splicing
- Takes place in the nucleus and is a post-transcriptional change
- Leftover exons form mRNA strands
- Some exons are removed to form dif. mRNA strands by alternative splicing
∴ more than 1 amino acid sequence created = more than one protein can be produced from one gene
~ 95% of human genes have 1+ exons that undergo alternative splicing
50
Antibody heavy chain production
- Many exons in a gene for the heavy chains
- 2 code for the section that anchors
- To produce secreted antibody, alternative splicing removes these 2 exons
51
What is herd immunity?
Herd immunity = pool of infection ↓ w/ every vaccinated child, protecting those who can’t be vaccinated
52
Do memory cells give immunity?
YES!
Memory cells give immunity
- When a pathogen first enters, antigens on its surface activates the immune system
- Non-specific which then activates the specific = primary response
- Primary response is slow b/c low no. of B cells that can bind to antigen
- Eventually the body will produce the right amount to overcome the infection
- Symptoms will be seen during this time
- After exposure T and B cells produce memory cells
- These remain in the body for a long period of time
- T memory cells remember the specific antigen
- B memory cells remember the specific antibody
Person is now immune = immune system has the ability to respond quickly to a second infection
- If the same pathogen enters, secondary response occurs
- A quicker and stronger response
- T memory cells can divide into the correct type, B memory cells divide into plasma cells (B effector cells) to produce the right antibody
- Secondary response removes pathogen before symptoms are seen
53
Active immunity
Active immunity = immune system makes its own antibodies after being stimulated by an antigen (long term)
- Natural = immune after catching the disease
- Artificial = immune after a vaccine
54
Passive immunity
Passive immunity = given antibodies made by a dif. organism (short term)
- Natural = baby becoming immune b/c of antibodies from the mother
- Artificial = immune after being injected w/ antibodies
55
Vaccines
Vaccines = injection containing a harmless dose of antigen that triggers a primary response
- Gives immunity w/o causing a disease
- Vaccinations trigger the primary response, but no symptoms
- Memory cells are still produced so body becomes immune
- Some vaccines contain dif. antigens to protect against dif. strains of pathogens
- Dif. strains of pathogens are created by antigenic variation
56
Inflammation
- Damaged basophil WBCs and mast cells in connective tissue release histamines
- Causing inflammation
- Arteriole dilation = ↑ blood flow
- ↑ permeability of capillaries
- WBCs and antibodies can leave blood to the tissue easily
57
Human and Pathogen evolution
- Humans evolve better immune systems to fight a greater variety of pathogens
- Pathogens also evolve to evade our immune systems
- Evolutionary arms race = pathogens and immune systems trying to outdo each other
- Evidence for this comes from the dif. evasion mechanisms
Pathogens have the advantage
- Reproduce quickly, large population, mutations can be shared
58
HIV evasion mechanisms
It kills the immune system cells that it infects
- ↓ing overall no. = ↓ chance of HIV being detected
Has a high mutation rate in genes coding for antigen proteins
- Mutations change antigen structure = new strains = antigenic variation
- Memory cells from one strain won’t recognise a dif. strain = primary response
They disrupt antigen presentation in infected cells
- Preventing recognition and killing of infected cells
59
TB Evasion Mechanisms
- When engulfed by phagocytes, they produce substances preventing lysosome fusing w/ the phagocytic vacuole
- The bacteria aren’t broken down = can multiply undetected
- They disrupt antigen presentation in infected cells
- Preventing recognition and killing of infected phagocytes
60
Bacteriostatic and Bactericidal antibiotics
Antibiotics = chemicals that kill or prevent the growth of microorganisms
- Bactericidal = kill bacteria (suicidal)
- Bacteriostatic = prevent bacteria growth (keeps things static)
They inhibit bacterial metabolism
- Interfere w/ metabolic reaction crucial to growth and life of the cell
- Some inhibit enzymes needed to make chemical bonds in bacterial cell walls
- Bacteria can’t grow properly
- Weakened cell can’t take the pressure from osmosis = bursting
- Bactericidal
- Some inhibit protein production by binding to bacterial ribosomes
- No ribosomes = no proteins = no enzymes
- No metabolic processes can occur
- Bacteriostatic
- Don’t affect mammalian cells b/c they don’t have cell walls, have dif. enzymes and larger ribosomes than bacteria
- Don’t affect viruses b/c viruses don’t have their own enzymes or ribosomes
61
Must use aseptic techniques (similar to antimicrobial plants experiment)
1. Use a sterile pipette to transfer the bacteria to the agar plate
- Spread using a sterile spreader
2. Use sterile forceps to place paper discs soaked in dif. antibiotics on the plate
- Dif. conc. of antibiotics should be used
- Use a negative control disc soaked in sterile water
3. Lightly tape lid, invert and then incubate at 25-30°C for 24-48 hours
- Allows bacteria to grow
- Not 37°C so that no bacteria that can harm us can grow
4. Measure the average diameter of the inhibition zone
- Larger the zone = more the bacteria were inhibited
62
What are aseptic techniques?
- Prevent bacterial cultures from being contaminated w/ unwanted microorganisms
- Results won’t be affected by things interfering w/ growth
- Regularly disinfect surfaces to minimise contamination
- Use sterile equipment, which is discarded safely after use
- Work near a bunsen burner, microbes in air are drawn away from the culture
63
Hospitals
HAI = hospital acquired infections = infections caught while being treated in hospital
- Transmitted by poor hygiene
- Staff and visitors not washing their hands
- Coughs and sneezes not being contained
- Equipment and surfaces not being disinfected after use
- People are more likely to catch them b/c most have weakened immune systems
- Codes of practice have been developed to prevent and control HAIs
- Staff and visitors are encouraged to wash their hands before and after
- Equipment and surfaces are disinfected after use
People w/ HAIs are moved to an isolation ward to ↓ transmission
A Level Biology (SNAB)
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