Infection, immunity and forensics

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Time Of Death

Algor Mortis- body temperature (1.5-2.0 per hour) >24 hours 

Rigor Mortis- degree muscle contraction 6-9 hours 

. cells lack oxygen, anaerobic respiration  

. lactic acid, decrease in pH, enzymes denatured 

. atp no longer produced, bonds between muscles become fixed

. muscles can no longer slide over one another 

Decompositionhours- months

hours-days; enzymes break down cells- autolysis. Skin turns green 

days-weeks; microorganisms decompose, gases, bloating, blisters. 

weeks; tissues liquify, body deflates, decomposition slows. 

months; skeleton. 

Forensic entomology- insect lifecycle and succession on corpse depending on changing conditions. 

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Conditions Affecting Time Of Death

Immersion in water- cools faster in water 

Clothing- keeps the body warmer for longer 

External temperature- sigmoid curve, body cools to surrounding temperature 

Body weight- loose heat faster at lower body weight 


Air movement 

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Carbon Cycle


In- Combustion (fossil fuels/plants), Respiration (plants/animals/decomposers) 

Out- Photosynthesis (plants) 

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Obtaining DNA


Sample obtained- blood, saliva, seaman 


+ buffer solution (break down cell wall) 


+ protease 

+ ethanol 


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Polymerase Chain Reaction (PCR)

1. Mixture- primers (short complementary strands DNA), DNA polymerase and free nucleotides

2. Heated to 95; hydrogen bonds break and double strands separate 

3. Cooled to 50-60; allows primers to bond to strands 

4. Heated to 70; optimum temperature for DNA polymerase, free nucleotides complementary to the strand line up 

5. Repeated many hundreds of times = amplify DNA 

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Gel Electrophoresis

Double stranded DNA + Restriction Endonuclease

1. Fragment loaded into agar, conducts electricity 

2. Current passed through, negative DNA moves towards positive electrode (ve+) 

3. Strands separate according to length 

4. DNA transferred to nylon, strands seperate 

5. Viewed under X-Ray or Ultra violet light 

Smaller = travel faster = travel further 

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1. RNA polymerase attaches to double strand, hydrogen bonds break, strands separate and double helix unwinds

2. One strand used as template (antisense

3. RNA polymerase lines up free complementary nucleotides 

4. Moves along until a stop codon is reached 

5. RNA polymerase detaches and leaves the nucleus through the nuclear pore 

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Mrna modification/Genetic Code

Splicing- removes introns, pre translation. Only leaves exons, can happen in a number of different orders, provides variation. 

Degenerate- more than one codon per amino acid 

Triplet codons- variation= means 64 codons are available to make 20 amino acids 

No overlap- no confusion in amino acids 

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1. Mrna attaches to ribosome 

2. Trna (transfer) carries complementary triplet codon (anticodon) 

3. Complementary ones attach, this repeats!

4. Each pair of amino acids joined by peptide bonds 

5. Repeats until a stop codon is reached 

6. Detaches from the ribosomes 

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. Cell surface membrane 

. Mesosome- infolding of cell membrane; site of respiration 

. Circular DNA 

. Capsule

. Plasmid- ring of DNA 


. Ribosome

. Nucleic acid 


. Capsid 

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Non-Specific Immune Response


1. Macrophages (monocytes)- ingest 'non self', hold in vacuole 

2. Neutrophils- kill and form pus (short lived)- first to area of infection 

Interferon- prevent virus from multiplying, protein synthesis 

Inflammation- damaged white blood cell releases histamine, increased blood flow, permeability, arterioles dilate. = OEDAMA 

Lysosomes- enzymes break down cell wall and cause lysis 

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Specific Immune Response

T Lymphocytes;mature in thymus- made in bone marrow 

T-Killer; destroy non self antigen cells by creating pores in cell surface membrane, water enters causing lysis of the cell 

T- Helper; stimulate B cells which create antibodies specific to the antigen on a pathogens cell surface membrane 

T- Memory; remember specific antigens on pathogens cell surface 

B Lymphocytes;made in bone marrow 

B-Effector (plasma); produce antibodies 

B-Memory; remember specific antigens on pathogens cell surface 

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Primary Immune Response

Activate T Cells; 

Macrophage engulf pathogen with foreign antigen on surface, make an antigen presenting cell. Complementary CD4 receptor binds to APC, this causes cloning and activation of T helper and T memory cells. 

Cloning B Cells;

Macrophage engulf pathogen with foreign antigen on surface, make an antigen presenting cell. A complementary T helper cell binds, cytokines are used during clonal selection to make B effector (plasma cells) and B memory cells. 

T Killer Cell Activation;

Complementary receptor binds, this is stimulated by cytokines. Enzymes are released by the cell, these cause lysis of the pathogen with foreign antigens on the cell. 

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Secondary Immune Response

Much faster response

T and B memory cells- produce antibodies instantly on recognising the 'non self' or foreign antigen on the cell surface membrane on the pathogen. 

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Natural Barriers

1. Skin

Keratin- hard protective layer, skin flora- compete with bacteria for space and nutrients. 

2. Mucous membranes

Mucus binds to pathogens and cilia slowly move the pathogens out of the body. 

3. Stomach acid/gut flora

Low pH kills bacteria, also has to adapt to harsh conditions such as temperature and overcoming digestion 

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Types Of Immunity


1. Natural- immune by catching the disease, body produces memory cells (T/B) 

2. Artificial- immune by being given a vaccine, produces memory cells (T/B)

Passive- short lasting 

1. Natural- immunity passed on from mother placenta or breast milk 

2. Artificial- immune after being injected with antibodies 

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Bacteriostatic- prevent multiplication of bacteria 

Bactericidal- kill bacteria

How they work? 

. inhibit bacterial cell wall synthesis

. disrupt cell membrane 

. inhibit nucleic acid synthesis 

. inhibit enzymes 

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