Topic 6 Flashcards
What factors can be used to estimate time of death?
- Extent of decomposition
- Stage of succession
- Forensic entomology
- Body temperature
- Muscle contraction/rigor mortis
What is the extent of decomposition, and how can it be used to estimate time of death?
- Decomposers break down skin over several week by digestive enzymes
- What stage the body is at presents time since death.
- Effected by temp and oxygen availability
What is the stage of succession and how can it be used to estimate time of death?
- Changes in type of organisms found on a body over time
- Bacteria, fly, larvae, beetles
- Effected by where the body is located and availability of oxygen
What is forensic entomology, how can this be used to estimate time of death?
- Study of colonisation of insects on a body
- Different insects colonise a body at different times
- Blowfly are first to colonise
- Effects are humidity and temperature
How can pathologists use forensic entomology to estimate time of death?
- The number of species present
- Life cycle stages of insects present
- Succession of insect species
- Life cycle is dependent on temperature of environment
What is body temperature and how can this be used to estimate time of death?
- No metabolic reactions occur when dead and the temp should be 37 degrees
- Body temp decreases by 1-2 degrees each hour
- Effects are air temp, sa:v ratio, clothing worn
What is rigor mortis, and how can it be used to estimate time of death?
- Muscle contraction within 4-6 hours after death
- Lactic acid causes pH to fall so inhibits enzymes and ATP no longer produced
- ATP synthase loses shape of active site so no more muscle contraction and become fixed in position
- Effects are muscle development and temperature of surroundings.
What happens to muscle cells in rigor mortis?
- No more oxygen reaches cells so respire anaerobically which produces lactic acid.
- Decreases pH of cells, denaturing enzymes
- Without ATP muscles become fixed in a contracted state
How useful can body temperature be in providing evidence for time of death?
- Only useful for a short period of time following death
- Need to know ambient temperature
- Factors affect temp drop eg. clothing
- Drop in body temp is algor mortis
How do decomposers break down dead organic matter?
- Secrete enzymes that break large molecules into smaller ones
- CO2 and methane is produces
- Released into atmosphere and go through carbon cycle
What are introns vs exons?
- Introns - sections of DNA which do not code for proteins
- Exons - sections of DNA that code for proteins
What happens in the process of splicing?
- Pre-mRNA non coding intron sections are removed - Coding exons are joined together
- The resulting mRNA molecule contains only the coding sequences of the gene
- Forms mature mRNA
What is pre-mRNA?
- The mRNA that has been transcribed with both introns and extons
What is alternative splicing?
- Removing exons so different combinations of mature mRNA are formed.
- The exons of genes can be joined (spliced) together in many different ways to produce different mature mRNA molecules
- Therefore different amino acid sequences.
What is splicing catalysed by?
- Enzyme-RNA complex called spliceosome
How can DNA profiles be created?
- Isolating sample of DNA
- Copies produced using PCR
- Restriction enzymes to produce DNA fragments
- Gel electrophoresis of sample
- Analyse banding pattern of fragments by fluorescent dye/uv
What does PCR require?
- DNA sample to be amplified
- Primers
- Taq polymerase
- Free nucleotides
- Buffer solution
What are the stages of PCR reaction?
- DNA sample, nucleotides, taq polymerase and primer sequence are mixed
- Denaturation - thermocycler heated to 95 degrees to break hydrogen bonds so two single strands of DNA
- Annealing - temp increased to 50-60 degrees so primers bind to 3’ end
- Elongation - temp increased to 72 degrees so Taq polymerase can synthesise new complementary strands
How does gel electrophoresis work?
- Amplify using PCR
- Separate using restriction enzymes
- DNA loading dye is added to PCR tube and DNA fragments are inserted into well of agarose gel plate
- Electrical current is applied
- DNA moves to positive anode as it is negatively charged
- Smaller fragments move faster through gel so mass separates them
- DNA binding dye is added and UV is shone to compare bands
What is southern blotting?
- DNA profile transferred onto nylon membrane
- Buffer solution is placed on top.
- Radioactive probe attaches to band to expose xray paper
- Increases longevity of DNA profile
How can DNA profiles be compared?
- Total number of bands
- Position of bands
- Size/width of bands
What is a DNA profile?
- Specific pattern of DNA bands from an individuals genome
- Relies on short, repeating sequences of DNA found within non-coding regions of DNA
How does a DNA profile work?
- DNA obtained
- DNA amplified in PCR
- DNA separated into fragments using restriction enzymes
- Gel electrophoresis
- Southern blotting
- Fluorescent stain for UV light
- Analysed and compared
What are STRs?
- Short tandem repeats
- Short, repeating sequences of DNA
- Each locus will differ in number of repeats between homologous chromosomes and between individual
How is DNA extracted?
- DNA obtained from tissue samples via mouth, blood, hair, skin
- Amplified using DNA
What is DNA digestion?
- DNA is digested by cutting into small fragments using restriction endonucleases
- Endonucleases are an enzyme that cut up DNA at a specific sequence of bases called a recognition sites
- Cut DNA into fragments but leaves STRs intact
What type of cells are bacteria?
- Prokaryotes
What are the features of a bacterial cell?
- 70s ribosomes
- Lack of membrane bound organelles
- Single circular chromosome free in cytoplasm
- Peptidoglycan cell wall
- Cell membrane with mesosomes
What is a virus?
- Non-living pathogen
What is the features of a virus?
- Nucleic acid core surrounded by capsid
- Lipid envelope with proteins attached
What are the differences between structure of bacteria and viruses?
- Bacteria DNA is circular/Viral DNA is linear
- Bacteria have ribosomes/Viruses do not
- Bacteria are cells/Viruses are not
- Bacteria has cell wall/Viruses have protein capsid
- Bacteria have DNA/ Viruses have RNA or DNA
How do viruses reproduce?
- Replicate in living host cells they infect
- Hijack protein production machinery and cause lysis and kill the cell and build new virus particles
What is a disease?
- An illness or disorder to the mind/body leading to poor health
What is an infectious disease?
- Disease caused by pathogens which are transmissible and can be spread in population
How is TB spread?
- Through inhalation of droplets from a person infected by TB
What bacteria causes TB?
- Mycobacterium tuberculosis
How does TB cause illness?
- TB bacteria is engulfed by phagocytes
- Bacteria is reproduced when inside phagocytes and over time those infected become encased in tubercles in the lungs where it remains dormant
- When it is activated it overpowers immune system and creates a lesion (granuloma) so damages tissue and cause organ failure
What is primary TB?
- Infects lungs cause fatigue, fever, coughing, weight loss
What is secondary TB?
- Immunocompromised individual
- Produces extensive damage to respiratory system
Why do dormant TB not get destroyed by the immune system?
- Bacteria hides inside macrophages
- Thick waxy cell wall
- Lysosomes cannot fuse with phagocytotic vacuole
- Bacteria within tubercles cannot be destroyed
How does HIV infect human cells?
- GP120 on HIV attaches to CD4 receptors on T helper cells
- Allows HIV to enter host cells
How does HIV replicate once in blood?
- GP120 glycoproteins attach to CD4 receptors on T helper cells
- Capsid fuses with T helper cell membrane, releasing RNA
- Reverse transcriptase converts viral RNA into DNA then integrates the viral DNA into the cell DNA.
- Transcribed to generate mRNA which encodes HIV viral proteins, leading T helper cells to infect more T cells
What is HIV?
- Two single-stranded RNA retrovirus
- Containing enzyme reverse transcriptase
- Has attachment proteins embedded in lipid envelope.
What happens without T helper cells?
- Cytotoxic T cells can’t kill infected cells
- Specific antibodies cannot be produced
How does HIV lead to AIDS?
- After initial infection, replication rates drop (latency period)
- Virus reduces number of T helper cells
- B cells no longer activated so no antibodies are produced
- Decreased ability to fight diseases so weakens immune system
How do anti viral drugs work in the treatment of HIV?
- Drugs prevent viral replication
- Inhibit reverse transcriptase so viral DNA cannot be formed from viral RNA
- Inhibit integrase so viral DNA cannot integrate
- T helper cells will not be killed
What are the evasion mechanisms of HIV?
- Virus kills helper T cells reducing number of cells that could be detected
- Antigenic variability due to high mutation rate
- Infected cells don’t produce APCs so WBCs do not recognise and destroy infected cells
Why does AIDs lead to death?
- No longer any antibodies against pathogens
- Immunocompromised so unable to fight infections
What factors increase rate of progression into AIDs?
- Access to healthcare
- Age
- Number of infections
- Strain
What is the correlation of HIV and TB?
- Dormant TB may become an active infection when immune system weakened
- HIV causes immunodeficiency
What is an infection?
- When a pathogen gets inside human tissues or cells
What are the barriers to infection on the human body?
- Skin: physical barrier to infection
- Skin and Gut flora: microorganisms which compete with pathogens
- Stomach acid: HCL creates high pH (acidic) environment
- Lysozyme: Kills bacteria by breaking down cell wall causing lysis
How does flora protect the body from infection?
- Better adapted to conditions
- Prevents growth of microorganisms by providing competition
- Releases chemicals/toxins
What is the non-specific immune response?
- When a body defends itself against a pathogen but the response is not specific to pathogen
- Eg. phagocytosis, inflammation
How does bacteria cause a specific immune response?
- Bacteria engulfed by macrophages
- Antigen presenting cell produced
- T helper cells with complementary CD4 bind to APC
- Cytokine released causing cloning of B cells
- Plasma cells produce antibodies
How does inflammation work?
- Swelling of a tissue caused by infection to destroy invading pathogen
- Mast cells release Histamine
- Causes vasodilation to increase blood flow
- Increases permeability of capillaries to allow blood plasma to enter tissue
How do interferons work?
- Anti-viral proteins produced in infected cells which diffuse to surrounding cells
- Inhibits viral replication and microbial protein synthesis
- Activates WBCs involved in specific immune response
How does interferon respond to infection by viruses?
- Interferon prevents virus attaching to uninfected host cells by binding to receptors
- This therefore prevents the virus entering the cell
- Viruses cannot replicate and infect more cells
How does phagocytosis work?
- Phagocyte recognises pathogen as non self from the foreign marker (antigen)
- Phagocyte engulfs pathogen to form a phagosome (vacuole) by endocytosis
- Pathogen is broken down by enzymes (phagolysosome)
How does a macrophage ingest bacteria?
- By phagocytosis
- Bacteria enclosed inside a phagosome
- Bacteria is broken down by enzymes
- Present antigens on membrane (antigen-presentation)
What are phagocytes?
- Macrophages + neutrophils
What are antigen representing cells?
- Phagocytes engulf antigens which are then presented on cell surface membrane of antigen presenting cells
- Lymphocytes with receptors that are specific to antigens bind to APC.
What are self vs non self antigens?
- Self = antigens produced by organisms own body cells, do not stimulate immune response
- Non self = antigens not produced by organisms own body cells, stimulate immune response
What happens when a pathogen first infects tissue?
- Neutrophils arrive first and each engulfs 5-20 pathogenic cells
- Macrophages then arrive and engulf 100s of pathogenic cells
What are antigens?
- Markers on the cell surface which allow cell recognition
- Trigger immune response
How do antibodies disable pathogens?
- Bind to pathogen receptors to prevent pathogens infecting host cells
- Act as anti toxins by binding to toxins produced by pathogens
- Pathogens clump together (agglutination) so they can’t spread
What are antibody binding sites?
- They have specific shapes which makes them complementary to specific target antigens
What is the structure of antibodies?
- 4 polypeptide chains: 2 heavy chains, 2 light chains
- Y shaped structure
- Has a constant and variable chain
What is the constant region?
- Heavy chain
- No not vary within class of antibody
- Bind to all immune cell receptors
What is the variable region?
- Short chain
- Amino acid sequence is different on each antibody
- Bind to antigen to form antibody-antigen complex
What is the importance of the end of a variable region on the end of an antibody?
- It is the antigen binding site
- Gives antibody specificity for binding to the antigen
How are membrane bound antibodies different from those secreted into the blood?
- Membrane bound antibodies are attached to the surface of lymphocytes.
- In non bound antibodies, gene can undergo alternative splicing to remove extra section for attachment
What is the role of an antibody?
- Helps immune cells destroy pathogens
- Variable region binds to antigen forming antibody-antigen complex
- Constant region then binds to opsonin receptor on phagocyte
How do antibodies work?
- Antibodies have two binding sites
- Work by agglutination which cause pathogens to clump together
- For macrophage or neutrophils to engulf and destruct pathogens carrying the antigens (phagocytosis).
What is neutralisation?
- Antibodies bind to toxins released by pathogens
- Prevents toxins damaging
What is the primary immune response?
- The body’s initial response to the first time an antigen is encountered by the immune system
What is the secondary immune response?
- When the immune system encounters an antigen it has already been exposed to
Why does the primary response take a longer time?
- T and B cells have to be activated which takes time
- Plasma cells need to develop before antigen production begins
Why is the secondary immune response stronger and faster?
- Memory cells are present
- Antibodies are produced more quickly
- Eliminates pathogens before symptoms appear
What is active immunity?
- When antibodies are produced by own immune system
What is passive immunity?
- When specific antibodies are introduced from an outside source
What is natural vs artificial?
- Natural = natural process
- Artificial = Introduced
What are the two types of active immunity?
- Natural - pathogen exposure
- Artificial - vaccination
What are the two types of passive immunity?
- Natural - breast milk
- Artificial - transfusion of antibodies
What is produced in non-specific immunity?
- Macrophages + Neutrophils
- Recognise non-self pathogens and destroy by phagocytosis
What is produced in specific immunity?
- T lymphocytes + B lymphocytes
- Recognise specific antigens to produce an immune response
Where are T cells produced and where do they mature?
- Produced in bone marrow
- Mature in thymus
What do T cells have?
- Specific cell surface receptors (T cell receptors)
How are T cells activated?
- They bind to their specific antigen on the surface of an antigen presenting cell
- Shapes are complementary
- Called clonal selection
What is direct contact?
- Lymphocyte comes across pathogenic cell
What is indirect contact?
- Lymphocyte comes across APC which phagocytosed the pathogen
What is the process of cell mediated response?
- Phagocytosis by phagocytes
- Macrophages present antigen-presenting cells to T helper cells
- T cells release cytokines to trigger T killer cells
- Stimulate phagocytic cells, such as macrophages and neutrophils to engulf non-self pathogens.
What do T cells differentiate into?
- T killer cells - destroy own body cells infected by pathogens, display APC
- T helper cells - release cytokines to stimulate B cells to produce antibodies
- T memory cells - remain in blood enabling a secondary immune response
- T regulatory cells - inhibit immune response once pathogens destroyed so own body cells aren’t destroyed
What is the process of the humoral response?
- Phagocytosis by phagocytes
- Macrophages present antigen-presenting cells to T helper cells
- T cells release cytokines for B cell activation
- B cells form clones and differentiate into Plasma cells
- Produce memory cells
Where do B cells divide and mature?
- Bone marrow
How are B cells activated?
- B cell binds to antigen forming antigen-antibody complex. (APC)
- T helper cell binds to B cells and T helper cells releases cytokines to activate the B cell.
What do B cells differentiate into?
- Plasma cells - secrete antibodies into blood
- B memory cells - remain in blood to enable secondary immune response when same antigen is encountered
What is the role of antigen-presentation in body’s specific immune response to infection?
- Macrophages present antigen to T helper cells.
- Activates T killer and B cells
- B cells act as an antigen-presenting cell
- Result in plasma cells to produce antibodies
- T killer cells destroy infected host cells
What is a vaccine?
- Dead/weakened pathogens injected into the body
- Artificial active immunity
- Produce memory cells for strong immune response
What is the evolutionary race between pathogens and hosts?
- When one evolves, another catches up
- Pathogens evolve new methods to overcome the immune system.
How does the evolutionary race affect antigen presentation to T helper cells?
- Mutation occurs in bacterial DNA, changes APC
- Memory T cells will not recognise antigen
- Another primary immune response to activate more T helper cells
What is a selection pressure?
- External factor which affects organisms ability to survive
What is antigenic variation?
- Pathogens have resistant mechanisms
- Frequent pathogen mutations
- Vaccines no longer effective as antigens are no longer recognised
What is vertical evolution?
- Bacteria passing adv. allele from one generation to next
What is horizontal evolution?
- If adv. allele is passed from one bacteria to next but no change
Why might a vaccine be given to immediate family/health workers despite clinical trials being incomplete?
- Disease may be fatal
- Risk of disease is worse than risk from vaccine
- Very close contact
- Helps to reduce spread
What are the two types of antibiotics?
- Bactericidal - kills bacterial cells
- Bacteriostatic - Inhibits growth/multiplication
What are some of the mechanisms antibiotics use to disrupt bacterial cell growth?
- Inhibit bacterial wall synthesis
- Inhibit protein synthesis
- Damage cell membranes
- Inhibit nucleic acid synthesis
What is MRSA?
- Multiple resistant bacteria found in hospitals
What measures do hospitals have in place to reduce the spread of viruses?
- Regularly wash hands
- Isolation ward
- Surfaces should be disinfected
- No ties, watches, sleeves
What is the risk of antibiotic resistance?
- Difficult to treat as do not respond to regular antibiotics
- Cause serious health complications
What hospital practices have been developed to reduce the risk of antibiotic resistant bacteria?
- No antibiotic prescriptions for minor infections/diseases
- rotate the use of different antibiotics
- prescription of a narrow spectrum antibiotic to treat the infection
How does antibiotic resistance in bacteria arise?
- Random mutation in an individual
- Resistant survives and passes on mutation via binary fission
- Increases in frequency in the population
