Infection, Immunity and Forensics Flashcards
Describe introns.
Introgenic regions, non-coding blocks.
Within introns, there are series of repeated bases - short tandem repeats.
Define exons.
Expressed, coding regions.
Describe polymerase chain reaction.
A sample of tissue is added to DNA polymerase, DNA primers and nucleotides.
95°C the DNA separated into two strands. (30 secs)
55°C primers attach at the start of the short tandem repeat sequence. (45 secs)
70°C DNA polymerase attached, nucleotides are added. The STR and DNA sequence are replicated.
This is repeated to produce millions of STR fragments.
Describe how to obtain a tissue sample.
Broken down in a buffer solution of salt and detergent, separated by centrifuging. Protease enzymes are incubated and cold ethanol is added. DNA is washed in a buffer solution. Treated with restriction endonucleases. Cut at specific basr sequences.
Describe gel electrophoresis.
DNA is placed on gel agarose and submerged in buffer solution. Negatively charged fragments move through the gel. Smaller fragments travel faster.
Southern blotting transfers fragments to nylon/nitrocellulose. Incubated with excess DNA probes.
Describe body temperature as part of forensic analysis.
Body cools due to lack of heat producing reactions. Only useful for 24 hours after death. Measured via rectum or abdominal stab.
Fever or hypothermia will affect body temperature at time of death.
Body size, position, clothing, air movement, humidity and temperature of surroundings will affect cooling of the body.
Describe rigor mortis as part of forensic analysis.
Muscle cells are oxygen starved so oxygen dependent reactions stop. Respiration becomes anaerobic and cell pH falls due to production of lactic acid. Enzyme activity is inhibited. ATP is no longer produced. Bonds between muscle proteins become fixed and the body stiffens.
Passes after 36-48 hours as the muscle tissue starts to break down
Describe decomposition as part of forensic analysis.
Autolysis occurs when enzymes break down cells. Putrefaction is a green discoloration of the lower abdomen due microorganisms breaking down and digest lage amount of tissues which produces gas. Darkens to red-green then to purple-black.
Gas or liquid blisters may appear.
The body bloats.
What is forensic entomology?
Study of the succession of insects on the body after death.
How do viruses work?
Virus attached to the host cell. Virus inserts nucleic acids which replicate. The protein coats synthesise. New viral particles are formed and then released due to cell lysis.
What is the difference between specific and non-specific immune responses.
Non-specific are instant and immediate responses whereas specific are carried out over time.
Humoral response
Activation of T helper cells
Humoral Response
Response to particles and solutes and produces antibodies
Bacterium is engulfed by macrophages
The macrophage becomes an antigen-presenting cell (APC) as the antigens are presented by the major histocompatibility complexes (MHC).
The APC binds to a T helper cell with complementary CD4 receptors.
T helper cell is activated and divides.
Humoral Response
B Cells
The antigen of the bacterium binds to a b cell with complementary receptor
B cell then becomes an antigen presenting cell
The activated T helper cell binds to the APC and produces cytokines ( proteins) that stimulate the B cell.
B cell divides to produceB effector cells
The B effector cells then differentiate into plasma cells and B memory cells
The plasma secrete antibodies which then bind to the antigen.
Macrophages identify intruders marked with antibodies and engluf and destroy the antibodies also clump the bacteria together, which helps to stop them spreading and they can neutralize toxins.
If the same intruder invades again the B memory cells help the immune system to activate faster.
Cell-mediated Response
Virus infects the cell of the host.
The cell presents the antigens on cell surface and becomes an APC
T helper cell with complementary receptors then binds with the APC
Cytokines release from T helper to T killer
T cell divides to form two clones: Active and Memory T killer cells
The active T Killer cell binds to the infected cell
The T killer cells release chemicals that cause pores to form in the infected cell, causing lysis.
Describe the activity of neutrophils.
Leave capillaries through cells in the walls. They are short-lived and ingest and destroy bacteria.
Describe the activity of macrophages.
Begin as monocytes. Exit via walls of capillaries.
Become macrophages and engulf bacteria, foreign matter and cell debris. Ingested material is enclosed in a vacuole. Lysosomes fuse with the cell, releasing enzymes to destroy the bacteria.
Longer-lived.
Describe the activity of lysozyme.
Tears and mucal secretions contain the enzyme that kills bacteria by breaking down cell walls.
Describe inflammation.
Damaged white blood cells release histamines causing arterioles to dilate - causes redness, increase permeability of capillaries so vessels leaks; Plasma fluid, white blood cells and antibodies lead to oedema.
Describe lymph and interferon.
Lymph activates lymphocytes to destroy antigens.
Interferon inhibits viral replication through binding to the mRNA.
Describe physical barriers.
Skin, containing keratin. Skin flora, providing competitive bacteria. Mucus. Cilia. Stomach acid. Gut flora.
Describe tuberculosis.
Mycobacterium tuberculosis is carried in mucus and saliva and passed on through droplet infection.
Primary infection is asymptomatic. An anaerobic granuloma forms. There is an inflammatory response.
Active TB is symptomatic. Reduced immune system.
How is tuberculosis diagnosed?
Through skin and blood tests.
Positive skin tests are confirmed with a sputum sample or a chest x-ray.
Describe HIV.
Passed on in body fluids. Viral RNA enters the cell. Uses reverse transcriptase and integrase to integrate into the host DNA.
The acute phase is few symptoms, the release of HIV antibodies and the loss of T helper cells.
The chronic phase is asymptomatic, the virus rapidly reproduces and dormant diseases reappear.
The disease phase is when opportunistic infections occur.
How is HIV treated?
Reverse transcriptase inhibitors.
Protease inhibitors.
Suggested to use integrase inhibitors or fusion inhibitors.
What is a type of each: active artificial immunity, active natural immunity, passive artificial immunity, passive natural immunity.
Active artificial immunity - vaccination
Active natural immunity - memory cells
Passive artificial immunity - injection of antibodies
Passive natural immunity - maternal antibodies.
What is a vaccine?
Weakened viruses, killed bacteria, altered toxin or antigen-bearing fragment.
Define a bactericidal antibiotic.
Destroys bacteria.
Define a bacteriostatic antibiotic.
Prevents bacterial multiplication.
How do antibiotics work?
Inhibit cell wall, nucleic acid, protein synthesis, disrupt cell membrane, inhibit specific enzymes.
How can you avoid antibiotic resistance?
Antibiotics should only be used when needed.
Complete the course of antibiotics.
Infection control in hospitals.
How do bacteria spread genes?
Conjugation, via cell-to-cell contact.
Antibody
Immunoglobulin produce in response to the antigen
They have a constant and a varied region
Clonal Selection
The selection of a single B or T cells that reconfirmed the antigen from a pool of different antigen specificity
Clonal Expansion
B or T cell divide by mitosis to form a clone
Post Transcriptional Changes
Proves that one gene can code for more than one protein.
mRNA made in the nucleus is pre-mRNA
pre-mRNA is then modified by the removal of introns (non-coding regions)
This is carried out by spliceosomes
Exons (coded regions) are rejoined in different combinations
The mRNAs produced are different and are translated to produce different sequences of amino acids which results in different bonds stabilising the protein’s tertiary structure.
Antigen
Substances capable of eliciting the immune response
Summary of Rigor Mortis and Body temp
3 hours or less- warm and floppy
6 hours or less -warm and stiff
36 hours - cold and stiff
More than 48 hours - cold and floppy
Bacteria and virus differences
Bacteria - cell, virus - particle
Bacteria surrounded by cell wall, virus surrounded by capsids
Bacteria have plasmid/ribosomes, virus doesn’t
Bacteria dna, virus dna or rna
Bacteria circular dna and virus linear genetic material
Non-specific response
A response that is effective against a wide range of infectious agents, it does not involve the recognition of infectious agents and does not react to specific antigens.
Effects of different antibiotics on bacteria.
Wash hands. Work in aseptic technique. Flame forceps, pick up mast ring. Place in centre of agar. Tape dish. Keep upside down. Measure size of zones of inhibition.
