forensics immunity and infection Flashcards
what does gel electrophoresis produce?
a pattern of bands on the gel that represent DNA fragments of different length
what is the purpose of southern blotting?
to detect the presence of certain DNA sequences in a given genome
why do different sized molecules move through the gel at different rates? (gel electrophoresis)
pores in the gel allow smaller molecules to move quickly, but larger molecules move slower
in gel electrophoresis does DNA move towards the anode or the cathode and why?
the anode because DNA is negatively charged due to the presence of phosphate groups
what do PCR reactions require?
DNA/RNA to be amplified
primers
DNA polymerase
free nucleotides
buffer solution
what is a primer?
short sequence of single stranded DNA
have base sequences complimentary to 3’ end of DNA
define region that is to be amplified
identifying where DNA polymerase needs to bind
why is DNA polymerase suitable for PCR?
does not denature at high temps required during first stage
what is the purpose of the buffer solution in PCR?
ensures the optimum pH for reactions
what are the stages of PCR?
denaturation
annealing
elongation/ extension
explain the denaturation stage of PCR
double stranded DNA heated to 95ºC
breaks H bonds between strands
explain the annealing stage of PCR
50-60ºC
so primers can join to complimentary bases at the end of the single strands
explain the elongation/ extension stage of PCR
72ºC
optimum temp for polymerase to build complimentary strands of DNA to produce new identical double stranded DNA molecules
what can be analysed to determine the time since death?
core body temperature
degree of rigor mortis
state of decomposition
entomology
explain core body temp and time since death
heat from respiration and other metabolic reactions needed to maintain body temp around 37ºC
metabolic reactions end at death so no more heat produced so body temp drops to temp of surrounding environment
decreases by 1.5-2ºC per hour
what conditions affect the rate at which body heat is lost?
air temperature
sa: vol
presence of clothing
explain rigor mortis and time since death
no more oxygen reaches muscle cells after death so they respire anaerobically and produce lactic acid
lactic acid decreases muscle cell pH, denaturing enzymes that produce ATP
without ATP myosin heads cannot be released from actin filaments, locking muscles in a contracted state
begins in smaller muscles in head and ends in larger muscles of lower body
what affects the rate of rigor mortis?
high temp speeds up rate
level of muscle development
h
explain state of decomposition and time since death
carried out by decomposers- enzymes secreted from their cells break down biological molecules in dead tissue
break down cells/ tissues in few days- greenish skin
breakdown tissues/ organs in few weeks- produces gases eg methane which lead to bloating and sulphur which stinks. skin blisters and falls off body
soft tissues turn into liquid and leave body
what factors affect the rate of decomposition?
slower at lower temp, faster at higher
slower in anaerobic conditions
what are examples of decomposers?
bacteria
fungi
explain entomology and time since death
dead bodies provide ideal habitats for many insect species
entomology is the study of those insect colonies
diff species present at diff times after death
eg flies a few hours after but beetles later
blowfly eggs hatch after 24h so if larvae r present, it indicates that TOD was over 24h ago
what factors affect the progression of insect life cycles on dead bodies?
drugs present in the body
humidity of surroundings
oxygen availability
temperature
how is succession different in forensics than ecology?
in an ecosystem, pioneer species are out-competed and disappear as a system matures
in a dead body they stay as decomposition progresses
what factors affect succession on dead bodies
location such as underwater, buried in a coffin or soil
as insect accessibility and oxygen availability differ
what are the main ways that pathogens can enter the body?
broken skin- direct access to tissues and bloodstream
digestive system- when consuming contaminated food and drink
respiratory system- inhaling
mucosal surfaces- lining of body cavities eg nose, mouth, genitals
how is skin a barrier to infection?
physical barrier
if damaged, leaves exposed tissue vulnerable to pathogens
blood clotting prevents pathogen entry if skin damage but takes time so some pathogens could enter before blood clots form
how are microorganisms of the gut and skin barriers to infection?
compete with pathogens for resources, limiting the number of pathogens, limiting pathogen ability to infect body
how is stomach acid a barrier to infection?
HCl creates acidic environment which is unfavourable to pathogens present on food and drink
how is lysozyme a barrier to infection?
secretions of mucosal surfaces (eg tears, saliva, mucus) contain an enzyme called lysozyme
enzyme damages bacterial cell walls, causing the cells to burst
what is a non specific immune response?
has the same response regardless of which pathogen enters
what is a specific immune response?
immune system recognises specific pathogens due to presence of antigens on their cell surface
what are antigens?
proteins/ glycoproteins
identify a cell as self or non self
pathogens have non self
what is inflammation?
*surrounding area of a wound becomes swollen, warm, painful
*body cells called mast cells respond to tissue damage by secreting histamine
*histamine stimulates: vasodilation increases blood flow through capillaries
cap walls become more permeable allowing fluid to enter tissues to create swelling and some plasma proteins leave the blood
phagocytes leave blood and enter tissue to engulf foreign particles
cells release cytokines
what is histamine?
chemical signalling molecule
enables cell signalling or communication between cells
what are cytokines?
signalling molecule
triggers immune response in infected area
what are interferons?
cells infected by viruses produce anti viral proteins called interferons which prevent viruses from spreading to uninfected cells
how do interferons work?
*inhibit production of viral proteins, preventing virus from replicating
*activate wbc involved w specific immune response to destroy infected cells
*increase non specific immune response eg promoting inflammation
what are phagocytes?
*type of wbc responsible for removing dead cells and invasive microorganisms by phagocytosis
*travel thru body and leave blood by squeezing thru cap walls
*released in large numbers during infection
what is the process of phagocytosis?
*pathogens and body cells under attack release chemicals eg histamine, which attract phagocytes to the site where pathogens are
*phagocytes recognise antigens on pathogen as being non self
*cell surface membrane of phagocyte extends out and around pathogen, engulfing it and trapping it in a phagocytic vacuole (endocytosis)
*digestive enzymes eg lysozyme released into phagocytic vacuole when lysosomes fuse w it, and digest the pathogen
*phagocyte presents antigen of pathogen on its cell surface membrane and becomes an antigen presenting cell, which initiates specific immune response
what is a bacterial cell wall made from?
murein
what is the role of the capsule in bacterial cells?
helps protect bac from drying out
protects from attack by other cells of immune system
what is the flagellum in bacterial cells?
long tail like structures
rotate
enabling prokaryote to move
what is the pili in bacterial cells?
thread like structures on surface
enable bac to attach to other cells/ surfaces
involved in gene transfer during sexual reproduction
how can viruses reproduce?
infecting living cells and using their protein building machinery to produce new viral particles
what are some structures in viruses?
nucleic acid core
protein coat called a capsid
outer layer called envelope formed from membrane phospholipids of cell they were made in
attachment proteins
what bacteria causes the disease tuberculosis?
mycobacterium tuberculosis
how is TB transmitted?
infected ppl cough/ sneeze
bac enter air in droplets released from lungs
uninfected ppl inhale them
what happens when TB is engulfed by phagocytes in the lungs?
bac may be able to survive and reproduce inside phagocytes
individuals w healthy immune system dont develop TB at this stage
what happens to the TB phagocytes over time?
encased in structures called tubercles
bac remains dormant
what is the active phase of TB?
bac may become activated and overpower immune system at a later stage
what are the first symptoms of TB?
fever
fatigue
coughing
lung inflammation
what could happen if TB is left untreated?
bac cause extensive damage to lungs
respiratory failure leads to possible death
can spread to other body parts so possible organ failure
what type of proteins are antibodies?
globular
what do antibodies bind to antigens on pathogens to do?
block binding receptors
act as anti toxins by binding to toxins produced by pathogens
cause pathogens to clump together
what are the parts of an antibody?
constant region
variable region
disulphate bridges
heavy chains
light chains
antigen binding site
hinge region
where are T cells produced?
bone marrow
where do T cells mature?
thymus
when are T cells activated?
when they bind to their specific antigen on the surface of an apc
what happens to T cells after they are activated?
divide by mitosis and differentiate into: T helper, T killer, T memory
what is the function of T helper cells?
release chemical signalling molecules to help activate B cells
what is the function of T killer cells?
bind to and destroy any apc
what is the function of T memory cells?
remain in blood
enable faster specific immune response if same pathogens encountered again
where are B cells produces and mature?
bone marrow
how are B cells activated?
binding of B cell to specific antigen
cell signalling molecules produced by T helper cells
what happens once B cells are activated?
divide repeatedly by mitosis producing many clones
daughter cells differentiate into: effector cells, memory cells
what are the role of effector cells?
go on to form plasma cells
which produce specific antibodies that combine w antigen that entered body
what are the types of immunity?
active natural
active artificial
passive natural
passive artificial
what is the difference between the secondary and primary immune response?
secondary has memory cells produced in primary so
antibodies produced faster
in higher conc
eliminates pathogen before symptoms show
how do active immune responses occur?
antigen enters body triggering a specific immune response
memory cells produced so long term immunity
how do passive immune responses occur?
no immune response, antibodies gained from another source, not the infected person
no memory cells that can enable secondary response
what causes active natural immunity?
exposure to pathogens
what causes active artificial immunity?
vaccinations
what causes passive natural immunity?
babies- antibodies from breastmilk
foetuses- antibodies across placenta from mum
what causes passive artificial immunity?
injection/ tranfusion of antibodies collected from ppl/ animals whose immune system had been triggered by a vax to produce antibodies
what do vaccines contain?
dead/ weakened form of pathogen
antigens alone
less harmful strains of pathogen
genetic material that codes for antigens
antigenic variation:
vax needs to be constantly modified to keep up with the pathogen’s antigens mutating
what is a retrovirus?
a virus that can make DNA from RNA because they have reverse transcriptase
what is inside the core of HIV?
integrase
RNA
reverse transcriptase
what glycoprotein receptors do HIV have?
gp120
co receptor
how can HIV be transmitted in body fluids?
sexual intercourse
blood donation
mum to kid across placenta
breastmilk
sharing needles for intravenous drugs
mixing of blood between mum and kid during birth
what is the chronic phase of HIV?
no symptoms
years/ months
what symptoms occur immediately after HIV infection?
mild flu like
when does HIV develop into AIDS?
constant opportunistic infections
T helper cells drop below a critical level
what are opportunistic diseases?
diseases that would usually cause minor issues in healthy ppl
eg TB
what factors effect how quickly HIV progresses into AIDS, and how long a person w AIDS survives?
age
strain of HIV
access to healthcare
number of existing infections
what are introns
non coding sections of DNA
found in genes
what are exons
coding sections of DNA
what is splicing
during transcription both introns and exons are transcribed and pre-mRNA produced
before pre-mRNA leaves the nucleus
introns removed
exons joined together
what is alternative splicing
exons can be spliced in many diff ways
produce diff mature mRNA molecules
so a single eukaryotic gene can code for more than one polypeptide chain
what are antibiotics?
chemical substances that damage bacterial cells, with little or no harm to human tissue
what are the types of antibiotics?
bactericidal: kill bacterial cells
bacteriostatic: inhibit bacterium growth processes (high doses do kill)
how do antibiotics work?
inhibiting bacterial enzymes needed to form bonds in cell walls, prevents bac growth, death as cell walls weakened and burst under pressure of water entering by osmosis
bind to ribosomes and prevent protein synthesis so no enzymes produced so no metabolic processes
damage cell membranes so loss of useful metabolites or uncontrolled water entry
preventing bac DNA from coiling into rings so it no longer fits into bac cell
why are mammalian cells not damaged by antibiotics?
eukaryotic
no cell wall
diff enzymes
diff ribosomes
why are viruses not damaged by antibiotics?
no cellular structures eg
enzymes
ribosomes
cell walls
what is a hospital acquired infection (HAI) ?
infections contracted by patients while in hospital
what are some hospital measures to reduce HAI spread?
regular hand washing
quarantine of ppl w HAI
surfaces and equipment disinfected after every use
why is the risk of antibiotic resistant strains of bacteria arising high in hospitals?
antibiotics widely used in hospitals
which is a selection pressure for resistant stains to develop
what are practices in hospitals to reduce the risk of antibiotic resistant HAIs?
no antibiotics prescribed for viruses or minor infections
no antibiotics as a preventative measure
narrow spectrum antibiotics prescribed
rotate use of diff antibiotics
how many strands of rna does hiv have
2
in gel electrophoresis, do DNA fragments move towards the cathode or the anode
anode
