Topic 6 Flashcards
What decomposes organic matter?
Microorganisms
What cycle are microorganisms an important part of?
Carbon cycle
Give examples of microorganisms
Fungi and bacteria
How do microorganisms decompose organic matter?
Microorganisms in and on them secrete enzymes that decompose the dead organic matter into small molecules that they can respire.
What is produced when microorganism respire?
Methane and CO2 which recycles carbon back into the atmosphere.
What are the 5 factors needed to work out the time of death of a body?
Body temperature Degree of muscle contraction Forensic Entomology Extent of decomposition Stage of Succession
How does looking at body temp help work out time of death?
1) All mammals produce heat from metabolic reactions like respiration
2) From the TOD metabolic reactions slow down and eventually stop, causing body temp to fall until it equals the temp of its surroundings - process called algor mortis
What is algor mortis?
the second stage of death, is the change in body temperature post mortem, until the ambient temperature is matched.
What is the human core body temperature?
36.2 - 37.6
How is core body temp measured?
Via the rectum or through an abdominal stab.
A long thermometer is needed as an ordinary thermometer is to short and has too small a temp range.
An electric thermometer can also be used
Describe the normal curve a cooling body will produce
Sigmoid curve
- Initial temp plateau normally lasts between 30 and 60 mins
- Decreases then plateaus
What factors will affect post-mortem cooling?
Body size Body position Clothing Air movement Humidity Temp of surroundings
At what rate does a human body cool at?
1.5 - 2 per hour
What is rigor mortis?
About 4-6 hours after death the muscles in a dead body start to contract and become stuff
What determines the position (bent or straight) of the joints during rigor mortis?
Body position at TOD
Describe the process of rigor mortis.
1) Muscle cells become deprived of oxygen and oxygen dependant reactions stop.
2) Anaerobic respiration takes place in the muscle cells which causes a build up of lactic acid in the muscle
3) The pH of the cells decreases due to lactic acid, inhibiting enzymes that produce ATP
4) No ATP means bonds between the myosin and actin in the muscle cells become fixed and stiffen
5) The proteins can no longer move over one another to shorten the muscle, fixing the muscle and joints
What muscles contract first?
Smaller muscles in the head
What muscles contract last?
Larger muscles in the lower body
What factors affect rigor mortis?
Degree of muscle development
Temperature (high temp means rigor mortis sets in quicker but lasts for a shorter period)
If the person has been physically active before death
Why does a higher temp mean rigor mortis occurs quicker?
Chemical reactions in the body are faster
What is forensic entomology?
When somebody dies the body is quickly colonised by a variety of different insects, the study of this is forensic entomology.
How can forensic entomology be used to estimate TOD?
By identifying the type of insect present
- flies are often first insects to appear, usually a few hours after death
- Other insects such as beetles, colonise at later stage
Identifying the stage of life cycle the insect is in
- Blowfly larvae hatch 24 hours after they’re laid. If only blowfly larvae eggs were found, TOD was less than 24 hours previous
What affects the insect’s life cycle?
Drugs
Humidity
Oxygen
Temperature (high temp = faster metabolic reactions = shorter life cycle)
What happens if the stage of development of the insect is unclear?
Its allowed to mature which gives a date of pupation. If normal length of time for an egg to develop and pupate is subtracted from date of pupation, its possible to work out when the eggs where laid.
What is succession of a body?
The types of organisms found in a dead body change over time, going through a number of stages
What will happen if a dead body is left to decompose above ground?
1) Immediately after TOD the conditions are most favourable for bacteria.
2) As bacteria decompose tissues, conditions in a dead body become favourable for flies and larvae
3) When fly larvae feed on a dead body they make conditions favourable for beetles, so beetles move in
4) As body dries out conditions become less favourable for flies, so they leave. Beetles remain as they decompose dry tissue
5) When no tissue remain, conditions are no longer favourable for most organisms
What is the difference between plant succession and body succession?
Early insects remain on the body as other insects colonise it.
What affects the stages of succession?
Location of the body (above ground, underground, in water)
Where are eggs usually laid?
In wounds or at openings of the body
When is a post-mortem performed?
If there is a sudden or unexpected death or if cause of death is unknown
How is a post-mortem performed?
1) External examination
2) Internal examination
- incision down front of body
- organs taken out for detailed examination
3) Blood and tissue samples may be taken and tested for toxins, infections or tumours
4) Contents of stomach may be analysed
What is lysis?
The disintegration of a cell by rupture of the cell wall or membrane.
What is an antigen?
A toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.
What is an antibody?
An antibody, also known as an immunoglobulin, is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses.
What is an immunoglobulin?
Glycoprotein molecules produced by plasma cells (white blood cells). They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses and aiding in their destruction.
What is a lysozyme?
An enzyme that kills bacteria by breaking down their cell walls.
What is phagocytosis?
The ingestion of bacteria or other material by phagocytes and amoeboid protozoans.
What are phagocytes?
Cells that protect the body by ingesting (phagocytosing) harmful foreign particles, bacteria, and dead or dying cells.
What is a DNA fingerprint?
A fingerprint of an organism’s DNA
How is a DNA profile created? (6)
1) A sample of DNA is obtained from the organism the DNA profile is being made for
2) PCR is used to amplify the DNA - used to make millions of copies of specific regions of the DNA in just a few hours. DNA needs to be amplified so there is enough to make a DNA profile.
3) A fluorescent tag is added to all DNA fragments so they be viewed under UV light.
4) Gel electrophoresis is used to separate out the DNA fragments according to their length.
- DNA placed into wells in a slab of gel and covered in buffer solution that conducts electrciity
- Electric current passed through
- As DNA fragmentd are negatively charged they move towards anode
- Short DNA fragments move faster and travel further so are seperate via length
5) The gel is viewed under UV light - DNA fragments appear as bands under UV light.
6) Two DNA profiles can be compared to see how similar the pattern of bands on the gel is - a match could help identify a person or determine a genetic relationship
What are introns?
Non-coding blocks of DNA
What are exons?
Coding regions of DNA
What are short tandem repeats/satellites?
Sequence of repeated bases
How many bases and repeats can an STR contain?
2 to 50 base pairs
5 to several hundred repeats
How many genes does a human genome contain?
23000
3000 base pairs per genes
Where does STR occur on a pair of homologous pair of chromosomes?
same locus on both chromosomes of a homologous pair
Describe how PCR works (8)
1) Reaction mixture set up that contains DNA sample, free nucleotides, primers and DNA polymerase
2) DNA mixture is heated to 95 degrees to break hydrogen bonds between two strands of DNA
3) Mixture is then cooled to between 50 and 65 degrees so that primers can bind to strands
4) Reaction mixture heated to 72 degrees so DNA polymerase can work
5) DNA polymerase lines up free DNA nucleotides alongside each template strand. COmplementary base pairing means new complementary strands are formed.
6) Two new copies of fragment of DNA are formed and one cycle of PCR is complete
7) Cycle starts again with mixture being heated to 95 degrees and this time four strands are used as templates
8) Each PCR cycle doubles the amount of DNA.
Describe how Gel Electrophoresis works (14)
1) Agarose gel poured into gel tray and left to solidify
2) Row of wells created at one end of gel
3) Put gel tray in a gel box - end with wells is closest to cathode
4) Add buffer solution to reservoirs at sides of gel box so surface of gel is covered
5) Take fragmented DNA samples and using a micropipette ass same volume of loading dye to each - loading dye helps samples to sink to bottom of wells and makes them easier to see
6) Add a set volume (10µl) of DNA sample to first well - be really careful, make sure tip of pipette is in buffer solution and just above opening of well
7) Repeat this and add same volume of other DNA samples to other wells - use a clean micropipette tip each time
8) Record which samples were in each well
9) Put lid on gel box and connect leads from box to power supple
10) Turn on power supply and set it to required voltage (100v)
11) Current causes DNA fragments to separate according to length
12) Let gel run for 30 mins then turn power supply off
13) Remove gel tray from gel box and tip off excess buffer solution
14) Wearing gloves, stain the DNA fragments by covering surface of gel with a staining solution then rinsing the gel with water - band of different DNA fragments will now be visible
What is a primer?
Short pieces of DNA that are complementary to the bases at the start of the fragment you want
What is DNA polymerase?
An enzyme that creates new DNA strands
Why is DNA profiling used on plants and animals?
To prevent inbreeding which causes health, productivity and reproductive problems.
What effect does inbreeding have on the gene pool?
Decreases gene pool - number of different alleles decrease which can lead to increased risk of genetic disorders leading to health problems
What does PCR stand for?
Polymerase chain reaction
What does prokaryotic mean?
No nucleus
What are bacteria?
Single celled, prokaryotic microorganisms
What size are most bacteria?
Only a few micrometers
- TB in about 1µm
What are the features of bacterial cells? (8)
1) Flagellum - long hair-like structures (NOT ALL)
2) Plasmids - small loops of DNA, not part of chromosome (NOT ALL)
3) Ribosomes - produce proteins from mRNA
4) Cell wall - supports cell, made of glycoprotein
5) Plasma membrane - contain folds called mesosomes
6) Capsule of slime - protect bacterium from attack by cells of immune system
7) Bacterial chromosome - free floating DNA in one long, circular, coiled-up strand
8) Pili - short hair-like structures, help stick to other cells
What are viruses?
Microorganisms but not cells
Nucleic acids surrounded by protein
What size are viruses?
Smaller than bacteria
- HIV 0.1µm
What do bacteria have but viruses don’t?
Plasma membrane
Cytoplasm
Ribosomes
What are the features of viruses? (5)
1) Core of nucleic acid - either DNA or RNA
2) Capsid - protein coat around core
3) Envelope - stolen from cell membrane of a previous host cell (NOT ALL)
4) Attachment proteins - stick out from edge of capsid or envelop, let virus cling onto suitable host cell
5) Carry proteins inside capsid
What protein does HIV carry inside its capsid?
The enzyme, reverse transcriptase
What is a pathogen?
Any organism that causes disease
What is the cell wall of a bacterium made of?
Peptidoglycan - a polysaccharide cross-linked by peptide chains
What do gram-positive bacteria have?
Walls thickened with additional polysaccharides and proteins
What do gram-negative bacteria have?
A thinner wall but with a surface layer of lipids for protection
How does a virus enter and replicate within a host cell?
1) Virus attaches to host cell
2) Inserts nucleic acid
3) Viral nucleic acids replicate
4) Viral protein coats synthesised
5) New virus particles formed
6) Virus particles released due to cell lysis
What are the three types of white cells?
Neutrophils
Lymphocytes
Monocytes
What causes the disease symptoms of a virus infection?
When lysis occurs, cell contents is released into surrounding tissue. Many enzymes and other chemicals released can damage neighbouring cells.
How does HIV spread?
Spread through infected bodily fluids.
Infection of a new host occurs when these fluids come into contact with mucosal surfaces, damaged tissue or injected into the bloodstream
What type of cell does HIV replicate inside of?
T helper cell
How does HIV replicate? (6)
1) Attachment protein attaches to a receptor molecule on the cell membrane of the host T help cell
2) Capsid is released into cell where it uncoats and releases the genetic material
3) Inside the cell reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
4) From this, double-stranded DNA is made and inserted into human DNA
5) Host cell enzymes are used to make viral proteins from viral DNA found within human DNA
6) Viral proteins are assembled into new viruses which bud from cell and go on to infect other cells.
What bacterium causes TB?
Mycobacterium tuberculosis
What is lysozyme?
Mucosal surfaces produce secretions which contain the enzyme lysozyme. Kills bacteria by damaging cell walls and causes lsyis.
Describe the non-specific immune response (14)
1) Immune system cells recognise foreign antigens on surface of a pathogen and release molecules that trigger inflammation.
2) Molecules cause vasodilation (widening of blood vessels) around site of infection, increasing blood flow to it.
3) Molecules also increase permeability of blood vessels
4) Increased blood flow brings loads of immune cells to site of infection and increased permeability allows cells to move out of blood vessels and into infected tissue.
5) Immune system cells then start to destroy pathogen
6) infected cells produce proteins called interferons which prevent virus spreading to uninfected cells
7) They prevent viral replication by inhibiting production of viral proteins
8) Activate cells involved in specific immune response to kill infected cells
9) Activate other mechanisms of non-specific immune response, i.e. promote inflammation
10) Phagocyte recognizes antigens on pathogen
11) Cytoplasm of phagocyte moves round pathogen, engulfing it
12) Pathogen now contained in phagocytic vacuole in cytoplasm of phagocyte
13) Lysomome fuses with phagocytic vacuole, enzymes break down pathogen
14) Phagocyte presents pathogen’s antigens, it sticks antigens on surface to activate other immune system cells - now an antigen-presenting cell.
What are the sequence of symptoms of AIDS?
INITIAL SYMPTOMS - minor infections of mucous membranes and recurring respiratory infections due to lower than normal of T helper cells
PROGRESSES - T helper cells decreases, patients become more susceptible to more serious infections; chronic diarrhoea, severe bacterial infections and tuberculosis
LATE STAGES - very low number of T helper cells, suffer from range of serious infections; toxoplasmosis of brain and candidiasis of respiratory system
What is toxoplasmosis of the brain?
A parasite infection
What is candidiasis of the respiratory system?
Fungal infection
Describe how Mycobacterium tuberculosis can infect the body
1) Infection occurs when tiny droplets containing the bacteria are inhaled in the lungs
2) BActeria then taken up by a type of white blood cell called a phagocyte
3) They survive and replicate inside phagocytes
4) Immune system seals off infected phagocytes in tubercles
5) When sealed bacteria become dormant and infected person has no obvious symptoms
6) Later, dormant bacteria may become reactivated and overcome immune system causing TB
7) Reactivation is more likely in those with weakened immune systems
What are the sequence of symptoms in TB?
INITIAL SYMPTOMS - fever, general weakness and severe coughing caused by inflammation of the lungs
PROGRESSES - damage to lungs if left untreated and can cause respiratory failure, can lead to death
Can spread from lungs to other parts of the body (e.g. brain, kidneys), if left untreated lead to organ failure
Describe the specific immune response
1) A T cell is a type of white blood cell, their surface covered in receptors, each T cell has a different shaped recpetor
2) Receptors bind to antigens displayed by antigen-presenting cells such as macrophages
3) When receptor on surface of T cell meets complementary antigen it binds, so each T cell binds to different antigen
4) Activates T cell, it divides to produce clones of itself
5) Can divide into T helper cells, T killer cells and T memory cells
6) B cells are another type of white blood cell which are covered in proteins called antibodies, each B cell has different shaped antibodies
7) Antibodies bind to antigens to form an antigen-antibody complex
8) When antibody on surface of B cell meets a complementary antigen, it binds so each B cell binds to different antigens
9) This with substances from T cell, activates the B cell
10) B cell divides by mitosis into plasma cells (B effector cells) and B memory cells)
11) Plasma cells are clones of B cells which secrete loads of antibodies specific to antigen into blood
12) Antibodies bind to antigens on surface of pathogen to form lots of antigen-antibody complexes
What do T helper cells do?
Release substances to activate B cells, T killer cells and macrophages.
What do T killer cells do?
Attach to antigens on a pathogen infected cell and kill the cell.
How does an antibody bind to an antigen? (6)
1) Antibodies made of 4 polypeptide chains - 2 heavy chains and 2 light chains.
2) Each chain has a variable region and a constant region
3) Variable regions form antigen binding sites - shape of region is complementary to particular antigens, variable regions differ between antibodies
4) Hinge region allows flexibility when antibody binds to antigen
5) Constant regions allow binding to receptors on immune system cells, e.g. phagocytes. Regions same in all antibodies
6) Disulfide bridges hold polypetide chains together.
What are the three ways antibodies help clear infections
Agglutinating pathogens
Neutralising toxins
Preventing pathogen binding to human cells
How does agglutinating pathogens work?
Each antibody has 2 binding sites, so antibody can bind to 2 pathogens at same time - pathogens become clumped together.
Phagocytes then bind to antibodies and phagocytose lots of pathogens at once
How does neutralising toxins work?
Antibodies bind to toxins produced by pathogens.
This prevents toxins affecting human cells so toxins are neutralised.
Toxin-antibody complexes are phagocytosed
How does preventing the pathogen binding to human cells work?
When antibodies bind to antigens on pathogens they block cell surface receptors that pathogens need to bind to host cells.
Pathogens can’t attach to or infect host cells
What 2 forms can antibodies be found in?
Membrane-bound - attached to membrane of B cell
Secreted
How is mRNA modified before translation?
1) During transcription the introns and exons are both copied into mRNA. mRNA strands containing both introns and exons are called pre-mRNA
2) Introns are then removed by a process called splicing - introns removed and exons joined forming mRNA strands. Takes place in nucleus and is a post-transcriptional change
3) Sometimes, certain exons are removed as well as introns to form different mRNA strands. This is called alternative splicing.
4) More than one amino acid sequence and so more than one protein can be produced from one gene
What are antibiotics?
Chemicals that kill or inhibit the growth of microorganisms
What are the different types of antibiotics?
Bacteriocidal - kill
Bacteriostatic - prevent growth
How do antibiotics kill/inhibit bacteria?
Interfere with metabolic reactions:
1) Some inhibit enzymes that are needed to make chemical bonds in bacterial cell walls. Prevents bacteria from growing properly. Leads to cell death as weakened cell can’t take pressure as water moves into cell via osmosis which causes cell to burst - lysis
2) Some inhibit protein production by binding to bacterial ribosomes. All enzymes are proteins so can’t make enzymes. Can’t carry out important metabolic reactions needed for growth and development.
Why don’t antibiotics attack mammalian cells?
Mammalian cells are eukaryotic so don’t have cell walls, have different enzymes and have larger ribosomes
