Topic 6: Immunity, Infection and Forensics

Question 1

6.1) Time of death of a mammal can be determined by looking at…

Answer 1

1) Extent of decomposition
2) Forensic entomology
3) Body Temperature
4) Degree of muscle contraction

Question 2

6.1) How can the extent of decomposition be used to determine the TOD?

Answer 2

Bodies usually follow the same pattern of decay and decomposition:
1) hrs - a few days: Cells and tissues broken down by the body’s own enzymes and bacteria. Skin turns greenish.
2) A few days - a few weeks: Microorganisms decompose tissues and organs. Produces gases which cause the body to become bloated. Skin begins to blister and fall off.
3) A few weeks: Tissues begin to liquify and deep out into the area around the body.
4) A few months - a few years: Only a skeleton remains.
5) Decades to centuries: The skeleton disintegrates until there’s nothing left pf the body.

Factors affecting rate of decomposition: Temp and Oxygen availability (i.e. for microorganisms to respire).

Question 3

6.1) Forensic Entomology

Answer 3

The study of insects to determine the time of death.
TOD can be estimated by identifying:
- The type of insect present on the body (e.g. flies usually appear a few hours after death. Other insects colonise later on).
- The stage of the life cycle the insect is in (e.g. blowfly larvae hatch from eggs about 24 hours after they’re laid). Dif. conditions will affect an insect’s life cycle (i.e. drugs, humidity, O2, and temp).

Question 4

6.1) The Stage of Succession

Answer 4

As the body decays, the species colonising the body change, which can be used to estimate TOD:
1) Immediately after TOD - conditions favourable for bacteria.
2) As bacteria decompose tissues, conditions in dead body become favourable for flies and their larvae.
3) When fly larvae feed on a dead body they make conditions favourable for beetles.
4) As body dried out, flies leave but beetles remain as they can decompose dry tissue.
5) When no tissues remain, conditions are no longer favourable for most organisms.

The SOS depends on the location of the body

Question 5

6.1) How is Body Temperature used to estimate TOD?

Answer 5

Internal body temp is around 37degrees.
The temp of the body begins to decrease after death as heat-producing metabolic reactions stop.
Algor mortis: From the TOD, body temp cools at a rate of around 1.5-2.0 degrees per hour, until it equals the temp of its surroundings.
Conditions such as air temp, clothing, and body weight will affect the cooling rate.

Question 6

6.1) How can the degree of muscle contraction be used to estimate TOD?

Answer 6

Rigor mortis is when the muscles in a dead body start to contract and become stiff
1-6 hours = The onset of rigor mortis
12-36 hours = rigor mortis disappears
Smaller muscles in the head contract first, with larger muscles in the lower body contracting last

Question 7

6.1) Describe the process of Rigor Mortis

Answer 7

1) Muscle cells become deprived of O2
2) Anearobic respiration takes place instead of aerobic respiration causing lactic acid build up in muscles
3) This causes pH of cells to decrease, inhibiting enzymes that produce ATP
4) No ATP means the bonds between myosin and actin in muscle cells become fixed and the body stiffens

Question 8

6.2) Describe the role of micro-organisms in the decomposition of organic matter and the recycling of carbon

Answer 8

Microgorganisms (e.g. bacteria and fungi) secrete enzymes that decompose dead organic matter into small molecules which they can then respire. When microorganisms respire these molecules, methane and CO2 are released - this recycles carbon back into the atmosphere.

Question 9

6.3) How is DNA profiling used for identification and determining genetic relationships between organisms?

Answer 9

1) A DNA sample is obtained (e.g. from blood saliva etc).
2) PCR is used to amplify the DNA
3) Gel electrophoresis is used to seperate the DNA
4) The gel is viewed under a UV light andc can be compared to match identities or determine a genetic relationship.

Question 10

6.4) How can DNA be amplified using the polymerase chain reaction? (PCR)

Answer 10

1) A reaction mixture is set up by mixing the DNA sample, primers, free nucleotides and DNA polymerase.
2) The mixture is then heated to 95 degrees to break the hydrogen bonds between the two DNA strands.
3) The mixture is then cooled to between 50-65 degrees so that the primers (short pieces of DNA that are complementary to the bases at the stat of the fragment you want), can bind to the strands.
4) The reaction mixture is heated to 72 degrees so DNA polymerase can work. DNA polymerase creates a copy of the sample by complemenatry base pairing using the free nucleotides.
5) The cycle can then be repeated many times, giving rise to an amount of DNA sufficient to create a DNA profile.

Question 11

6.3) DNA digestion

Answer 11

• DNA consists of non-coding regions (introns) and coding regiona (exons). This gives rise to genetic variability between organisms. Introns consist of many repeating base sequences known as short-tandem repeats in sections known as satellites.
• In each individual the STR’s at each loci will differ in the number of repeats, therefore each individuals’s satellites will differ in length, resulting in a unique DNA profile.
• After PCR, specific restriction endonucleases are used to cut the DNA into fragments that leave the STR’s intact (they cut either side of the satellites).
• Since satellites differ in length between indivuals, the DNA fragments taken from dif. indoviduals will also differ in size.

Question 12

6.3) Gel electrophoresis

Answer 12

Restriction endonuclease are used to cut DNA into fragment which are then seperated out by gel electrophoresis:
1) The fragments are placed in wells in agerose gels and mixed with a loading dye, which makes the DNA samples visible It is then covered in a buffer solution that conducts electricity.
2) An electrical current is then passed through the gel - DNA fragments are negatively charged, so they move towards the anode (positive electrode) at the far end of the gel.
3) Short DNA fragments move faster and travel further through the gel, so the DNA fragments seperate according to length.
4) Once electrophoresis is complete the gel is stained with ethodium bromide/markers, which bonds to the DNA fragments and flouresces under UV light.
5) The DNA fragments now appear as bands under UV light - this is the DNA profile.
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 (if they are similar but not identical).

Question 13

6.4) Core Practical 14: Use gel electropherosis to seperate DNA fragments of different lenghth

Answer 13

Method:
1) Fragments of DNA are cut with restriction endonuclease enzymes (either side of the satellites/VNTR’s)
2) Agarose gel beds - remove dams/combs to expose wells.
3) Place gel beds into electrophoresis chamber, with the wells closest to the cathode (negative electrode) on the electrophoresis chamber.
4) Add buffer solution to submerge gel bed (buffer solution conducts electricity).
5) Add the same volume of loading dye (ethidium bromide) to each of your fragmented DNA samples - loading dye helps the samples sink to the bottom and makes them easier to see.
6) Load wells with fragmented DNA samples using mechanical pipettes (and changing the pipette head for each sample to avoid cross contamination).
7) Connect cathode and anode (via leads) to a power supply (from negative to positive). DNA is -ve so moves towards annode
8) Switch on power and leave for 45 minutes (or until gel has moved far enough up the gel bed).
9) Fragments of dif. sizes move at dif. speeds, according to mass to ‘bands’ appear.
10) Once the dye has reached the bottem, electricity is turned off and the banding pattern is visualised under UV light.

Control Variables: Set volume of DNA sample to each well, clean mechanical pipette each time, set volume of loading dye.

Hazards, risks, and prevention:
Buffer solution - allergy, ingestion - gloves, googles
Agarose gel - heat when preparing, burns, allergy, ingestion - gloves, googles
DNA sample - ingestion - use mechanical pipettes (not mouth pipettes)
Electrical equipment - Liquid, PAT tested - no loose or exposed wires, avoid/clear up spills

Question 14

6.3) uses of DNA profiling

Answer 14

• To determine genetic relationships in humans (i.e. paternity tests).
• To prevent interbreeding in animals and plants by only breeding the least related individuals.
• To identify people in forensics

Question 15

6.5) Compare the structure of bacteria and viruses

Answer 15

• Viruses are significantly smaller than bacteria.
• Bacteria have a **cell membrane, cell wall and cytoplasm, as well as other organelles such as ribosomes, plasmids, flagellum and pili. Viruses possess no such structures.

Question 16

Viruses

Answer 16

• Viruses are one of the main disease causing pathogens in humans.
• Viruses are non-living structures which consists of nucleic acid (either DNA or RNA) enclosed in a protective protein coat called the capsid, sometimes covered with a lipid layer called the envelope (which is stolen from the cell membrane of a previous host cell).
• Attachment proteins stick out from the edges of the capsid or envelope to allow viruses to cling on to a suitable host cell.
• Some carry proteins inside their capsid
• They require a host to survive

Question 17

Bacteria

Answer 17

Bacteria are single celled prokaryotes, meaning that they have no membrane-bound organelles.
They consist of:
- A Bacterial chromosome - one long, circular, coiled up strand of DNA, which floats free in the cytoplasm.
- Plasmids (small loops of DNA found in some bacteria)
- pili (found in some bacteria, help bacteria stick to other cells and used in gene transfer)
- slime capsule (for protection in some bacteria) and enables prokaryotic cells to attach to surfaces in its environment.
- plasma membrane sometimes contains mesosomes.
- cell wall made of a glycoprotein
- flagellum help with movement in some bacteria
- 70s ribosomes

Question 18

6.II i) What are the four major routes through which pathogens can enter the body?

Answer 18

1) Through cuts in the skin.
2) Through the digestive system via contaminated doos or drink.
3) Through the respiratory system by being inhaled.
4) Through other mucousal surfaces, e.g. the inside of the nose, mouth and genitals.

Question 19

6.II ii) Describe the role of barriers in protecting the body from infections.

Answer 19

Skin
- made of dead cells, which act as a physical barrier.
- Consists of keratin, which strenghtens the barrier.
- Cab secrete antimicorbial fluid (sebum) - acts as a chemical (acidic) defense.
- Contains skin flora.

Stomach acid
- hydrocholric acid and enzymes in the stomach help to kill any bacteria which enters.

Gut and skin flora
- Harmless microorganisms, which cover your skin and intestines. They compete with pathogens for nutrients and space, limiting the number of pathogens living in the gut and on the skin, making it harder for them to infect the body.

Lysozymes
- mucosal surfaces (e.g. eyes, mouth and nose) produce secretions (e.g. tears, saliva and mucus). These secretions all contain an enzyme called lysozyme. Lysozyme kills bacteria by damaging there cell walls, making bacteria burst open (lyse).

Question 20

Define pathogen

Answer 20

A pathogen isany organism that causes disease. E.g. Viruses, bacteria, fungi, and parasites.

Question 21

What are antigens?

Answer 21

Antigens are molecules such as proteins or glycoproteins located on the surface of cells; their role is to indentify a cell as being ‘self’ or ‘non-self’ (foreign). Pathogens have foreign antigens, which activates cells in thre immune system, triggering either the specific or non-specific immune response.

Question 22

6.7) What does the Non-sepcific immune response involve?

Answer 22

begins immediately after a pathogen invades tissues. Is the same for every pathogen and includes:
- Inflamation
- Interferons
- Phagocytosis
- lysozyme action

Question 23

6.7) How does the body respond to cut skin?

Answer 23

If the skin is cut the body responds by clotting the blood to reduce the entry of pathogens:
1) Damaged endothelium (i.e. cut skin), release platelets, which plug the damaged area.
2) plateletes trigger release of thromboplastin which mixes with calcium ions in the blood, converting prothrombin to thrombin.
3) Thrombin catalyses the reaction of fibrinogen (a solule protein) to fibrin (an insoluble protein, whihc forms and mesh and traps RBC’s = a blood clot)

Question 24

6.7) Inflamation

Answer 24

1) Tissue is damged
2) mast cells secrete histamine (a chemical signalling molecule)
3) Histamine stimulates:
- Vasodilation: Increases blood flow to the affected area causing it to feel hot + appear red. Increased temp reduces the ability of pathogens to reproduce.
- Increases permaebility of blood vessel/capillary walls: Allows more fluid to enter the tissues and creates swelling ( an odema). This prevent use of injured area to promote healing. Also allows wbc to move out of blood vessels into infected tissue.
4) Mast cells also release chemicals called cytokines, which attract phagocytes to the damaged tissue in order to carry out phagocystosis of any pathogens present. Some cytokines travel to the hypothalamus, triggering an increases in body temp or fever, which reduces the ability of pathogens to reproduce.

Question 25

6.7) What is a phagocyte?

Answer 25

Phagocytes are a type of white blood cell responsible for removing dead cells and invasive micro-organisms by ingesting/engulfing them.

Question 26

6.7) Describe the process of phagocytosis and lysozyme action

Answer 26

During infection:
1) Chemicals released by pathogens, as well as chemical released by the body cells under attack e.g. histamine, attract phagocytes to the site where pathogens are located.
2) They move towards pathogens and recognize the antigens on the surface of the pathogen as being non-self.
3) The cell surface membrane of a phagocyte extends out around the pathogen engulfing it and trapping the pathogen within a phagocytic vacuole - endocytosis.
Lysozyme Action:
4) Enzymes are released into the phagocytic vacuole when lysosomes fuse with it. These digestive enzymes , which includes lysozyme, digest the pathogen.
Initiation of Specific immune response:
5) After digesting the pathogen, the phagocyte will present the antigens of the pathogen on it’s cell surface membrane, becoming an antigen presenting cell, which initiates the specific immune response.

Question 27

6.7) Describe the function of interferons

Answer 27

• Interferons are anti-viral proteins produce by cells when they are infected by viruses. They prevent viruses from spreading to uninfected cells by:
  1) protein synthesis in viruses, so stopping their replication.
  2) Activating WBC’s involved with the specific immune response to destroy infected cells.
  4) increasing the non-specific immune response e.g.. by promoting inflammation.

Question 28

6.7) Lysozyme action

Answer 28

lysozyme is an enzyme found in secretions such as tears and mucus which kills bacteria cells by damaging their cell wall (causing lysis).

Question 29

6.8) Antibody structure

Answer 29

• Y shaped molecule, consisting of 4 polypeptide chains, two ‘heavy’ chains attached by disulfide bonds to two ‘light’ chains.
• Each polypeptide chain has a constant region (which does not vary within a class of antibody) and a variable region (which are different for each antibody.
• The specific antigen binding site is at the end of the variable region.
• Some antibodies have hinge regions (where the disulfide bonds join the heavy chains), which provide flexibility for binding.

Question 30

6.8) Antigens

Answer 30

markers on the cells surface membrane, which allow for cell-to-cell recognition. They are usually glycoproteins and can be ‘self’ (produced by the body) to ‘non-self’ (not produced by the organism’s own body).

Question 31

6.8) Antibody function

Answer 31

• can bind to receptors on host cells to prevent pathogens for infecting them.
• Can act as anti-toxins by binding to toxins produced by pathogens and neutralizing them.
• Can cause agglutination , where pathogens clump together to prevent them from spreading and allow macrophages to engulf many pathogens at one time.

Question 32

The specific immune response

Answer 32

is antigen specific and produces responses specific to one type o0f pathogen only. Relies on lymphocytes (B cells and T cells) produced in the bone marrow.

Question 33

6.9) B cells

Answer 33

Mature in the bone marrow and are involved in the humoral response. They have specific antibody receptors on their cell surface membrane and each B cell can bind to a different type of antigen.
Once activated B cells can differentiate into:
a) B effector cells, which go on to form plasma cells. Plasma cells produce specific antibodies to combat non-self antigens.
b) B memory cells Remain in the blood to allow a faster immune response to the same pathogen in future.

Question 34

6.8) Plasma cells

Answer 34

Plasma cells are differentiated B-lymphocyte white blood cells capable of secreting immunoglobulin or antibodies.

Question 35

6.9) T cells

Answer 35

produced in the bone marrow and then move to the thymus where they mature (produce T cell receptors). They are involved in both the humoral and the cell-mediated response.
Once activated T cells can divide and differentiate into three main types:
- T helper cells: Release chemical signaling molecules that help activate B cells.
- T killer cells: Bind to and destroy infected cells displaying the specific antigen.
- T memory cells: Remain in the blood and enable a faster specific immune response if the same pathogen is encountered again in future.

Question 36

T helper activation

Answer 36

• Pathogen is engulfed by a macrophage. Antigens are displayed on the surface of the macrophage on MHCs. The macrophage acts as an antigen presenting cell (APC) and is now a CD4 macrophage
• CD4 Macrophage binds to T helper cell with complementary receptor proteins.
• Cytokines are released by the CD4 macrophage, which activates the T helper cell.
• The T helper cell then divides by mitosis, to form T memory cells and active T helper cells. T helper cells release interferons.

Question 37

Humoral Response

Answer 37

Stage 2: Effector stage
- B cells with a complementary receptor bind to antigens on the pathogen, itself becoming an APC.
- An activated T helper cell (from the previous stage) with a matching CD4 protein to the antigens bind to the B cell APC. It produces cytokines.
- Cytokines stimulate B cells to divide by mitosis and from B memory cells and B effector cells.
- B effector cells differentiate into plasma cells, which synthesize antibodies.
- Antibodies destroy the pathogen by: agglutination, lysis, opsonization (coating pathogens and marking them for phagocytosis), precipitation (soluble toxins are made insoluble), and neutralization (of harmful toxins).

T suppressor cells stop the immune response.

Question 38

Cell Mediated response

Answer 38

When the pathogen invades a host cell (i.e a virus):
1. The host cell displays the antigens on its MHCand becomes an antigen presenting cell.
2. an active T helper cell with complementary receptor proteins bind to the APC.
3. Cytokines secreted by active T helper cell activate and stimulate the T killer cell to divide by mitosis.
4. T killer cell divides to form active T killer cells and T memory cells (which remain in the body to provide immunity).
5. Active T killer cells bind to APCs and secret chemicals (perforin) which cause pores to form in the cell membrane.
6. The infected cell lyses and dies.

Question 39

6.11) What are the different ways of developing immunity?

Answer 39

Natural active immunity: An individual develops a disease, and the immune system makes antibodies and memory cells.
Natural passive immunity: A mother passes on antibodies to a baby (e.g. through the placenta).
Artificial Active immunity: Is aquired through a vaccination (i.e. and inactive pathogen), which stimulates the immune system and leads to production of antibodies.
Passive artificial immunity: Is where antibodies (i.e. from another animal) are injected into the body.

Question 40

6.11) Herd immunity

Answer 40

Herd immunity is when enough people have been vaccinated to make transmission of a disease very unlikely. Requires 80-90% vaccination.

Question 41

6.11) Immunisation

Answer 41

Immunisation is the process of protecting people from infection with passive or active artificial immunity via vaccination.

Question 42

6.11) Define Vaccination and explain how it induces immunity.

Answer 42

Vaccination is the process by which immunisation is achieved. Vaccines may introduce live but weakened straiins of a pathogen (attenuated antigens) or a pathogen/toxin that has been inactivated/killed.

Vaccination is a method of inducing immunity, by prompting a secondary immune response. The first infection results in the production of memory cells, this is the primary respoonse. Memory cells can remain in the blood for a long time and provide protection upon re-infection, this is the secondary immune response. As a result, the production of antibodies occurs faster and in greater number, as the lag time to produce active lymphocytes in reduced.

Question 43

6.6) Describe the process of transmission and infection of Mycrobacterium tuberculosis

Answer 43

1) Infected ppl cough/sneeze and the mt enters the air in droplets of liquid released from the lungs.
2) Uninfected ppl inhale these droplets, which enter the lungs.
3) Inside the lungs, TB Bacteria are engulfed by phagocytes.
4) Primary infection: bacteria survive and reproduce inside the phagocytes.
5) Immune system often seals the infected phagocytes in tubercles in the lungs, where the bacteria remain dormant.
6) Active phase: Dormant bacteria may become activated and overpower the immune system at a later stage.

Question 44

6.6) Describe the symptoms of tuberculosis

Answer 44

Initial symptoms: coughing, fever, fatigue, lung inflammation
Untreated: extensive lung damage, respiratory failure, can spread to other body parts causing organ failure, death

Question 45

6.6) Why is tuberculosis difficult to treat with antibiotics?

Answer 45

Mycobacterium tuberculosis has a waxy cell wall, which has low permeability for many antimicrobial drugs, making it difficult to treat.

Question 46

6.6) Describe how HIV infects cells and the consequences of infection

Answer 46

HIV is a retrovirus transmitted via bodily fluids (sexual intercourse, mother to child via placenta or breast milk, blood)

Infection:
1) HIV enters bloodstream and infects CD4 T helper cells (by attaching to a receptor).
2) The capsid enter via endocytosis and releases the RNA it contains.
3) The viralRNA is used as a template for reverse transcriptase enzymes to produce a complementary strand of DNA.
4) The DNA molecule can now be inserted/incoperated into the host DNA via Integrase
5) From here it uses the host cell’s enzymes to produce more viral components, which assemble and form new virsuses.
6) New viruses leave the host cell vias exocytosis and enter the blood, where they can infect other T helper cells and repeat the process.
7) This stage is called the active HIV syndrome stage and the individual may expereince flu-like symptoms.
8) This develops to asymptomatic or chronic stage where replication rates drops and the individual shows no symptoms (often for yrs).
9) Gradually the virus reduces the n.o. of T helper cells and therefore activated B helper cells and antibodies decrease. The Symptomatic disease stage begins and individual suffers from HIV related symptoms.
10) This progresses to aids when the T help cell drops bellow criticial level (resulting in less antibodies and phagocytosis) so the individual begins suffering from opportunistic infections which gradually become more serious)

Question 47

Give two differences between the genetic material of bacteria and viruses

Answer 47

1. Bacteria have DNA, viruses have DNA or RNA
2. Bacteria have circular genetic material, Viruses have linear/straight genetic material
3. Bacterial DNA is double stranded, viral (DNA/RNA) is single (or double stranded)
4. Bacteria may have plasmids, viruses do not have plasmids

Question 48

How to work out Time of deah using a henssge monogram

Answer 48

Step 1: Draw a straight line between the core temp of body and the ambient temp (= line 1).
Step 2: Draw a straight line that extends from the centre of the circle through the diagonal line, at the point where it crosses line 1 (= line 2).
Step 3: Read the time of death from the monogram at the point line 2 crosses the appropraite semircircle for the mass of the body.

Question 49

6.13) What is meant by ‘evolutionary race’?

Answer 49

The battle between host and pathogens in known as evolutionary race; each organism develops new ways in which to have an advantage over the other.
(Over time, vertebrates have evolved better immune systems, however pathogens have also evolved better ways to evade/avoid the immune systems of their hosts)

Question 50

6.4) How does HIV and Mycobacterium tuberculosis provide evidence for the theory of ‘evolutionary race’?

Answer 50

The development of evasion mechanisms:

HIV’s evasion mechanisms:
- The virus kills helper T cells, which reduces the number of cells that can detect the presence of the virus and activate the production of atibodies.
- HIV shows antigenic variability due to the high mutation rate in the genes coding for antigen proteins. This forms new strains, which will not be recognised by memory cells for other strains. The immune system has to produce a primary response for each new strain.
- HIv disrupts antigen presentation in infected cells. This prevents the immune system cells from recognising and killing the infected cells.

Mycobacterium tuberculosis evasion mechanism:
- Once inside pagocytes they produce substances that prevent the lysosomes fusing with the phagocytic vacuole. This means that the bacteria aren’t broken down and they can multiply undetected inside phagocytes.
- Disrupts antigent presentation in infected cells, which pevents the immune system cells from recognising and killing the infected phagocytes.

Question 51

6.14) How do antibiotics treat infections? Describe the two different types of antibiotics.

Answer 51

Antibiotics fight infections by killing the bacteria and stopping their growth. They are selectively toxic(the chemicals produced match the surface proteins of certain bacteria and kill only them). They can work in various ways: destroying cell wall cross links or perforating the cell membrane, causing lysis, Inhibiting protein synthesis by stopping translation of proteins, causing death, uncoiling bacterial DNA so that is no longer fits into the bacterial cell and the cell dies.

There are two types:
- Bactericidal antibiotics: Kill bacteria by destroying their cell wall, thus causing them to burst (lysis).
- Bacteriostatic antibiotics: Inhibit the growth of bacteria by stopping protein synthesis and production of nucleic acids so the bacteria can’t divide and grow.

Question 52

Describe the formation of antibiotic resistant bacteria

Answer 52

Some bacteria become resistant to antibiotics as a result of natural selection:
- Bacteria multiply in the body and few will mutate creating genetic varaition. Some mutations make the bacterium drug resistant.
- With the presence of an antibiotic, Bacteria are expsoed to an environmental change and the antibiotic becomes a selection pressure.
- The bacteria which are are not killed by the antibiotic possess a selective advantage - resistance which enables them to survive and reproduce.
- Therefore the allele for antibiotic resistance is passed on to their offspring thus creating an antibiotic resistant strain.

Question 53

6.15) What are the contributory causes of hospital aquired infections (HAIs) and how to hospitals control them?

Answer 53

Contributory causes:
- Hospital staff + visitors not washing their hands before and after visiting patient.
- Coughs and sneezes not being contained e.g. in a tissue
- Equipment and surfaces not being disifencted after use.
People are more likely to catch HIAs in hospitals because many patients are ill, so have weakended ammune system and they’re aound other ill people. Antibiotic resistant bacteria e.g MRSA are also more common in hospitals because more anitbiotics are used there, so bacteria are more likely to evolve resistance against them.

Codes of Practice to prevent and control transmisson of HAIs:
- Staff and visitors should wash hands before and after being with patient.
- Equipment and surfaced disinfected after use.
- Isolation wards for patients with HAIs.
- Control famites - bare below the elbow, clean bed linen, towels etc.

Codes of practice to prevent HAIs caused by antibiotic resistant bacteria:
- Doctors shouldn’t perscribe antibiotics for minor infections.
- Doctors should use narrow spectrum antibiotics if possible
- Doctors should rotate the use of different antibiotics
- Patients should be encouraged to take the full course of antibiotics.
- Professional and public education

Question 54

What is the difference between broad spectrum and narrow specturm antibiotics?

Answer 54

Broad spectrum antibiotics: Kill lots of different types of bacteria. Good if you don’t know what you’re treating (they get ride of ‘non-specific’ infections.). Bad because they kill beneficial bacterial too, and encourage more resistance.
Narrow-spectrum antibiotics: Are species specific. They are good if you know what you are treating and less bacteria is exposed so less general resistance. Reduce secondary infections. Bad because idenitfying the bacteria requires time and money.

Question 55

Explain why antibiotics do not damage eukaryotic cells or viral cells

Answer 55

Eukaryotics cells will not be damaged by anitbitotics because they do not have cell walls, they have different enzymes and different ribosomes.
Viruses also do not have cellular structure such as enzymes, ribosomes, and cell walls so they are not affected by antibiotics.

Question 56

How can the potential of antibiotic resistance be reduced?

Answer 56

• Take the full course of antibiotics to make sure the highest possible number of bacteria are killed.
• Correct dose
• Only prescribe when certain that the immune system by itself can’t deal with the infection, or the infection is going to cause too much harm.

Question 57

Antibodies are either bound to the membrane of WBC’s or are secreted directly into the blood. Some heavy chains of antibodies contain an extra section, which allows it to bind to the surface of a WBC. Explain how one gene can give rise to more than one protein.

Answer 57

RNA splicing is a post transcription modification of mRNA, which enables eukaryotes to produce more proteins than they have genes. RNA splicing enables more than one protein to be producede from one gene:
1) A gene is transcribed which results in pre-mRNA (the transcript of the whole gene).
2) All introns (non-coding regions) are removed. Sometimes, some exons (coding regions) are also removed - this is called alternative splicing.
3) The remaining genes are joined back up by enzyme complexes called spliceosomes. The same exons can be joined in a variety of ways to produce several different versions of mature functional DNA, which then leaves the nucleas to be translated into a polypepetide chain.

This process determines whether or not the extra section of protein is present in the heavy chain of an antibody.

Question 58

CORE PRACTICAL 15: Investigate the effect of different antibiotics on bacteria

Answer 58

IV: Type of antibiotics (e.g. P5, P10, S25)
DV: Zone of Inhibition around the antibiotic disc (mm^2)
CV’s: Control condition: Paper disk soaked in water, temperature, size of disc, volume and concentrations of antibiotics, time left to grow etc

Method:
1. Use aseptic techniques throughout.
2. Flame forceps and pick up paper disc.
3. Slighlty lift the lid of the petri dish and place the paper disc onto agar.
4. tape the dish with 2 pieces of sellotape (don’t tape all the way around to avoid conditions becoming anoxic).
5. Wash hands and disinfect bench.
6) Incubate for 24hrs at approx 25dc - to reduce the risk of growing harmful pathogens. Human pathogens thrive at body temp (37dc).
7) Measure the radius of the clear zone on the agar plats. Calc. area/zone of inhibition.
8) Repeats: collect 3 sets of data for each antibiotic calc. mean zone of inhibition (mm^2).

Graph: Plot a bar graphof type of antibiotic against mean zone of inhibition (mm^2).

Conclusion:
The area of Zone of inhibition will be more effective when the anitbiodtics are more effective against the type of bacteria being grown. How effective an antibiotic is depends on whether the bacteria is gram positive or gram negative, and what type of antibiotics is being used.

Risk Assessment:
Hazard = Disinfectent, Risk = flammable, precaution = keep away from naked fame
Hazard = Naked flame, Risk = Fire and burns, Precaution = tie up long hair, distance from flammable materials
Biohazard, Risk = Contamination, Precaution = Use aseptic techniques, wash hands, wear eye protection

Question 59

What aseptic techniques would you use when investigating the effect of different antibiotics on bacteria and why?

Answer 59

Aseptic techniques are used to avoid contamination, which is important for reliable, repeatable data and safety.
- Wipe surfaces with antibacterial cleaner before and after experiment.
- Use a bunser burner in the wirk space so that convection currents draw microbes away from the culture.
- Flame forceps before and after transferring discs - heat kills the bacteria.
- Open agar lid for minimum amount of time
- Steralise equipment (using autoclave) before and after.

Question 60

Why is bacteria culuture incubated at 25dc?

Answer 60

To reduce the risk of growing harmful pathogens. Human pathogens thrive at body temp (35dc).