infection, immunity and forensics

Question 1

How are molecules such as carbon dioxide and methane produced during decomposition?

Answer 1

• when plants/animals die, microorganisms on them secrete enzymes that decompose organic matter into small molecules
• when the microorganisms respire, they produce these molecules

Question 2

state the ways in which time of death can be estimated?

Answer 2

• body temp
• degree of muscle contraction
• forensic entomology
• extent of decomposition
• stage of succession

Question 3

Outline the procedure for PCR

Answer 3

• DNA sample, free nucleotides, primers and DNA polymerase heated to 95 degrees to break open the DNA
• the mixture is cooled to 50 degrees to allow primers to bind
• heated to 72 degrees to allow DNA polymerase to link free DNA nucleotides with the template strand

Question 4

outline the procedure for gel eletrophoresis

Answer 4

• DNA is placed into a well of an agarose tank, and covered w buffer
• electric current is passed through- DNA move towards anode
• fragments separate according to length

Question 5

name two of HIV’s evasion mechanisms

Answer 5

any of:

• kills immune system cells it infects
• high rate of mutation (antigenic variation) -> new primary response every time
• disrupts antigen presentation

Question 6

name two of TB’s evasion mechanisms

Answer 6

• produces substances which prevent the lysosome fusing with the phagocytic vacuole
• disrupts antigen presentation

Question 7

describe how antibiotics work to inhibit bacterial metabolism

Answer 7

• inhibit enzymes which are needed to make chemical bonds in cell walls -> cell bursts due to increased pressure from osmosis
• binds to bacterial ribosomes, inhibiting protein production (cant make enzymes)

Question 8

briefly describe aseptic technique

Answer 8

• regularly disinfect surfaces
• work near bunsen burner
• sterilising wire inoculation loop by passing through flame before and after use

Question 9

identify two methods of reducing the frequency of HAIs:

Answer 9

• hospital staff encouraged to wash hands

- people with HAIs moved to isolation ward

Question 10

explain how the stage of succession on a body is changed with time

Answer 10

• immediately after death, conditions favourable for bacteria
• bacteria decompose tissues, conditions become favourable for flies
• etc.
• eventually, no tissues remain and conditions are not favourable for any organisms

Question 11

why does rigor mortis occur?

Answer 11

• muscle cells deprived of O2 -> anaerobic respiration produced lactic acid
• conditions become more acidic, inhibits enzymes which produce ATP
• bonds between myosin and actin are fixed

Question 12

what is the constant region of antibodies responsible for?

Answer 12

binding to receptor sites on the immune system cells

Question 13

list 3 ways in which antibodies protect the body from pathogens

Answer 13

• agglunating pathogens
• preventing pathogens from binding to human cells
• neutralising toxins

Question 14

what is meant by ‘agglunating pathogens’?

Answer 14

each antibody has two binding sites, this means an antibody can bind to two pathogens at once.
-pathogens get clumped together and destroyed

Question 15

what is the difference between excreted and membrane bound antibodies?

Answer 15

-membrane bound antibodies contain an extra section of protein that anchors it into the B cell

Question 16

what is splicing?

Answer 16

a post transcriptional change in which introns are removed from pre-mRNA

Question 17

what is alternative splicing? How does it give rise to multiple proteins from the same gene?

Answer 17

• exons (coding blocks) are removed instead of introns
• this means the base sequence of the mRNA is different
• and the structure of produced protein is modified

Question 18

what does the primary response refer to?

Answer 18

when the body is exposed to pathogens, activating the specific and non-specific responses

Question 19

why is the secondary immune response quicker?

Answer 19

T + B memory cells produced in the primary response can quickly divide into T killer cells and correct plasma cells, secreting antibodies

Question 20

what is the difference between active immunity and passive immunity?

Answer 20

• active immunity takes a while to develop and is long lasting
• whereas passive immunity is immediate and short-term

Question 21

what is meant by the ‘evolutionary race’ between pathogens and their hosts?

Answer 21

• hosts evolve to have better immune systems

- pathogens evolve to have better evasion mechanisms

Question 22

what is antigenic variation?

Answer 22

when genes that code for antigen proteins are mutated, changing the structure of the antigens, so they are not recognised by the body