10. INFECTIOUS DISEASES Flashcards
Drugs used for the treatment of tuberculosis
Isoniazid
Rifampcin (transcription inhibitor)
Streptomycin
–
The antimicrobial drug that is synthetic and made in a laboratory
Isoniazid
Ways in which antibiotics interfere with some aspect of growth or cell metabolism
PrESSS
- activity of proteins in cell surface membrane
- enzyme activity
- synthesis of bacterial cell walls
- synthesis of DNA
- protein synthesis
Mode of action of penicillin
cell wall synthesis inhibitor
- prevents the synthesis of cross-links between the peptidoglycan polymers in the cell wall of bacteria
- by inhibiting the enzymes that build these cross-links
- it is only active against bacteria while they are growing
Antibiotics that are cell-wall inhibitors and what they do
PVC Penicillin Cephalosporin Vancomycin --> inhibit the enzymes that build cell wall cross-links
The enzyme secreted by growing bacterial cells that creates holes in the cell wall and mode of action of penicillin
autolysin
- -> makes little holes in the cell wall
- -> holes allow the wall to stretch so new peptidoglycan chains can link together
- -> penicillin prevents the peptidoglycan chains from linking together, but autolysin keeps making new holes
- -> cell wall becomes weaker and cannot withstand the high pressure of water in outside environment
- -> water enters cell by osmosis and cell bursts
Mode of action of quinonine
interferes with DNA replication
Why do antibiotics not act on viruses
- viruses don’t grow
- viruses do not possess the structures that antibiotics affect
- viruses don’t have cell walls or cells
- viruses replicate by using host cell’s mechanisms for transcription and translation and antibiotics to do not bind to the proteins that host cells use
A drug that is not sensitive to Mycobacterium tuberculosis and why
Penicillin
- Mycobacterium has a thick cell wall that is not very permeable
- contains a gene that codes for a protein that catalyses the breakdown of penicillin
Reasons antibiotics are not sensitive to bacteria
- contains gene that codes for a protein that catalyses the breakdown of antibiotic
- contains proteins in membrane that inactivate antibiotic so it has no effect
- contains proteins that pump out antibiotics if they enter the cytoplasm
- antibiotic cannot bind to intended site of action
What enzyme can penicillin be broken down by
Beta-lactamase
When does antibiotic resistance arise
antibiotic resistance arises when an existing gene within the bacterial genome changes spontaneously to give rise to a nucleotide sequence that codes for a slightly different protein that is not affected by the antibiotic. a mutation
Why do bacteria gain resistance to antibiotics easily
- have only one copy of each gene since they have only a single loop of double-stranded DNA
- a mutant gene will have an immediate effect on any bacterium possessing it
- bacteria divide by binary fission so each daughter cell is also resistant
Vertical transmission of bacterial resistance
- bacterial chromosome and plasmid replicate
- resistant parent cell divides into two by binary fission
- daughter cells each receive a copy of the plasmid and are resistant
Horizontal transmission of bacterial resistance
- happens during conjugation when a tube forms between two bacteria (can be of different species)
- a single DNA strand of the plasmid is transferred
- each bacterium then synthesises a complementary strand
- both cells are now resistant
Consequences of multiple resistance of bacteria for health authorities
1 risk of, further spread / wider epidemic, (from people still infected)
2 reduces chance of succesful treatment / higher death rates
3 increased, treatment / hospitalisation times, takes longer to treat, a more complex treatment
4 increased costs of treatment / strain on health budget
5 risk of, further resistance / resistance to all antibiotics
6 fewer antibiotics left that are effective
7 need to find, new antibiotics / alternative treatment
8 (so) cost of research
How can antibiotics be chosen carefully
- by testing antibiotics against the strain of bacterium isolated from people
- ensures the most effective antibiotic can be used in treatment
What is an antitoxin
- preparation of human antibodies
- collected from blood donors who have recently been vaccinated with a particular vaccine
- provides immediate protection but is only temporary
Why are antitoxins temporary
- they are not produced by the body’s own B cells
- are therefore regarded as foreign themselves
- removed from the circulation by phagocytes in the liver and spleen
Ways in which HIV is transmitted
- sexual intercourse
- infected blood transfusions
- sharing contaminated hypodermic needles
- across placenta from mother to foetus
- through breast milk
Problems involved in controlling the spread of HIV
- no cure or vaccine (because the virus changes it surface proteins)
- drugs are expensive
- people can be symptomless carriers and pass on the disease (due to HIV’s long latent stage)
- testing people for HIV is considered an infringement of personal freedom
- problems with educating about risks in poor countries
- providing condoms and raising awareness is expensive
- contact tracing can be expensive and difficult
- blood is not screened or treated to kill HIV in poor countries
What is the function of reverse transcriptase
uses the RNA as a template to produce DNA once the virus is inside a host cell
What are the two glycoproteins on the outer envelope of HIV
gp 120
gp 41
What is a retrovirus
A type of RNA virus that inserts a copy of its genome into the DNA of a host cell that it invades, thus changing the genome of that cell
