Practical MCQ Flashcards
who is the disease gout associated with
the disease of the kings because gout was experienced by people who were wealthy
what causes the turnover of DNA and RNA? and why is it important?
endonucleases turnover RNA and DNA molecules. this is important people, in DNA repair of double strands break, you need the cleaning of the double-strand break before the DNA can be repaired.
where are endonucleases prepared
on oligonucleotides
what do phosphodiesters give?
they give bases with the sugar units still attached.
what can be phosphorylated to nucleoside triphosphates
free bases
what can be done with nucleoside triphosphate
they can be reused
what are the 2 different pathways of nucleotide catabolism
1- re-usage of bases
this is the energy-efficient pathway
2- degradation
this pathway is taken when necessary
there is usually a balance between the 2 pathways
in the pathway of purine degradation, what does adenosine deaminase do?
it is an enzyme deaminating adenosine into inosine
in the pathway of purine degradation, what does guanine deaminase do?
it is an enzyme deaminating guanine into xanthine
in the pathway of purine degradation, what does xanthine oxidase do?
it changes hypoxanthine into xanthine
what does xanthine oxidase produce?
it produces uric acid from xanthine.
uric acid is either excreted by urine or reabsorbed by the kidneys.
in the practical, we looked at uric acid production by the enzyme xanthine oxidase
in the pathway of purine degradation, what has double-ring structure
- adenosine
- guanosine
in the pathway of purine degradation, what are the bases
- hypoxanthine
- xanthine
- guanine
what is associated with hyperuricaemia
uric acid is associated with hyperuricaemia.
uric acid is the end product of purine degradation
what is the normal amount of serum urate and whats the high amount of serum urate
Normal amount is 4.5 +/- 1.2 mg/dl in males
the high amount is exceeding 7 mg/dl
what is hyperuricaemia associated with
- impaired uric acid excretion
- secondary hyperuricaemia
what happens when there is a high concentration of urate in the bloodstream
urate salts precipitate
what happens due to crystals of urate salt in the joints
it may precipitate gout.
this leads to polyarthritis and nephropathy (problems with the kidneys)
how do urate salts look like
quite pointy, they look like needle-shaped crystals
what happens when urate salts precipitate
-when urate salts precipitate, they attract macrophages because they are in places they shouldn’t be
- the macrophages absorb/eat they crystals
- these crystals stimulate an inflammatory reaction. this is because when the macrophages eat the crystals, they call for help by releasing cytokines.
- these cytokines induce more inflammatory cells to differentiate
- they start the destruction of the underlying bone tissue and cause inflammation in the joint capsule.
middle age men have more incidents of gout
what is the treatment for gout
-dietary
they look at the diet, advice the patients how to improve their diet, especially reduction of purine-rich foods.
- xanthine oxidase inhibitors
because xanthine oxidase is the enzyme producing uric acid
what is incorporated into cellular nucleic acids in a small percentage
only small percentage of ingested nucleic acids is incorporated into cellular nucleic acids
what is dietary purines generally converted into and by what
dietary purines are usually converted to uric acid by intestinal mucosal cells
what happens to most of the uric acid that is produced
it enters the blood and is eventually excreted in the urine
what happens if we eat food that is rich in purine, like eggs and meat
then there will be a subsequent increase of uric acid in the circulation
how are attacks of gout described/compared to
- the agony of childbirth
- its like being jabbed with a ‘million tiny white-hot needles’
what food items increase the chance of gout attacks
- meat, because it contains a lot of cells including DNA and RNA
- alcohol, alcohol leads to dehydration, if you are dehydrated then you will have higher precipitation of uric acid and its also leads to a gout attack.
which 5 disease’s is hyperuricemia a risk factor to
- Atherosclerosis
- Hypertension
- cardiovascular diseases
- chronic kidney disease
- stoke
what are the 2 forms of hyperuricaemia?
- primary
- secondary
what is primary hyperuricaemia caused by
it is caused by either:
- overproduction of uric acid
- impairment of renal secretion
what is secondary hyperuricaemia caused by and with example
it is caused by underlying diseases, mostly diseases with increased cell turnover, e.g. psoriasis, and malignancies.
Example
tumour lysis syndrome, this is when chemotherapy is initiated and there is a lot of tumour cell death. these cells will then release their internal contents into the bloodstream. then this leads to an increase in uric acid.
what % of patients with gout are overproducers or have impaired renal uric acid secretion
15-25% are overproducers
75-85% of patients have impaired renal uric acid secretion
what happens in the kidneys with uric acid
uric acid is first reabsorbed before actively secreted in the tubular system
what leads to the formation of kidney stone
both a decrease in reabsorption and an increase in secretion
what is urate pool dependent on, and how is it balanced
urate pool is dependent on:
- dietary purine intake
- tissue nucleic acids
- endogenous purine synthesis
how is the urate pool balanced by:
- gut excretion
- renal excretion
what leads to hyperuricaemia in uric acid metabolism
overproduction of urate pool
underexcretion of urate pool
if the production of the urate pool is broken, which leads to overproduction or underexcretion then it leads to hyperuricaemia
what can hyperuricaemia cause
it can be asymptomatic
it can cause acute gout attack or chronic tophaceous gout
the main problem it can cause is renal manifestations
what are the 3 main benefits of uric acid
- uric acid is an important factor in lengthening primate lifespans as it protects against reactive oxygen species
- antioxidants are compounds such as vitamins A, C and E, uric acid is thought to be another antioxidant.
- urate microcrystals are immunostimulatory
uric acid was shown to be a principal endogenous danger signal released from injured cells. eliminating uric acid in vivo inhibits the immune response to antigens associated with injured cells except for antigens presented by activated dendritic (antigen-presenting) cells.
where is xanthine oxidase present in large amounts
- liver
- intestinal mucosa
- milk
what are the 2 forms of xanthine enzyme
- xanthine dehydrogenase (XD)
uses NAD+ as an electron acceptor
predominant in normal tissue - xanthine oxidase (XO)
it is the proteolytically processed form
uses O2 (oxygen) as an electron acceptor
what does the xanthine enzyme process
the enzyme processes
- FAD
- nonheme Fe-S centers
- molybdenum cofactor as electron transferring group, from MO4 to MO6
what does xanthine oxidase catalyse hypoxanthine and xanthine to and what is the byproduct
xanthine oxidase catalyses hypoxanthine into xanthine
it then catalyses xanthine into uric acid. it produces O2- as byproduct, which is reduced by NAD+ (XD)
what happens to O2- than is produced by xanthine oxidase
O2- is detoxified by superoxide dismutase and catalase/ glutathione peroxidase
what is allopurinol and what does it do
allopurinol is an inhibitor of xanthine oxidase
it inhibits xanthine oxidase because it remains tightly bound to the active site of the enzyme
other than allopurinol, what is another inhibitor of xanthine oxidase
Febuxostat is a non-purine-selective, non-competitive inhibitor of xanthine oxidase
what is reperfusion injury
it is tissue and cellular damage that occurs when inadequate blood is supplied to a region of the body, followed by the resumption of blood flow
what does inadequate perfusion lead to
it leads to a lack of oxygen, depletion of high energy molecules (e.g. ATP) and build-up of toxic metabolites
what is the consequence of reduced blood supply
reduce blood flow leads to the conversion of xanthine dehydrogenase to xanthine oxidase because of the increase of calcium that activates protease. this results in the production of O2- instead of NADH which leads to reperfusion.
what happens with the onset of reperfusion
with the onset of reperfusion, there is an increase in reactive oxygen species (ROS)
in reperfusion injury of the heart, what is it called when there is no later blood flow and what is the infarct size
myocardial ischemia in absence of reperfusion
infarct size - 70%
what is myocardial ischemia with reperfusion
it means there is reperfusion, which can be because of a stent or drugs which dissolve the block. this leads to a reduction in the infarct size by 40% but this has a 30% of infarct size because of lethal reperfusion injury which is preventable
what is myocardial ischemia with reperfusion and cardioprotection
it inhibits the release of the reactive oxygen species, which then lowers the infarct size.
the amount of damaged tissue is much lower, there is a further decrease of 25% with cardioprotective as it inhibits the increase in reactive oxygen species when there is reperfusion.
what are 2 buffers used in the practical
- hypoxanthine
- xanthine
how did we look at the release of oxygen reactive species in the practical
we looked at the release of oxygen reactive species when hypoxanthine is catalysed to xanthine
what did we measure in the practical
we measured the appearance of 02- (oxygen reactive species) and the appearance of uric acid.
uric acid can be measured by itself but 02- can’t be measured by itself thus you need to add cytochrome C to measure 02-
in the practical, what did we measure at 550nm and 300nm
at 550nm, we looked at what was happening to cytochrome C to see the appearance of 02-
at 300nm, we measured the appearance of uric acid
what does allopurinol do in purine degradation
why do you add superoxide dismutase in purine degradation
you add allopurinol as it is an inhibitor of xanthine oxidase
you also add superoxide dismutase as it is an important enzyme in the detoxification of reactive oxygen species (ROS). superoxide dismutase with catalase gets rid of 02-
in the practical, how do we measure cytochrome C
there is a colour change after 3 mins from the starting material to the end product after the enzyme has done its duty.
we measure the colour change using a spectrophotometer for 3 minutes.
what is the overview of the practical and how should the results/graph look like in the 2nd experiment
we have 2 buffers:
- xanthine
- hypoxanthine
in the practical, to both xanthine and hypoxanthine, you add superoxidase dismutase (SOD) and allopurinol.
in the 2n experiment,
when there is no inhibitor added (which is experiment 1,4 and the first mins of all the other experiments), then the line in the graph should be linear and rising.
when the inhibitor is added, then you should see a flat line because the enzyme is no longer able to convert.
