Practicals and Tutorials Flashcards
What is the structure of acyclovir?
Similar structure to deoxyguanosine but it does not have a 3’ -OH group
Why is acyclovir useful?
It has selective toxicity.
Acyclovir is activated by thymidine kinase which is only present in viruses.
Acyclo-GTP has a higher affinity for viral DNA polymerase than host cell polymerase so it only gets incorporated into viral DNA.
The lack of 3’ -OH group means that it halts production of viral DNA when it’s incorporated.
What are the isoenzymes of creatine kinase?
Creatine kinase is a dimer which is coded for by 2 different genes.
BB - Brain
MM - Skeletal muscle
MB - Myocardium
What causes creatine kinase to be found in the blood?
Cell membrane damage causes leakage - lack of ATP means active transport protein stops working so intracellular substances leak out.
How is creatine kinase activity detected?
Coupled assays are used to detect NADPH which is far more easily detected than creatine or creatine kinase.
NADPH is detectable by UV light.
How are the creatine kinase isoenzymes separated?
By electrophoresis.
SDS-PAGE gives the proteins uniform charge and separates them by mass.
ISOELECTRIC FOCUSSING makes the enzymes move across the gel to their isoelectric points.
How is myocardial damage diagnosed?
MB creatine kinase isoenzyme (elevated serum levels are directly proportional to the size of myocardial damage, 30 mins to 2.5 days).
Troponin I and T (specific to cardiac muscle, appear after 48 hours to 5 days).
Lactate dehydrogenase (not particularly specific and only peaks after 6 days).
Serum Glutamate Oxaloacetate Transaminase (peaks as CK goes down).
Why can DNOC and DNP pass through the inner mitochondrial membrane?
Undissociated DNOC and DNP are aromatic weak acids so they can easily pass through the phospholipid bilayer membrane and accept/donate H+
Why does DNOC cause an increase in respiratory rate?
Decrease in ATP synthesis results in the body trying to deliver more oxygen to the respiring cells so there’s a higher breathing rate.
Post mortem findings in the metabolic poisons tutorial
Absence of body fats - fatty acids and glycerols stored in adipose tissue are used in respiration.
Red marrow - excessive O2 consumption accompanying fat metabolism leads to tissue hypoxia so the body overcomes this by increasing ventilation and erythropoiesis in the bone marrow.
Rigor mortis - lack of ATP caused by DNOC means that the muscle is left contracted because ATP is required to displace ADP to relax muscle.
What is the main cause and feature of osteogenesis imperfecta?
Point mutation in Type 1 collagen - GGC to TGC - Glycine to Cysteine which causes a kink in the triple helix, affecting fibre assembly, and there are also inappropriate disulphide bonds formed.
Repeated fracture of long bones which is easily misdiagnosed as child abuse.
What are the consequences of deformed collagen?
Affected bone formation:
Bone is formed by laying down hydroxyapatite on an ordered scaffold of type 1 collagen so the mutation causes defects in the mineralisation process.
Patient has skeletal deformities and generally weak bones.
Prenatal diagnosis of osteogenesis imperfecta
Biopsy is impractical.
Obtain foetal DNA by CVS or amniocentesis + PCR amplification and then screen the DNA by designing specific probes to bind with the part of the DNA sequence where the mutation is known to occur.
What is the pattern of inheritance for osteogenesis imperfecta?
Autosomal dominant - because only one of the collagen chains needs to be affected to alter the entire collagen as the three chains are wound around each other.
What happens in Type 1 sensitivity?
Activation of Th2 cells causes switch to IgE production, IgE binds to mast cells, antigen binds to IgE and the cross-linking causes mast cells to degranulate.
