The test value at which we assume a positive result for a test with a scale of result values. Ie, the cut off point.
The criterion of positivity affects sensitivity and specificity.
When to optimize tests for specificity or sensitivity.
For fatal diseases with no treatment, you want to optimize specificity so that you don’t give someone false bad news (ie, that they have HIV when they don’t).
For treatable diseases, we want to optimize the test for sensitivity so that we can catch and treat the diseases.
How do you calculate accuracy?
Accuracy = (TP + TN)/ (TP + TN + FP + FN)
How do you calculate the positive predictive value?
Positive predictive value = TP / (TP + FP)
This reflects the probability that a positive test reflects the underlying condition being tested for.
How do you calculate the negative predictive value?
Negative predictive value: TN / (TN + FN)
A high NPV means that the test only rarely misclassifies a sick person as being healthy
What is a nucleoside and what is a nucleotide?
Nucleoside: Nitrogenous base + sugar (eg, deoxyribose).
Nucleotide: Nitrogenous base + sugar + phosphate.
Differentiate between DNA and RNA
DNA has Deoxyribose, so the 2nd carbon (the first is the anomeric carbon) has an H instead of OH.
DNA is double stranded, providing a longer half life, RNA is single stranded with a shorter half life.
DNA: A-T, C-G. RNA: A-U, C-G.
Ribonucleotides can also function as second messengers (cAMP, cGMP), energy donors (ATP, GTP), and carriers of electrons for oxidation-reduction reactions (eg, Nicotinamide adenine dinucleotide, aka NAD+))
What is the molecular structure of purines?
What is the molecular structure of pyrimidines?
What types of bonds are involved in DNA helices?
Phosphodiester bonds form between neighboring 3’ and 5’ hydroxyl groups to form the DNA backbone.
Hydrogen bonds between nitrogenous bases (A-T has 2 H bonds, C-G has 3 H bonds) keep the strands together.
Van der Waals forces stabilize the double helix structure.
Describe the pathway to nucleotide synthesis
Describe the pathway through which nucleotides are synthesized from intermediates in the degradative pathway for nucleotides (ie, nucleotide salvage).