Chemistry Flashcards
(711 cards)
Peak light absorption for NAD is ___ nm, while for NADH it is ___ nm.
Peak light absorption for NAD is 260 nm, while for NADH it is 340 nm.
While the terms “enzyme concentration” and “enzyme activity” are often used interchangeably, there is often a discordance due to…
While the terms “enzyme concentration” and “enzyme activity” are often used interchangeably, there is often a discordance due to inhibitors, macroenzymes, lack of cofactors, proteolytically-inactive enzymes, etc. Hence, enzyme activity usually underestimates the immunoassay.
What is a macroenzyme?
Macroenzymes are enzymes bound to antibodies, which inhibit enzyme function and block enzyme clearance.
What is plotted on a Lineweaver-Burke plot?
1/[S] (x-axis) vs. 1/v (y-axis). A Lineweaver-Burke plot is a means to express a non-linear asymptotic concept (how the rate of the reaction varies with the substrate concentration) in a linear fashion by using the reciprocals of substrate concentration and reaction rate.
Lineweaver-Burke plots, competitive inhibition, noncompetitive inhibition, uncompetitive inhibition.
Lineweaver-Burke plots are a means to express a non-linear asymptotic concept (how the rate of the reaction varies with the substrate concentration) in a linear fashion by using the reciprocals of substrate concentration (1/[S], x-axis) and reaction rate (1/v, y-axis). The x intercept is -1/Km, the y intercept is 1/Vmax, and the slope is Km. In competitive inhibition, the enzyme’s substrate and the inhibitor compete for the same binding site. This type of inhibition can be overcome by increasing substrate concentration. On the Lineweaver-Burke plot, the y intercept is unchanged and the slope is increased. In noncompetitive inhibition, the inhibitor binds the enzyme at a different site from the substrate binding site, effectively decreasing the amount of useful enzyme without affecting the binding of substrate to enzyme. On the Lineweaver-Burke plot, the Km (a function of binding) is unaffected, but the reaction rate decreases. In uncompetitive inhibition, the inhibitor binds and stabilizes the enzyme-substrate complex. On the Lineweaver-Burke plot, the Km is decreased (can’t bind enzyme if it’s in a stable complex), and the Vmax is decreased (product can’t be formed if the substrate and enzyme are stuck together).
What are the x-intercept and y-intercept on a Lineweaver-Burke plot, respectively?
-1/Km and 1/Vmax.
How is the International Unit (IU) defined?
An IU is the amount of enzyme that catalyzes the conversion of 1 micromole of substrate per minute. A katal is the amount of enzyme that catalyzes the conversion of 1 mole of substrate per second. 1 IU = 16.7 nanokatals.
AST and ALT. Which is more liver-specific?
ALT. ALT is mainly confined to the mitochondria (80%) of liver and kidney. AST is found in highest concentration in the heart.
Which LDH isoenyme is in highest concentration in serum?
LD2.
What is a flipped LD ratio?
Normally, the LDH isoenzyme LD2 is in a higher concentration in serum than LD1. The flipped ratio happens when LD1>LD2; this can be seen with acute MI, hemolysis, or renal infarction.
What conditons can be associated with a mildly increased alkaline phosphatase?
Unrecognized pregnancy. Some drugs, such as ibuprofen and acetaminophen. CHF. Hyperthyroidism. Hepatic metastases. Non-fasting Lewis (+) type B or O secretors after a meal.
In what 2 areas is GGT concentrated?
The biliary epithelial cells that line the small interlobular bile ducts and ductules. Smooth endoplasmic reticulum of hepatocytes.
What are the two main sources of ammonia in the body?
The gut and skeletal muscle. And the liver clears it.
Unconjugated bilirubin is a heme breakdown product; it is tightly bound to (what protein) in the bloodstream when it comes to the liver for (what enzyme process). The now water-soluble conjugated bilirubin can be excreted in bile, which intestinal bacteria convert to (what substance) for excretion in feces and urine.
Unconjugated bilirubin is a heme breakdown product; it is tightly bound to albumin in the bloodstream when it comes to the liver for glucuronidation. The now water-soluble conjugated bilirubin can be excreted in bile, which intestinal bacteria convert to urobilinogen for excretion in feces and urine.
What is dysproteinemia?
Dysproteinemia is the clinical state characterized by excessive synthesis of immunoglobulin molecules or subunits, resulting from clonal plasma cell proliferations or B-cell lymphoproliferative disorders.
What are the casts in light chain cast nephropathy AKA myeloma cast nephropathy composed of?
The are composed predominantly of a single monoclonal light chain, which is typically admixed with Tamm-Horsfall protein secreted by the thick ascending limb of Henle.
How can calcium phosphate and calcium oxalate crystals be distinguished by: H&E, von Kossa stain, Alizarin red S stain, and polarized light?
On H&E, calcium phosphate crystals often appear blue or purple, while calcium oxalate crystals appear translucent. With von Kossa stain, the stain reacts with the phosphate moiety of calcium phosphate, and does not stain calcium oxalate. Alizarin red S stains calcium specifically, and reacts with calcium phosphate at pH 7 and pH 4.2 while reacting with calcium oxalate at pH 7 (but not pH 4.2). Calcium phosphate is not birefringent under polarized light, while calcium oxalate is.
What conditions can lead to oxalate nephropathy?
Enteric hyperoxaluria, toxic exposures (such as ethylene glycol ingestion or excessive vitamin C intake (vitamin C is metabolized to oxalate)), excessive dietary intake of oxalate, and inborn errors of metabolism.
Pathogenesis/immunology of celiac disease.
Among autoimmune diseases, CD is one of the few where the offending antigen is known (gluten). Gluten is mostly made up of 2 groups of proteins: ethanol-soluble gliadins and ethanol-insoluble glutenins. Gliadin contains large amounts of the amino acids proline and glutamine. It is known that alpha-gliadin among other peptides is toxic to celiac patients. The pathogenesis of CD involves a CD4+ T-cell mediated immune response to gliadin peptides, activation of a CD8+ T-cell intraepithelial innate immune response, and production of antibodies against tissue transglutaminase, as well as anti-gliadin, anti-reticulin, and anti-endomysial antibodies. In 1997, tissue transglutaminase type II was identified as the major autoantigen of CD (and also the epitope recognized by anti-endomysial antibodies). Tissue transglutaminase is an 85-kDa enzyme that is expressed in multiple tissues. Gliadin can serve as a substrate of transglutaminase, which is activated upon injury of inflammation of the small bowel, and in the process becomes cross-linked to transglutaminase, thereby creating a neoantigen, which induces an immune response to the self-protein (transglutaminase). Moreover, tissue transglutaminase can selectively deamidate gliadin peptides, leading to enhanced T-cell stimulatory activity. The ensuing inflammatory cascade produces inflammatory cytokines, proteinases, and other tissue-damaging mediators that induce mucosal tissue damage, leading to the characteristic histopathologic alterations.
Serologic testing in celiac disease.
The most sensitive antibody tests detect IgA-class antibodies against tissue transglutaminase (tTGA) and endomysium (EMA). The anti-gliadin antibodies are no longer considered sensitive or specific enough to be used for routine clinical detection of CD, except in children younger than 18 months of age, because anti-gliadin IgA antibodies are considered to be the first autoantibodies to appear after intestinal exposure to a gluten-containing diet. Serologic IgA tTGA antibody testing is considered to be the most sensitive method for detecting CD, with sensitivity approaching 97% in clinical practice, while IgA EMA antibodes are highly specific markers for CD, approaching 100%. The presence of titers of both tTGA and EMA antibodies have been shown to correlate with the degree of mucosal damage. Seronegative CD does occur, accounting for up to 15% of all CD patients. Recently, a new test for detecting antibodies against deamidated gliadin peptides (DGP) was introduced, which displays promising results and a high specificity (99%). DGP IgA testing may have greater sensitivity for the detection of adequate adherence to a gluten-free diet.
What laboratory monitoring tests are used for the following anticoagulants: Coumadin, Heparin, LMW heparin, Fondaparinux, Rivaroxaban, Argatroban, Lepirudin, Bivalirudin, Dabigatran.
Coumadin: INR. Heparin: PTT, anti-factor Xa. LMW heparin: Anti-factor Xa if needed. Fondaparinux: Anti-factor Xa if needed. Rivaroxaban: Anti-factor Xa if needed. Argatroban: PTT. Lepirudin: PTT. Bivalirudin: ACT. Dabigatran: Thrombin time to test for residual drug. Dilute thrombin time to assess extent of anticoagulation or test for residual drug.
Coumadin reduces the synthesis of what coagulation factors?
Factors II, VII, IX, and X.
How are heparin and the LMW heparins different in mechanism of action?
Heparin inhibits the coagulation cascade at multiple sites; all of the activated coagulation factors, except factor III, are targets. The LMW heparins inhibit the action of factors II and X, and the different LMW heparins may inhibit them to different extents.
How is INR calculated?
INR = [Patient PT / Mean of normal PT range] ^ ISI. ISI = International Sensitivity Index for thromboplastin, used for PT determination. A patient with high ISI (ISI = ~2) will have low sensitivity to factor deficiencies. A patient with low ISI (ISI = ~1) will have high sensitivity to factor deficiencies.