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Step 1 Biochem
| Question | Answer |
|---|---|
| How is cytosine converted to uracil? | deamination |
| What is the rate limiting step of denovo pyrmidine synthesis? | carbamoyl phosphate synthase II (cytosol) |
| What type of proofreading capability does DNA Polymerase III have? | 3' to 5' exonuclease activity removes mismatched base pairs |
| What disorders are a result of improper base excision repair? | Ataxia Telangiectasia, Fanconi's anemia, Bloom's syndrome |
| What are the steps in base excision repair | glycosylase recognized and removes damaged base; endonuclease cuts at apyrimidine site, lyase cuts 3' end and removes empty sugar, DNA polymerase and ligase fill in gaps |
| Where is the triphosphate that creates the phosphoanhydride bonds in DNA synthesis located? | 5' end of incoming base |
| What fills in the gaps and aids in repair in eurkaryotic DNA? | polymerase beta |
| What is the function of histone acetyltransferase? | acetylation of the lysine residues decr binding to negatively charged DNA and thus opens up DNA for transcription |
| What is the cause of Kartagener's syndrome? | immotile cilia due to dynein arm defect (ATPase that links peripheral microtubule doublets and allows bending of cilium) |
| Where in the body is type II collagen found? | cartilage, vitreous body, nucleus pulposus |
| What cofactors are important in lysyl hydoxylase? | vit c and Cu |
| What step of collagen synthesis is defective in Ehlers Danlos syndrome? | defective proteolytic processing outside the fibroblasts to form tropocollagen; type III most frequently affected |
| What are microarrays used for? | profile gene expression levels or to detect single nucleotide polymorphisms |
| What type of technique is used to identify microdeletions? | FISH |
| How is Sanger DNA sequencing accomplished? | dideoxynucleotides halt DNA polymerization so sequences of various lengths are created and the original sequence can be deduced |
| What is a dominant negative mutation? | heterozygote produces a nonfunctional altered protein that also prevents the nl gene product from functioning |
| What is locus heterogeneity? | mutations at different loci can produce the same phenotype (Marfan's, MEN2b, and homocystinuria all have marfanoid habitus) |
| What is an example of an X-linked dominant disorder? | Hypophosphatemic rickets (phosphate wasting at proximal tubule) |
| What is the mutation in Huntington's disease? | trinucleotide repeat of CAG on chromosome 4 |
| What is the result of VHL gene deletion on chromsome 3? | constitutive expression of HIF (transcription factor) and activation of angiogenic growth factors |
| What happens to the CFTR channel intracellulary in Cystic Fibrosis? | deletion of Phe508, abnl protein folding (improperly glycosylated), degradation of channel before reaching cell surface |
| Why is the dystrophin gene susceptible to spontaneous mutation? | it's the longest known human gene |
| What are the clinical findings' in Williams syndrome? | chromosome 7 microdeletion (includes elastin gene); elfin facies, MR, hypercalcemia, extreme friendliness |
| What vitamin is required in the synthesis of niacin from tryptophan? | vit B6 (pyridoxal phosphate) |
| What is the rate limiting step of the TCA cycle? | isocitrate dehydrogenase |
| Which enzyme phosphorylates excess glucose after a meal after being induced by insulin? | glucokinase |
| What activates pyruvate carboxylase? | acetyl CoA |
| How can odd-chain fatty acids be metabolized to undergo gluconeogenesis? | yield proprionyl coA which can enter TCA cycle as succinyl coA |
| What enzyme deficiency causes fructose intolerance? | aldolase B; sx: hypoglycemia, jaundice, cirrhosis, vomiting |
| How does beta-galactosidase deficiency present? | abdominal distension and diarrhea; post-febrile gastroenteritis |
| What contributes to ESR? | IL-1, IL-6, TNFalpha - acute phase proteins recruit fibrinogen |
| What markers of macrophage proliferation are useful to measure extent of Gaucher's disease? | chitotriosidase and aCE |
| What does the NFI gene normally code for? | GTPase-activating protein |
| What are lish nodules? | iris hamartomas in NF-I |
| What do chylomicrons look like in spun plasma? | creamy supranate (VLDL is INFRAnate) |
| What are the clinical findings of Carnitine deficiency? | weakness, hypotonia, hypoketotic hypoglycemia, myoglobinemia |
| What enzyme deficiency results in metachromatic leukodystrophy? | arylsulfatase A; demyelination and ataxia |
| What is Krabbe's disease? | deficiency of galactocerebrosidase; peripheral neuropathy, optic atrophy and globoid cells |
| Which sphingolipidoses can result in aseptic necrosis of the femur and cause bone crises? | Gaucher's disease |
| In which glycogen storage d/o do limit dextrans accumulate? | Cori's disease type III; muscle and liver |
| A small amount of glycogen is degraded in lysosomes by what enyzme? | alpha,1-4 glycosidase (acid maltase) |
| What type of bonds do the branches and linkages have in glycogen | branches - 1,6; linkages - 1,4 |
| What enzyme deficiency leads to alkaptonuria? | homogentistate 1,2 dioxygenase; sx: dark CT, pigmented sclera, urine black on standing, degenerative arthritis |
| Which AA are hydrophobic and span the cell membrane? | valine, alanine, isoleucine, methionine, phenylalanine |
| What is sorbitol osmotically active? | can't cross cell membrane --> cataracts, retinopathy, peripheral neuropathy |
Created by:
ash0403
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