DIT XII: Biochem Flashcards
Rate limiting enzyme in pyrimidine synth
Carbamoyl phosphate synthetase II (CPS-2)
Name the pathway: carbamoyl phosphate synthetase 2, PPRP, ribonucleotide reductase, thymidylate synthase
Pyrimidine synthesis
CPS-1 vs CPS-2
CPS-1: urea cycle in mitochondria, uses ammonia. CPS-2: pyrimidine synth in cytocol, uses glutamine.
Name the disease and defect: incr orotic acid in urine, no hyperammonemia, FTT, megaloblastic anemia not responsive to B12/folic acid supplementation
Orotic aciduria: deficiency of UMP synthase, autosomal recessive
Rate limiting enzyme in purine synth
Glutamine PRPP amidotransferase
Tx for orotic aciduria
Supplemental dietary uridine
Name the pathway: xanthine oxidase, hypoxanthine guanine phosphoribosyltransferase (HGPRT), adenosine deaminase
Purine catabolism and salvage
Name the disease and defect: gout, intellectual disability, aggressive behaviour, self-mutilation (lip biting), choreoathetosis
Lesch-Nyan Syndrome: defect of HGPRT (hypoxanthine guanine phophoribosyltransferase), leading to overproduction of uric acid
Tx for Lesch-Nyan syndrome
Allopurinol
What can adenosine deaminase deficiency cause?
SCID: severe recurrent infections (Candida, PCP), chronic diarrhea, FTT, no thymic shadow
A boy with self-mutilating behaviour, intellectual disability, and gout
Lesch-Nyan Syndrome
Orotic acid in the urine + elevations in serum ammonia
OTC deficiency
Orotic acid in the urine + no elevations in serum ammonia
Orotic aciduria: deficiency of UMP synthase, autosomal recessive
Megaloblastic anemia that does not improve with folate and B12
Orotic aciduria: deficiency of UMP synthase, autosomal recessive
Types and functions of DNA polymerase
DNA Pol alpha: can make own primer, builds Okazaki fragments in lagging strand. Delta: builds leading strand. Beta: DNA repair. Gamma: mitochondrial DNA replication.
What is the defect in HNPCC and what is the risk?
Hereditary nonpolyposis colorectal cancer: mismatch repair defect, incr risk of colon and other cancers
Name the disease and defect: can’t repair pyrimidine dimers caused by UV light, incr risk skin cancers
Xeroderma pigmentosum: defect in nucleotide excision repair
What is the defect in Bloom syndrome, and what can it cause?
Mutation in helicase (DNA replication and repair), hypersensitivity to sunlight, incr leukemias and lymphomas, immunodeficiencies
Name the disease and defect: IgA deficiency, cerebellar ataxia, poor smooth pursuit with eyes, incr AFP after 8 mos
Ataxia-telangiectasia: dsDNA repair defects, sensitive to ionizing radiation
What do BRCA1 and BRCA2 mutations result in?
dsDNA repair defects, incr risk of breast cancer
Name 3 components of the gene promoter region
-75 CCAAT box, -25 Hogness/TATA box, -10 Probnow/TATAAT box
Name 4 common structural motifs allowing proteins to physically interact with DNA
Helix-loop-helix, helix-turn-helix, zinc finger, leucine zipper
When is the lac operon turned on, and what is its product?
On when excess lactose + absent glucose –> makes beta galactosidase (breaks down lactose into glucose + galactose)
What binds to the lac operon only in the absence of glucose?
Catabolite Activating Protein (CAP)
What is always bound to the lac operon unless lactose is present?
lac repressor
Name 2 methods by which prokaryotic RNA transcription is terminated
Rho factor in E. Coli: uses ATP to knock RNA Pol off DNA. Termination region in DNA (rho-independent): GC rich regions cause hairpin loop, subsequent uracil-rich regions cause region of weak bonds, RNA Pol separates
Types and functions of eukaryotic RNA polymerase
RNAP I: rRNA. II: mRNA. III: tRNA
Mushroom toxin, inhibits RNA Pol II, hepatotoxicity, liver failure
Alpha-amanitin
Types and functions of prokaryotic RNA polymerase, what inhibits it?
Only one type, makes all types of RNA, inhibited by rifampin
What enzyme ‘charges’ tRNA?
AminoacyltRNA synthetase
What do initiation factors do?
Assist in assembly of smaller ribosomal subunits to first tRNA (eg 30S)
What are the functions of the 3 sites in ribosomes?
A site (Aminoacyl): incoming aminoacyl tRNA binds. P site (Polypeptide): polypeptide tRNA binds, growing chain here. E site (Exit): free tRNA here before exiting
What do elongation factors do?
Help incoming aminoacyl tRNA bind to A site of ribosome
What toxins inhibit EF-2?
Diphtheria toxin, exotoxin A (Pseudomonas)
What are the 3 stop codons?
UGA, UAA, UAG
Name the type of inheritance: ragged-red muscle fibers on biopsy, Leber hereditary optic neuropathy, Leigh syndrome (subacute sclerosing encephalopathy)
Mitochondrial inheritance
Name the disease, defect, and Dx: hypotonia in infancy, almond-shaped eyes, downward turned mouth, hyperphagia, obesity, short stature, intellectual disability, behaviour disorders, hypogonadotropic hypogonadism
Prader-Willi Syndrome (15q11-q13 del in paternal chr), Dx with FISH
Name the disease and defect: intellectual disability, seizures, ataxia, inappropriate laughter
Angelman Syndrome (15q11-q13 del in maternal chr)
What is the Hardy-Weinberg equation?
p+q=1, p² + 2pq + q² = 1
What is a Southern Blot?
Use DNA probe to ID DNA sample
What is a Northern Blot?
Use DNA probe to ID RNA sample
What is a Western Blot?
Use Ab probe to ID protein sample (“Western beef = protein”)
What is a Southwestern Blot?
Use oligonucleotide probe to ID DNA-binding proteins
What is an indirect ELISA?
Add test antigen to patient’s blood to look for Abs (use known antigen to ID presence of Ab)
What is a direct ELISA?
Add Abs to patient’s blood (use known Ab to ID presence of antigen)
What is FISH?
Fluorescent In-Situ Hybridization: use fluorescent DNA or RNA probe)
In gel electrophoresis, which DNA fragments will travel the farthest, and towards which electrode?
Smallest fragments will travel the farthest, towards (+) electrode
Where is the malate-aspartate shuttle used, and how much ATP does it generate?
Heart, liver, kidneys; 32 ATP
Where is the glycerol-3-phosphate shuttle used, and how much ATP does it generate?
30 ATP
Where are GLUT-1 receptors found? Are they insulin dependent?
RBCs, endothelium of BBB, other tissues (mediate basal glu uptake); don’t need insulin
Where are GLUT-2 receptors found? Are they insulin dependent?
Cells that regulate glu (eg hepatocytes, beta cells of pancreas); don’t need insulin
Where are GLUT-3 receptors found? Are they insulin dependent?
Neurons, placenta; don’t need insulin
Where are GLUT-4 receptors found? Are they insulin dependent?
Skeletal muscle, adipose; insulin-dependent
Where are GLUT-5 receptors found? Are they insulin dependent?
Fructose uptake in GI tract, spermatocytes; don’t need insulin
Function and location of hexokinase and glucokinase
Phosphorylate glucose into G6P, trapping it in cells. Glucokinase in liver, beta cells of pancreas (cells that regulate glucose), induced by insulin. Hexokinase in most other tissues, low capacity and low Vmax, not induced by insulin.
Name the pathway: hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), pyruvate kinase
Glycolysis
What is the rate-determining enzyme in glycolysis?
Phosphofructokinase-1 (PFK-1)
How much energy is generated via glycolysis?
Net = 2 ATP (invest 2, get 4)
What is the main clinical manifestation of a glycolytic enzyme deficiency?
Hemolytic anemia: RBCs need to metabolize glu for ATP (don’t have mitochondria), so inability to maintain Na+/K+ATPase
Name the most likely enzyme def: elevated glycogen, elevated fructose-6-phosphate, decr pyruvate
PFK-1 (because buildup of fructose-6-phosphate
What is the relationship between insulin, glucagon, FBP-2, and PFK-2?
High glucagon: induces FBP-2, less active PFK-1, less glycolysis. Low glucagon (high insulin): active PFK-2, active PFK-1, more glycolysis
