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USMLE > DIT XII: Biochem > Flashcards

DIT XII: Biochem Flashcards

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USMLE® Step 1 flashcards
1
Q

Rate limiting enzyme in pyrimidine synth

A

Carbamoyl phosphate synthetase II (CPS-2)

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2
Q

Name the pathway: carbamoyl phosphate synthetase 2, PPRP, ribonucleotide reductase, thymidylate synthase

A

Pyrimidine synthesis

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3
Q

CPS-1 vs CPS-2

A

CPS-1: urea cycle in mitochondria, uses ammonia. CPS-2: pyrimidine synth in cytocol, uses glutamine.

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4
Q

Name the disease and defect: incr orotic acid in urine, no hyperammonemia, FTT, megaloblastic anemia not responsive to B12/folic acid supplementation

A

Orotic aciduria: deficiency of UMP synthase, autosomal recessive

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5
Q

Rate limiting enzyme in purine synth

A

Glutamine PRPP amidotransferase

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6
Q

Tx for orotic aciduria

A

Supplemental dietary uridine

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7
Q

Name the pathway: xanthine oxidase, hypoxanthine guanine phosphoribosyltransferase (HGPRT), adenosine deaminase

A

Purine catabolism and salvage

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8
Q

Name the disease and defect: gout, intellectual disability, aggressive behaviour, self-mutilation (lip biting), choreoathetosis

A

Lesch-Nyan Syndrome: defect of HGPRT (hypoxanthine guanine phophoribosyltransferase), leading to overproduction of uric acid

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9
Q

Tx for Lesch-Nyan syndrome

A

Allopurinol

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10
Q

What can adenosine deaminase deficiency cause?

A

SCID: severe recurrent infections (Candida, PCP), chronic diarrhea, FTT, no thymic shadow

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11
Q

A boy with self-mutilating behaviour, intellectual disability, and gout

A

Lesch-Nyan Syndrome

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12
Q

Orotic acid in the urine + elevations in serum ammonia

A

OTC deficiency

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13
Q

Orotic acid in the urine + no elevations in serum ammonia

A

Orotic aciduria: deficiency of UMP synthase, autosomal recessive

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14
Q

Megaloblastic anemia that does not improve with folate and B12

A

Orotic aciduria: deficiency of UMP synthase, autosomal recessive

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15
Q

Types and functions of DNA polymerase

A

DNA Pol alpha: can make own primer, builds Okazaki fragments in lagging strand. Delta: builds leading strand. Beta: DNA repair. Gamma: mitochondrial DNA replication.

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16
Q

What is the defect in HNPCC and what is the risk?

A

Hereditary nonpolyposis colorectal cancer: mismatch repair defect, incr risk of colon and other cancers

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17
Q

Name the disease and defect: can’t repair pyrimidine dimers caused by UV light, incr risk skin cancers

A

Xeroderma pigmentosum: defect in nucleotide excision repair

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18
Q

What is the defect in Bloom syndrome, and what can it cause?

A

Mutation in helicase (DNA replication and repair), hypersensitivity to sunlight, incr leukemias and lymphomas, immunodeficiencies

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19
Q

Name the disease and defect: IgA deficiency, cerebellar ataxia, poor smooth pursuit with eyes, incr AFP after 8 mos

A

Ataxia-telangiectasia: dsDNA repair defects, sensitive to ionizing radiation

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20
Q

What do BRCA1 and BRCA2 mutations result in?

A

dsDNA repair defects, incr risk of breast cancer

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21
Q

Name 3 components of the gene promoter region

A

-75 CCAAT box, -25 Hogness/TATA box, -10 Probnow/TATAAT box

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22
Q

Name 4 common structural motifs allowing proteins to physically interact with DNA

A

Helix-loop-helix, helix-turn-helix, zinc finger, leucine zipper

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23
Q

When is the lac operon turned on, and what is its product?

A

On when excess lactose + absent glucose –> makes beta galactosidase (breaks down lactose into glucose + galactose)

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24
Q

What binds to the lac operon only in the absence of glucose?

A

Catabolite Activating Protein (CAP)

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25
Q

What is always bound to the lac operon unless lactose is present?

A

lac repressor

26
Q

Name 2 methods by which prokaryotic RNA transcription is terminated

A

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

27
Q

Types and functions of eukaryotic RNA polymerase

A

RNAP I: rRNA. II: mRNA. III: tRNA

28
Q

Mushroom toxin, inhibits RNA Pol II, hepatotoxicity, liver failure

A

Alpha-amanitin

29
Q

Types and functions of prokaryotic RNA polymerase, what inhibits it?

A

Only one type, makes all types of RNA, inhibited by rifampin

30
Q

What enzyme ‘charges’ tRNA?

A

AminoacyltRNA synthetase

31
Q

What do initiation factors do?

A

Assist in assembly of smaller ribosomal subunits to first tRNA (eg 30S)

32
Q

What are the functions of the 3 sites in ribosomes?

A

A site (Aminoacyl): incoming aminoacyl tRNA binds. P site (Polypeptide): polypeptide tRNA binds, growing chain here. E site (Exit): free tRNA here before exiting

33
Q

What do elongation factors do?

A

Help incoming aminoacyl tRNA bind to A site of ribosome

34
Q

What toxins inhibit EF-2?

A

Diphtheria toxin, exotoxin A (Pseudomonas)

35
Q

What are the 3 stop codons?

A

UGA, UAA, UAG

36
Q

Name the type of inheritance: ragged-red muscle fibers on biopsy, Leber hereditary optic neuropathy, Leigh syndrome (subacute sclerosing encephalopathy)

A

Mitochondrial inheritance

37
Q

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

A

Prader-Willi Syndrome (15q11-q13 del in paternal chr), Dx with FISH

38
Q

Name the disease and defect: intellectual disability, seizures, ataxia, inappropriate laughter

A

Angelman Syndrome (15q11-q13 del in maternal chr)

39
Q

What is the Hardy-Weinberg equation?

A

p+q=1, p² + 2pq + q² = 1

40
Q

What is a Southern Blot?

A

Use DNA probe to ID DNA sample

41
Q

What is a Northern Blot?

A

Use DNA probe to ID RNA sample

42
Q

What is a Western Blot?

A

Use Ab probe to ID protein sample (“Western beef = protein”)

43
Q

What is a Southwestern Blot?

A

Use oligonucleotide probe to ID DNA-binding proteins

44
Q

What is an indirect ELISA?

A

Add test antigen to patient’s blood to look for Abs (use known antigen to ID presence of Ab)

45
Q

What is a direct ELISA?

A

Add Abs to patient’s blood (use known Ab to ID presence of antigen)

46
Q

What is FISH?

A

Fluorescent In-Situ Hybridization: use fluorescent DNA or RNA probe)

47
Q

In gel electrophoresis, which DNA fragments will travel the farthest, and towards which electrode?

A

Smallest fragments will travel the farthest, towards (+) electrode

48
Q

Where is the malate-aspartate shuttle used, and how much ATP does it generate?

A

Heart, liver, kidneys; 32 ATP

49
Q

Where is the glycerol-3-phosphate shuttle used, and how much ATP does it generate?

A

30 ATP

50
Q

Where are GLUT-1 receptors found? Are they insulin dependent?

A

RBCs, endothelium of BBB, other tissues (mediate basal glu uptake); don’t need insulin

51
Q

Where are GLUT-2 receptors found? Are they insulin dependent?

A

Cells that regulate glu (eg hepatocytes, beta cells of pancreas); don’t need insulin

52
Q

Where are GLUT-3 receptors found? Are they insulin dependent?

A

Neurons, placenta; don’t need insulin

53
Q

Where are GLUT-4 receptors found? Are they insulin dependent?

A

Skeletal muscle, adipose; insulin-dependent

54
Q

Where are GLUT-5 receptors found? Are they insulin dependent?

A

Fructose uptake in GI tract, spermatocytes; don’t need insulin

55
Q

Function and location of hexokinase and glucokinase

A

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.

56
Q

Name the pathway: hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), pyruvate kinase

A

Glycolysis

57
Q

What is the rate-determining enzyme in glycolysis?

A

Phosphofructokinase-1 (PFK-1)

58
Q

How much energy is generated via glycolysis?

A

Net = 2 ATP (invest 2, get 4)

59
Q

What is the main clinical manifestation of a glycolytic enzyme deficiency?

A

Hemolytic anemia: RBCs need to metabolize glu for ATP (don’t have mitochondria), so inability to maintain Na+/K+ATPase

60
Q

Name the most likely enzyme def: elevated glycogen, elevated fructose-6-phosphate, decr pyruvate

A

PFK-1 (because buildup of fructose-6-phosphate

61
Q

What is the relationship between insulin, glucagon, FBP-2, and PFK-2?

A

High glucagon: induces FBP-2, less active PFK-1, less glycolysis. Low glucagon (high insulin): active PFK-2, active PFK-1, more glycolysis

USMLE (23 decks)

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