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USMLE Step 1 flashcards > Biochemistry > Flashcards

Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

which substance is decreased in acetaminophen intoxication allowing the damaged of liver injury and why?

A
  • Glutathion→ detoxifies free radicals
    and peroxides.
    Is the fundament of treatment with N- acetyl cysteine
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2
Q

which is the cause of I cell disease?

A 
Defect in N-acetylglucosaminyl-1-phosphotransferase -  failure of the Golgi to phosphorylate
mannose residues (FAILURE IN TARGET)→ accumulation of serum levels lysosomal enzymes
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3
Q

Tell 8 symptoms of Scurvy

A
  1. petechiae
  2. poor wound healing
  3. hemarthrosis
  4. anemia
  5. swollen gums
  6. bruising
  7. perifollicular and periosteal hemorrhages
  8. weakened immune response
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4
Q

Alkaptonuria

A 
AR
Deficiency of homogentisate oxidase-- degredative pathway from tyrosine to fumarate
accumulate homogentisic acid in tissue
benign
dark pigment in tissue--- sclerae, urine
artharlgias
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5
Q

Homocystinuria vs Marfan sx

A
  • Homocystinuria: Cystathione synthase deficiency, -intelectual disability, thrombosis. Marfanoid habitus
  • Marfan sx: Fibrillin -1 gene mutation: No intelectual disability, no thrombosis.
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6
Q

Mc Ardle disease

A

AR
Glycogen storage disease— deficiency of glucogen phosphorylase (myophosphorylase) degrades glycogen in glycogen 1 phosphate (impaired muscle glycolysis)
Exercise intolerance – muscle pain and cramping

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7
Q

Dopamine Beta Hydroxylase deficiency

A

impaired sympathetic adrenergic activity
Infants: Hypotension, failure to thrive and hypothermia
Adults: postural hypotension, exercise intolerance, nasal cogestion and ejaculatory problems.

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8
Q

Which is the main characteristic of G- coupled receptors?

A

7 transmembrane hidrophobic alpha helical domain

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9
Q

Median chain acyl coa dehydrogenase deficiency

A

AR
disorder in fatty acid oxidation– decreased the ability to break down fatty acids into acetyl CoA
Hypoketotic hypoglycemia
lethargy, seizures, coma and liver disfunction (hematomegaly)

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10
Q

MODY

A

maturity onset diabetes of the young: AD, impaired insulin secretion, minimal or no effects in insulin action.
mutations in GLUCOKINASE (regularory role in pancreatic cells to insulin secretions) gene or transcripction factors—— Hyperglycemia is mild, as no longer need medication.

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11
Q

The only purely ketogenic a.a

A

lysine and leucine

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12
Q

essential a.a

A
  • methionine
  • valine
  • histidine
  • threonine
  • isoleucine
  • phenylalanine
  • tryptophan
  • leucine
  • lysine
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13
Q

Glucogenic a.a

A
  • methionine
  • valine
  • histidine
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14
Q

N- acetyl synthase deficiency

A

required cofactor carbamoyl phosphate synthase I
Absence of N- acetylglutamate—- hyperammonemia
neonates: poorly regulated respiration and body temperature, poor feeding, development delay, intellectual disability
Identical presentation of carbamoyl phosphate synthase I deficiency

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15
Q

Which enzyme is increased as a result of Lesch Nyhan syndrome

A

Phosphoribosyl pyrophosphate amidotransferase increased it activity because accumulation of uric acid leading increased production of purines.

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16
Q

Vit A toxicity

A

Acute: nausea, vomiting, vertigo and blurred vision
Chronic: alopecia, dry skin, hepatic toxicity, hepatomegaly, papilledema (pseudotumor cerebri) benign intracranial hypertension
teratogenic: cleft palate, cardiac abnormalities

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17
Q

AUG, UAG, UAA, UGA

A 
Initiation codon (methionine)
stop codons 
Do not code for a.a or bind to tRNA
When the ribosome encounters a stop codon --- releasing factor protein-- bind to the ribosome--- dissolution ribosome/mRNA coupling
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18
Q

In porphyrin synthasis

A

the rate limit enzyme is ALA synthase (cofactor B6)

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19
Q

tRNA structure

A
  • 3´ CCA— acceptor stem
  • D loop— proper aminoacyl tRNA synthase
  • Anticodon loop—- bind to mRNA codon
  • T loop—- TyC sequence —binds to ribosome
20
Q

Glucagon functions by…

A

bind to G protein receptor coupled—- increasing cAMP intracellular—- activating protein Kinase A

21
Q

B12 vitamin es a cofactor

A
  • conversion of methylmalonic acid to succinyl coA (Fatty acid metabolism) — the accumulation of methylmalonic acid damage myelin
  • Homocysteine to methione (as methal donor)
22
Q

Hormone sensitive lipase

A

In adipose tissue catalyses the movilization of TAG into free fatty acids and glycerol
Activated by Catecholamines, glucagon and acth
inhibited by insulin

23
Q

biotin

A

B7
cofactor
- Pyruvate carboxylase: pyruvate to succinil coA (gluconeogenesis)
- Acetyl CoA carboxylase: Acetyl coA to malonyl coA (fatty acid syntehsis)
- Propionyl coA Carboxylase: propionyl Coa to Methyl malonyl coA (fatty acid oxidation)

24
Q

Propyomelnocortin POMC

A

Polypeptide precursor produce:

  • beta endorphins
  • ACTH
25
Q

Splicing

A

postranscriptional modification that removes noncoding DNA regions (introns) from precursor mRNA.

Alternative splicing: different combinations of DNA coding regions are included or excluded —- alternet sets of proteins

26
Q

Dihydrobiopterine reductase deficiency

A

Hyperphenylalanemia: BH4 is a cofactor of phenylalanine hydroxylase
Elevated prolactin: BH4 is a cofactor of DOPA decarboxylase (decreasing Dopa levels—- there is not inhibition of prolaction———— increased levels)

27
Q

Where is the location of heme production?

A

mitochondria

In erythrocyte precursors

28
Q

which kind of proteins are synthesized by RER and smooth endoplasmic reticulum?

A

RER: secretory, lysosomal and membrane proteins
SER: steroid proteins and phospholipid biosynthesis

29
Q

Ketogenic a.a

A

lysine and leucine

30
Q

Acyl coA dehydrogenase deficiency

A

Hypoketotic hypoglycemia

Defective in Fatty acid beta oxidation

31
Q

Integrins

A

transmembrane protein receptors —- interact with extracellular matrix by binding to collagen, fibronectin and laminin.
* differential expression of integrin subtypes affects the interaction properties—-correlates with malignant behavior (melanoma)

32
Q

Telomerase

A

ribonucleoprotease that adds TTAGGG repeats to 3´ end of chromosome (telomere region)
Similar to other reverse transcriptase enzymes (synthesize a single stranded DNA from a single stranded of RNA)
Stem cells hace very long telomerase (have a great telomerase activity) like in basal layer of epidermis

33
Q

which substrates need to convert pyruvate in phoenolpyruvate in gluconeogenesis?

A

pyruvate to PEP cannot convert directly because pyrvate kinase is unidirectionaly
- The reaction is catalyzed by pyruvate carboxylase (convert pyruvate in oxaloacetate)— is activated by acetyl coA (produced by beta oxidation of fatty acids)

34
Q

DNA Laddering

A

DNA fragments in multiples of 180 base pairs: indicating apoptosis
- laddering arises from the action of endonucleases during karryorrhexis

35
Q

Internal ribosome entry

A

alternative method of translatiion when eukaryotic initiation factors are degradated by apoptosis.

36
Q

Cell differentiation is determined by…

A

transcription factor

37
Q

G protein coupled receptors

A

Bind glycoprotein hormones (TSH- LH- FSH) contain three major domains:

  • extracellular domain (ligand binding)
  • transmembrane domain (hydrophobic a.a)
  • intracellular domain (coupled with G protein)
38
Q

hydrophobic a.a

A

valine, leucine, isoleucine, alanine, methionine, proline, glycine, thyptophan, phenylalanine.

39
Q

Ribosomes

A

free ribosomes: floating cytosol, translated proteins that find in cytosol, nucleosome, mytochondrial membrane and peroxisomes.
Attached with RER: synthesized membrane proteins, nuclear membrane proteins, lysosomes.

40
Q

Reticulocyte

A

is larger and bluer that mature RBC

lacks nucleus but remains basophilic reticular residual ribosomal RNA

41
Q

Phosphatidil choline

A

equal of lecithin
lecithin/ sphingomyelin ratio=lung maturiry turns to be equal in third trimester because lecithin is going increase
> 35 weeks: L/S= 2:1 of higher

42
Q

two that produce glucose in fasting

A

liver and kidney has capability to produce glucose in fasting ( gluconeogenesis)

43
Q

Fabry disease

A

alpha galactosidase A deficiency
Accumulation of alpha galactosidase A and globotriasulceramide (Gb3)ceramide trihexoside
Neuropathic pain, hpohydrosis, angyokeratomas and telangiectasias
cerebrovascular and cardian disease
renal failure

44
Q

increase alpha feto protein in amniotic fluid

A

fetal neural tube defect

45
Q

The nucleolus contains

A

Ribosomal DNA
Encodes 28 S, 5.8S, 18 S ribosomal RNA components — are translated in cytoplasm from mRNA

Primary function of nucleolus is synthesis of 60 and 40 S Ribosomal subunits— then are exported to fully mature in cytoplasm

46
Q

MC Ardley disease

A

myophosphorylase (Glycogen phosphorylase)– Glycogeolysis deficiency

USMLE Step 1 flashcards (10 decks)

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