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USMLE Step 1 > Biochemistry - First Aid > Flashcards

Biochemistry - First Aid Flashcards

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USMLE® Step 1 flashcards
1
Q

Charges/Composition of DNA and histones

A

DNA: negatively charged; nucleic acids linked by phosphodiester bonds

Histones: positively charged; rich in amino acids lysine and arginine ;
8 subunits make up a nucleosome core (two each of 4 histone types - H2A, H2B, H3, H4)

Note that DNA loops around histones 2x.
Both DNA and histone synthesis occurs during S phase

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2
Q

DNA methylation

A

Represses transcription when methylated at CpG islands.

During replication, the template stand is IDed by the mismatch repair enzymes via methylation of A and C.

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3
Q

Nucleotide excision repair defect

A

xeroderma pigmentosum
predisposes to SCC, BCC, and melanoma
*Nucleotide excision repairs prymidine dimers during G1 phase because of UV light exposure; via specific endonucleases, DNA poly, and ligase;

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4
Q

Mismatch repair defect

A

HNPCC (hereditary nonpolyposis colorectal cancer (Lynch syndrome)
*mismatch repair fixes new strands during G2 phase

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5
Q

Base excision repair

A

Important in repair of spontaneous/toxic deamination throughout the cell cycle.
Via: base specific glycosylases remove altered base, endonuclease cleaves 5’ and lyase cleaves 3’, DNA poly, and ligase.

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6
Q

alpha-amanitin

A

found in amanita phalloides (death cap mushrooms) - inhibits RNA poly II (which makes mRNA, snRNA, microRNA)

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7
Q

RNA polymerase and rifampin

A

Prokaryotes only have 1 type of RNA poly that carries out the cell functions.
Note that rifampin inhibits it in prokaryotes

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8
Q

RNA polymerase and Actinomycin D

A

Inhibits RNA poly in both prokaryotes and eukaryotes

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9
Q

Splicing of pre-mRNA

A
  1. Primary transcript (heterogenous RNA) combines with snRNPs and other proteins to make spliceosome.
  2. lariat shaped (loop) intermediate is generated
  3. lariat released to precisely remove intervening introns and join 2 exons

Ab to spliceosome snRNPs (anti-smith ab) are highly specific for SLE.
Anti-U1 RNP ab are highly specific for mixed connective tissue disease.

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10
Q

tRNA structure

A

Acceptor stem: 3’ end CCA to carry amino acids via covalent bond
T arm: contains thymine, pseudouracil, cytosine sequences necessary for tRNA ribosome binding
D arm: contains dihydrouracil residues necessary for tRNA recognition by correct amino acyl tRNA synthetase

anticodon loop opposite the 3’ acceptor stem

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11
Q

Hydroxyurea

A

inhibits ribonucleotide reductase in pyrimidine production;

leads to inhibtoin of UDP to dUDP

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12
Q

Posttranslational modifications

A

Trimming: Removal of N or C terminal propeptides from zymogen to generate mature protein (ex. trypsinogen to tryspsin
Covalent alterations: phosphorylation, glycosylation, hydroxylation, methylation, acetylation, ubiquitination

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13
Q

Bonds in the primary structure of proteins

A

Peptide bonds

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14
Q

Typically the genetic code is considered universal (i.e., conserved throughout evolution). What is one noteworthy exception to this rule?

A

Human mitochondrial DNA, which is not conserved

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15
Q

Frameshift mutation

A

Deletion or insertion of number of nucleotides not divisible by 3 which leads to misreading of all nucleotides downstream, usually causing truncated, nonfunctional protein.
Ex. duchenne muscular dystrophy

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16
Q

DNA Polymerase 3

A

Prokaryote only
Elongates leading DNA strand adding to 3’,
elongates lagging DNA strand until it reaches primer of preceding fragment
3’ to 5’ exonuclease activity “proofreads” each added nucleotide

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17
Q

DNA polymerase1

A

Prokaryote only
Has same functions as DNA poly 3, but also excises RNA primer since it has 5’ to 3’ exonuclease activity, and replaces it with DNA

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18
Q

lac operon

A

Glucose normally surpresses adenylate cyclase.
If glucose absent, then increased AC, increased cAMP, increased CAP activation, and increased transcription (CAP acts as an activator for RNA poly)
High lactose unbinds the repressor (lactose acts as an inducer), so there is increased transcription.

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19
Q

Nonhomologous end joining

A

Brings together 2 ends of DNA fragments to repair ds breaks. No requirement for homology. Some DNA may be lost.
Mutated in ataxia telangiectasia and fanconi anemia

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20
Q

RNA polymerase 1

A

**Note the nucleolus is the primary site of ribosomal RNA transcription.
Also the nucleolus is involved in maturation of ribosomal subunits.
Ribosomal protein components are made in cytoplasm and then go to nucleolus where they combine with the rRNA to make the 40s and 60s . Then they go back to cytoplasm.
Generally as cells grow mature, they require less ribosomes and this process slows. But malignant cells with high metabolic activity use this process and have large numbers of active rRNA genes and prominent mucleoli.
ribosomal RNA (18s, 5.8s, 28S)

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21
Q

RNA polymerase 2

A

mRNA
snRNA
microRNA

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22
Q

RNA polymerase 3

A

tRNA

5S rRNA

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23
Q

P bodies

A

Where mRNA quality control occurs in the cytoplasm.
P bodies contain exonucleases, decapping enzymes, and microRNAs
mRNAs may be stored in P bodies for future translation

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24
Q

Rough ER function

A

The synthesis of secretory (exported) proteins and the addition of N-linked oligosaccharides to proteins

Goblet cells and plasma cells are very rich in RER!!

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25
Q

Nissl bodies

A

synthesis of peptide NTs for secretion

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26
Q

Free ribosome function

A

Unattached to any membrane; site of synthesis of cytosolic and organellar proteins

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27
Q

Smooth ER

A

Steroid synthesis; detoxification of drugs and poisons

adrenal cortex and hepatocytes are rich in SER!

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28
Q

Golgi

A

Distribution center for proteins and lipids from ER to vesicles and plasma membrane.
Modifies N oligosaccharides on asparagine.
Adds O oligosaccharides on serine and threonine.
Adds mannose 6P to proteins for lysosomal trafficking

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29
Q

Endosomes

A

sorting centers for material from outside the cell or from the golgi, sending it to lysosomes for destruction or back to the membrane / golgi for further use.

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30
Q

Signal recognition particles (SRPs)

A

abundant, cytosolic ribonucleoproteins that traffic proteins from ribosome to RER. Absent or dysfunctional SRP means that proteins accumulate in the cytosol!!

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31
Q

Vesicular trafficking proteins

A

COPI: golgi to golgi retrograde transport; cis golgi to ER

COPII: ER to cis golgi (anterograde)

Clathrin: trans-golgi to lysosomes; plasma membrane to endosomes

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32
Q

Microtubules

A

Movement and cell division; microtubules

cilia, flagella, mitotic spindles, centrioles, and axonal trafficking (ex. dynein and kinesin)

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33
Q

Intermediate filaments

A

maintain cell structure.

vimentin, desmin, cytokeratin, lamins, glial fibrillary acid proteins (GFAP), neurofilaments

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34
Q

Microfilaments

A

Muscle contraction, cytokinesis

Actin

35
Q

Vimentin stains identify which type of cells?

A

Connective tissue

36
Q

Desmin stains identify which type of cells?

A

Muscle

37
Q

Cytokeratin stains identify which type of cells?

A

Epithelial cells

38
Q

GFAP stains identify which type of cells?

A

Neuroglia

39
Q

Neurofilaments stains identify which type of cells?

A

Neurons

40
Q

Kartagener syndrome

A

Primary ciliary dyskinesia
immotile cilia due to dynein arm defect.
Results in male and female infertility due to immotile sperm and dysfunctional fallopian tube cilia; also increased risk ectopic pregnancy.
Can cause bronchiectasis, recurrent sinusitis, and situs inversus

41
Q

Types of Collagen and location

A

Type 1: Bones, skin, tendons, dentin, fascia, cornea, mature scar
Type 2: cartilage (vitreous body, nucleus pulposus, hyaline cartilage, and articular surface of joints)
Type 3: reticulum (vessels, granulation tissue, keloid, etc)
Type 4: basement membrane, basal lamina, lens

42
Q

Collagen synthesis

A
  1. Synthesis (RER) : Precollagen with peptides of Gly-X-Y
  2. Hydroxylation (RER): of proline and lysine (requires Vit C!! deficiency vitamin c = scurvy.)
  3. Glycosylation (RER): of pro-alpha-chain hydroxylysine residues and formation of procollagen via hydrogen and disulfide bonds. ie formation of triple helix. If problems with this, then osteogenesis imperfecta can result.
  4. Exocytosis: procollagen to extracellular space
  5. Proteolytic processing: cleave disulfide residues making insolule tropocollagen
  6. cross linking : covalent lysine-hydroxylysine cross linking by copper containing lysyl oxidase to make collagen fibrils. Problems with cross linking = Ehler Danlos sydrome, Menkes disease etc
43
Q

Elastin

A

Stretchy protein within skin, lungs, large arteries, elastic ligaments, vocal cords, ligamenta flava.
Rich in nonhydroxylated proline, glycine, and lysince residues.
Tropoelastin w/fibrillin scaffolding.
Cross linking takes place extracellularly and gives elastin its elastic properties.
Broken down by elastase, which is normally inhibited by alpha1 antitrypsin

44
Q

I-cell disease results in ____ (increased/decreased) phosphorylation of mannose residues on glycoproteins. What enzyme defect contributes

A

Decreased; defect in N-acetylglucosaminyl-1-phosphotransferase
It’s an inherited lysosomal storage d/o. Enzyme deficiency leads to proteins being secreted extracellularly since they can’t be sent to lysosomes for lack of golgi to phosphorylate mannose residues

Features: coarse facial features, clouded corneas, restricted joint movement, and high plasma levels of lysosomal enzymes. Often fatal in childhood

45
Q

A 13-year-old boy presents with hearing loss, hematuria, and end-stage kidney disease. What type of collagen is most likely defective?

A

Type IV—disease is Alport syndrome

46
Q

A boy exhibits hyperphagia, obesity, intellectual disability, hypogonadism, and hypotonia from birth. How is this condition inherited?

A

Prader-Willi is due to deletion or mutation of Paternal copies of genes on chromosome 15—25% of cases from maternal uniparental disomy

47
Q

McCune Albright syndrome

A

Due to mutation affecting G protein signaling.
Presents with unilateral cafe-au-lait spots, polyostotic fibrous dysplasia, precocious puberty, multiple endocrine abnormalities.
Letal if mutation occurs before fertilization (affecting all somatic cells); Survivable in pts with mosaicism.

48
Q

vitamin D̫ resistant rickets / Hypophosphatemic rickets

A

X-linked dominant disorder; inherited from the father, as no sons affected.
Ex. A girl has proximal tubule phosphate wasting. All of her sisters, but no brothers, have this issue.

49
Q

What findings in the prenatal quad screen indicate possible Down syndrome?

A

Decreased α-fetoprotein and estriol, increased β-human chorionic gonadotropin, and inhibin A

50
Q

Hereditary hemorrhagic telangiectasia

A

Osler-Weber-Tendu syndrome.
Autosomal Dominant
Inherited d/o of blood vessels.
Findings include: branching skin lesions (telangiactasias), recurrent epistaxis, skin discoloration, AVMs, GI bleeding, hematuria.

51
Q

X linked recessive Disorders

A

“Be Wise, Fool’s GOLD Heeds silly HOpe”

Bruton (X linked) agammaglobulinemia, Wiskott Aldrich sydrome, Fabry’s disease, G6PD deficiency, OTC deficiency, Lesch-Nyhan syndrome (HGPRT), Duchenne’s (and becker’s) MD, Hunter’s syndrome, Hemophilia A and B, Ocular Albinism

52
Q

Trinucleotide Repeat Disorders

A 
Huntingtons (Auto dom, CAG)
Fragile X (X linked, CGG)
Myotonic type 1 (Auto dom, CTG)
Friedreich Ataxia (GAA)
53
Q

Robertsonian translocation

A

Acrocentric chr. 13,14,15,21,22

54
Q

What chromosome is implicated in Wilson disease

A

Chromosome 13

55
Q

What chromosome is implicated in Wilms tumor

A

Chromosome 11

56
Q

What chromosome is implicated in Prader Willi and Angelman syndromes?

A

Chromosome 15

57
Q

What chromosome is implicated in Williams syndrome?

A

Chromosome 7

same as with CF

58
Q

What chromosome is implicated in VHL/RCC

A

Chromosome 3

59
Q

Fat soluble vitamins

A

ADEK

60
Q

Water soluble vitamins

A 
B1, thiamine
B2, riboflavin
B3, niacin
B5, pantothenic acid
B6, pyridoxine
B7, biotin
B9, folate
B12, cobalamin
C, ascorbic acid
61
Q

B complex defieciencies

A

Generally result in dermatitis, glossitis, diarrhea

Note that B12 (years) and B9 (months) can be stored for a long time in the liver

62
Q

Antioxidant Vitamins

A

A, C, E

63
Q

BeriBeri

A

B1 deficiency

Dry beriberi: polyneuritis, symmetrical muscle wasting

Wet beriberi: high output cardiac failure (dilated cardiomyopathy), edema

64
Q

Vitamin B2 or riboflavin deficiency

A

Important for FAD and FMN, used as cofactors in redox reactions.

Cheilosis (inflammation of lips, scaling and fissures at corners of mouth).
Corneal vascularization

65
Q

A man presents with dementia, diarrhea, and skin darkening in sun-exposed areas. What characteristic cervical-area finding might he have?

A

This is B3 (niacin) deficiency, which may present with a C3/C4 dermatome circumferential “broad collar” rash (Casal necklace)

Niacin is derived from tryptophan and synthesis requires vitamins b2 and b6

Niacin can be used to treat dylipidemia since it raises HDL and lower VLDL

66
Q

Pantothenate (vitamin B5) deficiency

A

Adrenal insufficiency, hair loss, dermatitis, and diarrhea

Enzymes affected: coenzyme A and fatty acid synthase

67
Q

Vitamin B6 (pyridoxine) deficiency

A

Note isoniazid and contraceptives can induce deficiency.

Convulsions, hyperirritability, peripheral neuropathy, sideroblastic anemia.

68
Q

Biotin (B7) is a cofactor for which enzymes

A

Carboxylation enzymes.
Biotin and pyruvate carboxylase catalyze what reaction? Conversion of pyruvate to oxaloacetate
Biotin and acetyl-CoA carboxylase? acetyl-CoA to malonyl-CoA
Biotin and propionyl-CoA carboxylase? propionyl-CoA to methylmalonyl-CoA

69
Q

Where are Vitamins A and B9 found?

A

Vitamin A: liver and leafy vegetables

Folate: Leafy green vegetables

70
Q

Folate (B9) deficiency

A

mc vitamin deficiency in US - seen with alcoholism and pregnancy
*see increased homocysteine levels

Folate is required for THF synthesis. THF is coenzyme of 1-carbon transfer/methylation reactions, needed for nitrogenous base synthesis in RNA/DNA

71
Q

Wernicke-Korsakoff syndrome

A

Confusion, ophthalmoplegia, ataxia = classic triad
Also confabulation, personality change, memory loss.
Due to medial dorsal nucleus of thalamus, mammillary bodies.

Commonly seen as Vitamin B1/thiamine deficiency in alcoholics

72
Q

Vitamin B12/ cobalamin deficiency

A

Found in animal products.
Macrocytic, megaloblastic anemia; subacute combined degeneration, paresthesias, optic neuropathy
*see increased homocysteine and methylmalonic acid levels

73
Q

Vitamin C (ascorbic acid) deficiency

A

Scurvy, due to decreased hydroxylation of collagen. A patient presents with swollen gums, bruising, anemia, poor wound healing, hemarthrosis, recurrent infections, and “corkscrew hair.
Also necessary for DA ßhydroxylase (DA to NE)

74
Q

Glucose infusion and B1 deficiency

A

Worsened by glucose infusion because whatever thiamine was left in the system gets depleted.

75
Q

Vitamin D (names)

A

D2: ergocalciferol
D3: cholecalciferol
25 OH D3: storage form
1,25 (OH)2 D3: calcitriol

76
Q

Vitamin E (names)

A

Tocopherol/tocotrienol

  • Note that vitamin E can enhance the anticoagulant effects of warfarin
  • Note that in deficiency neuro presentation may mimic B12 deficiecy ( with posterior column and spinocerebellar tract demyelination), but w/o megaloblastic anemia, hypersegmented PMNs, or increased serum methylmalonic acid levels
77
Q

Neonatal hemorrhage

A

Most likely due to Vitamin K (phytomenadione, phylloquinone, phytonadione) deficiency - esp if neonates not given K injection at birth. Neonates have sterile intestine initially and are unable to synthesis vitamin K.

Note there is increased PT and aPTT, but nl bleeding time in neonates.

78
Q

Kwashiorkor

A 
MEAL:
Malnutrition (protein)
Edema
Anemia
Liver (fatty)
79
Q

Marasmus

A

Total calorie malnutrition resulting in tissue and muscle wasting, loss of subcutaneous fat, and variable edema

*Marasmus results in muscle wasting

80
Q

Hartnup disease and pellagra

A

Impaired absorption of tryptophan, which is used to synthesize niacin (needs B2 and B6 to synthesize)

81
Q

Where is folate absorbed?

A

Jejunum

82
Q

Malignant carcinoid syndrome and pellagra

A

Through increased metabolism of tryptophan, which is used to synthesize niacin

83
Q

Which 2 vitamins does breast milk not provide?

A

Vitamin K

Vitamin D

USMLE Step 1 (9 decks)

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