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USMLE Step 1 Quick Notes > Biochemistry > Flashcards

Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the only RNA molecule to have thymidine?

A

tRNA

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2
Q

What are people with fabry disease at risk for?

A

CVD and renal failure

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3
Q

What is the problem if you have methylmalonyl acidemia?

A

Defect in the isomerization reaction that forms succinyl coA from methylmalonyl coA

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4
Q

What did propionyl coA carboxylase do?

A

Convert propionyl coA to mehylmalonyl coA and requires B7 (biotin)

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5
Q

What makes propionyl coA?

A

Methionine, Threonine, Valine, Isoleucine

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6
Q

Where does repressor bind?

A

Operator

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7
Q

What is a positive regulator of the lac operon?

A

cAMP - CAP

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8
Q

What prevents lactose fermenting bacteria to stop fermenting when glucose added?

A

Glucose depletes cAMP so cAMP - CAP can’t positively regulate lac operon.

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9
Q

What does it mean if collagen containing disulfide rich globular domains present?

A

Procollagen deficiency

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10
Q

What does citrate synthase use?

A

B5

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11
Q

Several tissues use TG breakdown products as intermediates in energy generation and glucose synthesis. Which is a liver specific enzyme that facilitates this?

A

Glycerol kinase: TG broken down into glycerol and FA by lipase. The glycerol is phosphorylated in the liver to glycerol 3 phosphate then converted to DHAP. Can be used for glycolysis or gluconeogenesis.

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12
Q

What is Rotenon?

A

Inhibits complex 1 of ETC

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13
Q

What is antimycin?

A

Inhibits complex III of ETEC

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14
Q

What do CN, CO inhibit?

A

Complex IV of ETEC

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15
Q

What is Oligomycin?

A

Inhibits complex V aka ATP synthase of ETC

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16
Q

Do even chain or odd chain yield glucose?

A

Odd chain

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17
Q

What is Osler-Weber-Rendu?

A

Hereditary hemorrhagic telangiectasia: epistaxis, telangiectasia, skin discoloration, AVM

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18
Q

What do you see on histology for Duchenne MD?

A

Fibrofatty change in muscle

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19
Q

What is type I familial dyslipidemia?

A

Problem with LPL. Acute pancreatitis, eruptive xanthomas, hepatosplenomegaly

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20
Q

What is type II familial dyslipidemia?

A

LDL receptor problem. Tendon xanthomas, xanthelasmas, increased atherosclerosis

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21
Q

What is type IV familial dyslipidemia?

A

VLDL overproduction. Get acute pancreatitis

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22
Q

What does succinate DH use?

A

Riboflain to make FADH2

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23
Q

Where does proteolytic processing of collagen occur?

A

Cleavage of N & C terminal occurs outside of cell

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24
Q

What is the problem with collagen processing in scurvy, osteogenesis, ehler’s danlos?

A

Scurvy: Hydroxylation
Osteogenesis Imperfecta: triple helix formation
Ehler’s Danlos: proteolytic processing or cross-linking

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25
Q

What is the problem in XP?

A

Endonuclease messed up

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26
Q

What is a long term consequence of alkaptonuria (aka ochronosis)?

A

Debilitating arthritis (homogentisate is harmful to cartilage)

Other sx: dark CT, brown sclera, urine turns dark on prolonged exposure to air

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27
Q

What do the TATA and CAAT boxes do?

A

Promoters of transcription in eukaryotic cells. CAAT is more upstream than TATA. This is where RNA Pol II binds

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28
Q

What is a protein with seven alpha helical transmembrane domain?

A

GPCR

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29
Q

What causes different length fragments to be produced on RFLP?

A

SNPs

They change where restriction enzyme would cleave and so the DNA is no longer cleaved there and would be bigger on gel electrophoresis

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30
Q

What is MCAD?

A

AR characterized by inability to degrade medium length fatty acids by beta oxidation. Present early in childhood with hypoketotic hypoglycemia and hepatic dysfunction

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31
Q

What does a short alpha helical fragment with leucine residues every 7th position do?

A

Part of leucine zipper dimerization domain in transcription factor (basic zipper proteins)

Other DNA binding protein: helix loop helix and zinc fingers

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32
Q

If radiolabeled CO2 added to proliferating cells and gets added to DNA, where was the first step?

A

Cytoplasm

De novo purine and pyrimidine synthesis occurs in cytoplasm

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33
Q

What catalyzes the first step in pyrmidine synthesis?

A

Carbamoyl phosphate synthase II

carbamoyl phosphate synthase I is in the urea cycle

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34
Q

How do you tell Cori and Von Gierke’s apart?

A

Fructose administration will not improve von Gierke’s but will improve Cori

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35
Q

Where is the enzyme deficiency in pompe’s?

A

LYSOSOMES!

It is the only one of the glycogen storage disorders to be a lysosomal defect

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36
Q

What does increased malonyl coA inhibit?

A

Fatty acid oxidation

37
Q

What can classic galactosemia lead to in neonates?

A

E. coli sepsis

38
Q

What is glucose oxidase test for?

A

To test for amount of glucose in urine

39
Q

What is propionyl coA carboxylase deficiency?

A

Pw/ vomiting, dehydration, acidemia, anion gap acidosis, ketosis

High propionyl coA levels

40
Q

What is propionyl coA made from?

A

Threonine, methionine, isoleucine, valine

41
Q

What presents with kinky matted hair, growth retardation, and hypotonia?

A

Menke’s (Impaired CU absoption due to lysyl oxidase activity)

42
Q

What do transketolase/transaldolase do?

A

Converts ribose 5 phosphate to fructose 6-phosphate and glyceraldehyde 3 phosphate

43
Q

What controls cytoplasmic quality of mRNA?

A

P bodies

44
Q

What cofactors required for pyruvate DH?

A

Lipoic acid and B1 - B5

45
Q

How does base excision work?

A

Glycosylase creates apurinated/apyrimidated site –> endonuclease cleaves 5’ and lyase cleaves 3’ –> DNA pol fills in –> ligase rejoins

46
Q

What disease causes tryptophan deficiency leading to pellagra symptoms due to no tryptophan to make B3?

A

Hartnup

47
Q

Which cells have high telomerase activity?

A

Epidermal cells and WBC

48
Q

What does disruption of Fas/FasL cause?

A

Increasing number of autoreactive leading to autoimmune disorders?

Fas is what destroys them in the thymic medulla during negative selection

49
Q

How does sunlight cause production of vitamin D?

A

Causes conversion of 7-dehydrocholesterol to cholecaciferol?

50
Q

What does fabry present with and what accmulates?

A

Ceramide Trihexoside

Angiokeratomas (rash on your lower abdomen), peripheral neruopathy, renal and CV sx

51
Q

What gives elastin its elastic properties?

A

Crosslinking (lysine cross linked)

Elastin is not hydroxylated (collagen is not)

52
Q

What is the primary source of glucose after 12-18 hours of fasting?

A

Gluconeogenesis

53
Q

Why do you get cataracts from galactose enzyme deficiencies?

A

Due to aldose reductase converts galactose to galactitol which accumulates in the eye and causes cataracts?

54
Q

What causes hemolytic anemia and posterior column, spinocerebellar tract demyelination?

A

Vitamin E deficiency

55
Q

What is needed for the first step of urea cycle (ie positive regulator thing)?

A

N-acetylgluamate (activates carbamoyl phosphate synthease I)

56
Q

What is the major source of nitrogen in urea cycle?

A

Aspartate

57
Q

Where are promoters and where are enhancers/repressors?

A

Promoters can be anywhere

Enhancers/repressors can be anywhere

58
Q

What removes RNA primers?

A

DNA Pol I

59
Q

What the lactose test for lactase deficiency?

A

Hydrogen breath increased and stool pH decreased from

60
Q

What is the difference between Vit B12 and Vit E difference?

A

B12: megaloblastic anemia, and does corticospinal tract

E: hemolytic anemia and does not do cortiscospinal tract

61
Q

Which part tRNA binds amino acid?

A

3’ where the CCA is

62
Q

What is H1?

A

Outside nucleosome and helps to package nucleosomes into more compact structures by binding and linking dna between adjacent nucleosomes

63
Q

Where does PPP occur?

A

Cytoplasm

64
Q

What type of channel does CFTR encode?

A

ATP gated Cl channel

65
Q

How does CFTR affect ENaC?

A

Inhibits ENac to dec Na absorption

66
Q

What is the NaCl nasal mucosa test in CFTR?

A

Can apply isotonic NaCL to nasal mucosa and measure electrical difference between mucosa and interstitium: person with CF will show more negative difference due to inc Na absorption

67
Q

What happens with FMR1 in fragile x?

A

Affects methylation and expression of FMR1 gene

68
Q

What is southwestern blot?

A

Use double stranfded DNA to detect DNA binding protein

69
Q

How do glucagon and epinephrine increase glycogenylosis?

A

via cAMP

70
Q

How does active muscle increase glyocgenolysis?

A

Via Ca

71
Q

What does 16s do?

A

Binds shine delgarno and initiates protein synthesis?

72
Q

Why is fructose rapidly metabolized by the liver?

A

Because it bypasses the regulation of PFK-1 (rate limiting step)

73
Q

How is glucose metabolized to fructose?

A

Glucose –> sorbitol –> fructose

74
Q

What is the mTOR pathway?

A

Receptor –> tyrosine kinase –> PI3K –> AKT –> mTor to nucleus

75
Q

What happens when there is abserrant serine and threonine phosphorylation of insulin tyrosine kinase?

A

Insulin resistance

Can occur in presence of TNF-alpha, catecholamines, glucagon, GC

76
Q

What is JAK/STAT pathway used by?

A

GH, prolactin, cytokines

It is receptor associated tyrosine kinase

77
Q

What is MAP kinase pathway?

A

Insulin, IGF, FGF, PDGF, EGF

It is intrinsic tyrosine kinase

78
Q

What two things can’t use ketones for energy?

A

Liver and RBC

79
Q

What breaks down very long chain FA, branched FA (phytanic acid)?

A

Peroxisomes

80
Q

What presents with trouble releasing handshake/doorknob, gonadal atrophy, frontal balding, cataracts?

A

Myotonic dystrophy

81
Q

What converts pro carcinogens to carcinogens?

A

CYP (microsomal monooxygenase)

82
Q

Where is alanine’s ammonia group to transfered to?

A

Alpha ketoglutrate

83
Q

What is seen with genomic imprinting?

A

Methylation of DNA since it silences the gene

84
Q

What do the bisophosphatases (FBPases 1 & 2) promote?

A

Gluconeogenesis (FBPase 2 converts fructose 2,6 bisphosphate to fructose 6 phosphate)

85
Q

What does fructose 2,6 bisophosphate do?

A

Activates PFK-1 and promotes glycolysis

(lots of 2,6 made when there is a lot of glucose)

Insulin promotes fructose 2,6 bisophosphate formation

86
Q

What does alanine get converted to?

A

Pyruvate

87
Q

What is a liver specific enzyme that promotes TG breakdown?

A

Glycerol kinase (uses glycerol for TG breakdown and phosphorylates so that it can make glycerol 3 phosphate then DHAP - a glycolysis intermediate)

88
Q

What does isoniazid cause?

A

Peripheral neuropathy due to decreased B6

GIVE PLP!

89
Q

What does homocystinuria present with?

A

Kyphoscoliosis, lens subluxation, intellectual disability, osteoporosis, tall, THROMBOSIS, ATHEROSCLEROSIS

USMLE Step 1 Quick Notes (17 decks)

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