CHEAT SHEET FOR USMLE STEP 1 PREP

B I O C H E M
D N A R E P L I C A T I O N E N Z Y M E S
-ORIGIN OF REPLICA TION- REPEA TED A’S AND T’S, THE TATA BOX IS
PROMOTER SITE
- REPLICA TION FORK- Y SHAPED, WHERE LEADING AND LAGGING STRAND ARE
SYNTHESIZED
-HELICASE- UNWINDS DNA----->DEFICIENT IN BLOOM SXN (BLM GENE
MUT ATION)
- TOPOISOMERASE- CREA TES SINGLE OR DOUBLE STRANDED BREAK IN THE
HELIX TO ADD OR REMOVE SUPERCOILS AS NEEDED-----INHIBITED BY
FLUOROQUINOLONES (T OPO 2 AKA DNA GYRASE, AND TOPO4)
-PRIMASE- MAKES RNA PRIMER ON DNA SO POL YMERASE CAN ST ART
REPLICA TION
-POL YMERASE 3-ONL Y PROKAR YOTES! ELONGA TES LEADING STRAND BY
ADDING DEOXYNUCLEOTIDES TO THE 3’END (LAGGING) TIL IT REACHES
PRIMER
-POL YMERASE 1- PROKAR YOTES ONL Y! DEGRADES RNA PRIMER
-LIGASE- GLUE! JOINS OKAZAKI FRAGMENTS WITH PHOSPHODIESTER BONDS
-TELOMERASE- EUKAR YOTES ONL Y! REVERSE TRANSCRIPT ASE, ADDS DNA
‘TAG’ AKA TTAGGG TO 3’ ENDS OF CHROMOSOME TO AVOID LOSS OF GENETIC
MATERIALS!!!!
UPREGULA TED IN CANCER, DOWN REGULA TED IN AGING AND PROGERIA
SO SHOR TER TELOMERASE MEANS OLDER PERSON
EUKAR YOTE RNA POL YMERASES
RP 1- MAKES RRNA, ONL Y IN NUCLEOLUS
RP2- MAKES MRNA, SNRNA, AND MICRORNA
RP3- MAKES TRNA AND SSRNA, NO PROOFREADING BUT CAN INITIA TE CHAINS
AMANT APHALLOIDES AKA DEA TH CAP MUSHROOMS CONT AIN ALPHA AMANITIN
WHICH UPON INGESTION CAN CAUSE DYSENT ARY AND SEVERE
HEPATOTOXICITY -->LIVER F AILURE
N u c l e o t i d e d e fi c i e n c y d i s e a s e s
A D D - a d e n o s i n e d e a m i n a s e d e fi c i e n c y -ultimately leads to decrease in lymphocytes which then leads to SCID (severe
combined immunodeficiency)
-AUT OSOMAL RECESSIVE
L E S C H - N Y M A N S X N
-
X-LINKED RECESSIVE
-
ABSENT CONVERSION OF HYPOXANTHINE TO IMP AND GUANINE TO GMP
-
HGPR T- HYPERURICEMIA, GOUT , PISSED OFF , RED/ORANGE CR YSTALS
(SODIUM URA TE) IN URINE, TENSE MUSCLES(DYST ONIA)
-
HEY GREG PLS RE TWEET
PRADER WILLI SXN- POP (PRADER WILLI, OBESITY , PATERNAL ALLELE
DELETED)
-MATERNAL CHROMOSOME DUPLICA TED, P ATERNAL ALLELE IS DELETED OR
MUT ATED
-HYPERPHAGIA, INSA TIABLE HUNGER, OBESITY , INTELLECTUAL DISABILITY ,
HYPOGONADISM, HYPOT ONIA
ANGELMANN SXN
-PATERNAL CHROMOSOME DUPLICA TED, MA TERNAL ALLELE DELETED
-SEIZURES, ATAXIA, INTELLECTUAL DISABILITY , INAPPROPRIA TE LAUGHTER
(SAIL)
G l y c o g e n s t o r a g e d i s e a s e s - V P C A M - V i c e P r e s i d e n t
C a n t A c c e p t M o n e y
V- Von Gierke
●
No glycogenolysis no gluconeogenesis
●
High- blood lactate, triglycerides, uric acid
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Gout
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Deficient in glucose 6 phosphatase
P-Pompe
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Cardiovascular issues, hepatomegaly,
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Pompe=pump= heart, liver, muscle
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Deficient in galactosidase (??)
C-Cori
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Mild Von gierke
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Gluconeogenesis works!
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Deficient in DEbranching enzymes!
A-Andersen ●
Cirrhosis, intellectual delay, failure to thrive
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Deficient in BRANCHING enzymes
M-McArdle
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Glycogen stores in muscle and muscle cant break it down
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Myoglobinuria- RED URINE after strenuous exercise
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Mcardle=muscle
L y s o s o m a l e n z y m e d e fi c i e n c y d i s e a s e s
TaySachs- onion cherry
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Progressive neurodegeneration
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Cherry red spot on macula of eye, NO HEPATOMEGALY, ONION SKIN LYSOSOMES
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Deficient in hexokinase
Fabry
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EARLY STAGE: “think NAH!” neuropathy, angiokeratomas, and hypohidrosis
(angiokeratoma look like red wet acne)
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LATE: RENAL failure and CARDIOVASCULAR disease
●
Deficient in alpha galactosidase
Gaucher
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Gaucher cells- Macs that look like crumpled tissue paper
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Pancytopenia, osteoporosis, bone crises, femur necrosis
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Deficient in glucocerebridase
Metachromatic Leukodystrophy
●
Central and peripheral demyelination→ ataxia and dementia
●
Deficient in aryl sulfatase A
Krabbe- Mr Krabs eyes
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Deficient in galactocerebrisidase
●
Globoid cells, optic atrophy, peripheral neuropathy
Niemann-Pick- foam liver cherry
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Cherry red spot on macula, HEPATOMEGALY, foam cells
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Progressive neurodegeneration
●
Sphingomyelinase deficiency
Hurlers
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Corneal clouding
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Heparan and dermatan sulfate buildup
Hunters
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Mild hurlers
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No corneal clouding, AGGRESSIVE behaviour
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Heparan and dermatan sulfate buildup
V i t a m i n s !
Vitamin A aka retinoid, retinol, retinal