Biochemistry - USMLE Step 1

Protein

What is the most common intracellular buffer?

Bicarbonate

What is the most common extracellular buffer?

A molecule with one negative and one positive end

What is a Zwitterion?

The pH at which there is no net charge

What is the Isoelectric Point?

PFK-1

What is the rate limiting enzyme in Glycolysis?

Fructose -1,6-bishposhpatase 1

What is the rate limiting enzyme in Gluconeogenesis?

G-6PD

What is the rate limiting enzyme in the HMP shunt?

Glycogen synthase

What is the rate limiting enzyme in Glycogenesis?

Glycogen phosphorylase

What is the rate limiting enzyme in Glycogenolysis?

AcCoA carboxylase

What is the rate limiting enzyme in FA synthesis?

Carnitine Acetyltransferase -1 (CAT1)

What is the rate limiting enzyme in β- oxidation?

HMG CoA reductase

What is the rate limiting enzyme in Cholesterol synthesis?

HMG CoA synthase

*HOMG! I’m Starving!”

What is the rate limiting enzyme in Ketogenosis?

PRPP synthase

What is the rate limiting enzyme in Purine synthesis?

Carbomyl phosphate synthetase II

What is the rate limiting enzyme in Pyrimidine synthesis?

Isocitrate dehydrogenase

What is the rate limiting enzyme in TCA cycle?

(Carbamoyl Phosphate Synthase) CPS-I

What is the rate limiting enzyme in Urea cycle?

δ-ALA synthase

What is the rate limiting enzyme in Heme synthesis?

"ABC"

AcetylCoA production β-oxidation Citric acid cycle

What are the catabolic pathways that create energy?

"EFGH" ER

Fatty acid synthesis

Glycolysis

HMP shunt

What are the anabolic pathways that store energy?

"HUG"

Heme synthesis Urea cycle

Gluconeogenesis

What are the anabolic + catabolic pathways?

Creates an isomer

What does an Isomerase do?

Creates an epimer, which differs around 1 chiral carbon

What does an Epimerase do?

Moves sidechain from one carbon to another (intrachain)

What does a Mutase do?

Moves sidechain from one substrate to another (interchain)

What does a Transferase do?

Phosphorylates using ATP

What does a Kinase do?

Phosphorylates using Pi

What does a Phosphorylase do?

Forms C-C bonds (w/ ATP and biotin) using CO2

What does a Carboxylase do?

Consumes 2 substrates equally

What does a Synthase do?

Consumes 2 substrates, uses ATP

What does a Synthetase do?

Breaks phosphate bond

What does a Phosphatase do?

Breaks a bond with water

What does a Hydrolase do?

Cuts C-C bonds w/ ATP

What does a Lyase do?

Removes H with a cofactor

What does a Dehydrogenase do?

Breaks S bonds

What does a Thio do?

From high to low concentration

What is Diffusion?

Goes against concentration gradient

What is Active Transport?

Metabolism independent of concentration

What is Zero-order kinetics?

Constant drug percentage metabolism over time, depends on drug

What is 1st-order kinetics?

Max effect regardless of dose (lower w/ non-competitive antagonist)

What is Efficacy?

Vmax

What effects Efficacy?

Amount of drug needed to produce effect (lower w/ comp antagonist)

What is Potency?

Km

What affects Potency?

Concentration of drug that binds 50% of receptors

What is Kd?

Concentration of drug that produces 50% of maximal response

What is EC50?

Fights for active site, no ∆Vmax, potency decreases

What is Competitive Inhibition?

Binds a regulatory site, no ∆Km, efficacy decreases, ↓Vmax

What is Non-competitive Inhibition?

Consumes heat

What is an Endothermic Reaction?

Gives off heat

What is an Exothermic Reaction?

4 hrs after dose (too high => decrease dose)

What is the Peak level?

2 hrs before dose (too high => give less often)

What is the Trough level?

Half-life, the time it takes for the body to use half of the drug ingested

What is t1/2?

G-6Pase deficiency =>

hypoglycemia, hepatosplenomegaly

What is von Gierke?

Lysomal acid α-1,4-glucosidase deficiency (aka acid maltase) => DIE early

*Big Heart, hypotonia, Big tounge

What is Pompe's?

Debranching enzyme deficiency => short branches of glycogen

“Poor man’s von Gierke” → normal lactate, milder symptoms, liver issues

*CD! Cori = Debranching

What is Cori's?

Branching enzyme deficiency => long chains of glycogen

• Hepatosplenomegaly → FAILURE TO THRIVE IN INFANCY

*AB → Anderson - Branching

What is Anderson's?

Muscle phosphorylase deficiency => muscle cramps w/ exercise

What is McArdle's?

Fructokinase deficiency => excrete fructose (still have hexokinase)

What is Essential Fructosuria?

"Fructose intolerance" (Aldolase B deficiency ) => liver damage

What is Fructosemia?

Cataracts

What does a Galactokinase deficiency cause?

Cataracts, mental retardation, liver damage

• → FAILURE TO THRIVE ☹

What does Galactosemia cause?

FA transport out of the mitochondria

What does the Citrate shuttle do?

FA transport into the mitochondria

What does the Carnitine shuttle do?

Tay-Sachs, Neimann-Pick

What lysosomal diseases have a cherry- red macula?

Gaucher's, Hurler's

What lysosomal diseases have a Gargoyle-face?

Hexosaminidase A deficiency => blindness, incoordination, dementia

*Hexo A → TAy SaX

What is Tay-Sachs?

Hexosaminidase A/B deficiency

What is Sandhoff's?

Glucocerebrosidase deficiency => wrinkled tissue MP, bone pain

MOST COMMON LYSOSOMAL

What is Gaucher's?

Sphingomyelinase deficiency => zebra bodies

• → Progessive neurodegeneration and hepatosplenomegaly

What is Neimann-Pick?

α-galactosidase deficiency => corneal clouding, attacks baby's kidneys, Xlinked

What is Fabry's?

β-galactosidase deficiency => globoid bodies

• → Peripheral neuropathy, destroyed oligodendrocytes, developmental delay → CN II atrophy

What is Krabbe's?

Arylsulfatase deficiency => childhood MS

What is Metachromatic

Leukodystrophy?

Iduronidase deficiency, milder form of Hurler

*Hunters see clearly, no corneal clouding and agressive

What is Hunter's?

Iduronidase deficiency, worse form of the mucopolysaccharidoses

• → Developmental delays, hirsutism, skeletal anoolies

What is Hurler's?

(HGPRT deficiency) => gout, neuropathy, self-mutilation

• Hyperurecemia

• Gout

• Piss** off

• Red/Orange cystals in urine

• Tense muscles (dystonia)

What is Lesch-Nyhan?

Excess orotic acid → Ornithine transcarbamylase deficiency

What do white diaper crystals suggest?

Carboxylation

What does biotin donate CO2 groups for?

Nucleotides

What does THF donate methyl groups for?

All other reactions

What does SAM donate methyl groups for?

Heterochromatin = tightly coiled Euchromatin = loose (10nm fibers)

What is the difference b/w Heterochromatin and Euchromatin?

A, G

What are the Purines?

C, U, T

What are the Pyrimidines?

Changes leave the same amino acid

What is a silent mutation?

Changes 1 base

What is a point mutation?

Changes 1 purine to another purine or pyrimidine to pyrimidine

What is a transition?

Changes 1 purine to a pyrimidine or vice versa

What is a transversion?

Insert or delete 1-2 bases

What is a frameshift mutation?

Mistaken amino acid substitution

What is a missense mutation?

Early stop codon

What is a nonsense mutation?

DNA

What does a Southern blot detect?

RNA

What does a Northern blot detect?

Protein

What does a Western blot detect?

"PVT TIM HALL"

Phe Val

Trp

Thr

Ile

Met His

What are the essential amino acids?

ALinolenicrg

What are the essential fatty acids?

Asp, Glu

What are the acidic amino acids?

Lys, Arg

What are the basic amino acids?

Cys, Met

What are the sulfur-containing amino acids?

Ser, Thr, Tyr

What are the O-bond amino acids?

Asn, Gln

What are the N-bond amino acids?

Leu, Ile, Val

What are the branched amino acids?